The effect of surface modification of a porous TiO2/perlite composite on the ingrowth of bone tissue in vivo

The porous TiO2/perlite composite Ecopore is a synthetic biomaterial with possible clinical application in bone substitution. In our previous work, we demonstrated that surface modification of Ecopore with fibronectin (FN) enhanced spreading and growth of human osteoblasts in vitro. In the present study, we implanted untreated, alkaline-etched and FN-coated Ecopore cylinders into critical size defects of rabbit femora and applied pulsed polychrome sequence staining. After 6 weeks, sections of the implants were investigated via conventional and fluorescence microscopy. A partial ingrowth of bone matrix into the pore system of the Ecopore implants was observed. At the contact zones, the bone appeared to be directly connected to the implant without detectable gaps. Defect healing was complete within 6 weeks, while fibrous tissue generation or inflammation were absent in the implant modification groups, demonstrating basic Ecopore biocompatibility. The mean bone apposition rates within the implant cross-section were 4.1±0.6 μm/day (p<0.001) in the FN-coated group and 3.3±0.5 μm/day (p<0.05) in the NaOH-etched group. In both treated Ecopore modification groups, the apposition rates were significantly higher than in the non-modified control (2.9±0.6 μm/day), indicating bone growth stimulation by pre-treatment. Energy-dispersive X-ray analysis confirmed that significantly more bone tissue was formed inside the pores of the FN-coated implants compared to the unmodified control. The cross-sectional areas identified as ingrown bone amounted to 18.5±6.1% (p<0.05) in the FN group, 13.4±5.1% (p>0.05) in the NaOH-etched group and 10.2±5.5% in the unmodified group. In summary, we conclude that bone tissue tolerates Ecopore well and that tissue ingrowth can be enhanced by etching and coating with FN.