Hydroxyapatite formation with the interface of chitin and chitosan

Hydroxyapatite (HA) film atop artificial implants surface can provide bioactive, osteoconductive and bone-similar interface. Traditional technique utilizes collagen coating to induce HA mineralization via charged functional groups. However, collagen loss as aging might lead to unstable interface. In this study, we presume that chitin (CH) with acetamide group chelates calcium ion and chitosan (CS) with amine group chelates phosphate ion, providing an ambiance for the HA crystallite formation. The presumption is evidenced by molar conductivity experiments. Besides, the hydrogen bonds of CH and electrostatic repulsion force of CS render different molecular architecture for the tunnel-connected structure. Furthermore, it forms porous morphology after HA mineralization evidenced by SEM images. Interestingly, mixing CH and CS provides the interface for Ca²⁺/PO₄^3- capturing, rendering the formation of micro-crystallite with the 1.69/1.7 for the ratio of calcium to phosphate, being evidenced by EDX and AES experiments. Moreover, crystallinity index is calculated with XRD and FTIR spectra that CH–CS–HA possesses the highest crystallite to amorphous ratio. The HA film also shows good biocompatibility through L929 MTT test with 100% cell viability for the potential bio-applications. By the tapping-mode of AFM, the Young's modulus of CH–CS–HA surface is estimated to be 2.04 GPa near that of native bone.