Hydroxyapatite coating of cellulose sponge does not improve its osteogenic potency in rat bone

Regenerated cellulose sponges were coated biomimetically with hydroxyapatite to increase their osteogenic properties. Induction of apatite precipitation was carried out with bioactive glass in simulated body fluid (SBF) for 24 h and the final coating was carried out in 1.5 × concentrated SBF for 14 days. Biomimetically mineralized and non-mineralized sponges were then implanted into standard size femoral cortical defects of rats, and the invasion of bone into the implant was followed up to one year. The apatite coating did not improve the osteoconductive property of cellulose in this rat cortical defect model. In fact, it generated a strong and highly cellular inflammatory reaction and less osteoid tissue. The biomimetic implants contained more immunodetectable TGFβ1 (a strong stimulator of fibroblast activity) than untreated implants, and also bound more TGFβ1 in vitro, which could, at least in part, explain the fibrotic invasion of biomimetically mineralized sponges.