Hamed Bakhtiari

Bone plates are widely used in orthopaedic surgery to stabilise fractured bones and support healing following traumatic injuries or osteotomies. However, conventional metallic bone plates suffer from stress shielding and stiffness mismatch with bone, which can hinder optimal healing. Additive manufacturing enables the incorporation of novel metamaterial architectures into polymer-based implants to enhance mechanical properties. The fatigue behaviour of these implants during the healing period is critical to ensuring their structural integrity and long-term performance. In this study, the compressive fatigue performance of fused deposition modelling (FDM)-printed carbon fibre-reinforced polylactic acid (CF-PLA) bone plates were investigated. Four metamaterial structures—tetrachiral, re-entrant, rotating square, and hexagonal—were evaluated under strain-controlled cyclic loading at 20%, 40%, 60%, and 80% of their respective yield strains. The results showed a strong dependence of fatigue behaviour on lattice geometry. Among the tested configurations, the re-entrant structured bone plate exhibited the best overall fatigue performance, sustaining up to 100,000 cycles at moderate strain levels and showing delayed stiffness degradation under high strain conditions. In contrast, rotating square and hexagonal structures showed early stiffness loss and failure at higher strain levels. These findings highlight the importance of lattice design in fatigue performance, although FDM-induced printing defects significantly influence overall fatigue behaviour.

Background: Finger orthoses are essential for treating injuries, deformities, and disorders of the upper limbs by supporting, immobilizing, or correcting deformities. Recent advances in three-dimensional (3D) printing have significantly enhanced precision and customization compared to traditional fabrication methods such as thermoplastic molding, plaster or fiberglass casting, and the use of prefabricated splints. Methods: The present review was conducted using PubMed, Scopus, and other databases with keywords such as “hand therapy”, “additive manufacturing”, “finger and thumb”, and “orthosis”. Only English-language publications were considered, with a primary focus on articles published between 2010 and 2025. Key themes were identified and categorized into conditions necessitating finger orthoses, types and classifications, ergonomic design considerations, and advancements in additive manufacturing. Results: Finger orthoses address musculoskeletal injuries, inflammatory diseases, and neuromuscular disorders. Three-dimensional printing provides enhanced customization, reduced material waste, rapid prototyping, and the ability to create complex geometries, improving patient comfort and functionality. Conclusions: Finger orthoses effectively treat various conditions by supporting and stabilizing fingers. A thorough understanding of anatomy, biomechanics, and fabrication methods is crucial for achieving functional and comfortable designs. Three-dimensional printing offers a transformative approach to producing lightweight, customizable, and cost-effective orthoses, enabling innovative and personalized solutions. By bridging clinical needs and design strategies, this review may guide future innovations in patient-specific orthotic development.

Bone scaffolds serve a crucial role in tissue engineering, particularly in facilitating bone regeneration where natural repair is insufficient. Despite advancements in the fabrication of polymeric bone scaffolds, the challenge remains to optimize their mechanical resilience. Specifically, research on the fatigue behaviour of polymeric bone scaffolds is scarce. This study investigates the influence of pore architecture on the mechanical performance of poly-lactic-acid (PLA) scaffolds under quasi-static and cyclic compression. PLA scaffolds with a 60% porosity were fabricated using extrusion-based 3D printing in various designs: Gyroid, Lidinoid, Fischer–Koch, IWP, and Voronoi. Results demonstrated that Gyroid scaffolds had the highest compressive strength (6.6 MPa), followed by Lidinoid, Fischer–Koch, IWP, and Voronoi designs. Increased strut thickness was linked to higher compressive strength. However, normalized fatigue resistance showed a different pattern. While scaffolds resisted fatigue cycles at low strain amplitudes, fatigue damage was observed at higher strains. Voronoi structures exhibited the highest normalized fatigue performance, enduring around 58,000 cycles at 85% strain amplitude, followed by Gyroid, Fischer–Koch, Lidinoid, and IWP structures. Enhanced fatigue performance in different topologies correlated with the minimum cross-sectional area of scaffolds. Given the importance of both static and fatigue strength, the Gyroid topology emerges as the superior choice overall.

This article investigates an inverse approach to determine the coefficients of the Drucker-Prager model for magnesium powder. The approach involves conducting finite element simulations of the powder compression process within LS-DYNA software, employing the Drucker-Prager material model. The goal is to minimize the disparity between force-displacement outcomes derived from simulations and experimental data using a surrogate optimization method. Experimental data were obtained through a uniaxial compression test and served as a basis for adjusting the Cap model coefficients. A random selection of coefficients was made using the Latin cube method and simulations were performed based on the initial coefficients. The optimization was then performed using the particle swarm algorithm over 20 iterations. The optimized coefficients were validated against experimental data, demonstrating close agreement. By utilizing the extracted coefficients, the relative density of the samples was calculated at three different compaction speeds, i.e., 15.5 m s⁻¹ (using a Hopkinson bar), 8 m s⁻¹ (using a drop weight), and 1 mm min⁻¹ (using an Instron machine). The analysis revealed the highest relative density and stress in the densified sample via the Hopkinson bar method, reaching 99.83% and 1.1 GPa, respectively.

While the mechanical performance of fused filament fabrication (FFF) parts has been extensively studied in terms of the tensile and bending strength, limited research accounts for their compressive performance. This study investigates the effect of four process parameters (layer height, extrusion width, nozzle temperature, and printing speed) on the compressive properties and surface smoothness of FFF parts made of Polylactic Acid (PLA). The orthogonal Taguchi method was employed for designing the experiments. The surface roughness and compressive properties of the specimens were then measured and optimized using the analysis of variance (ANOVA). A microscopic analysis was also performed to identify the failure mechanism under static compression. The results indicated that the layer height had the most significant influence on all studied properties, followed by the print speed in the case of compressive modulus, hysteresis loss, and residual strain; extrusion width in the case of compressive strength and specific strength; and nozzle temperature in the case of toughness and failure strain. The optimal design for both high compressive properties and surface smoothness were determined as a 0.05 mm layer height, 0.65 mm extrusion width, 205 °C nozzle temperature, and 70 mm/s print speed. The main failure mechanism observed by SEM analysis was delamination between layers, occurring at highly stressed points near the stitch line of the PLA prints.

The advancement in 3D printing techniques has raised the hope to use additively manufactured parts as final products in various industries. However, due to the layer-by-layer nature of AM parts, they are highly susceptible to failure when they are subjected to fatigue loading. This review provides a detailed account of the influence of 3D printing parameters on the fatigue properties of parts manufactured by fused filament fabrication (FFF). Existing standards for fatigue testing of polymers and their limitation for 3D-printed parts are discussed. In addition, the cyclic behaviour of polymers is reviewed, and the impact of 3D printing parameters on the mechanical behaviour of FFF parts under tensile, compressive, flexural, and bending fatigue is investigated according to the published results in the literature. Finally, a summary of the works undertaken and suggestions for future research are provided. The influence of 3D printing parameters on the fatigue performance of prints can be different from that seen in the case of static loading and strongly depends on the fatigue loading type. While cross-over infill patterns, higher infill density, and higher layer height favour achieving higher fatigue strength in all loading types, raster orientation is best to be aligned parallel to the tensile loads and perpendicular to the compressive, flexural, and bending forces. In the case of tensile and flexural loading, Y build orientation yields the best result. Finally, print velocity was found to be less significant compared to other parameters, implying that it can be set at high values for faster printing.