Properties of promising cartilage implants based on cellulose-polyacrylamide composite hydrogels: results of in vivo tests carried out over a period of 90-120 days

High-strength composite hydrogels cellulose-polyacrylamide were synthesized by free-radical polymerization of acrylamide conducted inside the previously formed physical network of regenerated plant cellulose. Partial hydrolysis of the amide groups of these hydrogels yielded their ionic forms with a degree of hydrolysis of 0.1 and 0.25. The cylindrical hydrogel samples of three compositions were implanted in the preformed osteochondral defects of the rabbit's femoral knee joints. No signs of migration or disintegration of the tested implants were revealed in the course of in vivo tests as long as 90 and 120 days after the implantation. The mechanical behavior of both the virgin hydrogels-implants and the implants extracted from the joints after in vivo experiments was studied in detail. The morphology and chemical composition of the extracted implants were studied by SEM combined with the EDX method. The results obtained were shown that the mechanical characteristics of hydrogel implants remained practically unchanged after in vivo tests. The extracted implants, as well as the initial hydrogels, endured cyclic compression loading at the amplitude up to 50 %. Compression stresses up to 3-10 MPa were recorded in these tests, which is close to the data obtained by several authors for natural articular cartilages in the same conditions of loading. The principal differences in the chemical composition and morphology of the implant area adjacent to the subchondral bone for non-ionic and ionic types of implants have been revealed. If for non-ionic types of implants in this area intensive mineralization with formation of calcium phosphates inside the polymeric hydrogel network is observed, the border area of ionic implants practically does not undergo mineralization.