Preparation and characterisation of functional gradient nanohydroxyapatite reinforced polyvinyl alcohol gel biocomposites for articular cartilage

Functional gradient materials provided the authors with one new concept for artificial articular cartilage design with graded component and graded structure where one face of the material is high free water content, thereby providing excellent lubrication function and the opposite face of the material is high hydroxyapatite content, thereby improving the bioactivity of the material and stimulating cell growth. In this Letter, the functional gradient nanohydroxyapatite reinforced polyvinyl alcohol (nanoHA/PVA) gel biocomposites was prepared through a layer-by-layer casting method combing with freeze/thaw cycles technology. The microstructure and morphology were investigated by X-ray diffraction, transmission electron microscopy, scanning electron microscopy (SEM) and Fourier transform infrared. The results revealed that the size of HA particles in the biocomposites was on the nanometre scale. The nanoHA particles were distributed in a PVA matrix uniformly and it presented a needle-like microstructure because of the effect of PVA solution as a dispersant as well as soft template. The results of SEM observation showed that the microstructure of functional gradient biocomposites possessed micropores and lots of nanoHA powders in every layer. The size of micropores in the biocomposites presented a decreasing trend from the surface layer to the bottom layer. On the contrary, the nanoHA powders in the biocomposites increased from the surface layer to the bottom layer. This special structure of functional gradient biocomposites is beneficial for the improvement of lubrication and bioactivity properties of the biocomposites.