Pullout Strength of Triply Periodic Minimal Surface-Structured Bone Implants

YY Tsai and SW Chang, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, 237, 107795 (2023).

DOI: 10.1016/j.ijmecsci.2022.107795

Porous bone implants, such as triply periodic minimal surface structures (TPMS) bone implants, are thriving due to controllable physical properties, better osseointegration, and customized morphologies. However, the fixation of screws in such bone implants has yet to be discussed. Here, we investigated the insertion and pullout behavior of surgical screws in TPMS bone implants, including the Fisher Koch S and Gyroid solid-networks. We showed that the effective Young's modulus, insertion force, and pullout strength of the TPMS bone implants can be tuned by structural parameters. Our results revealed that the pullout strength is highly correlated with the maximum insertion force for both the TPMS and solid bone implants. Furthermore, the TPMS ones have significantly larger pullout strengths. We quantified the screw stability by the pullout strength to maximum insertion force ratio, which is 6.70 +/- 0.68 and 1.60 +/- 0.07 for the TPMS and solid bone implants, respectively. The significantly higher pullout strength of the TPMS bone implants results from the different bone failure mechanisms. Therefore, adopting TPMS architectures in bone implants can relieve the force required to place a surgical screw and enhance the screw stability.

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