Effect of hydroxyapatite as a component of biostable composites on population and proliferation of mesenchymal stem cells.

Three groups of biostable composite materials were studied. The initial binder polymers (polymethylmethacrylate, polyamide-12, superhigh-molecular-weight polyethylene) and hydroxyapatite-containing composites on the basis of these polymers were tested. Biostable polymers, including those containing hydroxyapatite, were nontoxic for fibroblasts and mesenchymal stem cells: the adhesion parameters for these cells were maximum for polyamide-12 and superhigh-molecular-weight polyethylene and did not depend on the presence of hydroxyapatite. Cell adhesion to "pure" polymethylmethacrylate was significantly lower than to other composites, but increased after integration of hydroxyapatite. The efficiency of proliferation of fibroblast and mesenchymal stem cell on the surface of polyamide-12 and superhigh-molecular-weight polyethylene was maximum and did not depend on the presence of hydroxyapatite. The efficiency of cell proliferation on the surface of "pure" polymethylmethacrylate was low, but increased significantly if it was combined with hydroxyapatite, particularly in areas of mineral particles accumulation. It seems that the presence of high amounts of hydroxyapatite in polymethylmethacrylate samples promotes cell adhesion and proliferation.

[Evolution of tissue structures in the mandible after implantation of plate from polymethylmethacrylate and its compositions with hydroxyapatite]. / Evoliutsiia tkanevykh struktur nizhnei cheliusti pri implantatsii plastin iz polimetilmetakrilata i ego kompozitsii s gidroksiapatitom.

Tissue reactions to active modified composite material were studied in experiments on Chinchilla rabbits. In the first series of experiments plates from composite material were implanted: polymethylmethacrylate (PMMA) plates were used in group 1, PMMA composition with hydroxyapatite (HAP) in group 2, and PMMA composition with HAP modified by polyacrylic acid in group 3. The content of HAP in each group was 30% by weight. Implantation of plates from pure PMMA induced atrophic processes with formation of connective tissue capsule at the site of implantation. In the second series of experiments the manifestations of inflammatory reactions in the bone and adjacent tissues, caused by HAP release into tissue, were observed, which were paralleled by activation of bone formation, which sometimes acquired the pattern of a hyperproductive reaction. PMMA/HAP composite modified by chemical bond proved to be the most effective: its implantation caused no manifest pathological reactions and inflammatory infiltration; no intraosseous deposition of crystals were detected. Intensive osteogenesis round the implanted plate was observed.