Influence of pre-freezing process on the performance of freeze-dried collagen-chitosan hemostatic sponge based on thermal analysis

Hemostatic sponges are porous biomaterials commonly used in surgery, emergency medicine, dentistry, and military medicine for bleeding control during surgical procedures and trauma, with associated reductions in blood loss risk and promotion of wound healing. Although freeze-drying is employed to prepare the collagen-chitosan hemostatic sponge (CCHS), the critical role of heat transfer is often overlooked. In this study, thermal analysis was employed to investigate the effect of the pre-freezing temperature on the performance of CCHS. Samples were pre-frozen at set temperatures of −30 °C, −45 °C, and −55 °C based on the glass transition temperature. Radiative, conductive, and convective heat transfer mechanisms were identified through thermal analysis during pre-freezing. The properties of CCHS, including water absorption, microstructure, maximum fluid absorption ratio, mechanical properties, and in vitro degradability, were characterized. The results showed that conduction dominated the heat transfer process during pre-freezing, and the convective heat transfer coefficient was quantified. Lower pre-freezing temperatures led to increased sample cooling rates, resulting in CCHS with more compact structures and smaller pore sizes. The pore structure of CCHS showed a significant influence on the absorption and mechanical properties. Combined with the thermal analysis and measurements, CCHS exhibited a better pore structure at the pre-freezing temperature of −45 °C. The analysis of the heat transfer mechanisms establishes a theoretical foundation for the microstructural design of CCHS, advancing the development of tailored materials for specific medical applications.