Unidirectional Porous Carbonate Apatite Fabricated by Gelatin-Based Freeze Casting for Bone Regeneration

Abstract

To develop bone grafts with superior osteoconductivity, we have fabricated unidirectionally connected porous carbonate apatite (CAp) via gelatin gelation combined with freeze-drying. A composite of calcium carbonate (CaCO₃) and gelatin was first gelled at low temperature and then subjected to directional freeze-drying to create well-aligned macroporous channels. The samples were then sintered to remove the organic components and subsequently phosphatized to convert the composition into CAp. The resulting material exhibited a porosity exceeding 80% with fully interconnected unidirectional pores favorable for cell migration and vascular infiltration. Bone regeneration was evaluated by implanting the material into rabbit femoral bone defects; a comparison was also made with nonoriented porous controls. Histological and radiographical analyses demonstrated that the unidirectional porous structure significantly enhanced directional ingrowth of new bone tissue and accelerated early-stage bone formation relative to the control. This study demonstrates that unidirectional porous CAp fabricated via a gelatin-based freeze-casting method is promising for bone regeneration, particularly in clinical applications requiring guided bone formation.

Impact Statement

The architecture of bone grafts plays a critical role in guiding cell migration, vascularization, and subsequent bone regeneration. While carbonate apatite (CAp) is widely recognized for its excellent osteoconductivity, strategies to precisely control its three-dimensional pore orientation remain limited. In this study, we demonstrated that a gelatin-based freeze-casting approach enables the fabrication of unidirectionally connected porous CAp with high porosity. This porous architecture significantly enhances directional bone ingrowth and early-stage bone formation in vivo. Our findings highlight the importance of pore orientation, beyond porosity alone, in optimizing osteoconductive performance and suggest that unidirectional porous CAp is a promising bone graft material for clinical applications requiring guided bone regeneration.