Morphological, structural, and in vitro bioactivity of core-shell-structured bioactive glass by multitechnical spectroscopic approach

The pioneeristic work of Hench led to the development of a calcium sodium phosphosilicate composition called 45S5 Bioglass (R), which has been investigated extensively for applications in the field of bone repair and regeneration because of its bioactivity, i.e., ability to form a bond to living bone. The bioactivity of silicate glass is qualitatively associated with the development over time of the apatite layer on a bioactive glass, while quantitatively it would be related to how fast the formation of this crystalline phase occurs. In this work, (Ca-molten salt bath(2+)vertical bar Na-glass(+)) ion exchange in a molten salt bath (MSB) was employed for modifying the glass surface aiming to create a more reactive glass in a thin shell that surrounds the vitreous core, which preserves all the bioactivity characteristics of 45S5 Bioglass (R) composition. The 45S5@Ca45S5 core-shell-structured bioactive glass is characterized by a vitreous matrix enriched with calcium and a highly depolymerized silicate network. The presence of calcium-rich glass composition restricted to a thin shell acts as a catalyst, accelerating all the earlier events that occur at the glass/solution interface. The kinetics of deposition of the silica-gel and apatite layers was investigated by FTIR and P-31 MAS NMR, respectively. The results suggest that the modification of the glass surface causes not only a reduction in the formation time of silica-gel and amorphous calcium phosphate on the glass surface but also induced the formation of the apatite phase with a higher degree of crystallinity.