Research On Nano-hydroxyapatite/poly (Vinyl Alcohol)/gelatin Composite

Damaged cartilage has a limited ability to repair itself due to the absence of vascularization and nerve endings in the tissue. Thus the treatment of cartilage lesion is one of the most important problems in orthopedic surgery. Reconstruction of articular cartilage defects using adult osteochondral allografts is lack of lateral integration of the grafts to the surrounding tissue, and sophisticated autologous chondrocytes transplantation can not provide implants with mechanical strength early.Hydrogel can be used as artificial cartilages due to their good lubrication and elasticity. Among various synthetic hydrophilic polymers used in the preparation of hydrogel, polyvinyl alcohol (PVA) hydrogel has definitely gained biomedical applications because of its inherent non-toxicity, good biocompatibility and desirable physical properties such as elasticity and high swelling property in aqueous solutions. Nano-hydroxyapatite (n-HA) has been proved to have good biocompatibility and osteoconductivity, and it is expected to induce calcification and biological bond between implant and subchondral bone. Gelatin (Gel), a connective tissue protein, is well known for its non-toxic, good biocompatibility and biodegradability. The incorporation of Gel in the composite is expected to enhance the biocompatibility.In this paper, an artificial cartilage material and a potential scaffold for cartilage tissue engineering based on PVA, n-HA and Gel were prepared, respectively. The contents included the following. 1. A novel composite, composed of n-HA, PVA and Gel, was prepared by blending them in solution. Water content and burning test were used to analyze the homogeneity of the composites. The materials were also characterized by Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and the water absorption rate of the hydrogels with different ratio of n-HA/PVA/Gel were tested. The results showed that the prepared hydrogels had good homogeneity and suitable water absorption rate. The n-HA/PVA/Gel hydrogel could be used as an artificial cartilage material.2. The n-HA/PVA/Gel composite was characterized by Fourier transform infrared absorption spectroscopy (FT-IR), X-ray diffraction (XRD) and the possible interior chemical bonds were also discussed. Hydrogen bonds and coordination bonds may exist between n-HA, PVA and Gel. Mechanical strength and water absorption of the prepared composite were investigated, respectively. The results show that water absorption of the samples is enhanced from 77% to 150% with the increase of PVA, and that n-HA/PVA/Gel composite has similar mechanical properties to natural cartilage. The composite has excellent biocompatibility in vivo.3. A novel porous composite material composed of n-HA, PVA and Gel was fabricated by emulsification. SEM showed that the material had a well-interconnected porous structure including a lot of micropores (less than 20μm) on the walls of macropores (100~500μm). The composite had a porosity of 78% and showed high water absorption rate up to 312.7% indicating a good water-swellable behavior. When immersed in water, the weight of the scaffold continuously decreased. However, after immersion in simulated body fluid (SBF), the weight continuously increased because Ca2+ and PO43- ions deposited on the surface and the internal surfaces of the material pores. The deposits were proved to be carbonated hydroxyapatite by thin-film X-ray diffraction (TF-XRD), FT-IR and EDAX. The composite was proved to be non-cytotoxicity by MTT assay. The n-HA/PVA/Gel material was also implanted subcutaneously in the dorsal region of adult female rats. After 12 weeks of implantation, the porous material adhered tightly with the surrounding tissue, and the ingrowth of fibrous tissue as well as the material's partial degradation was observed.4. PVA and Gel were used to fabricate a gelatinous composite. The PVA/Gel composite was characterized by IR and XRD, which indicated that PVA and Gel was cross-linked via hydrogen bondings. PVA/Gel scaffold was prepared by emulsification and its microstructure was observed with SEM. The scaffold had a high porosity up to 76% and the pore size is fit for tissue ingrowth. Water absorption of the scaffolds in deionized water and in SBF was monitored by gravimetric procedure. The scaffold was proved to be non-toxic for rabbit corneal fibroblasts by MTT assay. We observed that rabbit corneal fibroblasts proliferated intensively in fluorescence photos after 72 hours of cell culture. After 8 weeks immersion in water and SBF, the scaffold's weight varied obviously and a lot of apatite deposited along the internal surfaces of the porous structure, which demonstrated that the scaffold had good bioactivity and degradation property. The data herein reflect the promising utility of PVA/Gel scaffold as fringe scaffold of keratoprosthesis.