Core-clad phosphate glass fibers for biosensing

Unravelling the dissolution mechanism of polyphosphate glasses by 31P NMR spectroscopy: ligand competition and reactivity of intermediate complexes

Phosphate glass dissolution can be tailored via compositional and subsequent structural changes, which is of interest for biomedical applications such as therapeutic ion delivery. Here, solid-state ³¹P nuclear magnetic resonance characterisation of 45P₂O₅-xCaO - (55 -x)Na₂O glasses was correlated with dissolution studies using time-dependent liquid ³¹P NMR spectroscopy and quantitative chemical analysis. Glasses dissolved congruently in aqueous media, and the first dissolution stage was the hydration of phosphate chains. In deionised water and Tris buffer (pH₀ 7.4 or 7.9), trimetaphosphate rings and orthophosphates were the predominant species in solution, indicating relatively fast degradation. By contrast, long phosphate chains were identified in EDTA (pH₀ 10.0). Besides pH differences, coordination of phosphate species by metal cations appears to play a catalytic role in the hydrolysis mechanism via turning phosphorus atoms into suitable electrophiles for the subsequent nucleophilic attack by water. Hydrolysis rates were proportional to phosphate complex stability, with stronger complexes for chains than for rings. A competition between solvent and phosphate species for the metal ion occurred in the order EDTA > Tris > deionised water.

Impact of Glass Composition on Hydrolytic Degradation of Polylactide/Bioactive Glass Composites

Understanding the degradation of a composite material is crucial for tailoring its properties based on the foreseen application. In this study, poly-L,DL-lactide 70/30 (PLA70) was compounded with silicate or phosphate bioactive glass (Si-BaG and P-BaG, respectively). The composite processing was carried out without excessive thermal degradation of the polymer and resulted in porous composites with lower mechanical properties than PLA70. The loss in mechanical properties was associated with glass content rather than the glass composition. The degradation of the composites was studied for 40 weeks in Tris buffer solution Adding Si-BaG to PLA70 accelerated the polymer degradation in vitro more than adding P-BaG, despite the higher reactivity of the P-BaG. All the composites exhibited a decrease in mechanical properties and increased hydrophilicity during hydrolysis compared to the PLA70. Both glasses dissolved through the polymer matrix with a linear, predictable release rate of ions. Most of the P-BaG had dissolved before 20 weeks in vitro, while there was still Si-BaG left after 40 weeks. This study introduces new polymer/bioactive glass composites with tailorable mechanical properties and ion release for bone regeneration and fixation applications.