Phosphate-based glass fiber vs. bulk glass: Change in fiber optical response to probe in vitro glass reactivity

摘要

This paper investigates the effect of fiber drawing on the thermal and structural properties aswell as on the glass reactivity of a phosphate glass in tris(hydroxymethyl)aminomethane-buffered (TRIS) solution and simulated body fluid (SBF). The changes induced in the thermal properties suggest that the fiber drawing process leads to aweakening and probable re-orientation of the POPbonds.Whereas thefiber drawing did not significantly impact the release of P and Ca, an increase in the release of Na into the solution was noticed. This was probably due to small structural reorientations occurring during the fiber drawing process and to a slight diffusion of Na to the fiber surface. Both the powders from the bulk and the glass fibers formed a Ca-P surface layer when immersed in SBF and TRIS. The layer thickness was higher in the calcium and phosphate supersaturated SBF than in TRIS. This paper for the first time presents the in vitro reactivity and optical response of a phosphate-based bioactive glass (PBG) fiberwhen immersed in SBF. The light intensity remained constant for the first 48 h afterwhich a decrease with three distinct slopes was observed: the first decrease between 48 and 200 h of immersion could be correlated to the formation of the Ca-P layer at the fiber surface. After this a faster decrease in light transmission was observed from200 to ~425 h in SBF. SEManalysis suggested that after 200 h, the surface of the fiberwas fully covered by a thin Ca-P layer which is likely to scatter light. For immersion times longer than ~425 h, the thickness of the Ca-P layer increased and thus acted as a barrier to the dissolution process limiting further reduction in light transmission. The tracking of light transmission through the PBG fiber allowed monitoring of the fiber dissolution in vitro. These results are essential in developing new bioactive fiber sensors that can be used to monitor bioresponse in situ.