Reparative osteogenesis around magnesium-containing biodegradable implants in rabbit femoral bones

The demand for innovative biodegradable implants has stimulated the development of new manufacturing technologies. Implants made of biodegradable magnesium alloys demonstrate satisfactory biocompatibility; however, the characteristics of their biodegradation in body tissues, particularly in bone tissue, still require further investigation. Objective – to investigate tissue reactions around magnesium alloy implants during the course of their biodegradation in rabbit femoral bones. Materials and methods. In an experimental rabbit model, a tunnel defect was created in the distal epiphysis of the femur, into which pins made of MZZ-P or MZZ-MB magnesium alloys were implanted. After 8 and 16 weeks, histological sections were examined to assess tissue reactions around the pins, including connective tissue responses, osteogenesis, and implant biodegradation within the bone. Results. Degradation of MZZ-P and MZZ-MB magnesium alloys in the femoral bone was observed, accompanied by elimination of inorganic material against the background of an inflammatory reaction. At 2 and 4 weeks, the signs of reactive connective tissue complex formation around both types of implants were similar, while osteogenesis had only begun. The dynamics of local osteogenesis at 8 and 16 weeks around MZZ-P and MZZ-MB implants depended on the microenvironment determined by the level of implant biodegradation. MZZ-P degraded less intensively; however, this did not result in enhanced osteogenesis compared with MZZ-MB. At 16 weeks, the specific density of bone tissue did not differ significantly between the groups (35.7 ± 7.6 % and 41.6 ± 1.2 %, respectively; p = 0.12). Osteogenesis significantly progressed between weeks 2 and 16, increasing 2.6-fold and 2.2-fold, respectively (p < 0.001). Conclusions. Around both MZZ-P and MZZ-MB implants in the femoral bone, an increase in the number of bone trabeculae occurred during alloy biodegradation. Implant characteristics (chemical composition and biodegradation rate) had less influence on osteogenesis than the time factor.