| The aim of this work was to develop and characterize new calcium phosphate glass ceramics that would degrade in a controlled manner in the body environment, which could ultimately be used in regenerative surgery. Two glasses MK5 (45CaO-45P 2O5-5MgO-5K2O, mol%) and MT13 (45CaO-37P 2O5- 5MgO-13TiO2, mol%) were prepared in the meta-, pyro- and orthophosphate regions and crystallized to obtain MK5B and MT13B glass ceramics, respectively. The MK5B glass ceramic was prepared by controlled crystallization of base glass blocks whereas MT13B was prepared by sintering and crystallization of base glass powder discs. As a result of the heat treatment used to convert glass into glass ceramic, four crystalline phases were precipitated in the glassy matrix: KCa(PO3)3, beta-Ca(PO3 )2, beta-Ca2P2O7 and Ca 4P6O19 phases for MK5B and CaTi4(PO 4)6, TiP2O7, alpha- and beta-Ca 2P2O7 phases for MT13B. These two glass ceramics showed distinct in vitro and in vivo behaviour, which could be attributed to the different crystalline phases that were found in their microstructure. The in vitro biological performance of the MK5B and MT13B glass-ceramics was assessed by direct cell culture methods using MG63 osteoblast-like cells and human bone marrow osteoblastic cells. The results demonstrated that the cells were able to adhere and proliferate on both MK5B and MT13B surfaces, but the latter showed an enhanced biological performance. Experimental findings demonstrated that the MT13B glass ceramic had a stable surface throughout the experiment time whereas MK5B had a highly unstable surface with dissolution/precipitation processes occurring throughout the culture time, causing an initial inhibition on cell attachment and subsequent proliferation. These differences might be attributed to the significant differences in the surface degradation, which was directly correlated to the crystalline phase composition. Both glass ceramics were composed of distinct but relatively soluble phases, except the relatively insoluble CaTi4(PO4)6 phase, which jointly with the residual glassy phase led to each glass ceramic having a unique degradation behaviour. The in vivo biological response using a rabbit model showed that MT13B and MK5B had different in vivo degradation behaviour, however both materials demonstrated osteoconductive behaviour. The higher degradation rate observed in MK5B compared to MT13B caused a delay in new bone formation, which might be overcome for longer implantation periods. The results demonstrated that the initial composition of mother glass used and the heat treatments applied were efficient in preparing glass ceramic biomaterials. This work also showed that by modifying the initial composition of the mother glass as well as using different heat treatment cycles, significant changes in the microstructure and properties could be achieved. Therefore, glass ceramics materials with significant different degradation rates may be prepared covering several potential clinical applications. |
