Sustainable Valorization of Agri-Food By-Products Through 3D Printing: A Review of Advances, Multisectoral Applications, and Circular Economy Challenges

Abstract

Agri-food by-products and residues are increasingly being studied as raw materials for three-dimensional (3D) printing, especially to convert secondary streams into useful, more sustainable products. This review discusses recent advances in the use of these materials, focusing on how their origins, compositions, pretreatments, processing behaviors, and final applications are interconnected. Plant-, animal-, industrial-, and post-consumer-derived residues are considered, particularly when they provide fibers, proteins, polysaccharides, lipids, bioactive compounds, or biopolymers with technological value. The review also examines the main printing approaches used in this field, including extrusion-based printing, inkjet printing, sintering, and direct ink writing. Particular attention is given to factors that determine successful printing, including rheological behavior, viscosity, particle size, moisture content, structural stability after deposition, interlayer adhesion, and shape fidelity. Current applications range from functional foods and biodegradable or active packaging to biomaterials, controlled-release systems, biocomposites, construction materials, energy-related devices, textiles, and agricultural products. Although the reviewed studies show clear potential, most developments still face important barriers, including raw material variability, safety requirements, sensory acceptance, mechanical performance, scale-up, and regulatory uncertainty. Future progress will depend on moving beyond printable prototypes toward reproducible formulations, real-use validation, and clearer comparison criteria, in line with Sustainable Development Goal 12 and the transition toward higher-value circular production chains.

1. Introduction

The generation of agri-food by-products and residues is one of the most relevant challenges for the sustainability of food systems worldwide, due to their large scale and negative impact on natural resources and the environment [1]. These materials not only reflect significant inefficiencies in the use of raw materials, water, and energy but also contribute to environmental problems, such as pollution and greenhouse gas emissions, associated with their management and final disposal [1,2]. In addition, they are generated throughout the entire supply chain, from primary production to consumption, evidencing structural limitations of the linear economic model based on producing, using, and discarding [2]. In this context, their reduction and valorization have become a consolidated key strategy to promote more sustainable systems, aligned with the principles of the circular economy and efficient resource management [3,4].

In response to this problem, the valorization of agri-food by-products and residues has emerged as a key strategy to transform these materials into value-added resources, thereby reducing environmental impacts and improving the efficient use of raw materials [1]. This approach is based on the principles of the circular economy, which promote the reuse and reutilization of materials within new sustainable production chains [5]. From a compositional perspective, several studies have reported that they contain high-value compounds, including macronutrients, dietary fibers, and bioactive compounds, which can be recovered using various processing technologies [4,6,7]. These characteristics have promoted their application across sectors such as food, packaging, and functional products, as well as in emerging fields such as biomedicine and construction, consolidating their value as a relevant alternative for the development of sustainable solutions [4,8]. This approach is also aligned with the 2030 Agenda, particularly Sustainable Development Goal (SDG) 12, by promoting the use of secondary resources, reducing residues, and developing more sustainable processes. Complementarily, its applications in food, health, industry, and the environment link this strategy to SDGs 2, 3, 9, and 13.

Under this approach, 3D printing, or additive manufacturing, has emerged as a technology with high potential for valorizing agri-food by-products and residues, enabling the fabrication of three-dimensional structures through the controlled deposition of materials layer by layer [9,10]. Unlike conventional extrusion, molding, and blow molding, which generally produce predefined geometries, 3D printing enables mold-free layer-by-layer fabrication, rapid design changes, product customization, and complex structures with controlled material distribution [11,12]. These advantages not only improve the efficiency of production processes but also reduce waste, in accordance with the principles of sustainability and the circular economy [4,9]. Likewise, 3D printing enables these materials to be integrated into new functional matrices, expanding their applications across sectors such as food, packaging, biomedicine, and construction, thereby reinforcing their potential as a tool for developing sustainable solutions across industrial fields [8,9]. However, their effective implementation depends on critical factors such as the printability of the formulations, the rheological properties of the materials, and their compatibility with different printing technologies, all of which remain significant challenges for their industrial scale-up [13,14].

In recent years, the application of 3D printing to the valorization of agri-food by-products and residues has experienced sustained growth, becoming a consolidated emerging field within sustainable manufacturing [9,15]. Several studies have demonstrated the feasibility of these approaches across various printing technologies, particularly extrusion-based processes, thereby enabling their incorporation into functional matrices [8,9,16]. These applications range from the development of personalized foods to the production of biodegradable packaging, biomedical scaffolds, and construction materials, evidencing the transversal character of this technology [8,17,18,19,20,21]. Previous reviews have mainly focused on food applications and printing performance, whereas this review integrates materials, technologies, multisectoral applications, and sustainability within a common comparative framework [8,9,15]. Taken together, these advances reflect a significant evolution of the state of the art, oriented toward the efficient use of resources and the development of sustainable solutions. Therefore, this review is timely because the rapid expansion of the field requires an updated and integrative analysis that connects the characteristics of agri-food by-products with printing technologies, processability requirements, final applications, and sustainability challenges.

Despite the reported advances, the literature presents important limitations: studies are often fragmented and primarily focus on material development and process parameter optimization, with limited integration across materials, technologies, and applications. Likewise, there is limited comparison between approaches and limited evaluation of global performance, which makes an integrated view of the field difficult. Additionally, a lack of standardized criteria for evaluating the performance of the developed systems is evident, limiting the identification of more efficient materials and technologies. In this context, a scientific gap is identified, namely the absence of structured comparative analyses and methodologies to enable systematic evaluation of the different developed systems, highlighting the need for more integrative and up-to-date approaches. Accordingly, this review addresses three main questions: (i) which characteristics of agri-food by-products determine their suitability for 3D printing?; (ii) how do the main 3D printing technologies differ in terms of material compatibility, processability requirements, advantages, and technical limitations?; and (iii) what applications, performance criteria, knowledge gaps, and scale-up challenges currently define this field? In response to these limitations, the present review proposes a comparative and multisectoral approach aimed at analyzing in an integrated manner the potential of 3D printing in the valorization of agri-food by-products and residues, incorporating qualitative comparative criteria to analyze materials, technologies, and applications in different sectors, with the following objectives:

• To analyze the typology, composition, and potential of agri-food by-products for their use in 3D printing.
• To evaluate the main 3D printing technologies and their compatibility with different materials, considering critical parameters and technical limitations.
• To examine the multisectoral applications of 3D printing in the valorization of by-products, including food, packaging, biomedicine, and construction.
• To carry out a comparative analysis of the performance of materials, technologies, and applications, incorporating efficiency and sustainability criteria.
• To identify knowledge gaps, challenges, and future opportunities that guide the development of this field.

Figure 1 presents an integrative scheme of the study approach, in which agri-food by-products and residues, their composition and valorization potential, 3D printing technologies and their multisectoral applications, and the analysis criteria related to materials, technologies, and performance are articulated.

2. Narrative Review Methodology

This study was conducted as an analytical and integrative narrative review [4,22,23,24], aimed at examining the recent literature on the valorization of agri-food by-products and residues through 3D printing technologies. Rather than following a systematic review design, the purpose was to develop a critical and comparative view of the field by connecting material type, additive manufacturing technology, processability, and final application.

The literature search was conducted across Scopus, Web of Science, ScienceDirect, and Google Scholar. It was also complemented by direct searches on editorial platforms, including Multidisciplinary Digital Publishing Institute (MDPI), Elsevier, SpringerLink, Taylor & Francis, and Wiley. The review mainly considered studies published between 2020 and 2026 to include recent advances in 3D printing, the circular economy, biomaterials, sustainable packaging, functional foods, and biocomposites derived from agri-food sources.

Information was retrieved using combinations of English keywords, including 3D printing, additive manufacturing, food waste valorization, agri-food by-products, agro-industrial residues, biopolymers, printability, rheological properties, extrusion-based printing, direct ink writing, biocomposites, biodegradable packaging, and circular economy. These terms were combined using Boolean operators through a representative search structure: (“3D printing” OR “additive manufacturing” OR “direct ink writing”) AND (“agri-food by-products” OR “food waste” OR “agro-industrial residues”) AND (“valorization” OR “printability” OR “circular economy”). The syntax was adapted to each database, and the literature search was updated through July 2026. These terms facilitated the identification of studies on printable formulations and their applications in food, packaging, biomaterials, construction, and other emerging sectors.

The literature was selected through a progressive review of titles, abstracts, and full texts. Studies were included when they addressed the use of agri-food by-products or residues in 3D printing, described the composition or characterization of the material, evaluated properties relevant to processability, such as rheology, viscosity, stability, or printability, and presented a clearly defined functional or technological application. Priority was also given to studies that linked the origin of the by-product, the printing technology, and the performance of the resulting product.

Publications outside the established period, duplicate documents, studies with no direct relationship to 3D printing, works focused only on formulations without functional evaluation, articles with insufficient methodological information, and purely theoretical publications that did not provide experimental evidence or critical discussion were excluded. As a result of this process, 115 publications were selected to support the narrative and comparative analysis of the manuscript.

The collected information was organized according to three main dimensions: (i) type of agri-food by-product and predominant composition, (ii) 3D printing technology and processing parameters, and (iii) final application of the printed material. Complementary aspects were also analyzed, including pretreatment, rheological behavior, post-printing stability, functionality, technical limitations, scalability, and sustainability.

Although a formal protocol such as the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) was not used, an ordered selection process was maintained, consistent with the study’s narrative nature. The analysis was not intended to quantify the results statistically, but rather to critically integrate heterogeneous evidence from different materials, technologies, and application sectors. This approach enabled the identification of trends, knowledge gaps, and challenges in the development of 3D printing systems based on agri-food by-products.

3. Agri-Food By-Products and Residues: Classification and Potential

Agri-food by-products and residues constitute a heterogeneous source of materials with high potential for reincorporation into new value chains through sustainable transformation technologies. Their use depends on factors such as origin, chemical composition, degree of prior processing, storage stability, and compatibility with printable matrices. In the context of 3D printing, these materials are particularly relevant due to their content of fibers, proteins, polysaccharides, lipids, bioactive compounds, and biopolymers, which may contribute to both the functionality of the final product and the sustainability of the process [4,8,9,25].

The classification of these materials enables the identification of distinct valorization pathways and the establishment of relationships among composition, processability, and final application. In this regard, plant-, animal-, industrial-, and post-consumer-derived by-products and residues exhibit specific characteristics that govern their use in printing systems based on extrusion, gelation, sintering, direct ink writing, or biocomposite formulation. Therefore, it is necessary to analyze not only their composition but also their technological behavior, particularly rheology, printability, structural stability, and functionality.

3.1. Typology of Agri-Food By-Products and Residues

Plant-derived by-products and residues are among the most widely studied categories in agri-food valorization processes, mainly because of their high availability, low cost, and rich composition. This group includes peels, seeds, pulps, bagasse, stems, leaves, fibers, and residues from the processing of fruits, vegetables, cereals, legumes, and tubers. These materials commonly contain cellulose, hemicellulose, lignin, pectins, starches, phenolic compounds, natural pigments, and dietary fibers, making them attractive candidates for the development of printed foods, biodegradable packaging, hydrogels, biocomposites, and functional materials [7,8,20,25].

In food applications, they can be incorporated as functional ingredients to increase fiber content, provide antioxidants, or modify the texture of printable matrices. Flours, powders, or extracts derived from fruit and vegetable by-products can be mixed with hydrocolloids, starches, or proteins to produce pastes with rheological properties suitable for extrusion-based printing. In non-food applications, lignocellulosic fractions can act as reinforcements in biodegradable polymeric matrices, contributing to the development of packaging materials, lightweight structural components, or bio-based composite materials [16,20,25].

Animal-derived by-products and residues include materials generated during the processing of meat, fish, milk, eggs, and other livestock products. These include bones, skins, scales, collagen, gelatin, whey, myofibrillar proteins, chitin, chitosan, and mineral-rich residues. These materials have high functional value due to their protein content, gelling capacity, film-forming properties, bioactivity, and potential to form structured matrices. In 3D printing, animal proteins and derived biopolymers can be used in food formulations, biomaterials, controlled-release systems, and scaffolds for biomedical applications [8,21,26].

However, the use of animal-derived by-products requires greater sanitary controls, traceability, microbiological stability, and consumer acceptance. Their compositional variability and sensitivity to processing conditions, such as temperature, pH, and ionic strength, may also limit their direct application in 3D printing. For this reason, their valorization often requires prior extraction, purification, hydrolysis, dehydration, or functional modification processes to improve their compatibility with additive manufacturing technologies [26].

Industrial by-products correspond to residual streams generated during commercial-scale agro-industrial processing. They include brewer’s spent grain, grape pomace, coffee husk, cocoa residues, cereal bran, extraction pulps, oilseed cakes, whey, organic sludge, olive mill waste, and other residues derived from transformation processes. Unlike primary residues, these by-products often contain higher concentrations of specific compounds due to operations such as pressing, milling, extraction, fermentation, or filtration. This characteristic favors their use as sources of fibers, proteins, lipids, polysaccharides, pigments, phenolic compounds, or minerals [4,7,8,25].

In 3D printing, industrial by-products are particularly interesting due to their continuous availability and potential integration into scalable processes. Their incorporation can be directed toward the development of functional foods, packaging materials, bioplastics, adsorbents, biocomposites, or hybrid construction materials. However, their use requires overcoming challenges related to raw-material standardization, particle-size reduction, compatibility with polymeric or hydrocolloid matrices, and storage stability [8,9,25].

Post-consumer residues include materials generated after the use or consumption of agri-food products, such as food scraps, kitchen waste, household peels, expired products, restaurant discards, and urban organic waste. Although they represent a significant fraction of food waste, their direct application in 3D printing is more limited due to their high heterogeneity, microbiological risks, compositional variability, and difficulty in traceability. Even so, these residues can be indirectly valorized through bioconversion, advanced composting, fermentation, biopolymer extraction, or microbial biomass production, generating secondary materials with potential use in additive manufacturing [1,2,4,9].

From a circular economy perspective, the inclusion of post-consumer residues in 3D printing strategies represents an emerging opportunity, especially for non-food applications such as biodegradable materials, agricultural components, substrates, biocomposites, or low-sanitary-risk products. However, its implementation requires rigorous protocols for classification, sanitation, stabilization, and quality control.

3.2. Composition and Properties

The composition of agri-food by-products directly determines their potential for valorization through 3D printing. In this context, bioactive compounds, dietary fibers, proteins, and biopolymers are of particular interest for their ability to provide nutritional functionality, structural properties, antioxidant activity, gelling capacity, and biodegradability [6,7,8,25].

Bioactive compounds found in agri-food by-products include polyphenols, flavonoids, carotenoids, anthocyanins, tocopherols, organic acids, bioactive peptides, and other secondary metabolites. These compounds can provide antioxidant, antimicrobial, anti-inflammatory, or pigmenting properties, thereby expanding the possible applications of printed materials. In printed foods, they can contribute to the development of functional or personalized products; in packaging, they can provide antioxidant or antimicrobial activity; and in biomaterials, they can be involved in controlled-release systems or matrices with biological activity [6,7].

However, incorporating bioactive compounds into 3D printing is limited by their instability to temperature, light, oxygen, pH, and mechanical stress during printing. In addition, their interaction with polysaccharides, proteins, or lipids may affect the viscosity, gelation, and stability of the printed material. For this reason, strategies such as encapsulation, controlled drying, incorporation into hydrogels, or formulation with protective matrices are relevant for preserving their functionality [6,8,27,28].

Dietary fibers are among the most abundant components in plant and agro-industrial residues. Cellulose, hemicellulose, lignin, pectin, β-glucans, inulin, and other soluble and insoluble fibers can significantly modify the rheological properties of printable formulations. Their presence can increase viscosity, improve water retention, promote dimensional stability, and reinforce the product’s final structure. In printed foods, fibers can improve the nutritional profile and modify texture; in non-food materials, they can act as reinforcements in biocomposites and biodegradable matrices [8,20,25]. More specifically, Balk et al. demonstrated that lignosulfonate can be formulated as a recyclable structural ink for direct ink writing at room temperature [29].

Nevertheless, the effect of fiber depends on its origin, particle size, degree of hydration, solubility, concentration, and compatibility with the matrix. Excessive incorporation can lead to nozzle clogging, loss of homogeneity, poor interlayer adhesion, or structural defects. Therefore, particle-size control and proper fiber dispersion are critical aspects for ensuring printability [8,13,14].

Proteins present in animal- and plant-derived by-products have significant technological importance due to their ability to form gels, emulsions, foams, films, and three-dimensional networks. Proteins such as gelatin, collagen, caseins, whey proteins, legume proteins, gluten, zein, and cereal proteins can contribute to the formation of printable matrices with specific mechanical and functional properties. In food 3D printing, proteins can improve texture, nutritional value, and structural stability. In biomedical applications, some proteins can promote biocompatibility and scaffold formation. Protein functionality depends on factors such as pH, temperature, concentration, ionic strength, degree of denaturation, and the presence of other components. Under suitable conditions, proteins can improve the cohesion and stability of printed layers; however, they may also present problems such as aggregation, syneresis, poor flowability, or thermal sensitivity. For this reason, their use in 3D printing requires careful adjustment of formulation and processing conditions [26,27,28].

Biopolymers derived from agri-food by-products include polysaccharides, structural proteins, complex lipids, and microbial polymers obtained from organic residues. Among the most relevant are starch, pectin, cellulose, nanocellulose, alginate, chitosan, gelatin, lignin, and polyhydroxyalkanoates. These materials are of particular interest because of their biodegradability, renewable availability, and ability to form gels, films, hydrogels, or solid structures. Because they are heterogeneous macromolecular systems rather than single compounds with fixed molecular structures, their behavior in 3D printing is more strongly influenced by composition, molecular weight, degree of substitution, crystallinity, and interactions with the supporting matrix [16,22,25,28].

In additive manufacturing, biopolymers can act as the main components of the printable matrix or as functional additives that regulate viscosity, water retention, elasticity, interlayer adhesion, and mechanical strength. Their combination with by-products rich in fiber, protein, or bioactive compounds enables the production of hybrid materials with adjustable properties. This versatility makes them key elements for the development of printed foods, sustainable packaging, scaffolds, coatings, biocomposites, and structural materials [8,16,25,28].

3.3. Suitability for 3D Printing

The suitability of an agri-food by-product for 3D printing depends not only on its composition but also on its behavior during processing, deposition, and stabilization of the printed structure. In this regard, processability, functional properties, and technical limitations are fundamental criteria for evaluating its applicability in additive manufacturing technologies. Processability is closely related to the material’s ability to be transformed into a printable formulation. In extrusion-based technologies, which are the most widely used for agri-food matrices, the material must have a viscosity high enough to maintain its shape after deposition, but low enough to flow through the nozzle without requiring excessive pressure. This rheological balance is essential to achieve filament continuity, interlayer adhesion, dimensional stability, and geometric fidelity [8,9,13,14,28].

Agri-food by-products usually require prior operations to improve their processability, such as drying, milling, sieving, extraction, hydrolysis, fermentation, gelatinization, mixing with hydrocolloids, or incorporation into polymeric matrices. Particle size reduction is particularly important, since large or heterogeneous particles can cause nozzle clogging, irregular flow, and defects in the printed structure. Likewise, the moisture content of the material must be carefully controlled, as it influences viscosity, microbiological stability, shelf life, and behavior during drying or post-processing [8,9,28].

The functional properties of valorized by-products can provide specific advantages to the printed product. In foods, they can improve the content of fiber, protein, antioxidants, or bioactive compounds, enabling the development of personalized, functional, or need-specific products. In packaging, they can enhance biodegradability, antioxidant activity, barrier properties, or mechanical strength. In biomedical applications, some biopolymers and proteins can provide biocompatibility, controlled porosity, or controlled compound release. In construction and industrial applications, lignocellulosic and mineral fractions can act as reinforcements or functional fillers in biocomposites [8,20,21,25,26].

Despite this potential, compositional variability and limited post-printing stability remain key constraints. Differences in moisture, fiber, protein, fat, and bioactive compound contents hinder formulation standardization and product reproducibility [8,13,14]. In addition, poorly balanced viscosity and interactions among components may cause deformation, discontinuous extrusion, syneresis, phase separation, shrinkage, brittleness, or poor interlayer adhesion [13,14,28].

Safety-related restrictions must also be considered, especially when by-products are intended for food or biomedical applications. In these cases, the absence of contaminants, microbiological stability, traceability, and regulatory compliance must be ensured. For non-food applications, the main challenges are mechanical strength, durability, compatibility with polymeric matrices, scalability, and the assessment of real environmental impact.

Overall, the suitability of agri-food by-products for 3D printing should be evaluated through an integral approach that considers composition, pretreatment, rheological behavior, printability, post-printing stability, functionality, and sustainability. This evaluation enables the selection of materials with greater technological potential and the direction of their application to specific sectors, laying the groundwork for the comparative analysis of technologies and applications presented in the following sections.

Figure 2 integrates the classification of agri-food by-products, their components of interest, pretreatment stages, and the main suitability criteria for 3D printing, highlighting their transition toward applications in foods, packaging, biomaterials, and biocomposites.

The selection of a by-product for 3D printing should not be based only on its availability or compositional value, but on its actual ability to be transformed into a stable, safe, and reproducible matrix. This perspective allows for distinguishing between materials with immediate potential and those that require further conditioning or prior validation. Therefore, the next step is to relate these characteristics to available printing technologies, since the process’s feasibility ultimately depends on the compatibility among the material, the technique used, and the expected properties of the printed product.

4. 3D Printing Technologies

The selection of 3D printing technology is a determining factor in the valorization of agri-food by-products and residues, as each technique has specific requirements for material characteristics, rheological behavior, particle size, moisture content, thermal stability, and structural consolidation capacity. Unlike conventional synthetic polymers used in additive manufacturing, materials derived from agri-food residues often exhibit compositional variability, insoluble fibers, heterogeneous particles, heat-sensitive compounds, and limited post-deposition stability. Therefore, the choice of technology should consider the relationship between the nature of the by-product, the type of printable matrix, and the expected properties of the final product [30,31].

In the agri-food field, the most relevant technologies include extrusion-based printing, inkjet printing, sintering, and direct ink writing. Although all of them are based on the principle of layer-by-layer fabrication, they differ significantly in the physical state of the starting material, deposition mechanism, resolution, printing speed, need for post-processing, and degree of compatibility with food or bio-based matrices. These differences condition their application in functional foods, biodegradable packaging, biomaterials, biocomposites, and structured materials derived from agro-industrial residues [30,32].

4.1. Main Technologies

Extrusion-based printing is the most widely used technology for agri-food matrices because of its versatility, relatively low cost, and ability to process semi-solid materials, pastes, gels, purées, doughs, hydrogels, and biocomposites. In this technique, the material is forced through a nozzle using pneumatic pressure, a piston, a syringe, or a screw-driven system. It is deposited layer by layer onto a printing platform. Its main advantage is the ability to work with high-viscosity formulations and complex matrices containing polysaccharides, proteins, fibers, lipids, or particles derived from plant-, animal-, or industrial by-products [32,33].

In the context of agri-food residue valorization, extrusion is particularly suitable for incorporating flours from plant by-products, dietary fibers, starch gels, pectin, cellulose, plant proteins, gelatin, collagen, pulps, bagasse, and hydrocolloid-rich materials. However, its success depends on achieving a balance between flowability and structural stability. The material must flow continuously during deposition while retaining its shape after printing. When viscosity is too low, the structure may collapse; when it is too high, it may cause discontinuities, overpressure, nozzle clogging, or poor geometric resolution [33,34,35].

Inkjet printing is based on the controlled deposition of droplets of liquid or low-viscosity material onto a surface or onto previously deposited layers. This technology provides high spatial resolution and is useful for applying functional ingredients, bioactive compounds, aromas, natural colorants, gelling solutions, or binding agents onto food or bio-based matrices. Unlike extrusion, inkjet printing requires formulations with low viscosity, absence of coarse particles, and adequate colloidal stability; therefore, its direct application with untreated agri-food by-products is usually limited. In valorization processes, inkjet printing can be used as a complementary technology to functionalize printed structures by locally adding antioxidant compounds, antimicrobials, pigments, flavoring agents, or crosslinking solutions. Its potential is relevant in personalized foods, active packaging, and controlled-release systems. However, its compatibility with agri-food residues depends on previous operations such as filtration, extraction, clarification, or encapsulation of functional compounds. For this reason, it is better suited to liquid extracts, fine emulsions, or bioactive solutions than to heterogeneous fiber-rich matrices [30,31].

Sintering, particularly selective laser sintering, uses localized thermal energy to fuse powder particles and form solid structures layer by layer. In foods and bio-based materials, this technique has mainly been studied with powders rich in starch, sugars, proteins, or carbohydrate mixtures that can consolidate under controlled heating. Unlike extrusion, it does not require a fluid paste but rather powders with suitable flow properties, particle size, energy absorption, and the capacity for partial fusion. The application of sintering to agri-food by-products offers interesting opportunities to valorize dry fractions, flours, starch-rich powders, fine fibers, or mixtures with binding agents. However, this technology requires strict control over particle-size distribution, moisture content, powder flowability, transition temperature, and applied energy. In addition, lignocellulosic materials or those rich in heat-sensitive compounds may undergo thermal degradation, poor interparticle cohesion, or structural brittleness. Therefore, their use requires carefully adjusted formulations and, in many cases, the incorporation of components that promote particle bonding [36,37].

Direct ink writing is a direct deposition technique for viscoelastic inks, pastes, or gels. It is closely related to extrusion-based printing but is widely used for developing soft materials, hydrogels, bioinks, functional composites, and self-supporting structures. In this technology, the ink must exhibit pseudoplastic, or shear-thinning, behavior; that is, it must reduce its viscosity as it passes through the nozzle and rapidly recover its structure after deposition. This recovery is essential for maintaining the printed shape and supporting successive layers [38].

In the valorization of agri-food by-products, direct ink writing is particularly promising for formulating hydrogels, biopolymers, protein-based matrices, lignocellulosic suspensions, polysaccharide gels, and functional biocomposites. Its main advantage is the ability to design materials with controlled architecture, porosity, composition gradients, and adjustable mechanical properties. Nevertheless, it requires detailed control over ink rheology, yield stress, elasticity, thixotropy, and dimensional stability, which can be challenging when using residues with high compositional heterogeneity [38,39].

4.2. Material–Technology Compatibility

Compatibility between the material and the printing technology depends mainly on the formulation’s physical state, rheological behavior, particle-size distribution, stability during deposition, and capacity for subsequent consolidation. In the case of agri-food by-products, this compatibility should be assessed from an integrated perspective, as the same residue may behave differently depending on pretreatment, degree of milling, moisture content, chemical composition, and the supporting matrix [31,39,40].

Plant-derived by-products rich in fiber, starch, pectin, cellulose, or phenolic compounds are usually more compatible with extrusion-based technologies and direct ink writing, especially when they are processed into fine flours, pastes, gels, or suspensions stabilized with hydrocolloids. Fibers can improve dimensional stability and water retention capacity, but they can also increase viscosity, introduce heterogeneity, and promote nozzle clogging if their particle size is not properly controlled [33,34,40].

Animal-derived by-products, such as gelatin, collagen, myofibrillar proteins, whey, or chitosan, can be used in gelling matrices or bioinks because they can form three-dimensional networks, films, emulsions, or hydrogels. Their technological compatibility depends on factors such as temperature, pH, protein concentration, ionic strength, and gelation behavior. These characteristics make them suitable for extrusion, direct ink writing, and biomedical or food applications, although they require greater sanitary control, microbiological stability, and process standardization [31,38,39].

Industrial by-products, such as bagasse, pomace, husks, bran, and oilseed cakes, can be adapted to different technologies depending on their degree of processing. When used as dry powders, they may be suitable for sintering or biocomposite formulation; when hydrated or combined with biopolymers, they can be used in extrusion or direct ink writing. In these cases, compatibility is conditioned by homogeneity of the mixture, particle size, water-absorption capacity, the presence of insoluble components, and interactions with hydrocolloids or proteins [32,36,37].

Post-consumer residues, in contrast, present greater restrictions due to their heterogeneity, microbiological risks, variable composition, and difficulty in standardization. Their direct application in 3D printing technologies is limited; however, they can be used indirectly after bioconversion, biopolymer extraction, fermentation, or microbial biomass production. In this scenario, the selected printing technology will depend on the secondary material obtained, such as biopolymers, hydrogels, stabilized powders, or functional extracts.

The material–technology relationship is also influenced by the expected functionality of the final product. For personalized foods, extrusion and inkjet techniques are prioritized because of their ability to control shape, composition, and ingredient distribution. For biodegradable packaging and biocomposites, extrusion, direct ink writing, and, in some cases, sintering are relevant. For biomaterials and scaffolds, direct ink writing offers advantages by enabling the production of porous structures, complex geometries, and matrices with controlled viscoelastic behavior [30,32,38]. Table 1 summarizes recent experimental evidence on additive manufacturing and complementary printing approaches for the valorization of agri-food and bio-based by-products. It compares representative processing conditions, quantitative performance indicators, principal advantages, technical limitations, and typical applications reported in recent studies.

Overall, the reported results confirm that technological performance depends not only on the printing or deposition method but also on the physical state, composition, pretreatment, particle size, moisture content, and concentration of the incorporated by-product or bio-based feedstock. Because the studies used different formulations, equipment, geometries, and testing methods, the quantitative values should be interpreted as representative study-specific results rather than universal operating ranges.

4.3. Critical Parameters

Printability describes whether a formulation can be deposited continuously, form uniform filaments, adhere between layers, and retain its shape after printing [33,34,39]. In extrusion-based systems and direct ink writing, it mainly depends on shear-thinning behavior, yield stress, structural recovery, and elasticity. These properties can be adjusted with hydrocolloids, starches, proteins, fibers, emulsions, gels, or biopolymer blends, while excess solids or insufficient hydration may reduce flow and printing precision [31,38,39,40]. Viscosity must also balance flow and shape retention: low values favor spreading or collapse, whereas high values increase pressure requirements and the risk of clogging. Therefore, the appropriate viscosity depends on the printer, nozzle diameter, printing speed, pressure, temperature, and formulation [31,34,35,36,37,38,39].

Table 1. Recent experimental evidence on additive manufacturing and complementary printing approaches for the valorization of agri-food and bio-based by-products.

Printing Technology	By-Product and Matrix	Key Quantitative Evidence	Critical Interpretation	Application	Sources
Extrusion-based food printing	Gluten-free dough with 4 wt% beetroot by-product and baker’s yeast or baking powder.	The baking-powder formulation reached G′ = 6057 ± 72 Pa. Baker’s yeast with beetroot by-product provided greater dimensional stability, particularly in oval geometries.	Fiber enrichment and improved shape stability; however, performance depended on leavening agent and geometry, and 5–7 wt% by-product produced inadequate extrusion flow.	Customized gluten-free bakery products.	[41]
Extrusion followed by ionic gelation	Alginate formulations containing carrot and fish by-products or Ulva rigida.	Structures were sprayed with 1 mol/L CaCl2. Ca2+ generally increased hardness, reduced adhesiveness, and improved water resistance. The algal formulation showed ΔE = 5.77 after 24 h.	Enables nonthermal stabilization and manual handling; requires an additional spraying step, and storage effects differed among formulations.	Structured sustainable foods.	[42]
Direct ink writing	Aqueous ink with 70 wt% lignosulfonate, methyl cellulose, and glycerol.	Printed at room temperature with 0.2, 0.4, and 0.8 mm nozzles. Young’s modulus ranged from 2.4 ± 0.6 to 106.9 ± 17.3 MPa, and elongation from 18% to 26%. Shape stability reached 200 °C.	Solvent-free, mechanically tunable, and recyclable by rehydration; drying, shrinkage, glycerol content, and humidity affected final performance.	Recyclable prototypes and wood-like structures.	[29]
Piezoelectric inkjet printing	Betanin from red pitaya peel and anthocyanins from Kyoho grape peel.	Newtonian printable inks showed dynamic viscosities of 1.97–2.32 mPa·s and responded to five spoilage gases, with visible changes during shrimp deterioration.	Precise, low-volume deposition of waste-derived pigments; pigment stability to light and oxygen requires improvement, and the method functionalizes surfaces rather than producing bulk 3D structures.	Intelligent packaging indicators.	[43]
Selective laser sintering	Peanut shell powder and polyethersulfone composite.	Optimized conditions: 0.12 mm scan spacing, 1.8 m/s scan speed, 16 W laser power, 78 °C preheating, and 0.2 mm layer thickness. Bending strength reached 14.1 MPa, tensile strength 6.1 MPa, impact strength 2.12 kJ/cm2, and density 1.2 g/cm3.	Optimization improved mechanical performance and dimensional precision; results remained dependent on particle size, biomass content, mixture ratio, and processing conditions.	Wood, roofing, and furniture components.	[44]
Fused filament fabrication	Polylactic acid (PLA) reinforced with 0–7 wt% peanut hull powder.	At 7 wt%, tensile strength reached approximately 27 MPa and Young’s modulus 3.9 GPa. Printed parts retained antimicrobial activity and showed increased hardness.	Preserved tensile performance while increasing stiffness and functionality; higher contents caused roughness, porosity, brittleness, reduced flow, and nozzle clogging above 7 wt%.	Antimicrobial biocomposites and packaging.	[45]

Note: Reported values are study-specific because the materials, equipment, geometries, and testing methods differed. Inkjet printing is included as a complementary surface-functionalization approach, while lignosulfonate represents a bio-based industrial by-product.

Table 1. Recent experimental evidence on additive manufacturing and complementary printing approaches for the valorization of agri-food and bio-based by-products.

Printing Technology	By-Product and Matrix	Key Quantitative Evidence	Critical Interpretation	Application	Sources
Extrusion-based food printing	Gluten-free dough with 4 wt% beetroot by-product and baker’s yeast or baking powder.	The baking-powder formulation reached G′ = 6057 ± 72 Pa. Baker’s yeast with beetroot by-product provided greater dimensional stability, particularly in oval geometries.	Fiber enrichment and improved shape stability; however, performance depended on leavening agent and geometry, and 5–7 wt% by-product produced inadequate extrusion flow.	Customized gluten-free bakery products.	[41]
Extrusion followed by ionic gelation	Alginate formulations containing carrot and fish by-products or Ulva rigida.	Structures were sprayed with 1 mol/L CaCl2. Ca2+ generally increased hardness, reduced adhesiveness, and improved water resistance. The algal formulation showed ΔE = 5.77 after 24 h.	Enables nonthermal stabilization and manual handling; requires an additional spraying step, and storage effects differed among formulations.	Structured sustainable foods.	[42]
Direct ink writing	Aqueous ink with 70 wt% lignosulfonate, methyl cellulose, and glycerol.	Printed at room temperature with 0.2, 0.4, and 0.8 mm nozzles. Young’s modulus ranged from 2.4 ± 0.6 to 106.9 ± 17.3 MPa, and elongation from 18% to 26%. Shape stability reached 200 °C.	Solvent-free, mechanically tunable, and recyclable by rehydration; drying, shrinkage, glycerol content, and humidity affected final performance.	Recyclable prototypes and wood-like structures.	[29]
Piezoelectric inkjet printing	Betanin from red pitaya peel and anthocyanins from Kyoho grape peel.	Newtonian printable inks showed dynamic viscosities of 1.97–2.32 mPa·s and responded to five spoilage gases, with visible changes during shrimp deterioration.	Precise, low-volume deposition of waste-derived pigments; pigment stability to light and oxygen requires improvement, and the method functionalizes surfaces rather than producing bulk 3D structures.	Intelligent packaging indicators.	[43]
Selective laser sintering	Peanut shell powder and polyethersulfone composite.	Optimized conditions: 0.12 mm scan spacing, 1.8 m/s scan speed, 16 W laser power, 78 °C preheating, and 0.2 mm layer thickness. Bending strength reached 14.1 MPa, tensile strength 6.1 MPa, impact strength 2.12 kJ/cm2, and density 1.2 g/cm3.	Optimization improved mechanical performance and dimensional precision; results remained dependent on particle size, biomass content, mixture ratio, and processing conditions.	Wood, roofing, and furniture components.	[44]
Fused filament fabrication	Polylactic acid (PLA) reinforced with 0–7 wt% peanut hull powder.	At 7 wt%, tensile strength reached approximately 27 MPa and Young’s modulus 3.9 GPa. Printed parts retained antimicrobial activity and showed increased hardness.	Preserved tensile performance while increasing stiffness and functionality; higher contents caused roughness, porosity, brittleness, reduced flow, and nozzle clogging above 7 wt%.	Antimicrobial biocomposites and packaging.	[45]

Note: Reported values are study-specific because the materials, equipment, geometries, and testing methods differed. Inkjet printing is included as a complementary surface-functionalization approach, while lignosulfonate represents a bio-based industrial by-product.

Flowability should be evaluated according to the printing mechanism rather than as a universal material property. In printing by extrusion, processability depends on the balance between the material’s ability to pass continuously through the nozzle and its capacity to retain the deposited shape. Inadequate viscosity may cause deformation, discontinuous extrusion, or nozzle clogging [33,34,35]. In direct ink writing, printability also depends on shear-induced viscosity reduction, yield stress, viscoelasticity, and structural recovery after deposition [38,39]. Inkjet printing requires materials with low viscosity that can form and deposit stable droplets [30]. In contrast, selective laser sintering depends on the spreading and consolidation of powder mixtures, which are influenced by moisture and powder flow properties [36,37]. Therefore, processability should be assessed using parameters specific to each technology rather than through a general description of flowability alone.

Post-printing stability is also critical, especially when working with materials derived from agri-food residues. A printed structure may lose stability because of excess moisture, phase separation, syneresis, shrinkage during drying, poor interlayer adhesion, or thermal degradation. In foods, this stability is related to texture, appearance, acceptability, and shelf life. In packaging and biocomposites, it is associated with mechanical strength, structural integrity, barrier capacity, and durability. In biomaterials, it influences porosity, biocompatibility, and compound-release capacity [34,35,40].

Other process parameters also affect final performance, including printing speed, layer height, nozzle diameter, material temperature, platform temperature, infill pattern, environmental humidity, and post-processing conditions. In technologies such as inkjet printing, surface tension, viscosity, droplet size, colloidal stability, and the absence of particles are relevant. In sintering, powder flowability, applied energy, temperature, particle size, and degree of compaction are decisive. Therefore, optimizing 3D printing with agri-food by-products requires integrating the material properties with the operating parameters of the selected technology [30,36,37].

4.4. Technical Limitations

Industrial-scale application remains limited by the variability of agri-food by-products in composition, moisture content, particle size, and the contents of fiber, protein, lipid, and bioactive compounds. These differences depend on factors such as species, origin, season, processing, and storage, and may reduce formulation stability and product reproducibility [32,35]. In extrusion-based printing and direct ink writing, inadequate viscosity, excess water, large particles, or poorly adjusted parameters may also cause deformation, discontinuous deposition, poor interlayer adhesion, surface roughness, and reduced resolution [34,35,38].

In inkjet printing, the main limitations stem from the need for liquid, homogeneous, low-viscosity materials. Extracts from agri-food residues may contain particles, unstable colloids, or compounds that alter surface tension, leading to nozzle clogging, poor droplet formation, or irregular deposition. For this reason, their application requires prior filtration, clarification, stabilization, or formulation, which may increase the process cost and complexity [30].

In sintering, the restrictions stem from the need for homogeneous, dry powders with good flowability. Many agri-food residues exhibit irregular particle size, high hygroscopicity, low fusion capacity, or thermal sensitivity, which makes their layer-by-layer consolidation difficult. In addition, localized heating can induce degradation, browning, structural changes, or loss of functional compounds. These factors limit their direct application and necessitate the use of blends with binding agents or materials with better thermal behavior [36,37].

Another cross-cutting limitation is the lack of standardized criteria for evaluating printability and comparing results across studies. At present, various studies use indicators such as geometric fidelity, dimensional stability, extrusion force, resolution, texture, mechanical strength, or visual analysis, though not always consistently. This lack of standardization makes it difficult to compare materials, technologies, and applications, especially when working with by-products of variable composition [33,34,39,40].

Finally, material-related restrictions include safety, microbiological stability, shelf life, sensory acceptance, equipment compatibility, scalability, and regulatory compliance. In food and biomedical applications, it is necessary to ensure material safety, by-product traceability, and the absence of contaminants. In non-food applications, the main challenges are related to mechanical strength, durability, controlled biodegradability, and actual environmental performance. Taken together, these limitations show that 3D printing of agri-food by-products depends not only on residue availability but also on their transformation into a technically printable, stable, safe, and functional matrix.

Figure 3 summarizes the relationship between the types of agri-food by-products, the physical state of printable matrices, compatible 3D printing technologies, and the main critical process parameters, while also highlighting the technical limitations that may affect the quality, stability, and scalability of printed materials.

The choice of 3D printing technology cannot be assumed to be a general decision for all agri-food by-products, but rather the result of matching the material’s characteristics to the requirements of each process. Extrusion and direct ink writing show greater flexibility for wet, viscous, and heterogeneous matrices. In contrast, inkjet printing and sintering require materials with more controlled viscosity, particle size, colloidal stability, or thermal behavior. Therefore, progress in this field will depend on moving from merely printable formulations to systems that are truly functional, reproducible, and applicable under real-use conditions. This relationship between material, technology, and performance helps explain the main applications currently being developed in foods, packaging, biomaterials, biocomposites, and other emerging sectors.

5. Multisectoral Applications

The application of 3D printing to the valorization of agri-food by-products and residues offers a broad, cross-cutting field of use, owing to its ability to transform bio-based matrices into functional structures with controlled geometries, adjustable compositions, and specific properties. Unlike conventional transformation processes, additive manufacturing enables integration of design, functionality, customization, and material-use efficiency, which is particularly relevant when working with secondary resources derived from agri-food chains. In this context, by-products can serve as sources of fiber, protein, bioactive compounds, biopolymers, lignocellulosic fillers, or carbonaceous precursors, depending on the final application and the degree of processing required.

The multisectoral applications of 3D printing with materials derived from agri-food residues include functional foods, personalized nutrition, sustainable packaging, biomaterials, release systems, biocomposites, structural materials, and emerging uses in energy, textiles, and agriculture. This diversity shows that valorization should not be limited to ingredient recovery but can also be directed toward the design of advanced value-added products. However, the potential of each application depends on the compatibility between the material, printing technology, functional requirements, product stability, and scale-up feasibility.

5.1. Food Applications

Food applications are among the most developed areas of 3D printing using agri-food matrices, particularly because this technology can be used to design products with specific shapes, textures, nutritional composition, and functionality. In this field, 3D printing enables processing ingredients in the form of pastes, gels, purées, doughs, or formulations enriched with proteins, fibers, hydrocolloids, bioactive compounds, and natural extracts. This capacity is especially relevant for the valorization of plant-derived and industrial by-products, which can be incorporated as functional flours, fiber sources, antioxidants, or texturizing matrices [46,47].

In the development of functional foods, agri-food by-products can provide compounds of nutritional or technological interest, such as dietary fiber, polyphenols, carotenoids, proteins, pectins, starches, and natural pigments. These components can improve the nutritional value of the printed product while also modifying its rheological and structural properties. For example, fruit and vegetable residues can be transformed into functional powders or pastes for producing snacks, gels, purée-type products, fruit-based formulations, or antioxidant-enriched matrices. 3D printing also enables control over the spatial distribution of these ingredients, supporting the design of products with differentiated sensory and nutritional characteristics [47].

Personalized nutrition is another relevant application, as 3D printing enables food composition to be adjusted to individual requirements, including age, physiological condition, sensory preferences, energy needs, or dietary restrictions. This technology can facilitate the preparation of foods adapted to specific populations, such as older adults, children, athletes, or people with chewing and swallowing difficulties. In these cases, the use of printable matrices enriched with proteins, fibers, or bioactive compounds from agri-food by-products can contribute to the development of personalized foods with greater functional value [46,48].

Likewise, 3D printing can contribute to the development of foods for special medical purposes by enabling modification of texture, porosity, hardness, shape, and composition. This feature is useful for designing foods adapted to patients with specific nutritional needs, including easy-to-swallow diets, foods with controlled nutrient release, or products with personalized composition. Nevertheless, food applications require strict control of safety, microbiological stability, sensory acceptability, shelf life, and regulatory compliance, especially when ingredients derived from residues or by-products are incorporated [48].

Despite their potential, food applications face challenges related to post-printing stability, preservation of bioactive compounds, final texture, formulation reproducibility, and consumer acceptance. In addition, incorporating by-products can modify color, flavor, aroma, or mouthfeel, necessitating formulation optimization to balance functionality, processability, and sensory quality.

5.2. Sustainable Packaging

Sustainable packaging is one of the most promising applications of 3D printing in the circular economy, as it enables the transformation of agri-food residues into biodegradable materials, bioplastics, coatings, films, protective structures, and components for active and intelligent packaging. This approach can reduce dependence on petroleum-derived polymers while valorizing residues rich in cellulose, lignin, starch, pectin, hemicellulose, or lignocellulosic fibers [49].

In the development of bioplastics and biodegradable materials, agri-food by-products can be used as the main matrix, reinforcing fillers, or functional additives. Residues such as sugarcane bagasse, husks, bran, plant fibers, fruit residues, peels, or agricultural by-products can be incorporated into biopolymeric matrices to improve stiffness, reduce costs, modify biodegradability, or provide functional properties. 3D printing enables the fabrication of packaging with customized geometries, porous structures, lightweight designs, or shapes tailored to the food product, offering advantages over conventional molding or thermoforming processes [50,51,52].

Active and intelligent packaging is another area of interest. Through 3D printing, it is possible to incorporate indicators, sensors, natural pigments, antimicrobial compounds, or antioxidants into specific areas of the package. This capacity can be used to monitor freshness, detect pH changes, control the release of active compounds, or improve protection against food deterioration. In this context, extracts from agri-food residues rich in anthocyanins, phenolic compounds, or antimicrobial substances can act as functional components in advanced packaging systems [49].

3D printing also facilitates the fabrication of biodegradable packaging prototypes from bio-based materials, allowing rapid evaluation of geometries, thicknesses, mechanical strength, moisture behavior, and protective capacity. This flexibility is important for adapting packaging to specific products and reducing material waste during the design stage. In addition, the use of agricultural residues as a source of printable materials favors the integration of local valorization chains, especially in regions with high availability of residual biomass [51,52].

However, the development of printed packaging from agri-food by-products presents important limitations. These include moisture sensitivity, low mechanical strength in some matrices, material variability, the need for compatibilizers, compound migration, storage stability, and approval for food-contact applications. Therefore, sustainable packaging applications must evaluate not only biodegradability but also barrier properties, strength, safety, shelf life, and real environmental performance.

5.3. Biomedical Applications

Biomedical applications of 3D printing using materials derived from agri-food by-products primarily involve the development of scaffolds, biopolymeric matrices, hydrogels, controlled-release systems, and implantable or non-implantable devices. Although this field is subject to stricter regulatory and safety requirements, agri-food by-products can provide biopolymers, minerals, proteins, and bioactive compounds that have potential for the fabrication of biocompatible and biodegradable matrices [53,54].

3D-printed scaffolds enable the fabrication of three-dimensional structures with controlled porosity, geometry, and architecture, which are essential for applications in tissue engineering, regeneration, cell support, and local delivery systems. Materials such as chitosan, gelatin, collagen, cellulose, starch, pectin, and other biopolymers derived from or recovered from agri-food sources can be used as components of bioinks or structural matrices. Their ability to form gels, three-dimensional networks, or porous systems makes them attractive candidates for biomedical applications [54].

Controlled-release systems represent another relevant application. 3D printing enables the design of matrices that modulate the release of active compounds by controlling geometry, porosity, composition, infill density, and material degradability. In this context, biopolymers derived from agri-food residues can act as biodegradable carriers for the release of drugs, bioactive compounds, antioxidants, or therapeutic agents. This approach connects residue valorization with the development of more sustainable pharmaceutical systems [53].

The use of agri-food by-products in biomedical applications can also help reduce costs and improve the sustainability of the materials used. For example, residues rich in cellulose, proteins, chitosan, or minerals can be transformed into useful matrices for bioinks, scaffolds, or release systems, provided that they meet strict requirements for purity, biocompatibility, sterility, and reproducibility. Because of these requirements, in most cases, the residue is not used directly; instead, purified fractions, recovered biopolymers, or modified materials are employed [53,54].

Nevertheless, biomedical applications present greater barriers than food or packaging applications. The main limitations include biological characterization, contaminant control, material reproducibility, sterilization, storage stability, cell compatibility, and compliance with health regulations. Therefore, although the potential is high, biomedical implementation requires advanced processing, purification, and experimental validation.

5.4. Construction and Industry

The application of 3D printing in construction and industry offers opportunities to valorize agri-food by-products as fillers, reinforcements, or functional components in biocomposites and structural materials. In these sectors, the priority is usually not nutritional functionality but rather mechanical strength, stiffness, durability, thermal stability, low density, controlled biodegradability, and reduced environmental impact. Lignocellulosic residues, husks, bagasse, stems, bran, peels, and agricultural powders can be incorporated into polymeric, cementitious, or bio-based matrices to obtain printable composite materials [55,56].

Biocomposites based on biodegradable polymers, such as polylactic acid, represent an interesting alternative for incorporating finely milled agricultural residues. The addition of fibers or particles of agri-food origin can reduce the amount of virgin polymer, modify stiffness, provide surface texture, and support the valorization of residual biomass. Recent studies have shown that agricultural residues, such as tomato stems or buckwheat husks, can be incorporated into polymeric matrices intended for 3D printing. However, their effect on mechanical properties depends on concentration, particle size, interfacial compatibility, and dispersion quality [55,56].

In lightweight structural applications, by-products can serve as fillers or reinforcing materials, enabling the fabrication of low-weight parts, panels, modular components, prototypes, decorative elements, furniture, or insulating materials. Additive manufacturing enables control over internal geometry, infill patterns, and material distribution, which can partially compensate for the mechanical limitations of some bio-based matrices. In addition, the ability to produce parts on demand reduces waste associated with cutting, molds, and subtractive processes.

In the construction sector, the integration of agri-food residues can also be directed toward alternative bio-based materials, mycelium biocomposites, lignocellulosic blends, or hybrid materials. Although these applications are still under development, they show potential to reduce the environmental footprint of conventional materials and diversify pathways for residue valorization. However, requirements for strength, durability, moisture stability, thermal behavior, and structural safety are more stringent than those for low-risk products.

The main limitations in construction and industry include poor adhesion between the matrix and filler, moisture absorption, thermal degradation during processing, loss of strength due to excessive residue content, biomass variability, and the need for compatibilizers. In addition, structural applications require the evaluation of long-term performance, aging, dimensional stability, fire resistance, controlled biodegradability, and regulatory compliance.

5.5. Emerging Applications

Beyond food, packaging, biomedical, and industrial applications, 3D printing of materials derived from agri-food residues opens emerging opportunities in energy, textiles, and agriculture. These areas differ in technological maturity, but they share a common interest in using residual biomass as a source of functional materials, porous structures, biocomposites, and high-value precursors.

In the energy sector, agri-food residues can be used indirectly as precursors for carbonaceous materials used in electrodes, supercapacitors, batteries, and other electrochemical energy storage devices. Through processes such as carbonization, activation, or chemical modification, residual biomass can be transformed into porous carbons with high surface area and relevant electrochemical properties. 3D printing enables the organization of these materials into controlled architectures, thereby promoting ion transport, conductivity, mechanical stability, and the design of customized devices [57,58,59].

Although energy-related applications move away from the direct use of residues in foods or packaging, they represent an advanced valorization route for lignocellulosic fractions, peels, plant residues, and carbon-rich biomass. Their main advantage is the ability to convert low-value residues into functional materials for energy storage technologies. However, this route requires additional conversion processes, porosity control, conductivity adjustment, and the formulation of printable inks with adequate rheological stability [57,58].

In textiles, emerging applications include biocomposites, hybrid materials, flexible structures, textile scaffolds, and systems based on mycelium or biopolymers. The combination of 3D printing, bio-based matrices, and textile supports can generate materials with improved mechanical properties, adaptable geometries, and potential applications in design, lightweight architecture, coatings, sustainable fashion, or interior materials. Mycelium–textile systems, for example, show how a biological matrix can be integrated with textile structures to produce biocomposites with scale-up potential [60].

In agriculture, 3D printing offers opportunities to develop biodegradable pots, cultivation supports, nutrient-release systems, sensors, irrigation devices, protective covers, or components adapted to local needs. The use of agri-food by-products in this sector is especially consistent with the circular economy, as it allows materials of biological origin to be returned to agricultural production systems. A relevant example is the development of 3D-printed bioplastic pots from soybean by-products, which combine biodegradability with potential agronomic function [61].

Agricultural applications can also benefit from the geometric customization offered by 3D printing. It is possible to design structures with controlled porosity, programmed degradation, gradual nutrient release, or adaptation to different crop types. Nevertheless, it is necessary to evaluate soil stability, real biodegradability, interaction with microorganisms, compound release, mechanical resistance during use, and effects on plant growth.

Overall, emerging applications show that 3D printing can significantly expand the valorization pathways of agri-food by-products beyond traditional sectors. However, their consolidation will depend on the integration of material design, functional evaluation, environmental analysis, safety of use, and scalability. Therefore, progress in these applications requires interdisciplinary approaches that connect materials science, process engineering, sustainability, digital design, and the circular economy.

Table 2. Multisectoral applications of 3D printing in the valorization of agri-food by-products.

Sector	Valorized By-Product/Material	3D Printing Technology	Application	Reported Data or Detail	Main Benefit/Limitation	Sources
Functional foods	Spinach and kale stems as edible vegetable residues.	Extrusion	Printed purée-type foods/food inks for soft diets or dysphagia.	Nine food inks were formulated. Hexagonal structures were printed with a 1.5 mm nozzle; printability, rheology, syneresis, 30 min stability, and IDDSI (International Dysphagia Diet Standardisation Initiative) classification were evaluated.	Valorizes edible spinach and kale stems in visually attractive, texture-modified foods; high moisture and fiber may impair extrusion, stability, and syneresis.	[62]
Functional foods	Okara, a soybean by-product generated during soy milk and tofu production.	Direct ink writing (DIW)/ink extrusion	Printed snacks or food matrices with customized texture.	Printable ink: 33% w/w okara powder, particle size < 100 µm, yield stress 200 ± 40 Pa, and storage modulus 23,300 ± 300 Pa; texture was assessed by TPA (texture profile analysis).	Valorizes okara without rheological modifiers; particle size and concentration govern rheology, extrusion, and printability.	[63]
Functional foods	Orange by-product incorporated into apricot gels.	Extrusion/FDM (fused deposition modeling) of gels followed by freeze-drying	Fiber-enriched gel snacks.	Gelatin gels contained 30, 50, or 70% apricot pulp; orange by-product was added to reach 3% fiber. Printing used a 1.2 mm nozzle and 100% infill, followed by freeze-drying; rheology, accuracy, color, shear force, and bioactive compounds were evaluated.	Improves printability and produces fiber- and bioactive-enriched snacks; freeze-drying and orange by-product increase final hardness/crispness.	[64]
Functional foods	Orange peel waste.	Direct ink writing/pneumatic extrusion	Edible snacks and 3D-printed food structures.	Optimal ink: 20% orange peel powder and 1% xanthan gum; initial viscosity 22.5 kPa·s, yield stress 377 Pa, and storage modulus 44.24 kPa. Printing used a 20 gauge nozzle, 30 mm/s, 0.160 MPa, and 0.40 mm layer height.	Valorizes orange peel while preserving bioflavonoids and antioxidant capacity after printing; palatability, microbiological safety, and snack formulation require further optimization.	[65]
Functional foods	Apple pomace and lemon albedo.	Syringe-based extrusion/thick-paste 3D printing	3D-printed nutraceutical snack stabilized by microwave drying.	Mixtures contained 85–95% apple pomace and 5–15% lemon albedo with ultrasound pretreatment; optimum: 90/10%. Printing used a syringe paste extruder, 4 mm nozzle, 5 layers, 2 mm layer height, and 10 mm/s; microwave drying: 700 W for 3 min.	Valorizes fiber-, pectin-, and phenolic-rich fruit by-products; ultrasound improved printability, extrusion force, smoothness, and phenolic release during digestion. Sensory, digestibility, and scale-up validation remain necessary.	[66]
Functional foods	Watermelon rind.	Hot-extrusion 3D printing	3D-printed vegan gummies.	Watermelon rind purée was formulated with sugar, citric acid, and 0, 5, 10, 15, or 20% pectin. The 10% formulation was printed as a 30 × 30 mm twisted hexagon using a 0.84 mm nozzle, 80 °C, 800 mm/min, 60 rpm, 1.5 bar, and 75% infill.	Valorizes a bioactive-rich fruit residue and yields customized gummies with good sensory acceptance; pectin is required because watermelon rind is not inherently printable.	[67]
Functional foods	Grape pomace transformed into bioactive microparticles by pressurized liquid extraction and spray drying with maltodextrin.	Extrusion-based 3D printing of xanthan gum matrices	3D-printed functional food matrices, with potential for nutraceutical foods, dysphagia diets, and natural pH indicators based on anthocyanins.	Extract: 3.58 µg GAE/mL, 219.3 µg TA/mL, and 6.4 nmol FeSO4/mL. Spray-dried particles: 3.5 mg GAE/g, 514.1 µg TA/g, and 86.5 µmol FeSO4/g. Gels contained 6% xanthan gum, 3–9% particles, and sometimes 0.5% sodium alginate; printing used a 0.8 mm nozzle, 10 mm/s, 30% infill, and star or porous cylindrical designs.	Particles increased consistency index, storage modulus, viscoelasticity, deformation resistance, and fidelity while preserving phenolics and anthocyanins; physicochemical and microbiological stability, texture, and scalability require validation.	[68]
Functional foods	Pumpkin powder/purée formulated with gellan gum as a printable food matrix.	Extrusion-based 3D printing followed by freeze-drying	3D-printed crunchy pumpkin snacks with controlled internal structure.	Pumpkin purée: powder:water 1:2 and 0.75% gellan gum. Cubes (45 × 45 × 6 mm) used honeycomb, rectilinear, grid, or triangular patterns at 25, 50, 75, or 100% infill; printing used a 1.2 mm nozzle, 1.2 mm layer height, and 20 mm/s, followed by freeze-drying.	Internal design controlled crunchiness and fidelity; lower infill increased porosity/crunchiness, while 75% infill produced greater deformation. It does not directly valorize an agri-food residue.	[69]
Functional foods	Chenpi, aged citrus peel/pericarp, combined with kiwi juice and citrus pectin.	Extrusion-based 3D printing	3D-printed functional kiwi jelly with chenpi, aimed at developing functional snacks with antioxidant and anti-obesity potential.	Optimal formulation: 30.26% chenpi decoction, 35% kiwi juice, and 2.88% pectin; predicted/actual sensory scores: 95.20/94.2. Cuboid: 2.5 × 2.5 × 1.25 cm3; 0.84 mm nozzle, 15 mm/s, 90% infill, rectilinear pattern, and 40 °C. Composition/activity: 7.58 ± 0.32 mg GAE/g phenolics, 2.47 ± 0.13 mg RE/g flavonoids, 81.65 ± 2.65 µmol TE/g ABTS, 5.94 ± 0.21 µmol TE/g DPPH, and 15.49 ± 0.21 µmol TE/g FRAP.	Produces a customized, low-fat snack rich in phenolics with antioxidant, anti-inflammatory, and anti-obesity potential; chenpi is a processed citrus derivative rather than a fresh residue, so its inclusion requires explicit justification.	[70]
Functional foods	Carob pulp as an agri-food by-product, used to obtain a cellulose-rich fraction, combined with potato peel flour as a gelling base.	Extrusion-based 3D printing of cellulose-rich food gels	New 3D-printed foods enriched with dietary fiber.	Cellulose-rich fraction: 44.5 ± 3.0 g/100 g carob pulp, including 24.4% cellulose; swelling 5.9 mL/g, water holding 4.0 g/g, and fat adsorption 6.5 g/g. Gels had 15% total solids, potato peel flour, and 0–8% cellulose-rich fraction; 2–3% gave highest printability, whereas 6–8% reduced layer definition and stability.	Valorizes carob pulp as a fiber/cellulose source for functional foods; excessive fiber reduces viscosity, layer separation, and printability.	[16]
Functional foods	Broccoli and carrot imperfectly shaped and discarded due to commercial appearance standards.	Extrusion-based 3D printing	Healthy 3D-printed cracker-type snacks.	Vegetables were blanched, freeze-dried, milled, and sieved to ≤250 µm. Inks contained 25, 50, or 75% vegetable powder replacing wheat flour, plus salt, olive oil, and water. Foodini printing used a 1.5 mm nozzle, 6 mm-high flower, and 4 layers; baking: 177 °C for approximately 8 min. The 50 and 75% inks printed best; the 75% sample volume was 14.3 cm3 versus 14.6 cm3 for the model.	Valorizes imperfect vegetables in customized snacks with good shape stability and pseudoplastic flow; wheat flour is required as binder, and vegetable type alters viscosity, microstructure, color, and hardness.	[71]
Functional foods	Grape pomace and cracked wheat from the food industry.	Extrusion-based 3D printing	3D-printed functional cookies enriched with fiber and antioxidant compounds.	Doughs used cracked wheat with 4, 6, or 8% grape pomace; powders were sieved to 0.22 mm. Best conditions: 1.28 mm nozzle, 600 rpm motor, and 400 mm/min; baking: 130 °C for 12 min. The 6% formulation had highest sensory acceptance.	Valorizes streams usually used as animal feed, increasing protein, fiber, and antioxidants; higher pomace raises viscosity, lowers printability, and may darken or bitter the product.	[72]
Biodegradable packaging	Banana peel transformed into powder and combined with 1% w/w guar gum.	Extrusion-based 3D printing	3D-printed biodegradable food casings or packaging.	Banana peel was dried at 60 °C for 3 days, milled, and sieved to 0.125 mm. Powder properties: particle size 326.5 nm, surface area 15.792 m2/g, pore size 3.42 nm, and pore volume 0.045 cc/g. With 1% w/w guar gum, printing used a 1.2 mm nozzle, 6 bar, 150 rpm, 500 mm/min, 0.186 ± 0.002 g/min, and 0.8 mm nozzle height.	Banana peel alone was not extrudable; 1% guar gum enabled a printable paste and stable biodegradable packaging. Dependence on hydrocolloid remains the main limitation.	[73]
Biodegradable packaging	Sugarcane bagasse mixed with banana peel as lignocellulosic agro-industrial by-products.	Extrusion-based 3D printing	Customized 3D-printed food casings or packaging.	Extrusion used 3.2 bar, a 1.28 mm nozzle, and 240 rpm. Optimal settings: 500 mm/min, 0.304 ± 0.003 g/min, and 0.450 mm nozzle height. Casings underwent soil degradation, showed water sorption >0.07 g water/g solids at relative humidity >50%, and stored cake for 9 days.	Valorizes abundant lignocellulosic residues in biodegradable packaging; water uptake limits use mainly to low-moisture foods.	[74]
Biomedical	Okara, a by-product of soy milk and tofu production, used in composite sponges with silver nanoparticles (AgNPs).	3D printing and freeze-drying	Porous sponges for hemostasis, antimicrobial activity, and wound healing.	Okara–AgNP sponges had interconnected pores and liquid absorption. Results: blood coagulation index 24.5%, antibacterial activity 95.1% against Escherichia coli and 94.4% against Staphylococcus aureus, and 87.8% wound closure on day 9.	Combines okara valorization with absorption, hemostasis, and antimicrobial action; sterility, stability, biocompatibility, and preclinical performance require further validation.	[75]
Biomedical	Eggshell microparticles incorporated as a bioceramic reinforcement in a thermoplastic PCL matrix.	Extrusion-based 3D printing	Biocomposite scaffolds for bone tissue engineering.	PCL scaffolds contained 0–50% w/w eggshell microparticles. SEM, FTIR, TGA, DSC, XRD, compression, accelerated degradation, and MC3T3-E1 preosteoblast response were evaluated for 14 days; remaining mass after degradation ranged from 89.4 to 28.3%, depending on formulation.	Uses eggshell as a low-cost bioceramic for customized bone scaffolds; mineral loading must balance printability, strength, degradation, and cellular response.	[76]
Biomedical	Hydroxyapatite (HA) derived from fish scales, combined with chitosan (CS) and polycaprolactone.	Hot-extrusion 3D printing	HA/CS/PCL scaffolds for bone tissue engineering.	Fish-scale HA scaffolds with different HA/PCL and HA/CS/PCL ratios were printed at 80–90 °C, 6–8 mm/s, and a 0.3 mm nozzle. The 30% HA + 5% CS + PCL scaffold had 350 µm pores, higher tensile strength than pure PCL, and antimicrobial activity against E. coli and S. aureus.	Valorizes fish scales as biogenic HA with bioactivity, hydrophilicity, antimicrobial action, and bone regeneration potential; preclinical validation, HA reproducibility, and ratio optimization are required.	[77]
Construction and industry	Wheat middlings and rice husk as biofillers in PLA.	FDM	PLA–agro-industrial residue biocomposite filaments and printed parts.	PLA filaments contained 10–20% w/w residues and had a 1.75 mm diameter. Printing: 230 °C nozzle, 60 °C bed, 20 mm/s, 100% infill, and 0.5 mm nozzle. Rice husk reduced thermal expansion and may reduce shrinkage/warping.	Reduces virgin PLA and valorizes low-cost residues; particle size, dispersion, and matrix–filler adhesion must be controlled to prevent brittleness and poor interlayer bonding.	[78]
Construction and industry	Agricultural and marine residues: Opuntia ficus-indica and Posidonia oceanica as natural fillers in PLA.	FDM	PLA–residue parts and biocomposites for additive manufacturing.	PLA filaments contained 10 or 20% w/w natural filler and had a 1.75 mm diameter. Printing: 220 °C nozzle, 60 °C bed, 80% infill, 0.1 mm layer height, and 45 mm/s.	Replaces up to 20% of PLA without major processability loss; high filler loading reduces strength, elongation, and impact resistance through voids, agglomeration, and weak adhesion.	[79]
Construction and industry	Spent coffee grounds incorporated into a PLA matrix through a coffee masterbatch.	Large-format fused granulate fabrication (FGF/LFAM)	PLA–spent coffee ground biocomposites for complex parts and 3D-printed furniture.	PLA contained 5 or 10% w/w coffee masterbatch. Pellet extrusion used a 3 mm nozzle, 190 °C extrusion, 75–80 °C bed, and 10–30 mm/s. The 90PLA10CM formulation printed complex geometries, non-planar structures, and a table prototype.	Valorizes spent coffee grounds in large-format printing while avoiding filament production; variable dispersion and granulometry may affect homogeneity, recyclability, and finish.	[80]
Construction and industry	Cellulose fibers obtained from cocoa shell, incorporated as reinforcement in PLA.	FFF/FDM	PLA–cocoa shell cellulose biocomposite filaments for 3D printing.	PLA filaments contained 5% w/w untreated or treated cocoa-shell fibers and measured 1.75 ± 0.05 mm. Printing: 180 °C nozzle, 60 °C bed, 0.40 mm nozzle, 30–70% infill, and 0.10–0.20 mm layers. Maximum strength was 16.05 MPa with treated fibers, 70% infill, and 0.10 mm layers.	Valorizes cocoa-shell cellulose and reduces virgin PLA; treatment increased strength by 18%, but performance remained below pure PLA and requires better dispersion, adhesion, and printing optimization.	[81]
Energy/porous materials	Partially dehydrated dairy whey as a porous carbon precursor.	Robocasting/DIW followed by carbonization	3D porous carbons with potential for energy, adsorption, and catalysis.	Paste with 76% solids was printed through a 20 gauge nozzle at 20 mm/s and 0.6 mm layer height. After curing and carbonization at 850 °C, structures showed 23% shrinkage, approximately 70% porosity, surface area up to 500 m2/g, and compressive strength near 5 MPa.	Converts dairy surplus into high-value porous carbons; curing, carbonization, and washing are needed to lower ash, and device-specific validation remains necessary.	[59]

Note: Abbreviations: ABTS, 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid); DSC, differential scanning calorimetry; DPPH, 2,2-diphenyl-1-picrylhydrazyl; FFF, fused filament fabrication; FGF, fused granulate fabrication; FRAP, ferric reducing antioxidant power; FTIR, Fourier transform infrared spectroscopy; GAE, gallic acid equivalents; LFAM, large-format additive manufacturing; MC3T3-E1, murine preosteoblastic cell line; PCL, polycaprolactone; RE, rutin equivalents; SEM, scanning electron microscopy; TA, total anthocyanins; TE, Trolox equivalents; TGA, thermogravimetric analysis; XRD, X-ray diffraction.

summarizes the main multisectoral applications of 3D printing in the valorization of agri-food by-products, considering the type of residue used, the printing technology applied, the developed application, the reported experimental data, and the main associated benefit or limitation.

The reviewed applications show that 3D printing can considerably expand the use of low-value agri-food materials, not only in food and packaging, but also in biomaterials, biocomposites, energy, textiles, and agriculture. However, the level of development varies across sectors. While some food and packaging formulations are advancing toward practical application, biomedical, structural, and emerging uses still require additional technical, functional, environmental, and regulatory validation. Therefore, demonstrating that a material can be printed is not enough; its performance, stability, safety, scalability, and real contribution to sustainability must also be compared. This need supports the comparative analysis developed in the following section.

6. Comparative Assessment of Performance and Sustainability

The comparative assessment of performance and sustainability is essential to determining the true viability of 3D printing as a strategy for valorizing agri-food by-products and residues. Although the previous sections highlight the potential of these materials in food, packaging, biomedical, industrial, and emerging applications, their implementation does not depend solely on the availability of the residue or on the possibility of printing it. It also requires an integrated analysis of their mechanical, functional, and rheological properties; compatibility with specific technologies; process efficiency; technical limitations; and the environmental impacts associated with the material’s life cycle and the final product [68,69,70,71].

In this context, comparative assessment enables identification of the combinations of material, pretreatment, printing technology, and application that offer the best performance prospects. Likewise, it facilitates the recognition of differences among sectors in technological maturity, product stability, reproducibility, safety, scalability, and contribution to the circular economy. This approach is especially important for agri-food by-products, given their compositional variability and the need to transform heterogeneous residual streams into technically printable, functional, and sustainable matrices [71,72,73].

6.1. Material Assessment

The assessment of materials for 3D printing should jointly consider mechanical, functional, and rheological properties. In materials derived from agri-food by-products, these properties depend on the origin of the residue, its chemical composition, particle size, moisture content, fiber, protein, polysaccharide, and lipid contents, as well as its interaction with other components of the matrix. Therefore, material performance cannot be evaluated solely on compositional value but also on its behavior during extrusion, deposition, consolidation, and final use [68,69].

Mechanical properties are especially relevant in packaging, biocomposites, scaffolds, industrial components, and structural materials. Parameters such as tensile strength, elastic modulus, flexural strength, hardness, deformation, interlayer adhesion, and dimensional stability enable estimation of the material’s ability to withstand loads, handling, storage, or use conditions. In PLA- and biomass-based biocomposites, incorporating lignocellulosic fibers or particles can improve stiffness and reduce the use of virgin polymer; however, it can also lead to brittleness, printing defects, or loss of strength when filler dispersion is inadequate [70,71].

Functional properties vary according to the application. In printed foods, these factors relate to nutritional value, texture, appearance, stability, release of bioactive compounds, and sensory acceptability. In packaging, they include biodegradability, barrier capacity, antioxidant activity, antimicrobial activity, and moisture resistance. In biomedical applications, they are associated with biocompatibility, porosity, degradability, and controlled release. In energy applications, they are linked to conductivity, surface area, porosity, and electrochemical stability. Therefore, the same by-product may present different technological value depending on the expected function of the final product [69,72].

Rheological behavior is one of the most important criteria for evaluating printable matrices, especially in extrusion-based and direct ink writing technologies. Materials with pseudoplastic behavior, adequate structural recovery, sufficient yield stress, and controlled viscosity usually show better printability. Geometric fidelity, shape retention, and extrudability depend on parameters such as storage modulus, yield stress, phase angle, and stability of the deposited filament. In gelled matrices, a material that is too fluid may deform after deposition, whereas an excessively viscous material may cause nozzle clogging, flow discontinuity, or low resolution [68,69].

From a comparative perspective, food materials require a balance among rheology, texture, and safety; packaging materials require a balance among biodegradability, mechanical strength, and moisture stability; biomaterials demand biocompatibility and reproducibility; and industrial biocomposites prioritize strength, thermal stability, and processability. This diversity shows that there is no single performance criterion; rather, the assessment must be tailored to the application sector and the product’s functional requirements.

6.2. Material–Technology Interaction

The interaction between the material and the printing technology determines the success of the additive manufacturing process. In materials derived from agri-food by-products, this interaction primarily depends on the matrix’s physical state, particle-size distribution, moisture content, viscosity, thermal stability, homogeneity, and subsequent consolidation capacity. Therefore, the same residual biomass may be suitable for one technology and unsuitable for another, depending on the pretreatment applied and the formulation obtained [70,71].

Material–technology compatibility is more favorable when the material’s properties match the process’s requirements. Pastes, gels, and purées exhibiting viscoelastic behavior are usually compatible with extrusion and direct ink writing; liquid extracts, fine emulsions, or functional solutions are better suited to inkjet printing; dry, homogeneous powders can be processed by sintering; and biocomposite filaments require suitable thermal and rheological properties for FDM or FFF. In the case of agri-food by-products, particle size reduction, moisture control, and the incorporation of hydrocolloids, plasticizers, or support polymers are common strategies to improve compatibility [68,70,71].

Process efficiency should also be evaluated comparatively. In 3D printing, efficiency is not only about manufacturing speed but also about the rational use of materials, waste reduction, customization capacity, minimization of post-processing, and reproducibility. Additive manufacturing can reduce waste compared with subtractive processes, but it may also increase energy consumption or require highly processed materials. Therefore, efficiency should be analyzed by considering both the technical performance and the environmental impact of the entire process [74,75,76].

The main limitations of the material–technology interaction include nozzle clogging, poor interlayer adhesion, shrinkage during drying, deformation, loss of geometric fidelity, brittleness, thermal sensitivity, and batch-to-batch variability. These limitations are more critical when using by-products with high insoluble fiber content, heterogeneous particles, or heat-sensitive compounds. In polymeric biocomposites, the interfacial compatibility between the matrix and the filler is decisive for preventing strength loss and improving the mechanical stability of the printed material [70,71,73].

Therefore, technology selection should consider not only the possibility of printing the material, but also the quality of the final product, process efficiency, material stability, ease of scaling, and the regulatory or safety requirements associated with each application.

6.3. Multisectoral Comparison

A multisectoral comparison enables identification of key differences in the level of development and technical viability of 3D printing applied to agri-food by-products. In the food sector, the technology is relatively advanced, especially in formulations based on gels, pastes, purées, proteins, hydrocolloids, and matrices enriched with functional compounds. However, its industrial viability still depends on improving printing speed, post-processing stability, shelf life, and sensory acceptance [82,83,84].

In sustainable packaging, the potential is high, as fibers, starch, cellulose, bagasse, peels, and other lignocellulosic residues can be incorporated into biodegradable or bio-based matrices. This sector directly connects to the goals of reducing conventional plastics and valorizing residual biomass. Nevertheless, technical viability depends on achieving barrier properties, mechanical strength, moisture stability, and safety for food-contact applications, aspects that still require further experimental and regulatory validation [85,86,87].

Biomedical applications offer high added value but also entail greater technical and regulatory requirements. In this sector, the direct use of agri-food residues is limited; purified fractions, recovered biopolymers, or functionalized materials are generally employed. Viability depends on biocompatibility, sterility, reproducibility, stability, and regulatory compliance. Therefore, although delivery systems and scaffolds show high potential, their maturity is lower than that of food applications or non-biomedical biocomposites [86].

In construction and industry, biocomposites derived from agri-food residues and biomass represent a promising route for manufacturing lightweight parts, prototypes, non-structural components, furniture, design materials, and insulating elements. The combination of PLA or other polymers with plant fibers or biomass reduces the use of virgin polymers and improves the material’s environmental profile. However, technical viability depends on matrix–filler adhesion, mechanical strength, thermal stability, moisture absorption, and durability under real use conditions [84,85,87].

Emerging applications, such as energy, textiles, and agriculture, present a more heterogeneous level of development. In energy, valorization is usually indirect, through the conversion of biomass into functional carbonaceous materials. In textiles, integration with mycelium, biopolymers, or hybrid structures remains in the exploratory stage. In agriculture, potential applications include biodegradable pots, cultivation supports, and nutrient-release systems, but further evidence is needed on soil biodegradation, interactions with microorganisms, and agronomic effects. Overall, these sectors represent future opportunities, although with lower technological maturity than food, packaging, and industrial biocomposites [87,88].

From a comparative perspective, the sectors with the greatest short-term viability are functional foods, biodegradable packaging, and industrial biocomposites. Biomedical and energy applications offer higher added value but require greater levels of processing, validation, and control. Textile and agricultural applications are promising, though they still require further experimental studies, life-cycle analyses, and performance evaluation under real conditions.

6.4. Sustainability Assessment

The sustainability of 3D printing based on agri-food by-products should be assessed by considering waste reduction, resource efficiency, environmental impact, and contribution to the circular economy. Although additive manufacturing is often associated with lower material waste and greater customization, it is not always automatically more sustainable than conventional processes. Its environmental performance depends on the type of material, energy consumption, failure rate, need for post-processing, product lifespan, transport, scalability, and end-of-life scenario [88,89,90].

Waste reduction constitutes one of the main potential benefits. The use of agri-food by-products as secondary raw materials enables the diversion of biomass from low-value routes, such as final disposal, uncontrolled composting, or combustion, toward products with greater functionality. This strategy can help close material loops, reduce pressure on virgin raw materials, and create new value chains. However, for the benefit to be real, the residue must require reasonable pretreatment and must not generate environmental impacts greater than the benefits obtained [90,91,92].

Resource efficiency is related to the rational use of raw materials, energy, water, and additives. 3D printing can improve efficiency by manufacturing only the required geometry, reducing losses from cutting or molding, enabling on-demand production, and decreasing inventories. Nevertheless, some processes may require high energy inputs, long manufacturing times, or formulations containing high-impact additives. Therefore, the assessment should consider both the printing process and the previous stages of drying, milling, extraction, purification, mixing, filament extrusion, or post-processing [88,89].

Life cycle assessment (LCA) is a key tool for comparing the environmental impacts of printed products with those of conventional alternatives. This approach enables evaluation of categories such as carbon footprint, energy consumption, water use, resource depletion, emissions, and waste generation. For materials derived from agri-food by-products, LCA should include the origin of the residue, system boundaries, allocation of environmental burdens, pretreatment, and the product’s end-of-life. Without these elements, sustainability may be overestimated [89,90].

The circular economy provides the conceptual framework for integrating waste valorization, material design, additive manufacturing, and product end-of-life. 3D printing can contribute to circular strategies by using recycled or bio-based materials, distributed manufacturing, repair, customization, inventory reduction, and design for disassembly or biodegradation. However, barriers also exist regarding the quality of recycled materials, variability, certification, market acceptance, scalability, and the lack of specific standards [91,92,93].

Techno-economic feasibility should also be considered together with environmental performance. The potential advantages of on-demand production, reduced inventories, and lower material waste may be offset by the costs of by-product collection, pretreatment, additives, equipment, energy consumption, quality control, limited printing throughput, and post-processing. Therefore, future studies should compare 3D printing with conventional manufacturing using integrated techno-economic and environmental assessments that account for production scale, product performance, and added value. Consequently, sustainability should be assessed through integrated indicators that consider both technical and environmental performance. A printable formulation is not necessarily sustainable if it requires high energy consumption, non-renewable additives, or generates products with low durability. Similarly, a biodegradable material does not necessarily have a lower environmental impact if its production or processing incurs high environmental costs. Therefore, comparative analysis should balance functionality, efficiency, safety, environmental impact, and circularity.

6.5. Gaps and Opportunities

Despite recent progress, important gaps remain in the comparative assessment of the performance and sustainability of 3D printing applied to agri-food by-products. One of the main current limitations is the lack of standardized criteria for evaluating printability, structural stability, mechanical properties, and functional performance. Studies often use different methodologies, which makes it difficult to compare results across materials, technologies, and application sectors [82,83,87].

Another relevant gap is the limited availability of quantitative studies that integrate technical performance and sustainability. Many studies report rheological, mechanical, or functional properties, while others analyze sustainability, the circular economy, or environmental impact; however, studies that combine both dimensions within a single comparative framework are less common. This lack of integration limits the identification of material–technology–application combinations with the best balance between functionality and sustainability [88,89,90,91,92,93].

There are also limitations associated with the variability of agri-food by-products. The composition of these materials may vary depending on species, variety, season, geographical origin, industrial process, and storage conditions. This variability affects the reproducibility of formulations, printing quality, and the final properties of the product. Therefore, characterization, pretreatment, and quality control protocols are required to reduce variability and facilitate technology transfer [85,87].

In terms of technological gaps, it is necessary to improve the compatibility between residues and printable matrices, develop bio-based additives, optimize interlayer adhesion, reduce printing defects, and increase process speed. It is also necessary to advance hybrid technologies that combine 3D printing with drying, gelation, curing, fermentation, carbonization, or controlled post-processing. These strategies could expand the range of valorized materials and improve the quality of the final product [83,85,87].

Future opportunities focus on the development of smart materials, advanced biocomposites, active packaging, personalized foods, biomaterials, agricultural devices, and biomass-based energy systems. Likewise, integrating artificial intelligence (AI), rheological modeling, process simulation, and generative design can accelerate the optimization of formulations and printing parameters. These tools would enable predicting printability, reduce the number of experimental trials, and improve the efficiency of new product development [88,93].

Finally, to consolidate this field, it is necessary to move toward robust comparative studies, material databases, standardized protocols, life cycle assessment, economic evaluation, and pilot-scale validation. The valorization of agri-food by-products through 3D printing can only be consolidated as a sustainable strategy if it simultaneously demonstrates technical viability, product functionality, safety, scalability, and a real reduction in environmental impacts.

Table 3. Comparative criteria for assessing the performance and sustainability of materials derived from agri-food by-products in 3D printing.

Evaluated Dimension	Comparative Criteria	Suggested Quantitative Indicators	How to Evaluate It	Comparative Interpretation	Sources
By-product characterization	Cocoa-shell composition, particle size, pretreatment, thermal stability, and initial compatibility with the polymer matrix.	Cocoa shell ≈80% of fruit weight; lignocellulosic material ≈87% of dry weight; cellulose 35.4%, hemicellulose 37%, lignin 14.7%; particle size ≤ 44 µm; 5% fiber in polylactic acid; lower moisture loss after chemical treatment.	Wash, dry, mill, sieve, and apply alkaline treatment and bleaching; assess fiber morphology, chemistry, and thermal behavior before polymer incorporation.	Determines whether conditioned cocoa shell can reinforce 3D-printing filaments. Chemical treatment improves fiber cleanliness, removes impurities, and favors incorporation into the polymer matrix.	[81]
Food-ink formulation and printability	Incorporation of edible by-products into a hydrogel matrix to obtain stable, extrudable inks.	By-product type and concentration; particle size; hydration capacity; bulk density; viscosity; yield stress; structural recovery; printing pressure and speed; layer stability; printability score.	Dry, mill, and sieve the by-products; mix with a hydrogel matrix; characterize morphology, hydration, density, and rheology; print model structures and assess flow continuity, clogging, bleeding, deformation, layer stability, and repeatability.	Identifies by-products suitable for printable food inks. Formulations with 20% lettuce and brewer’s spent grain showed better stability; okara hindered extrusion because of high water-holding capacity, whereas sesame cake caused clogging through agglomeration and particle separation.	[94]
Mechanical properties and biodegradability of printed material	Effect of plant by-products in polylactic acid on strength, flexibility, and degradation.	By-product contents of 1, 3, and 5%; particle size <0.2 mm; flexural strength; flexibility; breaking stress; extensibility; weight loss after 60 and 120 days in air and soil.	Prepare filaments with polylactic acid, carrot pomace, and ground walnut shell; print standardized specimens; perform flexural and fracture tests; quantify weight loss under different storage conditions.	Assesses whether food-industry by-products improve environmental performance without excessive mechanical loss. A 5% addition increased flexural strength by up to 44.88% and flexibility by up to 38.3%, but reduced breaking stress; it also increased weight loss and favored biodegradability.	[95]
Mechanical, thermal, and functional properties of filament	Orange-peel particles in polylactic acid for sustainable filaments with mechanical performance and antioxidant activity.	Orange-peel content 2.5–20%; particle size; filament diameter; tensile strength; Young’s modulus; elongation at break; glass-transition, cold-crystallization, and melting temperatures; antioxidant activity.	Wash, dry, mill, and sieve orange peel; mix with polylactic acid; extrude filaments; evaluate tensile, thermal, chemical, and antioxidant properties using mechanical tests, thermal analysis, infrared spectroscopy, and antioxidant assays.	Defines the concentration that balances performance and functionality. At 2.5%, orange peel maintained good mechanical behavior and improved ductility; 10–20% reduced mechanical properties because of agglomeration and matrix saturation. Antioxidant activity increased with orange-peel content, supporting active-packaging applications.	[96]
Printable material performance	Viscosity, strength, moisture, microstructure, and post-printing shape retention.	Viscosity; gel strength; moisture content; extrusion force; stable height or layer number; printing speed; nozzle diameter; infill percentage.	Assess extrusion behavior, flow continuity, layer formation, structural stability, and deformation; examine the effects of proteins, starches, fats, hydrogels, and cellulose-rich ingredients.	Determines whether a formulation can be printed stably. Low viscosity, excess moisture, large particles, or insufficient strength promote deformation, collapse, or clogging, whereas balanced ingredients improve shape, texture, and stability.	[97]
Printability and shape stability	Relationship among flour content, extrusion, layer formation, and preservation of the designed geometry.	Nixtamalized corn-flour content (%); water content (%); apparent viscosity; stress required to initiate flow; adhesiveness; hardness; Young’s modulus; printed-piece weight and dimensions; acceptable dimensional deviation of ±10%.	Prepare doughs with different flour/water ratios; print standard figures by screw extrusion; measure weight and dimensions; evaluate viscosity, flow, adhesiveness, hardness, and deformation resistance.	Identifies the optimal formulation range for continuous extrusion and structural stability. Doughs with 30–32.5% flour best preserved shape; lower levels caused flattening, whereas higher levels made extrusion difficult or impossible.	[98]
Effect of formulation on printing stability	Influence of sucrose and pregelatinized rice flour on flow, stability, and printing accuracy.	Sucrose 0–4%; pregelatinized rice-flour content; maximum storage modulus; yield stress; printing percentage error; deformation factor.	Prepare pastes with different sucrose levels; measure rheology; print hollow cylinders and cuboids; determine printed area, error relative to the design, and post-printing deformation by image analysis.	Shows how formulation affects dimensional accuracy. Increasing sucrose weakened the starch network, reduced viscoelastic stability, and increased printing error and deformation; more pregelatinized rice flour improved shape retention.	[99]
Circularity and material–technology compatibility	Use of wood residues or lignocellulosic derivatives as reinforcement or matrix in printable materials.	Residue content; particle size; polymer matrix or binder; processing temperature; mechanical strength; thermal stability; proportion of recycled or bio-based material.	Classify residues by origin and contamination; characterize composition, particle size, and thermal stability; select material extrusion, binder jetting, powder sintering, or photopolymerization; evaluate printability and final properties.	Compares which lignocellulosic residues can be valorized and with which technology. Clean residues with controlled particle size have greater potential; heterogeneity, contamination, matrix incompatibility, and processing instability remain the main scale-up barriers.	[100]
Mechanical properties and circularity of printed material	Recycled polylactic acid, printing parameters, thermal treatment, and performance for sustainable packaging.	Layer thickness 0.10–0.20 mm; infill 50–100%; extrusion temperature 210 °C; build plate 60 °C; thermal treatment 75 °C for 3 h; tensile strength; Young’s modulus; elongation at break; crystallinity; average prediction error ≈6%.	Print specimens using different layer thicknesses and infill levels; apply or omit thermal treatment; perform tensile and crystallinity analyses; compare conditions and use predictive models to identify optimal combinations.	Assesses whether recycled polymer can retain suitable properties. Parameter optimization and thermal treatment improved strength, stiffness, elongation, and crystallinity, supporting sustainable packaging and reduced dependence on virgin material.	[101]
Environmental sustainability and techno-economic feasibility	Comparison of fused filament fabrication and injection molding for plastic packaging.	Package mass; energy per unit; production time; environmental impact; unit cost; equipment investment; minimum production volume; visual and functional quality.	Apply life-cycle assessment, cost models, net present value, and packaging-quality tests; compare energy, material use, cost, functionality, and surface finish.	Determines environmental and economic viability relative to injection molding. For mass production, 3D printing showed higher environmental impact and cost and lower quality because of energy use and long printing times; it may be more competitive for small, customized, or low-volume production.	[102]
Environmental sustainability of the printing process	Environmental impact of fused filament fabrication according to energy use, material, parameters, and filament origin.	Printing time; energy per part; infill percentage; layer thickness; material use; embodied energy; virgin, recycled, or bio-based filament; electricity source.	Apply life-cycle assessment from material extraction through filament production, printing, transport, use, and end of life; compare infill, layer thickness, materials, and energy sources.	Confirms that 3D printing is not sustainable by default. Impacts depend mainly on energy, printing time, and material; they decrease by avoiding unnecessary infill, shortening printing time, batching parts, using recycled or bio-based feedstocks, and relying on renewable electricity.	[103]
Circularity and valorization of polymeric waste	Use of recycled plastic waste as 3D-printing feedstock within a circular-economy model.	Polymer type; recycling-cycle number; recycled content; reinforcements; mechanical-property change; dimensional stability; filament quality; potential for further reuse.	Classify and clean waste; apply mechanical, chemical, or thermal recycling; fabricate recycled filaments and functional parts; evaluate mechanics, dimensional accuracy, thermal stability, and end-of-life recyclability.	Assesses whether 3D printing can close polymer-waste loops. Recycled polymers can yield useful products, but performance depends on sorting, contamination control, filament quality, material degradation, and matching the recovered properties to suitable applications.	[104]
Techno-economic feasibility and eco-efficiency	Recycled polylactic acid for functional 3D-printed parts, considering performance, environmental impact, and cost.	Tensile strength; fatigue strength; density; hardness; surface roughness; dimensional tolerance; part functionality; energy consumption; life-cycle cost; total environmental impact.	Manufacture parts with recycled and virgin materials; perform mechanical, dimensional, surface, and functional tests; compare environmental impact and life-cycle costs.	Determines whether recycled material can replace virgin feedstock in functional uses. Although recycled material showed lower strength and more defects, it remained technically viable for the evaluated part and was more eco-efficient because it reduced virgin-material demand and valorized plastic waste.	[105]

proposes a comparative framework for assessing the performance and sustainability of materials derived from agri-food by-products for 3D printing, integrating technical, functional, environmental, and scalability criteria through quantitative indicators and evaluation methods applicable across sectors.

In summary, the comparison among materials, technologies, and application sectors shows that the valorization of agri-food by-products through 3D printing should not be assessed solely by the ability to produce a printable structure. It should also consider technical performance, functionality, safety, scalability, and actual sustainability. This comparison makes it possible to distinguish applications that are closer to practical implementation from those that still require further validation under real use conditions. Progress in this field therefore requires integrated comparative frameworks to guide the selection of materials, processes, and applications with greater feasibility. These considerations provide the basis for discussing the cross-cutting challenges and future opportunities associated with consolidating this technology within circular economy frameworks.

More specifically, the critical comparison shows that incorporating agri-food by-products does not lead to uniform improvements. Higher fiber or solids content may enhance viscosity, shape stability, or stiffness, but may also cause nozzle clogging, irregular deposition, or brittleness. These differences depend on the composition, particle size, moisture content, pretreatment, supporting matrix, printing parameters, and post-processing conditions. Food, packaging, and biocomposite applications currently show greater technological maturity, whereas biomedical and other emerging applications still require further validation, standardization, and integrated technical, environmental, and economic assessment.

7. Cross-Cutting Challenges and Future Perspectives

Based on the reviewed literature, the main cross-cutting challenges in the valorization of agri-food by-products through 3D printing concern transforming heterogeneous residues into reproducible, safe, and technically printable matrices. Although by-products represent attractive sources of fiber, proteins, polysaccharides, bioactive compounds, and biopolymers, their compositional variability makes it difficult to standardize formulations and compare studies. In this sense, greater control is still required over moisture content, particle size, rheology, post-printing stability, and behavior during post-processing. In addition, the technology faces limitations associated with low printing speed, loss of geometric fidelity, nozzle clogging, low structural stability, and the need for equipment adapted to complex matrices [106,107,108].

From an economic and scaling perspective, the transition from laboratory trials to pilot or industrial applications remains a relevant barrier. 3D printing offers advantages in customization, waste reduction, and on-demand manufacturing. However, its large-scale adoption will depend on improving productivity, reducing pretreatment costs, ensuring the continuous availability of residual biomass, and demonstrating advantages over conventional processes. The integration of agri-food by-products into real value chains also requires supply models, traceability, quality control, and techno-economic assessment. Therefore, scaling should not be understood only as an increase in printing volume but as the ability to maintain performance, safety, sustainability, and reproducibility under real production conditions [106,107,108].

Regulatory and social challenges are equally important, especially in food, biomedical, and packaging applications. The use of materials derived from residues requires ensuring safety, the absence of contaminants, microbiological stability, traceability, and regulatory compliance, depending on the final application.

From a regulatory perspective, 3D-printed foods and packaging must comply with the requirements applicable to their ingredients and food-contact materials. In the United States, the Food and Drug Administration (FDA) regulates food additives, substances considered generally recognized as safe, and food-contact substances [109,110]. In the European Union, the European Food Safety Authority (EFSA) evaluates novel foods and substances used in food-contact materials [111,112].

In printed foods, in addition to safety, consumer acceptance will depend on perceptions of naturalness, nutritional benefits, appearance, taste, labeling information, and trust in the technology. Recent studies show that factors such as sensory appeal, food neophobia, risk perception, and environmental concern can significantly influence the intention to accept or purchase 3D-printed foods; therefore, scientific communication and transparency will be key to avoiding social rejection [106,107,113].

Future research should focus on intelligent, automated, and interconnected 3D printing systems. Artificial intelligence and machine learning could integrate compositional, rheological, and imaging data to optimize formulations and predict printability. Sensors, machine vision, real-time monitoring, and digital twins could support process simulation and automatic adjustment of printing parameters. Robotic manufacturing, automated material feeding and post-processing, and Industry 4.0 platforms could also improve reproducibility, traceability, productivity, and industrial scale-up. However, these developments require standardized datasets, interoperable monitoring systems, and pilot-scale validation for heterogeneous agri-food matrices [114,115].

The consolidation of 3D printing as a tool for valorizing agri-food by-products will depend on moving from isolated experimental demonstrations toward integrated technological development systems. This implies integrating residue characterization, formulation of printable matrices, technology selection, functional validation, sustainability assessment, and user acceptance within a single analytical framework. Consequently, progress in the field will require not only new materials but also standardized protocols, comparative criteria, pilot-scale validation, and transfer models that demonstrate that valorization through 3D printing is technically viable, environmentally favorable, and socially acceptable.

Figure 4 presents an integrative scheme of the main cross-cutting challenges and future perspectives for the valorization of agri-food by-products through 3D printing, linking technical, economic, regulatory, and social aspects with opportunities associated with material innovation, artificial intelligence, scaling, and multisectoral expansion.

The challenges show that the valorization of agri-food by-products through 3D printing will not advance solely through the availability of new materials or improvements in printing equipment, but through the ability to integrate both aspects into reproducible, safe, and sustainable systems. The next stage of the field should focus on demonstrating, with stronger comparative evidence, which combinations of residue, formulation, technology, and application offer real benefits over conventional alternatives. Only from this perspective will it be possible to move from promising experimental proposals to solutions with practical impact within circular value chains.

8. Conclusions

This review demonstrates that 3D printing can support the valorization of agri-food by-products when residue composition, pretreatment, printing technology, and final application are considered as an integrated system. By-products rich in fibers, proteins, polysaccharides, bioactive compounds, and biopolymers can provide functional, structural, and environmental benefits, including the development of customized foods, biodegradable packaging, biomaterials, and biocomposites while reducing dependence on virgin raw materials and creating added value from residual biomass.

The main technological benefit of extrusion-based printing and direct ink writing is their compatibility with wet, viscous, and compositionally heterogeneous matrices. However, their performance is limited by nozzle clogging, poor shape retention, structural collapse, and variability among by-product batches. Inkjet printing provides high deposition precision but requires low-viscosity and stable formulations with controlled particle size. Sintering enables the processing of dry powders and the fabrication of complex geometries. However, its applicability is restricted by powder flowability, thermal degradation, energy consumption, and the limited availability of suitable agri-food materials. Technology selection should therefore be based on the physical state, rheological behavior, particle size, thermal stability, and functional requirements of each material.

Food and packaging applications currently present the greatest potential for practical implementation because they combine technological feasibility with clear opportunities for product customization and waste valorization. Nevertheless, their industrial adoption still requires validation of safety, sensory acceptability, shelf life, barrier properties, mechanical performance, production capacity, and regulatory compliance. Biomedical, construction, energy, textile, and agricultural applications offer additional opportunities. However, their technological maturity remains lower because they require greater material purification, functional validation, standardization, and demonstration under real operating conditions.

Future research should move beyond demonstrating basic printability and focus on three interconnected priorities. First, standardized protocols are required to characterize raw materials, rheology, printability, structural fidelity, and final product performance. Second, pilot-scale studies should compare 3D printing with conventional manufacturing in terms of productivity, cost, energy consumption, environmental impact, safety, and added value. Third, automated control, artificial intelligence, real-time monitoring, and reliable supply chains should be integrated to reduce material variability and improve reproducibility. Addressing these priorities will determine whether 3D printing can progress from isolated laboratory demonstrations toward safe, scalable, economically viable, and environmentally beneficial applications.