Identification of an Optimal Gyroid Microarchitecture of 3D-Printed Hydroxyapatite Bone Substitutes for Vertical Bone Augmentation and Osteoconduction.

Triply periodic minimal surface (TPMS) microarchitectures combine low weight with high mechanical strength, and, in particular, G-gyroid-based microarchitectures represent a promising option for bone substitutes. Most studies on G-gyroid-based bone substitutes have reported only in silico or in vitro results, whereas in vivo data remain scarce and are generally limited to single G-gyroid microarchitectures. To identify the optimal G-gyroid microarchitecture for bone substitute applications, we compared three different G-gyroid designs with varying surface-to-surface distances to determine the most suitable architecture for osteoconduction and vertical bone augmentation. From a mechanical perspective, constructs with a wall-to-wall distance of 0.50 mm (gyroid05) exhibited higher compressive strength than those with distances of 0.80 mm (gyroid08) and 1.10 mm (gyroid11). In vivo assessment in a rabbit calvarial defect model demonstrated that defect bridging was improved by 44% with gyroid05 and by 40% with gyroid11 compared with gyroid08. In contrast, evaluation in a rabbit calvarial vertical bone augmentation model showed that bone height gain increased by 39% and 32% with gyroid08 and gyroid11, respectively, relative to gyroid05. Overall, the gyroid11 design demonstrated superior in vivo performance in defect bridging and bone augmentation, indicating that it may represent the most promising universal G-gyroid microarchitecture for bone substitutes.