Biodegradation Process of α-Tricalcium Phosphate and α-Tricalcium Phosphate Solid Solution Bioceramics In Vivo: A Comparative Study

This article reports the structure and morphology of the in vivo interface between implants composed of either alpha tricalcium phosphate (alpha TCP) or alpha TCP doped with 3.0 wt% dicalcium silicate (alpha TCPss) ceramic, and natural bone of rabbit tibias. Both interfaces developed a new bone layer in direct contact with the implants after 4 and 8 weeks of implantation. The specimens were examined using analytical scanning and transmission electron microscopy, up to the lattice plane resolution level. Degradation processes of the implants developed at the interfaces encouraged osseous tissue ingrowth into the periphery of the material, changing the microstructure of the implants. The ionic exchange initiated at the implant interface with the environment was essential in the integration process of the implant, through a dissolution-precipitation-transformation mechanism. The interfaces developed normal biological and chemical activities and remained reactive over the 8-week period. Organized collagen fibrils were found at the alpha TCPss/bone interface after 4 weeks, whereas a collagen-free layer was present around the Si-free alpha TCP implants. These findings suggest that the incorporation of silicate ions into alpha TCP ceramic promotes processes of the bone remodeling at the bone/alpha TCPss interface, hence the solubility rate of the alpha TCPss material decreased.