A study on the permeability and mechanical characteristics of ceramic scaffold for bone regeneration

Abstract

Poor healing of large bone defects is one of the biggest challenges in human orthopedic medicine, often leading to infections and other clinical complications, reoperations, poor functional outcomes, and ultimately limb loss, resulting in significant loss of quality of life and economic cost. Current remediation is associated with significant complications and associated cost. There is a clear need for improvement. Large bone defect healing requires fast growth of high-quality, mature bone. Bioceramics such as hydroxyapatite (HAp) are favored for their biocompatibility and compositional similarity to bone mineral, but as scaffolds these materials have yet to fully address the need due to a wide variety of limitations that are amplified when scaffolds are designed with high porosity to accommodate adequate gas, nutrient and waste exchange in large bone defects. Scaffold topologies such as triply periodic minimal surfaces (TPMS) have emerged to address this trade-off. TPMS structures provide a high surface area to volume ratio in a fully interconnected porosity that enhances bone cell proliferation and a continuous, smooth curvature that distributes load more uniformly to increase scaffold strength. Given a favorable biomaterial and scaffold structure, rigid stabilization that reduces segmental mobility is known to increase the rate and quality of bone growth. Strain in an osteogenic range below 5% has been shown to bias new bone development toward a faster, primary ossification pathway. Modulating this strain in a critical defect is the central focus of this research. HAp scaffolds with Gyroid and Fischer–Koch S TPMS topologies were fabricated and characterized for permeability and compressive mechanical properties. Following measurement of their respective permeabilities, the mechanical performance of these scaffolds was evaluated under clinically representative fixation conditions. Strain distribution was measured in Gyroid scaffold constructs using rosette strain gauges in a cadaveric ovine metatarsal critical defect model, with and without a novel endoprosthetic sleeve designed as an external reinforcement strategy. Axial compressive strain remained within the osteogenic range in both conditions. The endoprosthetic sleeve reduced transverse strain by approximately 30%, redistributing load around the scaffold perimeter and suppressing localized wall bending without attenuating the axial compressive stimulus essential for osteogenesis. Finite element modeling confirmed these experimental trends and established a parametric framework for optimizing sleeve geometry to further modulate the full multiaxial strain state. Collectively, these findings demonstrate that (1) TPMS topology modulates the strength–permeability balance; (2) external constraint such as an endoprosthetic sleeve can strategically modulate the in vivo strain environment, and; (3) computational modeling can enable rational design of ceramic scaffolds and endoprosthetic devices for load-bearing critical bone defect healing.