  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.
