The aim of the research unit 5250 “Permanent and bioresorbable implants with customized functionality“, funded by the German Research Foundation, is the development and validation of an integrated solution for the manufacturing, characterization, and simulation-based design of additively manufactured implants in maxillofacial surgery, considering the physiological conditions of the individual bone situation. The laser powder bed fusion (PBF-LB/M) process enables the production of fine TPMS lattice structures to minimize stress shielding effects between bone and implant using Titanium Grade 23 (Ti-6Al-4V). Strict requirements outlined in ISO 5832-3 govern the microstructure, chemical composition, and mechanical properties of the implant material. Due to high cooling rates in the PBF-LB/M process, heat treatment (HT) is necessary to ensure compliance with these specifications. This results in a uniform α+β structure and released residual stresses. In order to facilitate the safe design and simulation of these structures, it is crucial to develop a comprehensive understanding of the cross-scale damage tolerance during mechanical loading.
First, the macro-scale damage evolution under quasi-static and cycling loading of TPMS lattices was characterized by using innovative measurement techniques such as the potential drop method, acoustic emission, and high-resolution digital image correlation (DIC). Combining and correlating different measurement approaches leads to a comprehensive understanding of the damage evolution, which is important for safety-related lifetime predictions of patient-specific implants. Due to the potential scaling effects, the macro-scale geometry needs to be simplified and down-scaled for the micro-scale qualification. In this case, the mechanisms on the micro-scale will be investigated using an in-situ tensile/compression module combined with SEM to identify microstructural effects during different phases of crack propagation. In addition, microstructural investigations will be complemented to identify and correlate failure mechanisms to evaluate the damage tolerance of TPMS structures for reliable medical applications.

Acknowledgments: The authors would like to thank the German Research Foundation (DFG) for funding subproject 3 within the research unit 5250 ‘Mechanism-based characterization and modelling of permanent and bioresorbable implants with customized functionality based on innovative in vivo, in vitro and in silico methods’ (project no. 449916462). Further thanks to Laser Center Hannover e.V. for the supply of specimen manufacturing within an excellent scientific cooperation.