Developing Porous Ortho- and Pyrophosphate-Containing Glass Microspheres; Structural and Cytocompatibility Characterisation

Phosphate-based glasses (PBGs) are promising materials for bone repair and regeneration as they can be formulated to be compositionally similar to the inorganic components of bone. Alterations to the PBG formulation can be used to tailor their degradation rates and subsequent release of biotherapeutic ions to induce cellular responses, such as osteogenesis. In this work, novel invert-PBGs in the series xP(2)O(5)·(56 − x)CaO·24MgO·20Na(2)O (mol%), where x is 40, 35, 32.5 and 30 were formulated to contain pyro (Q(1)) and orthophosphate (Q(0)) species. These PBGs were processed into highly porous microspheres (PMS) via flame spheroidisation, with ~68% to 75% porosity levels. Compositional and structural analysis using EDX and (31)P-MAS NMR revealed that significant depolymerisation occurred with reducing phosphate content which increased further when PBGs were processed into PMS. A decrease from 50% to 0% in Q(2) species and an increase from 6% to 35% in Q(0) species was observed for the PMS when the phosphate content decreased from 40 to 30 mol%. Ion release studies also revealed up to a four-fold decrease in cations and an eight-fold decrease in phosphate anions released with decreasing phosphate content. In vitro bioactivity studies revealed that the orthophosphate-rich PMS had favourable bioactivity responses after 28 days of immersion in simulated body fluid (SBF). Indirect and direct cell culture studies confirmed that the PMS were cytocompatible and supported cell growth and proliferation over 7 days of culture. The P30 PMS with ~65% pyro and ~35% ortho phosphate content revealed the most favourable properties and is suggested to be highly suitable for bone repair and regeneration, especially for orthobiologic applications owing to their highly porous morphology.