Design of 3D printing osteotomy block for foot based on triply periodic minimal surface

Abstract Introduction: The advantages of triply periodic minimal surfaces (TPMS) lie in their smooth surface and connected hFole height, while the overall structure is precisely controlled by implicit functions. This study was to explore the application of this method in designing and modeling porous structures for 3D printing of foot osteotomy blocks. Methods: The TPMS for designing porous structures of G (Gyroid) and D (Diamond) structures was determined using Matlab R2020a based on implicit functions. Porous samples were prepared through EBM technology, and mechanical performance data were obtained by conducting mechanical testing on the samples. Comparative analysis was performed to identify the optimal porous structure for designing a bone block implant, and subsequently, the shaping design of the porous osteotomy block was completed based on the determined structure. Results: The relative density exhibits a negative correlation with the variable parameters, and as the relative density decreased in a porous structure, its volume fraction also decreased. The optimal t values for the porous G and D structures were 0.61, 0.92, 1.22 and 0.49, 0.76, 1 respectively, corresponding to relative densities of 30%, 20%, and 10%. The G structure demonstrated a progressive collapse damage mechanism from bottom to top layer by layer, while the D structure exhibit a shear failure zone at a 45° angle which was not conducive to energy absorption and was more susceptible to brittle fracture compared to the G structure. In terms of stress-strain curve repeatability for porous samples with a unit size of 1.5 mm, the G structure showed strong consistency while there was significant deviation in samples with D structure. Among samples with the same unit size, those with a relative density of 30% in G structure possessed higher mechanical strength as well as larger elastic modulus compared to others. Although samples with a relative density of 20% did not exhibit as high mechanical strength as mentioned above counterparts did have lower elastic modulus and larger porosity rate instead. The designed foot osteotomy blocks can adjust aperture size and porosity rate of beam-like structures by modifying function parameters using aforementioned methods. Conclusion: The foot osteotomy block's porous structure based on TPMS design, exhibits characteristics such as porosity, smoothness, and connectivity. This makes it an excellent method for preparing 3D printed specimens of foot osteotomy blocks.