Mimicking bone cortex: Cold sintering of hydroxyapatite-gelatin powders provides dense nanocomposites resemblant to bone mineral

Bioceramics based on hydroxyapatite (HAP) are widely used in bone healing applications. However, mimicking both the HAP-collagen composition and microstructure in dense materials is challenging due to high sintering temperatures. Recent advancements in cold sintering processes allow for the fabrication of HAP-based composites at significantly lower temperatures. Here, we report on cold sintering of HAP-gelatin powders (with 79 wt% of ceramic phase) under high pressures and near-room temperatures. The powders synthesized by precipitation in gelatin gel consisted of nanocrystalline HAP and gelatin, mimicking bone microstructure and composition. These properties were preserved in the cold-sintered samples, which resulted into high strength and ductile behavior. However, we observed that increasing consolidation pressure can cause a decline in mechanical strength, which we attribute to changes in gelatin structure and distortions in HAP crystals. Our findings demonstrate novel HAP-based composites potential for bone-replacement materials and provide new insights into cold sintering of ceramic-polymer systems.