The topography and proliferative activity of cells immunoreactive to various growth factors in rat femoral bone tissues after experimental fracture and implantation of titanium implants with bioactive biodegradable coatings.

BACKGROUND: Biodegradable implant coatings promote proliferation and expression of BMP-2, VEGF, and TGF-ß2 genes and enhance BMP-2, VEGF, and TGF-ß2 regulatory effects at different stages of reparative osteogenesis. OBJECTIVE: To study the topography and ratio of PCNA-, VEGF-, BMP-2-, and TGF-ß2-immunoreactive cells in rat femoral bone after closed fracture and implantation of titanium implants with biodegradable calcium phosphate and hydroxyapatite coatings. METHODS: Standard titanium implant screws and similar implants with bioactive coatings were used. A total of 18 rats were randomly divided into three groups, two experimental and a control one. The rats in the first experimental group were implanted with implants without specific coating, while those in the second group, with implants with specific coatings. The control rats were subjected to the same fracture as the experimental ones without subsequent implantation. On days 7, 14, and 30 of experiment, the rats were sampled for histological examination. Histological sections were prepared and processed for PCNA, BMP-2, VEGF, and TGF-ß2 immunoreactivity. RESULTS: In the regeneration zone, PCNA-immunoreactive cells substantially outnumbered other immunoreactive cell types. During the first two weeks after fracture, in the immediate vicinity of implant surface, the rate of VEGF production increased in osteoblast subpopulations and level of TGF-32 immunoreactivity decreased in chondroblasts. The level of TGF-32 was maximum on day 30 of experiment. BMP-2-immunoreactive osteocytes were found in the zone of external general plates. They accumulated at implants with calcium phosphate coating. Their number gradually increased by day 30 of experiment. CONCLUSIONS: The present data suggest that biodegradable implant coatings promote proliferation and expression of BMP-2, VEGF, and TGF-ß2 genes and enhance BMP-2, VEGF, and TGF-ß2 regulatory effects at different stages of reparative osteogenesis.