Search Results (1,088)

Fused deposition modeling (FDM) is an emerging trend for producing nerve guidance conduits (NGCs). This technique allows distinct designs and dimensions to mimic peripheral nerve architecture and promote nerve regeneration. In this study, commercially available TPU 90A and 95A filaments were used for the fabrication of hollow simple wall (non-porous), grooved and gyroid multichannel conduits. The segmented polyurethanes were identified as PBA-MDI-BO-based polyurethanes by ¹H NMR, FTIR and Raman spectroscopy. Thermal analyses, such as DSC and TGA, demonstrated that both TPUs possess sufficient thermal stability to be processed safely under the printing conditions employed. Tensile mechanical tests accounted for their differences in hard segment content in agreement with the Shore A hardness. The measured elastic modulus, in particular, was within a range that may be advantageous for peripheral nerve repair. The gyroid multichannel design showed enhanced resistance to radial compression and highly interconnected internal structure that supported primary neural cell viability and preserved cellular functionality. Therefore, polyurethane-based nerve guidance conduits can be manufactured by FDM, rendering high printability, favorable mechanical performance without compromising biocompatibility. Full article

Polyethylene Terephthalate Glycol (PETG) is a thermoplastic material used in Fused Deposition Modelling for prosthetic applications, where mechanical properties are strongly dependent on process parameters. This study investigated the effects of carbon fibre (CF) content, print orientation (PO), and print temperature (PT) on the mechanical performance of PETG, fabricated using a Bambu Lab A1 printer. Tensile, three-point bending and impact testing were conducted to characterise the mechanical response of printed specimens. A Taguchi L9 array was employed to evaluate parameter effects while minimising experimental runs, and factor effects were quantified using per-response general linear models. Findings indicated that PO and PT significantly affected tensile behaviour, while CF content dominated flexural stiffness and impact response, with the strongest tensile response at 240 °C attributed to improved interlayer bonding. CF reinforcement increased stiffness and flexural strength but had limited effect on tensile strength and a reduced impact resistance at higher loadings, indicating increased brittleness. PO was identified as the most influential factor, with upright specimens exhibiting superior tensile performance, consistent with more favourable alignment of filament deposition with the loading direction. These findings demonstrate that the mechanical behaviour of CF-PETG is strongly process-dependent, informing its future application within prosthetic limb design. Full article

This study investigated the manufacturing and impact of critical input parameters in fused filament fabrication (FFF) on the ultimate tensile strength (UTS) of tailor-made recycled PLA/wood bio-composite specimens. As technology advances rapidly, several wood-based polymer composites have emerged as promising materials for wood-based interior applications. In the current work, recycled PLA material is combined with wood powders to form composite 3D printing filaments. The solution casting method is used to recycle the PLA and a single-screw extruder is used to fabricate the composite filament. 3D printing parameters play a major role in enhancing the characteristics of the wood-based polymers. This study considers the printing temperature (PT), layer height (LH), and printing speed (PS) as input parameters at five levels. Taguchi Design of Experiments (L25 orthogonal array) was employed to minimize experimental runs, followed by ANOVA analysis to find influencing factors. The results demonstrated that layer height (83.91% contribution) is the most critical parameter, with 0.1 mm identified as the optimal amount for achieving the maximum UTS response, while printing temperature (2.47%) had a moderate effect and printing speed (2.28%) showed negligible influence. In the present work, the tensile properties of the composite filament were predicted using machine learning methodologies, including random forest (RF), support vector regressor (SVR), Gradient Boosting Regression (GBR), Extreme Gradient Boosting (XG Boost), and Adaptive Boosting (Adaboost). The results indicate that support vector regressor (SVR) outperformed all other models in terms of generalization, as it generated the lowest test errors (mean squared error (MSE) = 0.0169, mean absolute error (MAE) = 0.0953, mean squared logarithmic error (MSLE) = 0.0065 and mean absolute percentage error (MAPE) = 0.2246) and the highest predictive power (coefficient of determination (R²) = 0.8679). Full article

Transient extrusion defects are a fundamental process control challenge in fused granular fabrication (FGF), arising from the finite melt pressurization time of screw-driven extruders at each start–stop event. This study presents an integrated experimental and analytical framework for the characterization and open-loop feedforward compensation of these transient dynamics, demonstrated on two composite thermoplastic feedstocks: a recycled random polypropylene (RPP1) and a 20 wt% wood-fiber-reinforced polypropylene composite (WFPP). Unlike prior filament- or single-material feedforward strategies, this framework derives and statistically validates material-specific compensation parameters across two rheologically distinct feedstocks. Single-layer road experiments were conducted on a custom instrumented FGF platform across a 2³⁻¹ half-fraction factorial design varying melt temperature, print acceleration, and nozzle diameter, with screw speed stepped among 20, 40, and 80 RPM to excite transient states; deposited road geometry was digitized and spatially registered to the synchronized process signals. Main-effects regression confirmed that nozzle diameter is the dominant predictor of mean road width, while screw velocity exerts a significant negative effect attributable to speed-dependent backflow. Prediction-error minimization on the pooled multi-experiment dataset yielded a parsimonious first-order transfer function, G(s) = 0.990/(1 + 1.909s), whose time constant is physically attributed to melt compressibility in the barrel volume upstream of the nozzle restriction. This model was embedded in a G-code post-processor implementing two sequential corrections: a material-specific steady-state slip gain and a discrete linear-advance term parameterized by the identified time constant. For RPP1 at the nominal gain, the print latency interquartile range decreased from 5–20 mm to 2–8 mm without degrading steady-state dimensional accuracy; the combination of nominal gain with active retraction further reduced latency to near-zero. Analysis of covariance (ANCOVA) confirmed that optimal feedforward gains are statistically material-dependent across all three quality metrics (p < 0.05), providing statistical justification for material-specific compensator parameterization. The results establish a practical, hardware-agnostic route to reduce transient deposition defects in pellet-based additive manufacturing, extensible to additional feedstocks. Full article

Additive manufacturing, particularly Fused Filament Fabrication (FFF), enables the production of multi-material components with tailored mechanical properties; however, the compressive behavior of dual-material polymer systems remains insufficiently explored. This study investigates the compressive mechanical performance of dual-material PLA/ABS specimens fabricated by FFF, with emphasis on the influence of key process parameters. An experimental design based on the Taguchi method was employed to evaluate the effects of raster angle, raster angle variation, and material volume ratio. Compression tests were conducted in accordance with ASTM standards, and the resulting stress–strain data were analyzed to evaluate the compressive response and deformation characteristics. The results indicate that compressive stress values range from approximately 103 MPa to 138 MPa, with the highest performance obtained for specimens with 60% PLA and 40% ABS. Among the examined parameters, the material composition was identified as the most influential factor, followed by raster variation strategy. These findings demonstrate that dual-material configurations can achieve improved compressive performance through appropriate parameter selection, while also highlighting the significance of interfacial integrity between dissimilar materials. The study provides practical insights into the process–structure–property relationships of dual-material FFF structures, showing how raster strategy and PLA/ABS volume ratio influence compressive response and offering experimentally supported guidance for the fabrication of compression-dominated polymer components. Full article

Material extrusion additive manufacturing, commonly implemented as fused deposition modeling (FDM) or fused filament fabrication (FFF), has evolved into a manufacturing route for reinforced thermoplastic composites, including particle-filled, short-fiber-reinforced, and continuous-fiber-reinforced systems. The process is governed by a layer-by-layer thermal cycle. Deposited roads cool rapidly, are repeatedly reheated by subsequent material deposition, and finally cool non-uniformly as part of the growing structure. This thermal history generates residual-stress that may cause warpage, build–platform detachment, delamination, dimensional error, and reduced mechanical performance. This review synthesizes residual-stress formation, measurement, modeling, parameter effects, and mitigation in material-extruded reinforced thermoplastic composites, with emphasis on short and continuous-fiber systems. Stress formation is discussed in terms of constrained thermal contraction, crystallization shrinkage, anisotropic stiffness, fiber-constrained deformation, porosity, and fiber–matrix thermal expansion mismatch. Experimental methods, including hole drilling, layer removal, curvature methods, embedded fiber Bragg gratings, digital image correlation, photoelasticity, and warpage metrology, are critically compared for anisotropic and porous printed composites. Analytical and numerical models are reviewed from layerwise shrinkage formulations to crystallization-coupled thermo-viscoelastic finite element simulations. Finally, mitigation strategies are evaluated. A central conclusion is that reinforcement can suppress visible distortion while increasing stress retained in a stiffer structure. Therefore, warpage alone is not a sufficient residual stress metric. Full article

Fused filament fabrication (FFF) is one of the most widely adopted additive manufacturing methods for thermoplastic polyurethane (TPU)-based soft pneumatic actuators, enabling low-cost fabrication, geometric customization, embedded pneumatic architectures, and rapid prototyping for soft robotic systems. However, despite these advantages, achieving reliable airtightness remains a major challenge due to process-induced anisotropy, interlayer voids, incomplete filament fusion, residual porosity, seam discontinuities, material permeability, and interface-related leakage. These defects can significantly reduce pressure retention, actuation efficiency, deformation repeatability, and long-term pneumatic reliability. This review systematically examines the dominant leakage mechanisms affecting FFF-printed soft pneumatic actuators and comparatively analyzes fabrication approaches, TPU material systems, geometric design factors, post-processing methods, sealing strategies, and leakage characterization techniques. Representative experimental observations, including pressure-decay testing, submerged-bubble visualization, microscopy, and localized thermal surface treatment, are also discussed to connect the findings reported in the literature with experimentally observed leakage behavior. Emerging analytical leakage models, sensing technologies, AI-assisted predictive monitoring, and digital-twin-enabled manufacturing frameworks are reviewed as promising approaches for developing leakage-aware soft robotic systems. The review highlights current limitations related to standardized leakage testing, cyclic durability evaluation, scalable sealing strategies, and intelligent manufacturing integration. Overall, airtightness is identified as a coupled material-process-geometry challenge that must be systematically addressed to improve the reliability, scalability, and long-term operational stability of next-generation TPU-based soft pneumatic actuators. The review was conducted following the PRISMA-ScR framework and includes 248 studies published between 2017 and 2026. Full article

Growing environmental concerns over petroleum-based plastics have increased interest in sustainable and biodegradable alternatives such as polyhydroxybutyrate (PHB). PHB is a naturally produced biopolymer synthesized by microorganisms and is widely recognized for its biodegradability, biocompatibility, renewability, and thermoplastic properties. Despite these advantages, PHB use remains limited by brittleness, high crystallinity, low thermal stability, a narrow processing window, and high production costs. This review discusses the production, properties, biodegradation behavior, and applications of PHB, with a focus on strategies to improve its performance. Modification approaches, including copolymerization, polymer blending, filler reinforcement, plasticization, and hybrid composite formulation, are critically reviewed to evaluate their effects on the thermal, mechanical, and processing behavior of PHB-based materials. The review also highlights recent developments in additive manufacturing, particularly fused deposition modeling/fused filament fabrication (FDM/FFF) for the extrusion of biodegradable PHB composite filaments. In addition, the biodegradation of PHB under various environmental conditions, including soil, compost, freshwater, marine, aerobic, and anaerobic environments, are discussed. Current challenges, research gaps, commercialization barriers, and future opportunities related to sustainable feedstocks, advanced composites, additive manufacturing, and circular economy integration are addressed. Overall, PHB shows strong potential as a sustainable alternative for packaging, biomedical, agricultural, and three-dimensional (3D) printing applications. Full article

This work presents the design evolution, fabrication, and characterisation of an additively manufactured ring-type thermal airflow sensor for in-pipe flow monitoring, developed employing exclusively Fused Deposition Modelling (FDM) additive manufacturing technology and a commercially available Carbon Nanotube (CNT)-enriched Biopolymer Polylactic Acid (PLA) composite filament. The design evolution proceeds through three progressive stages. In the first stage, a flat heater element is characterised through Constant-Current (CC) Joule heating experiments in order to derive the corresponding Temperature Coefficient of Resistance (TCR) and Thermal Resistance from the obtained experimental data. Consequently, a Finite Element Method (FEM) model implemented in COMSOL Multiphysics^® and calibrated with the extracted material parameters validates the experimental temperature–power relationship and predicts the convective cooling behaviour at various airflow velocities. In the second stage, the geometry is optimised by introducing a conductive trace with a reduced-cross-section central region; as a result, an equivalent thermal localisation is achieved at approximately 26% lower supplied power with respect to the initial heating element, enabled by the design freedom inherent in the FDM process. We should note that the specific sensing geometry can also be directly embedded into any 3D-printed structural component (e.g., a bracket or housing), enabling simultaneous local thermal heating and/or thermal monitoring together with structural functionality within a single printed part. In the third and final stage—the target device—a fully monolithic ring-type airflow sensor is directly integrated into a 3D-printed pipe segment during the printing process. Under constant-current excitation at 40 mA, the device exhibits a monotonically decreasing resistance with increasing airflow (ΔR ≈ 117 Ω over 0–4 m/s) due to convective cooling, while in a single flow-interruption cycle, approximately 79% of the flow-induced resistance change was recovered upon flow removal, with a residual offset of approximately 3% of the heated baseline. A coupled electrothermal FEM model of the device further supports the experimental response by comparing the simulated temperature rise with the values inferred from resistance measurements, while also clarifying the role of the effective internal convective cooling conditions imposed by the pipe geometry. Key features of the proposed device are low raw-consumables cost, fast on-site manufacturing employing a commercially available desktop 3D printer, monolithic construction free of wire-bonded interconnections, and simplicity, indicating its potential for flow monitoring and condition-based maintenance systems aboard vessels as well as in a wide range of industrial sectors. We should note that the present characterisation was performed under laboratory conditions employing a single prototype per design stage; the effects of humidity, salt exposure, vibration, temperature cycling, and material-batch variability remain to be assessed prior to shipboard deployment. Full article

Material Extrusion (MEX), particularly Fused Filament Fabrication (FFF), commercially known as Fused Deposition Modeling (FDM), has become one of the most widely used additive manufacturing technologies for producing polymer components. However, the mechanical performance of printed parts remains limited by weak interlayer bonding and internal porosity. This study investigates the effectiveness of controlled low-frequency bed vibration in improving the physical and mechanical properties of PLA components manufactured by vibration-assisted FFF/FDM. The influence of printing speed, raster angle, and vibration level was experimentally evaluated through tensile, flexural, surface roughness, Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy (SEM) analyses. Response Surface Methodology (RSM) was employed to optimize the process parameters with respect to tensile strength, yield strength, flexural strength, and surface quality. The results demonstrate that moderate bed vibration (Level 2) provides the best overall performance, improving the mechanical properties by approximately 8–15% compared with conventional printing. SEM observations revealed an approximately 60% reduction in average pore size, together with enhanced filament fusion and interlayer adhesion, while FTIR analysis confirmed that the chemical structure of PLA remained unchanged. These findings demonstrate that controlled mechanical bed vibration is a simple and effective strategy for enhancing the quality, reliability, and structural performance of FFF/FDM-printed PLA components. The proposed approach also provides practical guidelines for optimizing additive manufacturing processes and supports the development of advanced polymer manufacturing capabilities in Hail’s growing industrial sector. Full article

Cultural Heritage (CH) is becoming increasingly vulnerable to the impacts of climate change, aging, and environmental decay, necessitating advanced preventive conservation strategies. This study presents the results of the SPIDER project, focused on Marquis’s Palace in Botrugno, a small but representative case study in Southern Italy of a municipality overwhelmed with the management of valuable CH sites. The approach integrates multi-sensor surveys, subsurface diagnostics, HBIM modeling, and IoT microclimatic monitoring into a lightweight information model designed for operational flexibility. In addition to that, the possibility of producing new, eco-friendly filaments for Fused Filament Fabrication (FFF) printing from industrial stone dust waste was explored through a preliminary morphological, structural, and chemical–physical investigation of the stone material historically used in construction, with the aim of identifying materials similar to the original using a simplified, low-cost process. The findings highlight that economic and social factors such as limited resources and the “digital divide” hinder effective technology transfer. Consequently, this study investigates whether a “lightweight” Asset Information Model (AIM) can provide a more sustainable alternative to complex Digital Twins for small municipalities and other public bodies. For this reason, this research proposes a scalable, wide but basic framework of information management tools and methods aimed at enhancing territorial capacity building, fostering technology integration and social inclusion, and valorizing multidisciplinary approaches to address the challenges affecting CH. Full article

Additive manufacturing (AM) has evolved from a rapid prototyping technique into a versatile platform for fabricating advanced functional materials and complex engineering components. While polymers remain the dominant material class due to their processability and tunable properties, recent developments have expanded AM to include high-performance composites, nanocomposites, and metallic materials. This review provides an overview of functional materials for additive manufacturing, emphasizing the relationships between material design, processing conditions, microstructure evolution, and resulting properties. Key functional polymer systems are discussed, including conductive, stimuli-responsive, elastomeric, high-performance, bio-based, and nanocomposite materials reinforced with nanoparticles, carbon nanomaterials, MXenes, and fibers. This review also examines processing–structure–property relationships common to polymer- and metal-based AM, highlighting the roles of anisotropy, defect formation, residual stresses, and post-processing in determining component performance. Finally, current challenges and emerging trends—including multi-material and 4D printing, machine learning-assisted optimization, and digital materials design—are discussed. Overall, the review highlights how advances in materials science and intelligent manufacturing are expanding the capabilities of additive manufacturing for multifunctional engineering and biomedical applications. Full article

Waste material valorization as a feedstock for net-zero waste manufacturing processes has emerged as a key sustainability strategy. Process technologies such as Additive Manufacturing (AM) have helped to limit material waste and allowed the production of complex designs with lower required costs and less time than other conventional manufacturing methods. In this study, an investigation of the addition of end-of-life Ground Tire Rubber (GTR) waste to a Polyamide 12 (PA12, nylon 12) matrix was conducted. Three different PA12-based powders were produced in a lab-scale environment with different weight fractions (wt.%) of reused GTR and specimens for static tensile, cyclic tensile, compression testing, Dynamic Mechanical Analysis (DMA), and vibrational analysis were designed assessing both the static and dynamic mechanical response. The specimens were 3D printed using Selective Laser Sintering (SLS) AM, a technique that promotes thermal coalescence between adjacent powder particles and successive layers, resulting in a more interconnected material structure and potentially reduced directional anisotropy compared to Fused Filament Fabrication (FFF) AM, although process-induced anisotropy may still be present, while the material used has a low powder refresh requirement of 22%. The results showed that the introduction of reused GTR helped improve the damping properties of the material. Combining the strength of PA12 even at high thermal stresses with the increasing damping properties of the GTR can be vital for vibration isolators in industrial, structural, and automotive applications while simultaneously reducing the material footprint. Full article

In polymer selective laser sintering (SLS), powder acts as a support material during additive manufacturing, generating significant amounts of un-sintered powder exposed to prolonged thermal cycles. Although partial reuse with virgin powder is common practice, material degradation eventually renders the powder unsuitable for further SLS processing. This study investigates a sustainable approach for valorising SLS waste powder through its conversion into filament feedstock for fused filament fabrication (FFF). Polyamide 12 filaments containing 0, 2, 3, and 4 wt.% multi-walled carbon nanotubes (MWCNTs) were produced by twin-screw extrusion to tailor the electrical conductivity of the polymer matrix. The filaments were processed by FFF to manufacture specimens for thermal, mechanical, and electrical characterization. Differential scanning calorimetry revealed the influence of reprocessing on the thermal behaviour of the reused material and resulting filaments, while thermogravimetric analysis demonstrated improved thermal stability with increasing MWCNT content. Tensile testing showed increased Young’s modulus (up to 9.4%), despite an initial drop, and tensile stress at break (up to 56.3%) with increasing nanofiller concentration. In addition, distinct electrostatic-discharge (ESD) protection ranges were achieved depending on the MWCNT loading. The results demonstrate the potential of reused SLS powder as a sustainable feedstock for functional AM materials suitable for ESD-sensitive applications. Full article

This work investigates the potential of additive manufacturing (AM) technologies for prototyping and developing functional components in thermal systems, with particular emphasis on thermal and mechanical performance. The study focuses on two complementary prototyping strategies: (i) the use of metal-filled polymer filaments in Fused Deposition Modeling (FDM), also known as Material Extrusion (MEX) according to ISO/ASTM 52900:2022, and (ii) a hybrid approach combining polymer 3D printing with conductive coating and electrochemical copper deposition. While metal-filled filaments provide a rapid and low-cost solution for early-stage prototyping, their mechanical properties remain similar to those of the polymer matrix, limiting their applicability in load-bearing structures. In contrast, the hybrid method enables the fabrication of hollow metallic geometries with improved thermal and electrical conductivity. This approach is more time-consuming and process-intensive and is therefore considered a subsequent stage in the prototyping workflow following initial MEX-based design iterations. Compared with conventional polymer-based MEX, several AM approaches enable the development and fabrication of fully metallic or metal-functional structures, including Powder Bed Fusion (PBF), Directed Energy Deposition (DED), and hybrid polymer–metal methods based on electroplating. Furthermore, understanding mechanical properties such as tensile strength is essential for assessing the applicability of AM materials in energy system components. The results contribute to bridging the gap between rapid prototyping and the implementation of advanced AM technologies in thermal-related applications. Full article