Tribological Performance Enhancement in FDM and SLA Additive Manufacturing: Materials, Mechanisms, Surface Engineering, and Hybrid Strategies—A Holistic Review

Abstract

Additive Manufacturing (AM) techniques, such as Fused Deposition Modeling (FDM) and Stereolithography (SLA), are increasingly adopted in various high-demand sectors, including the aerospace, biomedical engineering, and automotive industries, due to their design flexibility and material adaptability. However, the tribological performance and surface integrity of parts manufactured by AM are the biggest functional deployment challenges, especially in wear susceptibility or load-carrying applications. The current review provides a comprehensive overview of the tribological challenges and surface engineering solutions inherent in FDM and SLA processes. The overview begins with a comparative overview of material systems, process mechanics, and failure modes, highlighting prevalent wear mechanisms, such as abrasion, adhesion, fatigue, and delamination. The effect of influential factors (layer thickness, raster direction, infill density, resin curing) on wear behavior and surface integrity is critically evaluated. Novel post-processing techniques, such as vapor smoothing, thermal annealing, laser polishing, and thin-film coating, are discussed for their potential to endow surface durability and reduce friction coefficients. Hybrid manufacturing potential, where subtractive operations (e.g., rolling, peening) are integrated with AM, is highlighted as a path to functionally graded, high-performance surfaces. Further, the review highlights the growing use of finite element modeling, digital twins, and machine learning algorithms for predictive control of tribological performance at AM parts. Through material-level innovations, process optimization, and surface treatment techniques integration, the article provides actionable guidelines for researchers and engineers aiming at performance improvement of FDM and SLA-manufactured parts. Future directions, such as smart tribological, sustainable materials, and AI-based process design, are highlighted to drive the transition of AM from prototyping to end-use applications in high-demand industries.

1. Introduction

Additive manufacturing (AM), or simply 3D-printing, is increasingly a revolutionary manufacturing process for the direct fabrication of complex geometries from digital models in a layer-by-layer deposition process. Among all the various AM technologies, Fused Deposition Modeling (FDM) and Stereolithography (SLA) are the most widely used for the fabrication of polymeric and resin-based components because of their availability, material flexibility, and design freedom [1,2,3]. However, the extensive functionality of these technologies in functional industries such as aerospace, biomedical, automotive, and microfluidics has been accompanied by setbacks in some respects, particularly, surface finish and tribological performance.

Tribology, the physics of friction, wear, and lubrication, is critical to determining AM part performance under dynamic contact, motion, or load conditions. For traditionally produced parts, tribological response is deterministic and typically optimized by machining, surface treatment, or material choice. FDM and SLA parts, however, contain inherent anisotropy, stair-step surface roughness, and internal porosity that degrade wear resistance and frictional stability [4,5,6]. These issues arise from the inherent layer-by-layer manufacturing process, where interlayer discontinuities are stress raisers and sites for wear initiation. Optimizing the tribological performance of FDM and SLA parts is, therefore, critical to their migration from prototyping to end-use. FDM-printed components, which are usually printed in a thermoplastic such as PLA, ABS, or PETG, are noted for high surface roughness and anisotropy due to the layers [7,8]. The FDM process with extrusion causes rough layer lines and bad filament bonding, which are the primary reasons for high coefficients of friction (COF) and load wear [9]. In addition, process parameters such as infill density, nozzle diameter, raster orientation, and build direction also significantly contribute to tribological behavior and define the mechanical continuity and surface morphology of the component. On the other hand, SLA uses photopolymerization to print parts from liquid resins using intense light sources. SLA parts generally exhibit better surface finish (Ra ≈ 2–3 µm) and dimensional accuracy than FDM [10,11,12]. SLA parts are mechanically brittle, exhibit low impact strength, and are prone to micro-crack formation or delamination due to tribo-loading, particularly if there is poor post-curing. SLA resins are generally non-biodegradable and environmentally unsound too, a sustainability problem. Consequently, there is a significant requirement for surface engineering in AM, and specifically for FDM and SLA processes. This is a collection of mechanical, chemical, thermal, and coating-based techniques of changing or enhancing the surface characteristics of a part without altering its bulk [13,14]. In AM, some post-processing techniques, such as mechanical polishing, acetone vapor smoothing, UV/thermal curing, and thin-film coatings, have been found to work well in surface roughness reduction, tribo-improvement, and part life. For example, ABS part acetone vapor treatment has been found with up to 60% maximum surface roughness reduction, and metallic and ceramic coatings have been found to enhance hardness and wear resistance by more than 300% under certain conditions [15,16,17].

Recent publications show growing academic and industrial interest in tribology-focused research in AM, but serious gaps remain. Ng et al. [18] compared FDM head-to-head with SLA and reported that surface roughness (Ra ≈ 2 µm vs. 12–13 µm) and tensile strength (up to 70 MPa) are superior for SLA compared to FDM, but FDM outperforms SLA on cost, throughput, and sustainability, especially when using biodegradable materials like PLA. But in the present work, mostly simple metrics were evaluated and there was no test of long-term wear performance and friction processes in working conditions.

Regarding wear mechanisms, many research papers characterize abrasion, adhesion, fatigue, and delamination as being dominant in AM parts. PLA printed by FDM, for instance, exhibits wear due to plowing and micro-cutting due to the layer microstructure of the material, whereas SLA parts undergo brittle crack growth. A study by Miao et al. [4] on additive manufacturing of structural ceramics focuses on the fact that polymer-based AM parts do not have widespread applicability in high-load tribo-applications unless they are reinforced with functional fillers or surface coatings. FDM filaments reinforced with carbon fiber, graphene, and ceramic nanoparticle-based reinforcements have been explored to enhance mechanical and tribological properties. Uniform dispersion and interfacial bonding remain difficult to obtain. Post-processing techniques have been addressed by Boschetto and Bottini [19], who indicated that barrel finishing can reduce Ra in FDM parts by 40–60%, but typically at the expense of geometrical distortions. Thermal post-processing techniques, such as laser surface remelting (LSR), are being investigated more and more because they are able to selectively enhance surface microstructure without damaging the inner layers. Similarly, solvent-based methods, such as solvent vapor smoothing (e.g., ABS with acetone) and plasma etching, were also found to create sealed, hydrophobic surfaces with COF reduction of as much as 50%. These methods are material-specific and require parameter control for structural integrity. The use of surface coatings like metallic (e.g., Ni, Cr), ceramic (e.g., Al₂O₃, TiN), and polymeric (e.g., PTFE, Parylene) has been shown to confer substantial benefits in enhancing surface hardness, reducing friction, and extending wear life [20]. Spray-coating and dip-coating operations are widely used but suffer from limitations towards coating adhesion and thickness control. Emerging techniques such as plasma spraying and atomic layer deposition (ALD) are under investigation but are currently too costly for most AM applications. Another emerging area is hybrid manufacturing, where subtractive processes like CNC machining, grinding, or rolling are integrated with AM to produce functionally graded surfaces. For example, rolling of FDM parts post-printing has resulted in significant improvement in surface hardness and wear resistance because of the residual compressive stresses generated. Such techniques attempt to capitalize on the geometric versatility of AM and the surface quality of traditional processes. Despite these advances, few studies integrate process parameters, material selection, post-processing techniques, and tribological performance fully. Furthermore, model and simulation activities in this field are immature. Contact analysis and wear estimation finite element models (FEM) are rare, and their precision is limited by the complex anisotropic and heterogeneous nature of AM parts. Machine learning (ML) methods for the prediction of COF or wear rate from process parameters are still in the beginning stages, though initial results show promise for optimization of the process.

This review is necessitated by the growing demand for tribology-enhanced AM parts, particularly in high-value sectors such as aerospace, biomedical, and industrial tooling. The paradoxes and gaps in the current literature, especially in the fields of surface morphology-bridging, process engineering, and tribo-performance, necessitate an integrative, overarching review.

Unlike earlier reviews that often focus only on mechanical or thermal properties, this work offers a comprehensive and comparative analysis of tribological behavior in both FDM and SLA, integrating discussions on hybrid manufacturing strategies, advanced surface engineering, AI-based predictive tools, and sustainability trends. This unified perspective highlights how these approaches collectively address the unique wear challenges of polymer-based AM parts, providing actionable insights for design and manufacturing engineers. Despite these advances, current research often remains fragmented, focusing separately on materials, process parameters, post-processing, or wear mechanisms, without a fully integrated framework linking process, structure, and tribological performance. Predictive modeling using finite element methods (FEM) and emerging machine learning (ML) tools also remains limited, primarily due to the anisotropic and heterogeneous nature of AM parts and insufficient datasets for robust training and validation.

Recognizing these gaps and the rising demand for tribology-optimized AM parts in high-value sectors, this review aims to provide a comprehensive, comparative, and forward-looking synthesis of the field. Specifically, the distinctive contributions of this review are as follows:

• A comparative tribological analysis of both FDM and SLA processes within a unified discussion.
• Integration of material selection, process parameters, and surface engineering strategies to enhance wear resistance and surface durability.
• Examination of hybrid manufacturing techniques that merge additive and subtractive methods for functional surfaces.
• A critical overview of FEM and ML-based predictive frameworks for wear and friction performance in AM parts.
• Discussion of future directions, including smart tribological materials, sustainability considerations, and AI-driven process optimization.

Through this integrative approach, the present review not only highlights existing research but also critically analyzes gaps, practical trade-offs, and emerging solutions to enhance the tribological performance of FDM and SLA parts. The following sections sequentially explore the fundamentals of these technologies, comparative analysis of their tribological behavior, surface engineering strategies, predictive modeling tools, and the outlook for future industrial applications.

Literature Search Methodology

To ensure a comprehensive and balanced review, an extensive literature search was performed across major scientific databases, including Scopus and Web of Science. The search focused primarily on publications from 2016 to 2025, while also including selected foundational studies from earlier years to provide historical context.

Key search terms were combined using Boolean operators and included: “FDM tribology”, “SLA wear mechanisms”, “surface engineering in additive manufacturing”, “hybrid manufacturing for polymers”, and “additive manufacturing post-processing”.

The inclusion criteria prioritized:

• Peer-reviewed journal articles, authoritative review papers, and high-impact conference proceedings.
• Studies offering experimental or simulation-based insights into friction, wear, lubrication, and surface modification in FDM and SLA processes.

The selection process consisted of initial title and abstract screening, followed by full-text review for technical depth, novelty, and relevance. Additional references were identified through backward and forward citation tracking. This methodological approach aimed to build a rigorous and current foundation for the comparative analysis presented in this review.

2. Fundamentals of FDM and SLA Additive Manufacturing

The most widely used additive manufacturing (AM) technologies for polymeric part fabrication are Fused Deposition Modeling (FDM) and Stereolithography (SLA), both having distinct mechanisms, materials, and process limitations that strongly influence surface properties and tribological performance [21,22,23]. FDM extrudes thermoplastic filaments (e.g., PLA, ABS, PETG, and their composite reinforcements) out of a heated nozzle, depositing material in layer form along a G-code-defined trajectory. The build plate descends incrementally after every layer to allow successive solidification of thermoplastic strands, which bond primarily through thermal bonding [4]. Extrusion temperature, cooling rate, raster orientation, nozzle diameter, build direction, and infill density strongly influence layer adhesion success and resulting mechanical integrity. These parameters regulate the degree of interlayer diffusion, porosity, and residual stress, influencing surface finish, dimensional accuracy, and wear resistance. SLA builds parts by photopolymerizing photosensitive resins with a laser or digital light projector. Bottom-up systems use a UV light source to cast cross-sectional patterns onto a resin bath, curing one layer at a time before a platform lift to allow new resin to flow underneath. SLA’s photopolymerization basis provides higher resolution and surface smoothness (typically Ra ~2–3 μm), but mechanical brittleness and poorer load-bearing behavior are still limiting factors due to incomplete cross-linking or oxygen inhibition during curing. Process sensitivity to light dosage, exposure time, layer thickness, and resin viscosity directly influences microstructural homogeneity and surface durability [24,25,26]. SLA materials are based on acrylate and epoxy-based resins, with increasing interest in toughened and bioresorbable formulations for biomedical use. On the other hand, FDM makes the use of recyclable thermoplastics and biodegradable filaments, such as PLA-carbon fiber or PETG-carbon fiber blends, more sustainable and structurally compatible. Most importantly, the microstructural anisotropy inherent to FDM, manifested in stair-stepped side walls and internal porosity, significantly affects the tribology of dynamic-loading surfaces, resulting in premature delamination and fatigue wear [27,28]. SLA, although less prone to delamination due to monolithic curing, suffers from brittle fracture under impact and tribo-fatigue due to low elongation at break. Process defects in both systems require post-processing corrections, but the nature and extent differ. FDM parts often undergo mechanical sanding, vapor smoothing (e.g., acetone for ABS), or laser remelting to repress roughness and seal layer gaps. SLA parts compensate more to post-cure thermally or by UV, enhancing cross-link density, followed by mild polishing to prevent loss of fine geometries. SLA materials can also be engineered with nanoparticles or elastomeric inclusions to modulate modulus and fracture toughness, whereas FDM capitalizes on composite filaments with carbon fibers, graphene, or ceramic fillers to enhance the strength-to-weight ratio and repress surface deterioration under contact wear. Advanced versions of both processes now support hybrid material systems multi-material FDM heads or SLA resin switching to print functionally graded materials with spatially variable properties [29,30,31]. These innovations overcome the monolithic print limitation by enabling optimization of tribo-surfaces within one structure. However, predictability of the processes remains an issue: FDM’s mechanical properties are highly direction-sensitive, while SLA parts can be beset by shrinkage, curling, or residual stress gradients that affect the final geometry and surface reliability. Simulation software and in situ monitoring hardware are beginning to bridge this gap, using thermal imagery, laser scanners, or machine learning algorithms to forecast surface quality outputs from live process inputs. Researchers are also looking at the incorporation of subtractive finishing tools (e.g., micro-milling or abrasive blasting) into AM processes to fabricate surfaces with complex geometry as well as engineered frictional behavior [32,33]. Materials-wise, FDM is more flexible, with thermoplastics having glass transition temperatures of 50–150 °C, while SLA is restricted to brittle thermoset resins with limited thermal stability [34,35,36]. Nonetheless, SLA is more appropriate for microfluidics and dental prosthetics, while accuracy and surface finish are more important than mechanical toughness. FDM is more appropriate, in turn, for structural components such as brackets, gears, or biomedical scaffolds, where toughness, reparability, and surface engineering via coating are feasible. Of special interest, inclusion of nanoscale additives, such as CNTs, Al₂O₃, or TiN, into FDM filaments or SLA resins introduces new complexity, where interfacial bonding, particle agglomeration, and variability in thermal conductivity influence surface performance under tribological loading. Figure 1 illustrates the fundamental working principles of FDM and SLA processes, highlighting the material feed mechanisms, platform orientation, and object formation strategies that govern the layer-by-layer fabrication of parts.

Tribo-enhancement through selection of materials is thus intrinsically connected with processability. SLA’s resin chemistry must be UV-transparent and low viscosity, while FDM filaments must maintain flowability and avoid nozzle clogging [37,38]. These constraints necessitate materials innovation in AM. Hybrid polymers, such as TPU-carbon fiber or bio-based PETG with nanoclay infusion, for example, are being engineered to bridge the gap between flexibility and wear resistance, with improved layer fusion and reduced surface degradation. Ultimately, an understanding of the interaction between process physics, material response, and surface formation mechanisms is the key to optimizing AM parts for contact-rich environments. Emerging trends include digital twin models to predict roughness and wear from input parameters, and AI-based slicers modulating layer height or extrusion speed adaptively with respect to part geometry and anticipated contact zones. In summary, the physics of FDM and SLA are different in nature—thermal extrusion of thermoplastics versus photopolymerization of resins—with corresponding differences in surface morphology challenges, tribological durability, and material compatibility. Control of their process parameters along with intelligent material selection and surface modification processes will be the hallmark of the next generation of performance-based additive manufacturing [39,40,41].

Table 1. Comprehensive summary of recent studies on tribological behavior of FDM and SLA 3D-printed polymers and composites, highlighting research domains, key challenges, objectives, methodologies, major findings, and remarks for future research.

Author et al.	Area	Challenges	Objective	Methodology	Finding	Remark
Mzali et al. [42]	Tribological behavior of 3D-printed PLA parts with different raster directions.	Effect of raster orientation on friction, wear, and surface roughness in 3D-printed parts is not well understood.	To assess how the orientation of raster influences the surface roughness, friction, and wear behavior of PLA under different loads.	Tribological testing: Reciprocating tribometer on PLA samples printed with four raster user data under two contact pressures. 3D-profilometry for wear analysis.	[+45°/−45°] to [0°/90°] orientation change under low load reduced friction by ~71% and track width by ~41%.	Raster orientation is a critical factor in optimizing tribological performance of 3D-printed components.
Jagadeesha et al. [43]	Tribology, 3D-printing (FDM), polymer composites dedicated to wet sliding of PETG materials.	Knowledge concerning the wear and friction performance of FDM-printed PETG parts under dry and lubricated conditions is limited. Wear behavior is dynamic with respect to time and usage.	To compare the Coefficient of Friction (COF), wear rate, and time-dependent tribological behavior of PETG components under wet and dry sliding conditions through pin-on-disc tests.	PETG specimens were prepared through FDM. Print parameters were tested through the pin-on-disc machine under dry and wet conditions, and surface roughness was measured with the profilometer.	COF decreased from 0.5 (dry) to 0.2 (wet). Wear rate improved from 5 × 10−4 mm3/Nm (dry) to 1 × 10−4 mm3/Nm (wet). Profilometer results showed reduced Ra, Rq, and Rz values post-sliding.	Lubrication significantly enhances tribological performance. PETG parts show potential for functional applications in automotive and aerospace sectors with improved wear resistance.
Li et al. [9]	Additive manufacturing (FDM) of high-performance polymer composites with improved tribological behavior for aerospace, biomedical, and industrial applications.	Agglomeration of nanoparticles at high concentrations (>10 vol.%) reduces wear resistance; obtaining uniform dispersion of fillers still remains a challenge.	To present a review of recent progress in wear-resistant polymer composites for FDM and discuss parameter optimization, filler influence, and emerging trends.	Survey and analysis of previous research targeting Print parameters, types of fillers (nano/micro), and tribological performance results.	Nano-fillers (<5 vol.%) reduce wear rate by 3–5×; Short fibers (10–30 vol.%) improve wear resistance by 3–10×; Hybrid fillers show synergistic effects but need controlled distribution.	AI-based design and parameter prediction are emerging tools that can accelerate innovation; further research is needed for scalable, reliable solutions.
Tian et al. [44]	Tribology and dynamics of FDM-printed ABS parts for various build orientations.	Effect of layer orientation on friction, wear, noise, and system stability is not well explored.	To investigate the impact of sliding angle with respect to layer lines (0°, ±45°, 90°) on tribological performance.	Pin-on-disc tests at different loads/speeds; orientations: 0°, ±45°, 90°.	90° shows highest COF but lowest wear; 0° has lowest COF but highest wear. −45° generates maximum noise due to stick-slip; FEM wear results < 7% error; noise prediction up to 15% error.	Layer orientation significantly impacts wear-life and dynamic response of printed parts. FEM modeling offers accurate wear prediction, but dynamic noise modeling needs refinement.
Reddy et al. [45]	Tribological behavior of polyether ether ketone (PEEK) for dental implant applications.	Limited knowledge of the influence of orientation on coupled mechanical and tribological behavior.	To compare experimental data with FEM and lumped-parameter modeling for wear and stability.	FEM applied for wear/temperature; lumped-parameter model for dynamic stability analysis.	Both forms of PEEK showed similar performance, with lower friction and wear in saliva, comparable to natural enamel.	PEEK proves to be a promising alternative for dental crowns, offering durability under oral-like conditions.
Zhang et al. [46]	Additive manufacturing (FDM) to the fabrication of self-lubricating materials based on PA and ABS polymers.	Standard dental materials such as titanium and zirconia exhibit limitations during masticatory wear.	To evaluate extruded and 3D-printed PEEK against enamel-coated Co–Cr tribologically under simulated oral conditions.	Friction coefficients and wear rates were investigated with linear reciprocating sliding tests in dry conditions and artificial saliva environments.	Lower printing speed and higher infill density improve surface quality; infill density has the most significant impact on CoF reduction.	FDM-fabricated resin samples show self-lubricating behavior, and the developed models enable performance optimization within 10% error.
Aslan et al. [47]	Tribology of 3D-printed biopolymer composites (PLA, PP, PLA–PP blend) based on material extrusion methods.	Quantifying the influence of FDM parameters on tribological properties is challenging because of variability between printers, particularly with layer height.	To explore how FDM printing parameters affect the coefficient of friction (CoF) and surface quality in self-lubricating components.	Design of experiments with four levels of printing speed, infill density, and layer height; regression analysis and model validation were performed.	PLA–PP blend showed intermediate hardness (63 Shore D); honeycomb pattern gave best accuracy; PLA and PP had COFs of ~0.35 and ~0.31, respectively.	A novel study presenting first insights on 3D-printed PP and PLA–PP blends’ tribology; foundational data for future wear-resistant biopolymer applications.
Toktaş et al. [48]	Tribological behavior of 3D-printed PLA parts with varying internal patterns.	Limited work on 3D-printed polypropylene and its tribological properties; parameter influences on friction and wear are yet to be comprehensively understood.	To determine the best production parameters and study friction and wear characteristics of PLA, PP, and PLAPP composites.	Composite filaments were printed and extruded; tribological experiments (pin-on-disc), hardness testing, FTIR, TGA, and Taguchi analysis were carried out.	Pattern significantly impacts tribological performance; PLA1 showed lowest friction, PLA3 best wear resistance.	Highlights the limited research on 3D-printed pattern effects and emphasizes its tribological impact.
Lin et al. [49]	Fused Deposition Modeling (FDM) of poly(ether ether ketone) (PEEK) for mechanical and tribological purposes.	Wear behavior of 3D-printed components depends on printing patterns, making durability vary.	To assess how variations in infill patterns impact friction and wear in PLA parts.	Pin-on-disc tests according to ASTM G-99 on 50% infill PLA samples with various patterns.	Annealing at 190 °C significantly reduced wear rate (by 34%) and improved part density and dimensional fidelity; at 170 °C, PEEK showed stable wear resistance under high load.	This approach shows strong potential for high-load gear and bionic joint applications using FDM-printed PEEK with simple thermal post-treatment.
Xu et al. [50]	Tribological properties of 3D-printed PEEK and PEEK-based composites on metal substrates.	Poor interlayer adhesion and low mechanical strength in 3D-printed PEEK parts.	To improve mechanical strength, interlayer adhesion, and wear resistance of FDM-printed PEEK through annealing treatment.	PEEK components were 3D-printed using FDM and post-print annealed at diverse temperatures (170–190 °C); tribological and structural tests were performed.	Neat PEEK showed lower wear on aluminum; tribocomposite showed higher COF and wear on aluminum; thermal conductivity of substrates influenced performance.	Substrate material significantly alters heat dissipation, thereby affecting wear mechanisms and tribological efficiency.
Prajapati et al. [51]	Additive manufacturing of high-performance engineering polymers (PEEK) for tribological applications like bush bearings.	Understanding how different metallic substrates influence wear and friction behavior under varying load conditions.	To study the influence of aluminum and steel substrates on tribological properties of FFF-printed PEEK sliding layers.	Plate-on-ring (PoR) dry sliding wear tests were performed on 100Cr6 steel and aluminum substrates; thermal simulation was carried out.	Layer thickness influenced crystallinity, hardness, surface roughness, and friction. A 0.3 mm thickness showed the highest wear rate (8.3 × 10−5 mm3/Nm) and friction coefficient (0.62).	Layered grooves served as debris traps and lubricant pockets, affecting transfer film formation and altering wear mechanisms during sliding.
Miao et al. [4]	Additive manufacturing of advanced structural ceramics and composites for tribological applications.	Understanding how varying layer thickness influences surface features, mechanical properties, and tribological behavior in dry sliding conditions.	To examine the influence of layer thickness on the surface morphology, wear behavior, and frictional performance of 3D-printed PEEK samples.	PEEK cuboid samples were 3D-printed with different layer thicknesses and tested under dry sliding conditions using a pin-on-disc setup for one hour.	AM enables fabrication of wear-resistant, structurally complex ceramic parts with superior tribological performance compared to conventional methods.	Additive manufacturing is a promising route for next-gen ceramic components in tribology; integration of material-process-structure insights is critical.
Kwon et al. [52]	Digital Light Processing (DLP) 3D-printed polyurethane (PU) components’ tribological performance.	Traditional manufacturing limits the fabrication of complex ceramic components with optimized tribological properties; lack of comprehensive review in this niche.	To research how ceramic additive manufacturing may improve wear resistance and frictional performance in industrial and biomedical applications.	Review and analysis of current AM technologies, ceramic materials, and their influence on micro/macrostructures affecting tribological behavior.	Polishing notably enhances friction and wear resistance, especially at 75° printing angle, which showed optimal performance under high load.	Identifies optimal DLP printing parameters and polishing effects, providing a foundation for performance-driven fabrication of PU components.
Stoica et al. [53]	Friction material tribological behavior in transmission belts of pharmaceutical packaging manipulators.	Friction and wear characteristics of PU components are highly dependent on printing directions and post-processing without optimized parameters.	To study the effect of printing angle and surface polishing on the tribological behavior of DLP-printed PU parts.	Surface and mechanical characterization (morphology, roughness, wettability, hardness) and tribological tests under varying loads, supported by finite element analysis (FEA).	TPU 60A showed highest COF but high wear; TPU 95A had lower COF but excellent wear resistance; material and infill strongly influenced tribological performance.	This preliminary study offers valuable insights into selecting friction materials for packaging manipulators under realistic conditions.
Aslan et al. [54]	Mechanical and tribological performance testing of 3D-printed PETG with varied infill patterns.	Fatigue travel-braking cycles induce severe wear on belt surfaces, with effects on performance and lifespan.	To study and compare the wear resistance and braking efficiency of original and 3D-printed TPU-based friction materials.	Dry environment testing of three samples (original, TPU 60A, TPU 95A) with different infill percentages; COF and wear measurement.	Triangular infill yielded highest mechanical strength (+133%) and modulus; honeycomb and grid were best for wear resistance; infill directionality impacted wear homogeneity.	Infill pattern selection critically influences structural performance, enabling tailored design for strength, wear, or flexibility in engineering applications.
Tyagi et al. [55]	Study of wettability, wear, and morphology of MoS2- and SiC-reinforced PLA 3D-printed composites.	Limited understanding of the effect of internal infill geometry on tensile and wear behavior of PETG for functional components.	To study the influence of four unique infill patterns on tensile and wear characteristics of 3D-printed PETG samples.	PETG samples printed with honeycomb, grid, triangular, and gyroid infill; tested for tensile strength, wear rate, friction coefficient, SEM, hardness, thermal response, and dimensional accuracy.	Lowest wear rate of 0.00141 g/N-m achieved with optimized parameters; MoS2-SiC reinforcement increased hydrophilicity, roughness, and surface energy.	The developed PLA/MoS2-SiC composite shows promise for biocompatible, wear-resistant implant applications.
Lasch et al. [56]	Additive manufacturing using polymer materials, including PLA, TPU, and bronze-filled PLA (BRO), made with Fused Deposition Modeling (FDM).	Enhancing wear resistance and surface quality of biodegradable PLA composites to foreseen biomedical uses.	To investigate the optimum 3D-printing and extrusion conditions for the fabrication of PLA/MoS2-SiC composites possessing improved tribological and wettability properties.	Composite filaments extruded with different temperature and screw speed; Taguchi L9 design employed for 3D-printing; wear tested through pin-on-disk; surface and wettability examined.	Pure BRO showed the lowest wear; pure PLA had the lowest friction coefficient. The blend of 75% BRO and 25% PLA provided optimal wear resistance close to BRO with friction similar to PLA.	Material blending can achieve balanced tribological properties suitable for 3D-printed components. Wear mechanisms and tribo-film formation on steel were critical factors influencing performance.
Palaniyappan et al. [57]	Tribological response (friction and wear) of the above materials when they are slid against steel in pin-on-disc tests.	Clarification of friction and wear behavior of pure and composite polymer filaments for enhanced durability.	Compare coefficient of friction (CoF) and wear resistance of pure PLA, TPU, BRO, and their blends in different ratios.	Production of pins from single and hybrid filaments (PLA, TPU, BRO) using FDM printing.	Addition of almond shell particles decreased tensile and flexural strength; 0° printing showed highest tensile strength; lowest friction coefficient (0.22) achieved with almond shell composite at 0° orientation and 10 N load.	The developed compostable bio-composites demonstrate potential for use in disposable orthotic foot appliances due to good tribological behavior and surface accuracy.
Prajapati et al. [58]	Creation of bio-composite filaments from polylactic acid (PLA) reinforced with almond shell particles for 3D-printing; investigation of printing orientation effects on mechanical and tribological properties.	Optimization of material pairs for balancing low friction and high wear resistance in 3D-printed parts.	Pinpoint the blend with maximum trade-off between friction reduction and wear resistance.	Pin-on-disc wear testing against SAE 1020 steel, monitoring wear rates, CoF, and surface wear mechanisms.	3D-printed PEEK shows improved wear resistance over extruded rods; surface voids from infill density enhance lubricant storage and reduce friction, especially with PAO-based grease.	Surface engineering via infill control in 3D-printed PEEK offers a promising route for improved tribological performance, enabling efficient lubrication without oil in applications like journal bearings.
Kowalewski et al. [59]	Additive manufacturing of semicrystalline engineering polymers such as PEEK for engineering parts such as sleeves and bushes. Emphasis on tribological behavior dependent on 3D-printing conditions.	The addition of natural fillers such as almond shell particles lowers mechanical strength; optimization of printing parameters to compromise strength, surface quality, and tribological performance.	To prepare PLA and almond shell particle reinforced composite filament, print 0°, 45°, and 90° samples and analyze their surface, mechanical, and tribological properties.	Filaments containing 10% almond shell particles were extruded and fabricated with fused filament fabrication; mechanical properties (tensile, flexural, compressive, hardness) and tribological properties under different speeds and loads were tested.	All composites showed enhanced wear resistance but no significant friction reduction; microhardness decreased with good filler dispersion; PTFE composite with filler agglomeration had best overall tribological and micromechanical performance.	DLP 3D-printing effectively produces sliding composites with improved wear resistance, highlighting filler dispersion’s impact on properties.

reviews recent works on the tribological behavior of FDM and SLA 3D-printed materials with a focus on polymers as well as their composites for various engineering applications.

In recent years, the sustainability of additive manufacturing (AM) has become a growing concern due to rising environmental regulations and the need for resource-efficient production. Fused Deposition Modeling (FDM) and Stereolithography (SLA) differ significantly in their ecological footprint. FDM typically employs thermoplastic filaments, such as PLA, ABS, PETG, or composites, many of which are recyclable or bio-based. In contrast, SLA relies on photopolymer resins, which are chemically complex and harder to recycle. Moreover, SLA post-processing involves isopropyl alcohol washing and UV curing, generating chemical waste. FDM, on the other hand, often requires only mechanical trimming and minimal thermal finishing. Energy-wise, SLA printers consume more electricity due to the high intensity of UV sources and constant resin agitation, while FDM machines are relatively energy efficient for small- to medium-scale parts.

Table 2. Sustainability Comparison between FDM and SLA Processes [3,4,42,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59].

Parameter	FDM	SLA
Material Type	Thermoplastic filament (PLA, PETG, ABS, composites)	Photopolymer resin (acrylate-based)
Material Recyclability	High (especially PLA, PETG)	Low (chemical resins are typically non-recyclable)
Energy Consumption	Moderate (localized heating)	High (UV curing, continuous agitation)
Post-Processing Impact	Low (minimal or mechanical trimming)	High (solvent use, UV curing, waste generation)
Toxicity of Byproducts	Low to moderate (mainly fumes from ABS)	High (uncured resin waste, IPA wash-off)
Use of Bio-based Materials	Yes (PLA, bio-PETG)	Limited
Waste Generation	Low (only support and brim material)	High (unused resin, cleaning solvents)
Sustainability Score (Overall)	High to Moderate	Low to Moderate

summarizes key sustainability indicators for both processes, providing a clearer picture of their environmental trade-offs.

In summary, FDM and SLA represent fundamentally different approaches to additive manufacturing, each with distinct advantages and limitations affecting tribological performance. FDM offers design freedom and material recyclability but suffers from anisotropic properties and rougher surfaces, whereas SLA delivers smoother finishes and higher dimensional accuracy at the expense of brittleness and sustainability challenges. Understanding these differences in process physics, material selection, and resulting surface morphology is critical for optimizing part durability and wear resistance in functional applications.

3. Comparative Tribological Performance of FDM and SLA Parts

The tribological performance of additively manufactured (AM) components produced by Fused Deposition Modeling (FDM) and Stereolithography (SLA) is dictated by a complex interplay of process parameters, material composition, reinforcement strategies, and layer-induced microstructures [60]. Despite sharing the layer-by-layer deposition principle, the two technologies exhibit fundamentally different wear behaviors, driven by their contrasting fabrication mechanisms and material chemistries. In FDM, fused thermoplastic filaments such as PLA, PETG, or ABS are extruded along predefined paths, creating layered structures characterized by surface roughness and anisotropic mechanical properties. Among observed wear mechanisms, abrasive wear dominates in these thermoplastics, where hard counterface asperities plough or micro-cut the relatively soft polymer matrix, leading to progressive material removal [60]. Adhesive wear emerges under conditions where thermal softening or molecular affinity promotes local welding and material transfer, while fatigue wear is linked to cyclic stresses concentrating at interlayer voids or weak bonding sites, initiating micro-cracks that propagate over time.

Process parameters critically affect these wear responses. High infill densities (90–100%) reduce porosity, improve load-bearing capacity, and enhance wear resistance. Raster angle and build orientation guide polymer chain alignment: printing at 0° relative to the sliding direction distributes stress uniformly, lowering wear rates, whereas ±45° or 90° orientations increase anisotropy and delamination risk. Nozzle diameter also matters: larger nozzles extrude thicker beads, reducing voids but compromising surface resolution, while smaller nozzles achieve finer detail but may introduce inter-bead gaps susceptible to cracking [61,62,63,64]. Layer thickness shows a similar trade-off; thinner layers (0.1–0.2 mm) yield smoother surfaces but can increase thermal gradients, whereas thicker layers improve bulk strength but elevate roughness. Material selection adds further complexity. PLA, while stiff and biodegradable, lacks toughness, making it prone to adhesive wear at higher contact pressures. Studies show that adding ~5 wt.% silicon fillers to PLA reduces wear rate by ~66% by promoting tribo-film formation, which smoothens surfaces and protects against abrasive action. Carbon fibers and graphene nanoparticles further decrease friction by forming lubricating transfer films and stiffening the matrix. PETG offers better impact resistance and fatigue life than PLA but remains vulnerable to ploughing unless reinforced. ABS provides superior ductility and toughness, enhancing adhesive wear resistance, but its amorphous structure can soften under heat, destabilizing transfer films [65,66]. Figure 2 contrasts the filament-based FDM deposition, with inherent interlayer defects, against SLA’s photopolymer curing process, which produces smoother and more isotropic surfaces. The use of nano-fillers like silicon, ZnO, and SAN in FDM has been shown to significantly enhance thermal stability and wear resistance [67,68,69,70]. Neat PLA, with a COF around 0.24, sees reductions to ~0.11–0.13 with these reinforcements attributed to stable tribo-films that minimize adhesive bonding and reduce abrasive groove formation, as confirmed by SEM analysis. Ceramic fillers also induce superlubricity under humid conditions by reacting with water to form protective transfer layers, further lowering adhesion and wear [71,72]. Yet, uniform filler distribution remains critical; loadings beyond ~5–7 wt.% can cause extrusion defects like necking or bulging, leading to localized wear concentration. Optimal filler content typically balances mechanical benefits and printability without degrading dimensional accuracy.

Emerging approaches, such as nano-engineered fillers like CNTs, MoS₂, and Si₃N₄, alongside machine learning–assisted parameter tuning, have demonstrated further potential in optimizing wear performance [73,74,75,76]. Print layer thickness, raster angle, and cooling rate can all be algorithmically adjusted to minimize wear rates and COF.

Table 3. Overview of recent research on tribological performance in advanced additive manufacturing (AM) materials and composites, highlighting innovations in SLA, FDM, DIW, and DLP processes.

Author et al.	Area	Challenges	Objective	Methodology	Finding	Remark
Swathi et al. [77]	Optimization of wear behavior in hexagonal boron nitride (h-BN)-reinforced stereolithography (SLA) composites based on Taguchi method.	Enhancing wear resistance through the optimization of SLA processing parameters with different h-BN reinforcement under controlled test conditions.	To determine the best balance of material composition and printing conditions that reduce wear rate in SLA composites.	Synthesized ASTM G99 standard cylinder samples with different h-BN wt%, pin-on-disc tested wear, SEM, EDAX, Taguchi S/N ratio, and ANOVA used for analysis.	Material composition contributed most to wear rate, followed by build angle, post-curing time, and lift speed; best parameters obtained for minimum wear.	Taguchi method efficiently optimizes tribological characteristics of SLA h-BN-reinforced composites for improved application performance.
Ramkumar et al. [78]	Tribological performance of PEEK-based graphene oxide (GO) nanocomposites produced by stereolithography (SLA) additive manufacturing.	Decreasing friction and wear in SLA-printed PEEK composites under different loads and sliding velocities.	To explore the influence of varying percentages of GO reinforcement (0.25%, 0.50%, 0.75%) on PEEK composite friction and wear resistance.	Synthesis of PEEK-GO nanocomposites via SLA; tribological testing at loads (25–100 N) and sliding speeds (50–200 RPM); surface analysis done by SEM.	GO addition greatly diminishes coefficient of friction (by up to 30.6%) and wear loss (by up to 40.4% reduction); SEM exhibits enhanced surface integrity because of GO.	GO functions as a self-lubricating agent in forming a protective film, thus verifying the effectiveness of SLA for high-performance PEEK nanocomposites with specially designed tribological characteristics.
Snarski et al. [79]	Tribological and mechanical characterization of 3D-printed dental/orthodontic biomaterials.	Orthodontic material performance differs due to exposure to complex oral environmental conditions.	To determine the impact of oral cavity conditions on friction and wear behavior of two commercial 3D-printed dental materials.	Hardness, modulus, stiffness, cyclic loading, and tribological testing on GR-10 and NextDent SG 3D-printed with ASIGA and Phrozen printers. SEM–EDS as a tool for surface analysis.	NextDent SG was of greater hardness and elastic modulus; GR-10 exhibited superior scratch resistance. Friction was comparable, but under different conditions, wear was different.	Environmental conditions strongly influence material performance; the choice should consider clinical conditions.
Xu et al. [80]	Slip-resistant tread design through additive manufacturing for enhancing dry and wet surface traction, especially in workplace and elderly safety applications.	Avoiding slip and fall accidents on slippery surfaces through optimization of tread pattern and material response under wet and dry conditions.	To assess the impact of alternate tread designs and rubber-like materials on grip performance and deformation in alternate friction environments.	CAD modeled tread patterns 3D-printed using FFF and SLA with TPR filament and elastomeric resin. Friction and deformation evaluated with a friction tester and high-speed camera in dry/wet conditions.	Tread shape and material have a big impact on frictional force, deformation, and drainage of water, on slip resistance on glass.	Optimal tread pattern design with appropriate AM methodologies and materials can be used to improve surface grip and mitigate accident risks efficiently.
Wang et al. [81]	Tribology and materials engineering bioinspired ceramic composites with improved wear resistance.	Ceramic parts tend to endure excessive friction and wear under a range of operating conditions.	To synthesize and test multiscale bioinspired Al2O3 ceramics with enhanced tribological properties using material and structural synergy.	Fabrication by DIW 3D-printing and femtosecond laser; MoS2 film deposition by RF magnetron sputtering; tribological testing under dry conditions and lubricated conditions.	Bioinspired ceramics had reduced friction (0.3 dry, 0.148 lubricated) and increased wear resistance through multiscale structure and synergy of lubrication.	This research provides an innovative, synergistic solution integrating structure and material to maximize ceramic tribological performance.
Wang et al. [82]	Dental materials—3D-printing of zirconia prostheses and their performance after low-temperature degradation (LTD).	Fuzzy wear resistance and biological response of 3D-printed zirconia restorations following LTD.	To compare 3D-printed versus milled zirconia wear behavior and biocompatibility following autoclave-induced LTD.	Wear tests with enamel antagonists, surface analysis (SEM, AFM, XRD), and biocompatibility evaluation with hGFs through RT-PCR and immunofluorescence.	3D-printed zirconia demonstrated increased defects and enamel wear after LTD but had comparable cell response and protein expression to milled zirconia.	Although biocompatibility is similar, 3D-printed zirconia displays lower wear resistance under LTD conditions.
Xu et al. [83]	Thermoplastic rubber (TPR) and flexible SLA resin materials for 3D-printed outsole applications in footwear.	Poor comprehension of the influence of diverse geometries and materials on wear resistance, friction, and mechanical performance in outsole parts.	To compare systematically the wear and mechanical response of TPR and SLA resin materials through 13 geometries via experimental and simulation methods.	Abrasion tests (weight loss, COF, temperature, deformation) on 26 samples; FEM simulations based on the Ogden hyperelastic model to investigate stress and wear.	TPR reflected 27.3% reduced weight loss and more even wear, and SLA revealed greater COF (65%) and temperature increase (94%); FEM confirmed stress and deformation behavior.	TPR is better suited for high-load outsole applications; research provides insights for maximized material selection and design in footwear technology.
Kozior et al. [84]	Tribology and additive manufacturing (3D-printing for casting models).	Difference in tribological behavior as a result of different 3D-printing technologies and processing parameters.	In order to analyze and compare the tribological performance of parts manufactured through SLS, PJM, and FDM for casting uses.	Linear wear and friction coefficient were determined over various printing conditions (direction, layer thickness, energy density).	Process parameters have a significant impact on tribological properties; technology choice allows for control of wear and friction.	3D-printing can successfully create casting models with tunable tribological behavior, minimizing time-to-production.
Raj et al. [22]	Tribology and lubrication in 3D-printed products in various industrial applications (open systems, biotribology, nanotribology, tribotronics, aerospace).	Insufficient durability and poor performance of 3D-printed components due to insufficient tribological optimization.	In order to discuss and emphasize the contribution of tribology towards improving the performance and longevity of 3D-printed parts.	Systematic review and synthesis of published literature on tribology in additive manufacturing.	Tribological performance is paramount for the functional use of parts printed via 3D-printing, with particular requirements for various industries.	The research closes knowledge gaps and informs the future enhancement of 3D-printed system reliability by tribological design.
Farooq et al. [85]	Additive manufacturing (AM), with emphasis on metal AM and its mechanical and tribological behavior.	AM components have unique tribological characteristics because of their layer-by-layer construction, and they need thorough research to provide consistent performance.	In order to discuss the impact of material, surface topography, and post-treatment on the tribological properties of AM parts.	Review approach based on novel materials and post-processing technologies enhancing surface quality and minimizing wear/friction.	Material selection and post-processing greatly impact tribological performance; present developments indicate promise but need focused research.	Additional research into novel materials and surface coatings is essential to enable AM use in tribology-critical industries.
Du et al. [86]	Oil-filled polymer composites for tribological use with self-lubricating capabilities and 3D-printability.	Current oil-loading methods are difficult to form, hard, and tend to compromise mechanical strength through excessive porosity.	In order to create a simplified synthesis procedure for producing oil-loaded polymer composites with optimum lubrication and mechanical properties.	Mesoporous silica nanoparticles loaded with oil, embedded in a vat photopolymerization 3D-printing polymer matrix in one pot.	The final composite exhibited excellent oil retention (through 467 m2/g surface area), and friction coefficient and wear rate improvements of 85.7% and 97.7%.	Illustrates a scalable, high-precision technique to fabricate complex-shaped, high-performance self-lubricating materials.
Kowalewski et al. [87]	Additive manufacturing by Digital Light Processing (DLP) tribological use; fabrication of solid-lubricant-filled sliding composites.	Enhancing wear resistance and minimizing friction in DLP-printed parts while achieving trade-offs with mechanical hardness.	To analyze the influence of solid lubricant fillers (graphite, MoS2, PTFE) on tribological and micromechanical properties of DLP-printed composites.	UV-curable resin suspensions were loaded with solid lubricants in wt% ranges, DLP-printed, and evaluated through COF, wear factor, microhardness, and SEM analysis.	Composites in all series demonstrated increased wear resistance; PTFE-filled composites provided the optimal tribological balance, albeit with diminished hardness due to filler agglomeration.	Illustrates the viability of DLP 3D-printing for manufacturing wear-resistant materials featuring solid lubricants, particularly PTFE, for commercial use.
Onu et al. [88]	Tribological properties of 3D-printing materials and methods, particularly friction, wear, and lubrication of layer-by-layer deposition.	Knowledge on how various 3D-printing materials and processes influence tribological behavior and performance of printed parts.	To analyze tribological characteristics of different 3D-printing materials and processes and propose guidelines for performance enhancement.	Friction, wear, and lubrication behavior investigation through experimental analysis for various 3D-printing materials and methods.	Identified how printing processes influence tribological behavior, highlighting key factors affecting wear and friction.	Offers information and recommendations for improving tribological performance; indicates areas for future additive manufacturing research.
Peter et al. [89]	Tribology and surface roughness in environmentally friendly 3D-printing manufacturing.	Surface roughness variation influences friction and wear in 3D-printed parts because of varying printing and post-processing techniques.	To realize tribological characteristics of different 3D-printing materials and design optimal printing parameters for enhanced surface quality and sustainability.	Assess tribological behavior for various 3D-printing methods; examine process parameter and post-processing influences on surface roughness and friction.	Surface roughness significantly influences friction and wear; optimizing printing and post-processing reduces friction and enhances sustainability.	Recommendations established for optimizing tribological performance of printed parts to enable sustainable manufacturing.
Pieniak et al. [90]	Contact strength and tribological features of 3D DLP-printed resin spare parts of two printer models.	Post-processing variation impacts functional and surface properties that determine durability and wear.	Assess mechanical surface characteristics and tribological behavior under rotary and linear movements.	Applied indentation tests, micro- and nanotribometers, and microscopy (SEM, WLI, optical) to analyze surfaces and wear.	Significant correlations found between indentation parameters and tribological durability across post-processing methods.	Findings emphasize post-processing effects on functional performance and inform optimization of printed parts.
Channi et al. [91]	Tribology in 3D-printing influences wear, friction, and lubrication of SLS, FDM, and stereolithography parts.	Material, orientation, and post-processing influence tribology more than tribological properties; mechanical performance is emphasized over tribological properties.	To examine the effect of printing parameters, materials, and surface treatments on tribological behavior and wear resistance of 3D-printed components.	Literature review and bibliometric study of papers from 2018 to 2023 on polymers, metals, composites, and surface treatments in 3D-printing tribology.	Tribology can be enhanced by optimizing printing parameters, using wear-resistant materials, and applying coatings or lubrication strategies.	Improved knowledge of tribology in 3D-printing has the potential to enhance manufacturing quality and expand industrial applications across fields.
Nabi et al. [92]	Tribological performance of porous 3D-printed PLA+ materials with the built-in anaerobic methacrylate lubricant.	Determining the influence of infill pattern and density on friction and wear in dry and lubricated conditions.	To explore the effect of infill pattern and density on friction coefficient and wear volume and evaluate the effectiveness of the lubricant.	Evaluated samples with different infill patterns (grid, concentric, triangles) and densities (20%, 60%, 100%) in dry and lubricated conditions.	Friction with increased density; wear with decreased density; lubricant diminishes wear by up to 90.8%, particularly in 20% grid pattern samples.	Self-impregnated anaerobic methacrylate substantially enhances tribological performance by creating a low-shear lubricant film.
Liow et al. [93]	Tribological performance of FDM 3D-printed composites, namely, glass fiber-reinforced PLA (PLA-GF).	FDM products are less robust than injection-molded products; there is a requirement for improving mechanical and wear properties.	Examine the effect of glass fiber reinforcement on friction and wear of FDM PLA composites at different speeds and directions.	Perform tribological testing of PLA-GF composites fabricated using a novel composite fabrication technique, with changing linear sliding velocities and raster directions.	PLA-GF composites also exhibited lower wear rates and greater friction than neat PLA; increased speeds lowered friction and wear; perpendicular raster direction raised both.	Glass fiber reinforcement enhances tribological performance of FDM PLA, and speed and print orientation have a noticeable effect on the results.
Alebrahim et al. [94]	Detailed review of new developments in 3D-printing ceramics with emphasis on tribological characteristics and Direct Ink Writing (DIW) technique.	Limited knowledge of tribological characteristics in 3D-printed ceramics and issues in manufacturing high-performance ceramic structures through DIW.	To examine the viability of DIW for manufacturing intricate ceramic components and characterize knowledge gaps in tribological performance.	Reading current literature on 3D-printed ceramics, tribological testing, and DIW process innovations.	DIW is promising for demanding applications of complex ceramics but understanding tribology behavior is incomplete.	Future studies must aim to develop the material properties and eliminate gaps in order to increase the application area of 3D-printed ceramics.
Stravinskas et al. [95]	Creation of a new ceramic-composite resin for SLA 3D-printing to enhance dental restorations with better mechanical properties and less material waste.	Convention CAD/CAM dental restorations are subtractive, resulting in material waste and restriction of personalization; current photopolymer resins do not have adequate mechanical strength.	Develop and test a ceramic-composite resin with light-curing capability supplemented by enhanced tensile strength and resistance to wear for dental use.	Designed the resin and carried out testing of printability, tensile strength, and wear resistance for comparison with conventional photopolymer resins.	The ceramic-composite resin had a tensile strength of ~73 MPa (compared with 42 MPa for conventional resin) and also displayed better friction and wear resistance.	The paper puts forward an economical, effective method for creating long-lasting, patient-specific dental restorations, which can revolutionize dental prosthetics manufacturing.

in this study collates experimental evidence, highlighting these process–property relationships across various thermoplastic systems and industrial applications.

By contrast, SLA employs photopolymerization of UV-curable resins, producing parts with inherently smoother surfaces (Ra < 2 µm) and higher dimensional precision [96]. This fine finish greatly reduces initial abrasive wear under mild contact. However, SLA parts face different challenges: brittleness, curing sensitivity, and limited elongation at break. Under tribological loading, SLA resins predominantly exhibit brittle fracture mechanisms: crack nucleation, propagation, and delamination rather than plastic flow. These failures are often initiated at stress concentrators like sharp corners, support removal points, or internal voids left by incomplete curing. Post-curing through additional UV or thermal exposure is therefore essential to enhance cross-link density, increase surface hardness, and stabilize wear resistance. Experimental studies demonstrate that cracks in SLA parts may shift from tensile-dominated (mode I) to shear-dominated (mode II) propagation depending on loading orientation [97,98,99,100]. Finite element modeling corroborates this, showing peak von Mises stresses localizing near layer interfaces and crack tips, especially where slicing introduces anisotropic weak zones. Moreover, SLA’s brittle nature under dynamic loads often leads to catastrophic fracture rather than the gradual wear seen in FDM thermoplastics.

To facilitate practical decision-making,

Table 4. Trade-offs in FDM and SLA strategies for tribological optimization [4,19,20,33,71,73].

Strategy	Technology	Advantages	Trade-Offs/Limitations	Best Suited For	Cost Level	Sustainability Score
Carbon/Graphene- Reinforced Filaments	FDM	Improved wear resistance, lower COF, lightweight	Nozzle clogging, uneven dispersion, moderate cost	Load-bearing functional parts	Medium–High	Moderate
Photopolymer Blends (Toughened Resins)	SLA	Improved toughness and finish	Brittle under cyclic load, non-biodegradable	Dental and precision components	Medium	Low
Laser Surface Remelting (LSR)	FDM/SLA	Enhances surface hardness, localized processing	Equipment cost, possible thermal distortion	High-load or contact surfaces	High	Moderate
Vapor Smoothing (e.g., Acetone)	FDM	Reduces surface roughness up to 60%, fast process	VOC hazard, polymer-specific	Consumer products, aesthetic prototypes	Low	Low–Moderate
Thin-Film Coatings (e.g., Ni, TiN, PTFE)	FDM/SLA	High tribo-performance, low COF, good wear protection	Expensive, adhesion variability	Biomedical and aerospace interfaces	High	Low
Hybrid Manufacturing (e.g., Rolling)	FDM	Improves structural integrity via residual compressive stress	Integration complexity	Functional engineering surfaces	Medium	Moderate–High
ML-Based Process Optimization	FDM/SLA	Predictive tuning of wear, COF, process efficiency	Requires large datasets and tuning	Smart manufacturing and process control	Medium	High
High Infill + 0° Raster Orientation	FDM	Optimizes strength and wear resistance	Longer print times, material intensive	Structural and sliding-load components	Low–Medium	High

presents a comparative evaluation of FDM and SLA strategies for tribological enhancement, including their respective advantages, limitations, cost implications, and sustainability potential. Techniques such as vapor smoothing and thin-film coatings have shown notable improvements in surface finish and wear resistance but vary significantly in cost-effectiveness and environmental footprint [19,20,71]. Meanwhile, hybrid methods like post-print rolling and emerging machine learning (ML)-driven optimization frameworks offer promising paths for performance tuning with higher sustainability and process adaptability [4,33,73]. This table serves as a design-oriented synthesis to guide researchers and engineers in selecting strategies aligned with specific performance and sustainability goals.

Nevertheless, SLA excels in applications prioritizing high surface accuracy and complex geometries, such as dental prosthetics, microfluidic devices, and MEMS, where tight tolerances outweigh impact strength concerns. Figure 3 illustrates comparative COF and wear rates, highlighting that while filler reinforcement is common in FDM, it remains underexplored in SLA though it offers promising pathways for enhancement. In dentistry, SLA-fabricated crowns and splints provide superior surface conformity and patient comfort but face wear limitations under mastication. Post-processing treatments such as plasma surface activation, nano-particle reinforcement with silica or alumina, and thin-film coatings like PTFE or parylene help reduce friction and block crack initiation [101,102]. SLA’s compatibility with acrylate and PEG-diacrylate resins also makes it valuable in biomedical scaffolds and surgical guides, where smooth lumens minimize tissue shear and inflammation.

Mixed-mode fracture studies suggest that, in well-cured SLA parts, resin composition and build orientation have limited impact on elastic modulus and toughness, indicating relatively isotropic bulk properties [103,104,105]. Digital image correlation (DIC) techniques have revealed strain localization before visible cracks appear, offering predictive cues for maintenance or design adjustment. Unlike thermoplastics that gradually wear via smearing, SLA parts tend to flake, exposing fresh resin surfaces that dynamically shift COF.

To mitigate brittleness, researchers are developing toughened SLA resins using urethane dimethacrylate blends or ceramic fillers, which trade minimal resolution loss for higher fracture toughness. Build orientation also influences wear: vertical prints can lower edge chipping by distributing load along layers, while horizontal prints improve layer cohesion but risk concentrated wear at base surfaces. SLA’s precise surface finish remains an advantage in static friction-critical or dimension-sensitive applications, though cyclic loading still necessitates hybrid or multi-material approaches. In biotribology, SLA enables the design of patient-specific implants with controlled surface texturing, directly influencing protein adsorption, lubrication film formation, and cellular migration—key factors for integration into biological systems.

Table 5. Comprehensive summary of multidisciplinary research across biomedical implants, surface engineering, additive manufacturing, sustainable energy, and smart materials.

Author et.al	Area	Challenges	Objective	Methodology	Finding	Remark
Bhojak et al. [106]	Biomedical implants; biodegradable magnesium metal matrix composites (Mg-MMCs).	Traditional implants induce toxicity, stress shielding, and need to be removed after healing.	To assess Mg-MMCs as a promising biodegradable, biocompatible substitute for conventional implant materials.	Brief review of reinforcement strategies, surface treatments, and synthesis techniques, such as the friction stir process.	Reinforced Mg-MMCs exhibit enhanced microstructure, mechanical strength, and corrosion resistance.	Mg-based composites minimize the implant removal requirement, emphasizing their potential in microbial uses.
Prabakaran et al. [107]	Electrochemical energy storage; supercapacitor electrode materials; nanostructured materials.	Increased supercapacitor development needs to overcome low electroconductivity and poor cycling stability of conventional electrode materials.	To synthesize and analyze carbon-decorated cobalt ferrite nanoparticles with improved supercapacitor performance.	Two-step synthesis: chemical oxidation of CoFe2O4 and carbon coating using glucose, annealing at 400 °C and 600 °C in N2 atmosphere.	Carbon modification enhanced specific capacitance to 323 F/g and lowered charge-transfer resistance to 17 Ω at 600 °C; 84% capacitance retention following 4000 cycles.	Carbon-functionalized CoFe2O4 nanostructures demonstrate potential to be economically affordable, high-performance. supercapacitor electrode materials.
Demirci et al. [108]	Biomaterials; surface engineering; additive manufacturing (DMLS, EBM); biomedical implants	Unavailability of comparative information on micro/nanoscale topographies and bioactivity performance between DMLS and EBM Ti-6Al-4V alloys.	To create and compare micro/nanoscale textures on Ti-6Al-4V surfaces from DMLS and EBM procedures and test their in vitro bioactivity after SEA treatment.	DMLS- and EBM-fabricated samples were treated by sandblasting, acid-etching, and anodization (SEA), and then surface and biological characterization.	DMLS and EBM attained nanoscale roughness (Ra: 0.76 µm vs. 0.86 µm), with DMLS exhibiting better wettability (contact angle: 19.24°) and greater HOB cell viability (97.03%).	SEA-treated DMLS surfaces possess improved hydrophilicity and bioactivity and are thus more amenable to biomedical implant applications.
Wang et al. [109]	Adsorption of strontium ions (Sr2+) from nuclear wastewater by modified metal-organic frameworks (MOFs).	High adsorption capacity and selectivity for Sr2+ in the presence of competing metal ions are challenging to achieve.	To create a new adsorbent by in situ modification of MIL-88B(Fe) with PEG-4000 and AMP for efficient and selective Sr2+ removal.	MIL-88B(Fe) was doped with PEG-4000 and AMP in DMF; structural study and adsorption investigations, including kinetics and isotherm modeling.	Demonstrated high Sr2+ adsorption (43 mg·g−1 in 30 min) with high selectivity and chemisorption controlled by NH4+ active sites of PAMP on MOF surfaces.	Modified MOF maintained intact morphology and structure; new mechanism demonstrates prevalence of ion exchange through NH4+ with minimal involvement of MIL-88B(Fe) matrix.
Kumbhar et al. [110]	Additive manufacturing (AM) and its application to rapid prototyping and product development.	Limited surface quality, limited physical properties, and reliance on specific raw materials.	To conduct a thorough literature review on post-processing methods in AM.	Surfacing existing literature’s review and analysis aimed at surface enhancement through process control and post-processing.	Several methods have been employed to enhance AM surface quality through parameter optimization and post-processing techniques.	While there are challenges, there are promising findings in overcoming AM shortcomings through enhanced post-processing methods.
Chohan et al. [111]	Surface enhancement techniques for FDM-based ABS prototypes in additive manufacturing.	To summarize pre- and post-processing methods that enhance surface quality and dimensions accuracy of FDM-ABS parts.	Examined different methods independently; carried out a case study with vapor smoothing on hip implant models.	Deteriorating surface finish, instability in dimensions, and absence of affordable, automated mass finishing methods.	Pre-processing is not very flexible; post-processing enhances finish but imparts part strength and accuracy.	Vapor smoothing has the potential for uniform, low-cost implant manufacture with enhanced surface finishes.
Han et al. [112]	Solid oxide fuel cells (SOFCs), cathode material engineering, Cr-tolerant catalysts.	Sr-based cathodes are subject to Sr segregation and Cr poisoning, constraining durability and performance.	To improve the Cr-tolerance and ORR catalytic performance of LSCF cathodes by surface modification.	Entropy-enhanced surface engineering with high-entropy doped CeO2 ((La0.2Pr0.2Nd0.2 Sm0.2Gd0.2)0.2 Ce0.8O2−δ, HEDC) as a catalyst coating over LSCF.	LSCF-HEDC exhibits excellent Cr-resistance with minimal degradation (1.05 × 10−3 Ω·cm2·h−1), better than other coated and uncoated LSCF cathodes.	High-entropy surface coating provides synergistic protection and catalytic improvement, promoting durable cathode design for SOFCs.
Kantaros et al. [113]	Covers several post-processing methods thermal, chemical, and mechanical for AM technologies such as SLS, FDM, and SLA based on various raw materials.	Tackles major issues like surface roughness, dimensional inaccuracy, and less-than-optimal material properties in AM parts.	To analyze and improve post-processing processes for improving AM component quality, minimizing production time and cost.	Detailed review and assessment of post-processing methods, such as heat treatment, coating of the surface, ultrasonic finishing, and HIP, on various AM processes.	Custom post-processing enhances surface finish and mechanical properties and diminishes defects; suggested new strategies incorporate these steps into the AM process.	The research forms a body of knowledge and hands-on experience for researchers and manufacturers who seek to enhance AM quality standards effectively.
Zhou et al. [114]	Sustainable nanomaterials; cellulose nanofibrils (CNFs); green bio-based composites	Conventional pretreatment technologies induce irreversible surface modifications and morphology damage in CNFs.	To create an effective surface engineering technique to harvest CNFs with high aspect ratios and reversible surfaces.	Low swelling and esterification followed by saponification for exfoliating and functionalizing CNFs from bioresources.	Obtained CNFs with ultrahigh aspect ratio (~1400), 98% yield, 12.4 kJ/g energy consumption, and recovered hydroxyl surfaces.	Facilitates robust hydrogen bonding for 1D–3D cellulose materials, revealing avenues for next-generation sustainable materials.
Wu et al. [115]	Triboelectric Nanogenerators (TENGs) for energy harvesting, self-powered sensors, wearables, and high-voltage sources.	Limited efficiency due to less-than-ideal surface and structural configurations; absence of systematic design strategies.	To enhance TENG output performance via surface morphology analysis and structural design.	Assessment and examination of TENG working principles, morphological engineering, and structural design strategy.	Surface topography and particular structures greatly enhance TENG performance and broaden application range.	It is essential for structural and surface design optimization towards industrial-scale application and future device integration.
Trabelsi et al. [116]	Photovoltaics, anti-reflective coatings, thin-film surface engineering.	Low photon absorption due to reflectance from surfaces; necessity for stable, long-lasting, and efficient anti-reflection coatings.	To enhance the light absorption and power conversion efficiency (PCE) of polycrystalline silicon solar cells with SiO2, ZrO2, and SiO2–ZrO2 composite coating.	17 kV sputter coating process for 45 min; characterization based on FESEM, AFM, UV–Vis spectroscopy, I–V source meter, and four-probe technique.	SiO2–ZrO2-covered cells demonstrated minimum reflectance (6%) and maximum PCE (17.6%); electrical resistivity was minimized to 2.89 × 10−3 Ω-cm.	SiO2–ZrO2 mixture provides superior anti-reflection capability, supporting enhanced efficiency and prospects of commercial solar cell applications.
Yang et al. [117]	Solar desalination using interfacial heating and advanced 3D-printed photothermal materials.	Low energy efficiency, accumulation of salt, and low material durability constrain existing solar systems for desalination.	To create a long-lasting, effective solar evaporator based on EGaIn nanodroplets and DLP 3D-printed hydrogels.	Designed LMTE nanodroplets with AGE-grafted TA; incorporated into photothermal hydrogel ink for DLP printing.	Attained high evaporation rate (2.96 kg m−2 h−1) and energy efficiency (96.93%) with site-specific salt control.	The high-performance evaporator system provides a scalable solution for sustainable integration of water–energy-agriculture.
Zhang et al. [118]	Ni-rich layered oxide cathodes for high-energy lithium-ion batteries (LIBs).	Constitutional instability under crystallographic planar gliding and microcracking due to high voltage; oxygen vacancy generation and phase transitions.	To improve structural stability and cycling performance of single-crystalline LiNi0.83Co0.07Mn0.1O2 (SNCM) through multifunctional surface engineering.	Resurfaced SNCM with a Li1.25Al0.25Ti1.5O4 (LATO) layer and co-infused Al, Ti ions creating a surface-confined hybridization zone.	LATO coating increases Li+ transport and resists electrolyte degradation; surface/bulk stabilization inhibits defects, contributing 88.9% capacity retention at 1.0C after 400 cycles.	The double-role passivation layer presents a robust approach to commercialization of Ni-rich cathodes with enhanced electrochemical stability.
Do et al. [119]	Electrocatalyst stabilization and design for electrochemical reactions of energy conversion.	Degradation of surface nanostructure under high polarization and aggressive microkinetics.	To summarize degradation mechanisms and to study approaches to stabilize electrocatalysts.	Analysis from advanced operando methods, computational models, and the literature.	Determined major degradation pathways and stable stabilization strategies over reactions.	Provides insights into rational design and indicates future directions to improve catalyst durability.
Jiang et al. [120]	3D-printed food technology with emphasis on dough fermentation monitoring in real-time using NIR spectroscopy.	Achieving the best fermentation periods in 3D-printed dough and acquiring useful rheological information rapidly and without destruction.	To create a quick, smart approach to track dough fermentation phases and forecast rheological characteristics by using NIR spectroscopy.	NIR spectra underwent SIPLS-CARS processing to extract relevant wavelengths; SVM models were constructed and compared to PLS models.	SVM models attained good predictive accuracy (Rc2 up to 0.95) for rheological parameters; NIR models performed better compared to conventional rheo-fermentation analysis.	NIR spectroscopy is a promising, non-destructive technique for real-time monitoring and quality control in 3D food printing.
Kuntoğlu et al. [121]	Selective Laser Melting (SLM) of titanium alloys for surface integrity and tribological investigations in engineering industries like aerospace, automotive, biomedical, and defense.	Limited information on the influence of SLM parameters and particle properties on wear behavior and surface quality. Uncertainty in the effect of post-processing treatment.	To thoroughly survey the impacts of SLM process parameters, particle properties, and post-processings on tribological performance and surface integrity of titanium alloys.	A comprehensive literature-based review of SLM-fabricated Ti alloy components, assessing the impact of printing conditions and treatments on mechanical, thermal, and surface responses.	Particle size distribution, morphology, and flowability have a major influence on tribological performance. Peening is one of the surface treatments that improve surface integrity after fabrication.	This review fills a gap in existing academic-industry knowledge and directs further optimizations in SLM-fabricated Ti components for engineering applications of advanced level.
Stutz et al. [122]	Experimental fluid mechanics; Particle Image Velocimetry (PIV) data analysis.	High-speed, high-dimensional PIV creates enormous datasets with spurious vectors that are hard to recognize efficiently post-processing.	To assess the Mahalanobis distance as a statistical outlier rejection tool for dealing with large PIV databases.	Development and testing of the Mahalanobis distance function on duplicate PIV experiments for determining spurious vectors.	Mahalanobis distance was found to be computationally effective and efficient in rejecting outliers in higher-dimensional PIV data.	The approach provides a scalable, robust alternative to commercial software-based outlier detection for PIV processing.
Wang et al. [123]	Corrosion behavior and surface modification of Nickel Aluminum Bronze (NAB) alloys for application in naval environments.	To investigate corrosion mechanisms and evaluate surface modification techniques to improve the corrosion resistance of NAB alloys.	Cast NAB experiences extreme corrosion in harsh marine environments. Current surface treatments must be optimized to meet tough service conditions.	Survey and contrast of surface enhancement methods laser surface hardening, shot peening, friction stir processing, thermal spraying with an examination of processing parameters.	Surface modification strongly improves corrosion resistance; process parameters directly affect the treatment’s effectiveness.	Future studies should investigate laser and arc additive manufacturing to further enhance NAB alloy performance and manufacturability.
Wang et al. [124]	Aqueous rechargeable zinc-ion batteries (AZIBs) for electrochemical energy storage.	Zinc dendrite growth, hydrogen evolution reaction (HER), and corrosion side-reactions jeopardize AZIB stability.	To improve cycling stability and performance of AZIBs through a surface-engineered Zn anode.	A montmorillonite (MMT) film was deposited on Zn anode; DFT computations and water contact angle measurements were performed.	MMT@Zn anode provides zincophilic ion channels, improved Zn2+ adsorption, and hydrophobicity; achieves 5600 h cycling and superior full-cell rate performance.	The MMT coating approach maximally enhances AZIB durability and has strong promise for scalable energy storage applications.
Wang et al. [125]	Micro/nanostructures on steel surfaces by femtosecond laser-assisted self-assembly for multifunctional purposes.	Fabrication of high-resolution and multifunctional micro/nanostructures is still challenging; it requires accurate control and stability as a main problem.	To design and test a new method of combining self-assembly and femtosecond laser processing to create multifunctional micro/nano surfaces.	Silica microspheres self-assembled through liquid–air surface tension gradients; subsequent to water patterning using femtosecond laser by employing different process parameters.	Surface modifications demonstrate tunable wettability, enhanced self-cleaning, decreased ice adhesion, and effective photothermal de-icing abilities.	The technique allows for long-lasting, intelligent surfaces with both super-hydrophilic and super-hydrophobic areas, which are ideal for a wide range of surface engineering applications.

summarizes recent innovations in material formulations, tribological performance, and engineering implications specific to SLA.

In summary, while FDM offers broader material options, ductility, and reinforcement flexibility, it suffers from anisotropy and surface roughness affecting wear behavior. SLA delivers unmatched surface quality and accuracy but struggles with brittle failure modes and limited reinforcement strategies. Both processes demonstrate strong parameter sensitivity where design choices like layer thickness, infill, raster angle, and curing protocols can markedly influence COF and wear life. Emerging strategies from nano-reinforcement and machine learning-based process control in FDM to resin toughening and hybridization in SLA point toward future solutions. Together, they illustrate that achieving reliable tribological performance in AM parts requires integrating material science, process optimization, and post-processing to match specific functional demands.

4. Surface Engineering, Hybrid Strategies, and Predictive Tools

Achieving reliable tribological performance in FDM and SLA parts demands more than optimized printing parameters; it requires systematic surface engineering, hybrid manufacturing, and increasingly, predictive digital tools to address the intrinsic challenges of layer-by-layer fabrication, such as the staircase effect, interlayer voids, and anisotropic bonding [126,127,128].

4.1. Mechanical, Thermal, and Chemical Surface Treatments

Surface treatment and post-processing play pivotal roles in overcoming inherent AM deficiencies. Mechanical techniques like abrasive flow machining (AFM), vibratory finishing, shot peening, and CNC milling reduce surface roughness and improve dimensional accuracy. AFM is particularly effective for polishing complex internal geometries, achieving Ra reductions over 60% by selectively smoothing high points while preserving functional features [126,129,130]. Thermal methods, such as laser polishing and thermal annealing, locally reflow surface asperities. Laser-assisted processes—including continuous wave, pulsed, and beam wobbling techniques—can lower surface roughness from ~7.5 µm to sub-micron levels (~0.2 µm) and increase subsurface hardness through rapid thermal cycling [131]. This enhances resistance to wear initiation and fatigue cracking. Chemical treatments like acetone vapor smoothing, solvent dipping, and plasma etching mobilize surface polymer chains, welding layer interfaces and lowering roughness by up to 95%, without mechanical abrasion. These processes are especially effective for materials like ABS and PLA. For metal AM parts, electrochemical polishing selectively dissolves surface peaks, improving corrosion resistance and removing trapped powders [132,133,134].

Complementing these, functional coatings tailor surface properties for specific applications. Metallic coatings (Ni, Cr, Cu) increase wear resistance and electrical conductivity, polymeric coatings (PTFE, parylene) reduce friction and add biocompatibility, and ceramic coatings (Al₂O₃, SiC, ZrO₂) provide exceptional hardness and thermal stability [135]. Hybrid coatings, embedding particles into metallic or polymer matrices, produce multifunctional tribological surfaces. Together, these approaches can reduce Ra from ~8–15 µm to <1 µm and improve wear resistance by up to an order of magnitude [136]. Figure 4 illustrates how wear in composites evolves from mild adhesive wear to severe fiber pullout and delamination, underscoring the need for robust surface engineering.

4.2. Integrated and Hybrid Post-Processing

Beyond smoothing, post-processing also improves bulk properties: acetone-smoothed ABS parts show tensile strength gains up to 20%, and laser remelting or polishing enhances flexural toughness and fatigue life by sealing micro-cracks and introducing compressive residual stresses [137,138]. Combining thermal and chemical treatments—e.g., laser smoothing followed by chemical etching—improves surface uniformity by filling voids and removing oxidation or debris. Process design must consider geometry: chemical dipping can cause dimensional distortion, particularly in thin-walled components, mitigated by oversizing CAD models or selective masking. Uniformity over complex surfaces requires advanced setups like rotary vapor chambers, multi-axis laser heads, or custom electrochemical fixtures. Emerging hybrid additive–subtractive systems integrate milling or polishing heads directly on AM platforms, enabling real-time, in situ finishing. This reduces handling errors, shortens production cycles, and maintains tight dimensional tolerances. Machine learning models predict surface outcomes based on input parameters including layer thickness, build orientation, and cooling rate, helping engineers optimize post-processing without costly trial-and-error.

These improvements extend AM’s reach: smoother surfaces enhance osseointegration in implants, lower bacterial adhesion in medical devices, and deliver the gloss and abrasion resistance needed for consumer electronics and automotive parts [139,140,141]. However, trade-offs remain: chemical treatments may raise sustainability concerns if solvents are not recycled; mechanical finishing can be labor-intensive or geometry-limited; and thermal methods risk residual stresses or microstructural changes if not carefully controlled.

Table 6. Extensive compilation of multidisciplinary research focused on tribological behavior, surface engineering techniques, additive manufacturing innovations, biomedical materials, and modeling strategies.

Author et al.	Area	Challenges	Objective	Methodology	Finding	Remark
Li et al. [142]	Surface treatment of additively manufactured Ti6Al4V alloys with magnetorheological polishing (MRP) and molecular dynamics (MD) simulation.	Conventional machining induces work-hardening, ablation, and inferior surface finish in Ti6Al4V alloys.	To improve surface quality and comprehend nanoscale tribological behavior of Ti6Al4V under MRP.	Coupled MD simulations (with EAM–Tersoff–Morse potential) and MRP experiments, such as nano-scratch tests.	Surface roughness has a non-linear relationship with pressure; material removal is higher; residual stress reduces by 76.75%.	Robust simulation–experiment correlation confirms the research and provides insight into aerospace and biomedical surface optimization.
Fan et al. [143]	Surface treatment in metal additive manufacturing by centrifugal disc finishing (CDF).	Degraded as-built AM surface finish; inconsistent topologies because build orientation influence finishing results.	To investigate how AM build orientation and CDF parameters affect surface topology evolution.	Experimental study of surface evolution under different CDF conditions; feature-instance segmentation-based surface evolution prediction by machine learning.	Reached 90% prediction accuracy in surface evolution; proved CDF to be effective in enhancing AM surface finish.	The research presents a new method for optimizing the quality of complex metal AM surfaces by using innovative advanced mass finishing and predictive modeling.
Kano et al. [144]	Tribology in machining processes, including composite machining and additive manufacturing processes.	Subtle tribological interactions inhibit accuracy due to material metastability and inconsistency between initial and running states. Classical modeling is unable to model real-time system behavior.	To examine progress in controlling tribology impact in machining and investigate integration of real-time, data-driven strategies.	Literature review of the traditional modeling approaches, recent advances in in situ monitoring techniques, and novel machine learning-based predictive methodologies.	Real-time observations are useful for high-precision machining; machine learning facilitates adaptive control without explicit physical models.	Data-driven tribology promotes precision machining, signaling a transition toward smart, adaptive manufacturing systems.
Choudhary et al. [145]	Mechanical and tribological properties of mullite and SiC-based ceramic matrix composites in journal bearings.	Classical bearing materials such as Bronze and Babbitt exhibit shortcomings in friction, wear resistance, and thermal stability under harsh conditions.	To compare and assess the tribological and mechanical properties of mullite-SiC composites with traditional bearing materials for improved journal bearing performance.	Coupled experimental analysis (friction, wear, microhardness, SEM) and finite element modeling (stress, deformation, friction) under journal bearing.	Mullite-SiC composites exhibited low friction (0.15), high wear resistance (0.002 g), low deformation, and homogeneous stress distribution (max 2.93 MPa); SEM exhibited low abrasive wear.	The research confirms mullite-SiC composites as superior replacements for conventional materials, paving the way for their industrial use for high-performance bearings.
Zhou et al. [146]	Mechanical and tribological improvement of IN718 alloy processed through laser-based direct energy deposition (LDED).	LDED exhibits inherent flaws and inferior mechanical performance that restrict commercial usage.	To enhance mechanical and wear properties of LDED IN718 alloy by the application of synchronized high-repetition laser shock peening (HRLSP).	Layer-by-layer HRLSP treatment imposed; microstructure, mechanical testing, numerical simulation probed effects.	Densification was 99.5%, grain size decreased by 30.8%, UTS was 897 MPa with 24% elongation, wear resistance improved.	HRLSP efficiently develops compressive residual stress and dislocation strengthening, providing an innovative path to high-performance LDED IN718.
Jiang et al. [147]	Fabrication and tribological investigation of SiC3D/7050 Al interpenetrating phase composites via pressureless infiltration.	Enhancing wear resistance and tribological behavior under changing loads in metal matrix composites.	To study microstructure and dry tribological properties under load of SiC3D/7050 Al composites.	7050 Al alloy was infiltrated into 3D SiC reticulated foam at 850 °C for 2 h; wear tests were performed under various loads.	SiC3D/7050 Al composites exhibit a double-interpenetrating microstructure, very low wear rates, and development of a protective mixed layer.	SiC3D reinforcement is effective for wear resistance with optimal performance at 60 N load through mechanically mixed layer control.
Rizwee et al. [148]	Annealed LPBF Ti-6Al-4V (Ti64) alloy tribological behavior for biomedical use.	Wear resistance and microstructural instability of LPBF Ti64 under simulated body fluid exposure.	To enhance tribological behavior of LPBF Ti64 alloy through annealing and optimize porous sample production.	Wet reciprocating wear tests (5 N load, 5 mm/s) with SS304 ball in simulated body fluid; microstructural, mechanical characterization; parametric porosity simulation in ANSYS (ANSYS additive 2023 R1 software).	Annealing resulted in decomposition of α′ martensite to α + β phases; wear mechanisms associated with microstructure; enhanced wear resistance with annealing.	Annealing improves tribological performance by altering microstructure, lowering abrasive and adhesive wear modes in LPBF Ti64 alloy.
Raju et al. [149]	Additive manufacturing by selective laser melting (SLM) for complex AlSi12Mg alloy components; emphasis on surface finishing.	Surface quality and geometry accuracy in SLM parts influence wear resistance, hardness, and corrosion behavior.	To design an ultrasonic-assisted magnetic abrasive finishing (UAMAF) process to enhance surface quality of SLM parts effectively.	Used applied UAMAF with unbonded silicon carbide abrasives on AlSi12Mg alloy; conducted EDAX, hardness, wear, and corrosion tests on heat-treated and non-heat-treated samples.	UAMAF exhibited elemental constitution retention; hardness decreased by 6.34% (non-heat-treated) and 24.94% (heat-treated); wear resistance was enhanced in heat-treated ground-finish specimens; corrosion rate decreased by more than 90%.	UAMAF efficiently improves SLM part surface features, making them applicable for real-time use.
Ezhilmaran et al. [150]	Mechanical, tribological, and corrosion resistance improvement of 316L stainless steel manufactured by powder bed fusion.	Evidence of scanning patterns and energy densities on material properties such as porosity, roughness, and strength.	To study the effect of various scanning patterns and energy densities on tensile, compressive, hardness, tribological, and corrosion properties of 316L.	Experimental investigation with three scan patterns (line, spiral, chessboard) and energy densities of 30 to 95 J/mm3; examining mechanical and tribological properties.	Chessboard pattern at 95 J/mm3 provided maximum tensile strength (736 MPa), 41% greater than commercial 316L, better hardness (+21%), less friction (0.39), and improved corrosion protection.	Chessboard scanning pattern is best for production of 316L orthopedic implants because of enhanced mechanical and corrosion properties.
Romanova et al. [151]	Numerical solutions to boundary-value problems with morphological microstructure in crystal plasticity finite element models.	High computational intensity needed; costs have to be kept down while retaining quasistatic high-precision solutions.	Discuss computational considerations of explicit time integration in quasistatic deformation simulations of polycrystals.	Utilize crystal plasticity finite element models with explicit dynamics; validate and verify models on micro-, meso-, and macro-scales.	Successful simulation results presented for single- and polycrystalline aluminum confirming the method.	Evidence schemes trade off computation efficiency and accuracy in intricate quasistatic deformation modeling.
Streďanská et al. [152]	Non-specific lower back pain (LBP) treatment with hyaluronic acid (HA) viscosupplementation.	Native HA rapid metabolism restricts its effectiveness in LBP treatment.	Assess whether an HA derivative can substitute for native HA by preserving/enhancing frictional properties and enhancing in vivo stability.	Evaluated six native and derivatized HA lubricants in rabbit fascia tribological and synthetic models; performed pharmacokinetic studies in rabbits.	Lower HA derivative possessed improved tribological characteristics and greater in vivo residence; 316 kDa HA and lower HA had maximum stability based on molecular weight and concentration.	HA reduction is a novel viscosupplement for intrafascial injection with potential for extended therapeutic effect on LBP.
Singh et al. [153]	Dynamic recrystallization (DRX) in friction stir-welding/processing/additive manufacturing (FS-W/P/AM) impacting microstructure and mechanical properties.	High-strength material processing, microstructural heterogeneity, orientation control, size constraints, pre/post-processing needs.	To summarize DRX types, DRX-controlling factors, microstructural evolution, mechanical properties, and modeling methods in FS-W/P/AM.	Comprehensive literature review of material and process parameters on DRX, along with examination of numerical, computational, and AI-based modeling methods.	Grain size and second phase particles are most important material parameters; DRX is dictated by tool design, cooling, stir pattern, and reinforcements. Aerospace and electronics are leading applications; new application in medicine and construction.	AI and Industry 4.0 integration in modeling tools can improve FS-W/P/AM process efficiency and tailorability towards industrial requirements.
Tekin et al. [154]	Influence of zinc alloying (0.2–2%) on biodegradable magnesium alloys processed by powder metallurgy for biomedical applications.	Hardness, wear resistance, porosity balance; abrasive–corrosive wear control in simulated body fluids.	To investigate the influence of different Zn content on the mechanical and wear characteristics of Mg alloys for bioresorbable implants.	Mechanical alloying, cold pressing, sintering, and wear tests in simulated body fluid with microstructural examination.	Zn evenly dispersed; hardness raised 40 to 70 HV; MgZn2 alloy exhibited superior wear resistance; porosity rose with density.	Mg–Zn alloys exhibit promising bioresorbable characteristics like bone mechanics appropriate for biomedical implant application.
Malakizadi et al. [155]	Dislocation-based flow stress modeling for Alloy 718 produced by laser and electron-beam powder bed fusion additive manufacturing.	Material behavior and machinability influenced by microstructural changes (precipitates, texture, grain size, dislocation density). Control of these has to be achieved.	To establish a physics-based model responsive to microstructural parameters to make predictions for additively manufactured Alloy 718 machinability.	Combine thermodynamic and kinetic simulation results with advanced characterization to guide the flow stress model and machining predictions.	Predicted cutting forces and chip shape values are consistent with experimental measurements.	Model is an effective tool to evaluate and improve machinability of AM Alloy 718 with microstructure effect.
Ohdar et al. [156]	Water-lubricated bearings with emphasis on surface texture, tribological performance, thermal effects, and materials.	Controlling wear, friction, material toughness, and thermal effects to maximize performance and life.	To investigate surface texture impact, tribology properties, material choice, and thermal response for enhanced water-lubricated bearings.	Detailed review of literature on surface texture, tribology, material properties, and thermal analysis of water-lubricated bearings.	Material composites and surface texture have a strong influence on friction and reduction in wear; thermal action affects bearing integrity.	This review points out existing knowledge deficiencies and outlines future research areas for the development of high-performance, environmentally friendly water-lubricated bearings.
Blanco et al. [157]	Wear prediction in lubricated sliding surfaces in complex multi-physics systems by contact mechanics and lubrication modeling.	Uncontrolled wear leading to catastrophic failure; requirement for precise lifetime prediction models that include surface roughness and lubrication effects.	To create a predictive model for wear by combining rough contact mechanics with mixed elastohydrodynamic lubrication under different conditions.	Integrated a nonlocal roughness-function with a mixed EHL model and multiscale roughness corrections; experimentally validated through journal bearing experiments.	Model was able to predict wear rates and depths correctly; exhibited roughness variations based on lubricant viscosity.	The methodology effectively connects surface roughness evolution and lubricant characteristics to wear prediction in sliding contacts.
Wu et al. [158]	Wear resistance of WC composite coatings on 42CrMo steel against glass fiber-reinforced polymer (PPS-40%GF) in injection molding screws.	Severe wear due to glass fiber-reinforced polymers on screws and barrels during plasticizing in injection molding machines.	Investigate and compare wear resistance and mechanisms of three WC composite coatings deposited onto 42CrMo steel.	High-velocity oxygen fuel spraying of WC-12Co, WC-20Cr3C2-7Ni, and WC-10Co-4Cr coatings; tribological tests with PPS-40% GF pins.	Wear rates of WC-12Co < WC-20Cr3C2-7Ni < WC-10Co-4Cr coatings were ranked; wear mechanisms examined and communicated.	WC-12Co coating exhibited maximum wear resistance against PPS-40%GF, indicating applicability to injection-molding parts.
Lai et al. [159]	Surface texturing for friction reduction and wear/fatigue resistance improvement in GCr15 bearing steel.	Limited literature available on the impact of texture design parameters on wear and fatigue resistance of bearing steel.	To improve anti-wear and anti-fatigue performance and increase service life of bearing steel through optimized micro-groove surface textures.	Micro-groove textures from hydrodynamic theory and made with nanosecond laser; different depth, spacing, and friction angle; conducted friction, wear, and rolling contact fatigue tests.	300 μm micro-groove spacing minimizes friction; 30 μm depth maximizes hydrodynamic pressure; 60° friction angle reduces CoF; RCF life enhanced by 36.5% through stress dispersion by grooves.	Optimized micro-groove textures enhance lubricity and lower friction than flat surfaces, leading to improved bearing steel performance.
Yu et al. [160]	3D-printed Ti-6Al-4V alloys for biomedical implants with emphasis on bio-tribological behavior and surface quality effects.	Surface roughness influences wear resistance of implants; greater roughness introduces stress concentration and sophisticated wear processes.	To examine the influence of various surface treatments on the bio-tribological behavior of Ti-6Al-4V alloys in simulated body fluid.	Ground, polished, and sandblasted samples; wear test with Si3N4 ball; simulated with finite element simulation.	Polished samples exhibited minimum wear rate and highest bio-tribological stability; rougher surface caused stress concentration and change in wear mechanism.	Guidance from studies optimizes surface quality control to promote implant longevity through reduced wear through enhanced surface finishing.
Souza et al. [161]	Tribological analysis of aviation engine lubricants by molecular dynamics under extreme conditions.	Expensive and environmental issues with physical testing; trouble in simulating lubricant behavior at molecular level under extreme T/P.	To evaluate tribological performance of polyol ester lubricants in gas turbines through molecular dynamics simulations.	Three-layer model with NiAl surfaces and polyol ester core; simulated under different sliding speeds, temperature, and pressure; RDF, MSD, and friction were analyzed.	Friction coefficient reduces with rising temperature and pressure; greater molecular interaction and lesser metal adsorption at higher speeds.	The simulation method provides useful quantitative and qualitative information as a predictive tool for lubricant response in extreme environments.

summarizes key challenges, methods, and reported outcomes across sectors like aerospace, biomedical, and energy, reflecting how integrated surface engineering enhances AM part reliability.

4.3. Hybrid Manufacturing Strategies

Hybrid manufacturing combines AM with subtractive, mechanical, and surface treatments to address persistent limitations: anisotropic bonding, poor layer adhesion, and low wear resistance [162,163,164]. For example, CNC milling or micro-machining refines external surfaces while preserving complex internal features; SLA parts benefit from polishing of mating surfaces or microfluidic channels affected by resin shrinkage.

Surface mechanical treatments like Ultrasonic Surface Rolling Process (USRP), laser shock peening, and shot peening introduce beneficial residual compressive stresses, refine grain sizes, and increase hardness, reducing wear volume by over 50% in steels like H13 [165,166]. These non-thermal methods prevent distortion and improve fatigue life, critical for SLA parts prone to brittle fracture. Hybrid processes also enable functionally graded materials (FGMs): dual-nozzle FDM systems print stiff, wear-resistant shells over softer, shock-absorbing cores; SLA systems switch resins layer-by-layer to build bio-inspired laminates or hydrogels with tailored frictional and swelling properties. Laser cladding and directed energy deposition can deposit hard particles or metallic layers, improving thermal conductivity and sliding wear resistance [167,168,169]. Microstructural studies reveal how these treatments introduce ~−933 MPa compressive stresses, achieve sub-2 µm grain sizes, and raise dislocation densities (~5 × 10¹⁵ m⁻²), boosting frictional stability and lowering wear rates in dry or semi-lubricated contact. AI-driven adaptive control further refines additive–subtractive cycles in real time, preventing over-processing and improving precision [170,171,172,173,174]. Platforms integrating SLA with ultrasonically assisted milling or layer-by-layer peening demonstrate closed-loop, hybrid AM [175,176,177]. Hybrid strategies thus transform AM from prototyping into production, delivering robust, wear-optimized parts suitable for aerospace brackets, biomedical devices, and tribo-critical machinery.

4.4. Predictive Tools and Future Trends

Despite progress, achieving tribologically stable FDM and SLA parts remains challenging due to anisotropic bonding, layer delamination, and the brittleness of cured resins [78,178,179]. Standard slicer software focuses on geometric accuracy rather than mechanical and tribological performance, neglecting contact stresses and wear paths, limiting reliability in high-performance applications like aerospace and biomedical implants [180,181,182,183]. Hybrid manufacturing helps bridge this gap by adding subtractive finishing, peening, and coatings [184,185,186]. Multi-material designs—core–shell geometries in FDM, resin switching in SLA—create functionally graded parts balancing hardness and ductility. Coatings, like ceramics or metals, add wear resistance, lubricity, and corrosion protection [187,188,189]. On the digital front, AI and ML promise significant gains: adaptive slicing could adjust infill patterns, raster orientation, and material allocation based on simulated load paths, while in situ sensors measure thermal profiles, roughness, and strain to enable real-time corrections [190,191]. Future trends include printable high-entropy polymers, self-healing composites, and bio-inspired textures, alongside solvent-free, recyclable coatings for sustainable production.

Figure 5 illustrates the hierarchical classification of tribological properties and applications of SLA (stereolithography) resins. It begins with standard SLA resins, focusing on their typical properties and tribological behavior. The next layer details functional SLA resins, which achieve enhanced tribological performance through reinforcement and lubricant modification. Finally, it presents specific examples and applications of these functional resins, such as graphene-infused materials, solid lubricants, and uses in dental, biomedical, and mechanical components.

Ultimately, bridging design freedom and durability requires cross-disciplinary integration of material science, process engineering, and AI, enabling AM parts to meet demanding tribological requirements in biomedical, aerospace, and energy applications.

Table 7. Categorization and comparison of surface engineering strategies for FDM and SLA in tribological applications [4,8,9,41,42,43,62,63,64,65,66,67,68,69,70,71,72,76,77,78,89,94,95,96,102,117,127,192,193].

Category	Technique	Applicable to	Effect on Tribology	Advantages	Limitations
Mechanical	Sanding/Polishing	FDM	Reduces surface roughness, improves contact uniformity	Simple, low cost	Manual, time-consuming, may alter dimensions
	Abrasive Blasting	FDM/SLA	Improves surface adhesion and microtexture	Uniform treatment, scalable	Material removal risk
Thermal	Annealing	FDM	Enhances bonding between layers, reduces internal stress	Improves mechanical strength	Requires temperature control
	Laser Surface Remelting (LSR)	FDM/SLA	Increases surface hardness and reduces wear rate	Precise, localized treatment	Equipment-intensive, potential warping
Chemical	Vapor Smoothing (e.g., acetone)	FDM (ABS/ASA)	Drastically reduces roughness, seals micro-pores	Fast, effective for aesthetics	Limited to specific polymers, toxic solvents
	Solvent Dipping (IPA, etc.)	SLA	Smoothens uncured surface layer	Enhances print clarity and frictional behavior	Chemical waste, limited depth effect
Coating/Deposition	PTFE or Graphite Coating	FDM/SLA	Reduces COF, enhances wear resistance	Excellent lubrication properties	Requires surface preparation, adhesion challenges
	Electroless Ni/TiN Coating	FDM/SLA	Increases hardness, reduces adhesive wear	Industrial-grade tribological performance	Costly, uneven coating possible
	Plasma Spraying	FDM (metal/polymer)	Creates dense wear-resistant layer	Excellent for aggressive environments	High-temp process, equipment need

presents a categorized summary of common surface engineering strategies applied to FDM and SLA parts with emphasis on their tribological performance enhancement. This structure allows for clearer understanding of which strategy is most suitable based on material type, desired surface effect, and processing constraints.

5. Conclusions and Future Directions

This review critically examined the tribological challenges and advancements in FDM and SLA additive manufacturing, showing how materials innovation, hybrid processes, and intelligent design are reshaping performance limits. While FDM remains constrained by anisotropic bonding and surface roughness, SLA faces brittleness and curing sensitivity that can cause crack initiation and unpredictable fatigue failures. Recent progress in nano-reinforcements and functional fillers has demonstrated significant reductions in friction and wear, complemented by mechanical, thermal, and chemical surface engineering strategies that lower roughness to sub-micron levels and improve fatigue life. Hybrid manufacturing methods combining additive deposition with peening, milling, and laser cladding emerge as a powerful route to introduce compressive stresses, refine grain structure, and produce functionally graded surfaces. Simultaneously, AI and machine learning tools enable predictive process control, mapping printing parameters to tribological performance and allowing real-time adaptive optimization. Sustainability trends, including bio-based filaments and solvent-free post-processing, align additive manufacturing with global environmental goals while retaining durability. Looking ahead, the integration of digital twin frameworks and self-healing polymers promises adaptive, self-optimizing AM parts for critical applications.

Key highlights of this review include:

• Detailed analysis of dominant wear modes linked to process parameters and anisotropy,
• Demonstration of how nano-fillers form protective tribo-films,
• Evaluation of surface treatments that reduce roughness and enhance mechanical integrity,
• Presentation of hybrid manufacturing as a route to wear-resistant, graded surfaces,
• Review of AI and ML for predictive optimization,
• Discussion of sustainable materials and greener processes, and
• Exploration of digital twins and smart polymers as emerging adaptive solutions.