Preparation And Characterization Of Hydroxyapatite/nano-cellulose Composites

Bacterial cellulose (BC), regarded as one of the most promising tissue engineering scaffold, has received much attention due to its excellent mechanical property, refined three dimensional nanofibrous network structure and good biocompatibility. BC nanofibers are similar to natural morphology collagen in bone. BC nanofibers can induce the formation of crystals, so BC is a potential engineering scaffold for bone tissue. However, the low surface activity restricts the application of BC as tissue engineering scaffold, therefore, the surface modification of BC is essential to promote cell adhesion and growth.Phosphoric acid esterification and chemical crosslinking technique were conducted in order to enhance the surface activity of BC. Scanning electron microscope (SEM), Transmission electron microscope (TEM), Energy dispersive X-ray spectral analysis (EDS), Fourier transform infrared spectroscopy (FTIR), universal testing machine and in vitro cell culture technique were utilized to analyze the micro-structures, chemical structures, mechanical property and biocompatibility of the resultant samples. The results indicated that phosphate (PO43-) groups were introduced to BC in order to obtain stable phosphorylated BC via phosphoric acid esterification method. Gelatin (Gel) andε-polylysine (ε-PL) could be fixed onto the surfaces of BC nanofibers via chemical crosslinking technique by using procyanidins (PA) as the crosslinker. The most suitable concentration of Gel andε-PL solution was 0.25%, which could achieve the optimal crosslinking effect. Gel andε-PL both reduced the mechanical properties of BC. The mechanical performance of BC/Gel was better than BC/ε-PL. Phosphorylated BC, BC/Gel and BC/ε-PL presented good biocompatibility according to cytocompatibility evaluation in vitro.In order to render the good osetoinductivity to BC, the hydroxylapatite (HAp) coatings were introduced onto BC nanofibers via biomineralization method. In this work, SEM, inductively coupled plasma emission spectrometer (ICP), EDS, X-ray absorption near-edge structure (XANES), X-ray diffraction (XRD), universal testing machine and in vitro cell culture technique were adopted to analyze the growth of apatite on BC nanofibers. The results indicated that negatively charged materials such as phosphorylated BC and BC/Gel were more conducive to the deposition of HAp than cationic materials (BC/ε-PL). It also showed that the biomimetic process of HAp in simulated body fluid (SBF) could be divided into amorphous calcium phosphate (ACP), calcium phosphate (TCP), octacalcium phosphate (OCP) and HAp. The growth rate of HAp on phosphorylated BC, BC/Gel and BC/ε-PL decreased gradually. Tensile strength and elongation rate of any kind of BC/HAp, BC/Gel/HAp and BC/ε-PL/HAp decreased with mineralization time increasing, and the tensile strength of these there materials decreased gradually; BC/HAp, BC/Gel/HAp and BC/ε-PL/HAp presented excellent biocompatibility according to cytocompatibility evaluation in vitro.This study provided a new approach to modify BC nanofibers and prepared HAp bone repair composites, and also shed a light on the development of next generation composites for tissue engineering.