Polymer 3D printing is an emerging technology with recent research translating towards increased use in industry, particularly in medical fields. Polymer printing is advantageous because it enables printing low-cost functional parts with diverse properties and capabilities. Here, we provide a review of recent research advances for polymer 3D printing by investigating research related to materials, processes, and design strategies for medical applications. Research in materials has led to the development of polymers with advantageous characteristics for mechanics and biocompatibility, with tuning of mechanical properties achieved by altering printing process parameters. Suitable polymer printing processes include extrusion, resin, and powder 3D printing, which enable directed material deposition for the design of advantageous and customized architectures. Design strategies, such as hierarchical distribution of materials, enable balancing of conflicting properties, such as mechanical and biological needs for tissue scaffolds. Further medical applications reviewed include safety equipment, dental implants, and drug delivery systems, with findings suggesting a need for improved design methods to navigate the complex decision space enabled by 3D printing. Further research across these areas will lead to continued improvement of 3D-printed design performance that is essential for advancing frontiers across engineering and medicine.

Advances in multimaterial 3D printing are enabling the construction of advantageous engineering structures that benefit from material synergies. Cellular structures, such as honeycombs, provide high-energy absorption to weight ratios that could benefit from multimaterial strategies to improve the safety and performance of engineered systems. In this study, we investigate the energy absorption for honeycombs with square and hexagonal unit cells constructed from acrylonitrile butadiene styrene (ABS) and thermoplastic polyurethane (TPU). Honeycombs were fabricated and tested for out-of-plane and in-plane compression using ABS, TPU, and a combination of ABS with a central TPU band of tunable height. Out-of-plane energy absorption for square honeycombs increased from 2.2 kN·mm for TPU samples to 11.5 kN·mm for ABS samples and energy absorption of hexagonal honeycombs increased from 2.9 to 15.1 kN·mm as proportions of TPU/ABS were altered. In-plane loading demonstrated a sequential collapse of unit cell rows in square honeycombs with energy absorption of 0.1 to 2.6 kN·mm and a gradual failure of hexagonal honeycombs with energy absorption of 0.6 to 2.0 kN·mm. These results demonstrate how multimaterial combinations affect honeycomb compressive response by highlighting their benefits for controlled energy absorption and deformation for tunable performance in diverse engineering applications.

Emerging polymer 3D-printing technologies are enabling the design and fabrication of mechanically efficient lattice structures with intricate microscale structures. During fabrication, manufacturing inconsistencies can affect mechanical efficiency, thereby driving a need to investigate how design and processing strategies influence outcomes. Here, mechanical testing is conducted for 3D-printed lattice structures while altering topology, relative density, and exposure time per layer using digital light processing (DLP). Experiments compared a Cube topology with 800 µm beams and Body-Centered Cube (BCC) topologies with 500 or 800 µm beams, all designed with 40% relative density. Cube lattices had the lowest mean measured relative density of ~42%, while the 500 µm BCC lattice had the highest relative density of ~55%. Elastic modulus, yield strength, and ultimate strength had a positive correlation with measured relative density when considering measurement distributions for thirty samples of each design. BCC lattices designed with 50%, 40%, and 30% relative densities were then fabricated with exposure-per-layer times of 1500 and 1750 ms. Increasing exposure time per layer resulted in higher scaling of mechanical properties to relative density compared to design alteration strategies. These results reveal how design and fabrication strategies affect mechanical performance of lattices suitable for diverse engineering applications.

Selective laser sintering (SLS) is a promising additive manufacturing process for design innovation, particularly for integrated systems with non-assembly parts. In this paper, minimum size features and mechanics for SLS parts are analyzed to inform the design and characterization of nylon lattices, springs, and joints using prosthetics as an exemplary framework. These characterizations inform the printing of complete nylon consolidated parts using SLS, which was demonstrated with fully functional parts printed without the need for any further assembly. Material testing demonstrated that the prints have low anisotropy with elastic moduli from 770 to 920 MPa for varied print orientations and tension/compression cases. Lattices with body-centered cubic unit cells with 30% and 50% relative densities had effective elastic moduli ranging from 18 to 45 MPa. Helical springs with 3–7 mm wire diameters showed a tunable stiffness from 0.3 to 16.8 N/mm. Springs demonstrated a minimal loss in strength after 20 cycles. A finger prosthetic designed with 0.2-mm gap sizes between components was printed that demonstrated a non-assembly print of functioning joints. Overall, the work demonstrates SLS’s manufacturing constraints and mechanics for consolidated designs with non-assembly mechanisms that enable innovation across wide-ranging engineering.

Additive manufacturing is increasingly used for functional design, where optimizing print parameters is essential for achieving desired mechanical performance while minimizing time and material usage. However, the large number of printing parameters with varied effects on mechanical properties makes design challenging. This study investigates the influence of infill density and infill pattern by creating an integrated experimental and computational approach with systematic design characterization. CAD models were generated from G-code using reverse modeling to represent the internal structure of printed parts, and tensile tests were simulated to evaluate stiffness with physical validation. This reverse CAD generation is automated to extract flow velocity from G-code and calculate the extruded filament shape, with no manual input. Parts with a line infill pattern oriented parallel to the loading direction exhibited the highest elastic modulus of 2346 MPa at 100% infill density, as well as the highest stiffness per unit printing time (59.6 MPa/s) and per unit mass. The lowest modulus (359 MPa) was observed in line-patterned parts with a 0° raster orientation at 50% infill density. The results demonstrate that the experimentally validated computational workflow can generate and evaluate large datasets of mechanically evaluated parts across print parameters, thereby supporting efficient design when many parameters require consideration.