Multifunctional Design of Triply Periodic Minimal Surface Structures for Temporary Pediatric Fixation Devices

Fracture fixation and limb deformity correction in pediatric orthopedics often use temporary metallic fixation devices. These devices' higher stiffness compared to cortical bone leads to stress shielding, causing significant bone density reduction, periprosthetic loosening, and bone growth interference. The 3D-printed triply periodic minimal surface (TPMS) structures present a promising engineering solution to match bone stiffness while ensuring reliable implant strength. In this study, finite-element modeling and experimental testing are employed to identify optimal multifunctional TPMS-based lattices that meet the required design constraints of 1) stiffness in the range of cortical bone, 2) strength in the range of cortical bone, 3) minimum osteointegration to facilitate the implant removal after healing, and 4) manufacturability with limited defect sensitivity. Six different types of TPMS structures in Ti-6Al-4V material manufactured via laser powder bed fusion are evaluated for their ability to target the lower and upper bounds of pediatric cortical bone stiffness. Lattices based on the Primitive unit cell design are superior, demonstrating the highest strength/stiffness ratio, best manufacturability, and potentially reduced osteointegration due to larger pore size, smaller surface area, and smallest negative Gaussian curvature compared to other investigated TPMS types. A metallic implant's higher stiffness compared to the surrounding bone leads to stress shielding problems, causing bone density reduction and bone growth interference in pediatric patients. 3D-printed triply periodic minimal surface structures present a promising engineering solution. In this study, an experimentally validated numerical workflow is highlighted considering mechanical and biological design criteria for temporary pediatric fixation devices. image (c) 2024 WILEY-VCH GmbH