Structural Engineering of Hierarchical Apatite/Hyaluronic Acid Nanohybrid Porous Membranes with Enhanced Physiological Stability.

The integration of nanoscale hybridization between inorganic components and biopolymers, and the formation of hierarchical porous structures capable of efficiently including and activating cells and proteins, has not yet been achieved in the design of bone substitutes for tissue regeneration. We fabricated a porous nanohybrid membrane based on hyaluronic acid (HyAc) and citric acid-coordinated apatite nanoparticles (Cit/ApNPs) and proposed a scaffold material design that integrates a dense nanohybrid structure with a hierarchical porous structure. Specifically, the network structure of HyAc molecules was utilized as a reactive field (i.e., free space) for the hybridization of Cit/ApNPs, and the high dispersibility of Cit/ApNPs effectively induced the interfacial interactions between HyAc molecules and the NPs at the nanoscale, thereby achieving nanohybridization. This nanohybridization induced the spontaneous formation of mesopores and smaller macropores (i.e., 0.05-10 μm), and additionally, larger macropores (i.e., 10-800 μm) were constructed through the freeze-drying process while maintaining the nanohybridization state. As a result, a hierarchical porous structure with three types of pores that will contribute to protein adsorption, pseudopodia interaction/extension, and cell inclusion was successfully obtained, and the membrane was confirmed to maintain its structure and shape even after immersion in simulated body fluid (SBF). Therefore, we suggest a biomaterial design concept that integrates interfacial interaction and hierarchical pore structuring, which is expected to be an effective approach for the tissue regeneration.