MECHANICAL PROPERTIES OF CELLULAR STRUCTURES MADE OF THERMOPOLYURETHANE TPU 95A WITH CONTROLLED POROSITY FOR PROSTHETIC DEVICES OF VARIABLE STIFFNESS, OBTAINED BY 3D PRINTING

Functional gradient materials with controlled porosity based on triple periodic minimum surfaces combined with 3D printing open up new possibilities for creating personalized prosthetic liners with variable stiffness. This paper presents research on the mechanical properties of cellular structures made of TPU 95A thermoplastic polyurethane, manufactured using 3D printing (FDM technology), for use in functionally graded prosthetic liners. Cyclic compression tests were performed on three topologies — gyroid, Schwarz surface (Primitive) and honeycomb structure — at porosities of 40 and 75% (cell size 10 mm). It was found that the minimum printable wall thickness is 0.8 mm without defects. According to the research results, the gyroid topology demonstrated the best elastic modulus results, which amounted to 17 MPa for 40% cell porosity and 10 MPa for 75% porosity. The honeycomb structure showed the lowest stiffness and anisotropy. The data obtained confirm the possibility of creating a stiffness gradient by varying the porosity of the gyroid structure, which is promising for personalized prosthetic devices with optimized load distribution.