Preparation And Performance Evaluation Of Hydrogel Biomimetic Articular Cartilage Materials

Development of artificial materials that filling the damaged area and integrating with surrounding tissue, preventing further degeneration of articular cartilage, is considered as a promising approach to repair cartilage defect. By imitating the material and function characteristics of nature articular cartilage, in the present work, n-HA/PVA composite hydrogels were prepared by in-situ synthesis, freezing-thawing combined with y-ray irradiation methods. A series of experimental methods were used to investigate properties of n-HA/PVA hydrogel biomimetic articular cartilage, the results are as following:1. PVA hydrogel prepared by repeated freezing-thawing method followed with y-ray irradiation had similar internal three-dimensional structure and water content (approximately 75%) as nature articular cartilage. Both uniaxial tensile and unconfined compressive properties of PVA hydrogel were found to exhibit nonlinear behavior. Mechanical strength increased as initial concentration of PVA and freezing-thawing cycles increased; the strength increased first with the increasing of irradiation dose and dropped when it reached 100kGy.2. HA active ceramic particles formed in PVA solution by in-situ synthesis method showed nano-sized needlelike structure. PVA polymer chains acted as template during the formation of HA particles. A hydrogen-bonding was observed to exist between dispersed HA phase and PVA polymer matrix. Internal structure observation by SEM technique showed a three-dimensional network structure and the structure became denser after y-ray irradiation.3. Uniaxial tensile and unconfined compressive mechanical properties of n-HA/PVA hydrogel conformed polynominal and exponential change rules, respectively. Mechanical strength of n-HA/PVA hydrogel increased first and then dropped with increasing of irradiation dose and n-HA content, it reached the maximum value when the irradiation dose was 100kGy and n-HA content was 6 wt%.4. A biphasic finite element model was used to simulate the load-bearing condition of liquid phase during indentation creep test, and it was derived that both nature articular cartilage and hydrogel presenting biphasic characteristics. Voight-Boltzmann model was established to describe creep respose of articular cartilage and hydrogel accurately. The results showed hydrogel prepared in our study had similar viscoelastic performance as nature articular cartilage. 5. Friction tests were performed on a reciprocating motion pin-on-plate machine. Friction coefficient rose gradually with increasing loading time up to a constanct value at about 30mins. Initial low friction coefficient was attributed to an effective biphasic lubrication action, after it reached an equivalent state, boundary lubrication mechanism came into action. Friction coefficient of hydrogel-cartilage contact was larger than cartilage-cartilage contact, but much smaller and stabler than stainless steel-cartilage contact. An increase in contact stress was found to increase the friction levels between the articulating surfaces of hydrogel and cartilage, and the change at low load condition was more significant than at high load condition. Frictional properties of hydrogel sliding against articular cartilage were controlled both by irradiation dose and n-HA content, the results showed that friction behavior reached an optimal level when the irradiation dose was 100kGy and n-HA content was 5wt%. It was found a concave on the wear track with the depth of 60μm after 1h loading during friction test, and surface roughness of hydrogel after friction test was smaller than before. Surface roughness of cartilage in hydrogel-cartilage contact was 3 times of it in cartilage-cartilage contact, but 60% of it in stainless steel-cartilage contact.6. Hemolysis and MTT tests showed that the hydrogel prepared in our study would not induce hemolytic effect to blood or cytotoxic effect to cells, and local implantation tests indicated that the hydrogel didn't bring toxicity to liver, kidney, spleen, muscle or capsule. The hydrogels showed to have excellent biocompatibility.