Research on the Long Time Swelling Properties of Poly (vinyl alcohol)/Hydroxylapatite Composite Hydrogel

Poly (vinyl alcohol)/hydroxylapatite (PVA/HA) composite hydrogel was prepared by repeated freezing and thawing. The water loss properties of the resultant hydrogel were investigated by using optical microscope. Long time immersion tests of PVA/HA composite hydrogel were carried out in the diluted calf serum solution to study the change laws of swelling properties with the freezing-thawing cycles and HA content. The micro-morphologies of PVA/HA composite hydrogel after long time immersion were observed by means of the high-accuracy 3D profiler. The results show that the swelling process of PVA/HA composite hydrogel is the converse process of its water loss. Long time swelling ratio curves of PVA/HA composite hydrogel in the calf serum solution are manifested as four stages of quick increase, decrease, slow decrease and stable balance, and its equilibrium swelling ratio decreases with the increase of freezing-thawing cycles and HA content. It is revealed that the network structure of the composite hydrogel immersed for a long period is significantly improved with the increase of HA content. Perfect network structures of PVA/HA composite hydrogel as well as full and equilibrium tissues after swelling equilibrium are obtained when the HA content is 3% and the number of freezing-thawing cycles is 7.