Preparation of Hydroxyapatite/Silk Fibroin Composite and Its Adoption in Posterolateral Spinal Fusion of Rats

Hydroxyapatite/silk fibroin (HAp/SF) composite was prepared and applied to the posterolateral spinal fusion model in rats to observe the effect of bone fusion. Method: Calcium chloride, diammonium phosphate, SF, and polyvinyl alcohol were used as raw materials, HAp/SF composites were prepared by chemical precipitation. The microstructure of the composite, crystal phase composition, and chemical structure were analyzed by the scanning electron microscope (SEM) and X-ray diffraction (XRD), and fourier transform infrared spectrometer (FTIR Spectrometer). Through the cultivation of osteoblasts MC3T3-E1 in vitro, the adhesion and proliferation (A&P) of cells on the face of materials were investigated. Thereby, the biocompatibility of the material was characterized. HAp/SF material was applied to the rat posterolateral spinal fusion model. The osteogenesis and spinal fusion were evaluated by the imaging observation, histological observation and manual palpation. The results showed that the rod-shaped HAp with uniform size and high purity was obtained, with a diameter of 20∼40 nm and a length of 200∼500 nm, similar to the apatite crystal in natural bone tissue (BT). In composite materials, a spatial network structure was formed by the interweaving of the SF fibers, and HAp was deposited on the face of the SF or in the middle of its network structure. In the obtained HAp/SF materials, the calcium ions of HAp and the carbonyl groups of SF were used to form thermally stable complexes through strong chemical bonds. Besides, SF was a template for the directional induction of HAp crystal growth, and the growth of HAp crystal along the C axis was regulated by SF. The growth direction was parallel to the long axis of SF fibers, and was consistent with the structure of apatite crystals deposited on the face of collagen fibers in natural BT. The results of cell culture in vitro showed that: after comparison with the control group (CG) with pure Hap, the adhesion ability of cells to HAp/SF material was significantly improved. The proliferation capacity of bone artificial bone (BAM) material and HAp/SF material was also significantly improved. The nuclear and skeletal staining results of MC3T3-E1 cells on the face of three groups of materials (HAp, BAM and HAp/SF) were combined, and the results also indicated that BAM and HAp/SF materials had good ability to promote cell A&P. The results of posterolateral spinal fusion in rats showed that HAp/SF materials group palpated the posterolateral spine for fusion. The formation of new BT on the posterolateral side of the spine was revealed by the Micro-computed tomography (Micro-CT) examination. In conclusion, HAp/SF composite had good osteoblastic compatibility and can achieve good spinal fusion effect.