Preparation And Characterization Of PVA-HA/PAA Composite Hydrogel

PVA-HA/PAA composite hydrogel was prepared by freezing-thawing and annealing methods using poly(vinyl alcohol),hydroxylapatite and poly(acrylic acid) as raw materials. Orthogonal design method was used to design experiments and analyze the effect of composition and preparation parameters on the mechanical properties of PVA-HA/PAA composite hydrogel to choose the optimal combination. The microstructure of PVA-HA/PAA composite hydrogel was observed and its swelling property was studied. The mechanical and viscoelastic properties were studied by tensile test and dynamic rheological test. The effect of load, speed, and torsional angle on tribological behaviours of PVA-HA/PAA composite hydrogel was studied under different motions.PVA-HA/PAA composite hydrogel had porous netlike structure similar to nature cartilage, and HA particles were distributed uniformly in the hydrogel matrix, a smooth and dense surface was obtained. Comparing with the water content and mechanical properties of 16 kinds of combination, the composite hydrogel with freezing-thawing cycles of 3, annealing temperature of 120℃, PVA of 16%, HA of 2%, PAA of 4%, had the best comprehensive properties.The partial crystallization of PVA, and interaction between HA, PAA and PVA was occurred, forming physical crosslinking points. In addition, annealing could improve the crystallinity and thermal stability of hydrogel. Swelling tests showed swelling ratio of PVA-HA/PAA composite hydrogel was related with composition, structure, solution medium. Annealing increased the crystallinity of hydrogel and promoted interaction between PVA and HA, PAA, increaseing the degree of crosslinking, network structure becoming denser, hindering the water molecules entering into the gel, thus reducing the swelling ratio.PVA-HA/PAA composite hydrogel tensile stress-strain curve showed a non-linear relationship, indicating that it is a kind of viscoelastic material. Annealed PVA-HA/PAA composite hydrogel had a high tensile strength and elastic modulus, 3.71 MPa and 0.98 Mpa respectively. The stress reponse of PVA-HA/PAA composite hydrogel in cyclic loading-unloading tests was similar to natural cartilage, indicating that PVA-HA/PAA composite hydrogel has the mechanical properties of stress hysteresis and self-healing properties. In dynamic rheological tests of PVA-HA/PAA composite hydrogel, through dynamic frequency, strain, temperature scanning variation, found that storage modulus was much higher than loss modulus, indicating the elasticity of material was the main part, and PVA-HA/PAA composite hydrogel has the best elasticity, strength and mechanical stability.In sliding friction tests, the friction coefficient of PVA-HA/PAA composite hydrogel increased with load, and first increased and then decreased with the increase of sliding speed. In torsional friction tests, the friction torque of PVA-HA/PAA composite hydrogel increased with load and torsional angle. In the early torsional friction, the state of the contact interface was in full slip state, as the cycles increased, the contact state turned into stick-slip state gradually. Under same conditions, average friction coefficient and friction torque of PVA-HA/PAA composite hydrogel were more similar to bovine knee cartilage.