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.
Emerging additive manufacturing technologies are enabling the design of engineered parts with complex geometries and mechanical capabilities. Polymer powder bed fusion (PBF) printing is a promising process that is becoming more economically accessible while providing capabilities for printing non-assembly mechanisms. These processes could enable the automated design of complex personalized biomedical designs, such as prosthetics with integrated lattices, springs, and joints. However, manufacturing constraints and mechanical capabilities of these 3D printed designs requires further investigation to determine their feasibility and capabilities. Here, we conduct dimensional characterization and mechanical testing of Nylon 11 printed parts. Minimum fabrication constraints were measured to determine the smallest beam size as approximately 0.7 mm with a minimum gap size between beams of 0.35 mm. Mechanical testing demonstrated low anisotropy of parts in compression/tension which led to the testing of mechanical lattices with approximate elastic moduli of 25 MPa to 55 MPa. Helical springs worked in compression with a stiffness of approximately 0.2 N/mm to 16.8 N/mm for 3 mm to 7 mm wire diameters. Minimum printable gap sizes were used to inform the fabrication of a fully functional finger prosthetic with joints working directly after print post-processing, with no assembly required. Overall, these are foundational steps in demonstrating design rules and constraints for automating customized designs from polymer powder bed fusion printing, which offers unique capabilities for diverse and mechanically complex 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.
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