Non-linear dissolution mechanisms of sodium calcium phosphate glasses as a function of pH in various aqueous media

Abstract

Phosphate glasses for bioresorbable implants display dissolution rates that vary significantly with composition, however currently their mechanisms of dissolution are not well understood. Based on this systematic study we present new insights into these mechanisms. Two-stage dissolution was observed, with time dependence initially parabolic and later linear, and a twostage model was developed to describe this behaviour. Dissolution was accelerated by lower Ca concentration in the glass, and lower pH in the dissolution medium. A new dissolution mechanism is proposed, involving an initial stage where diffusion-controlled formation of a conversion layer occurs. Once the conversion layer is stabilised, layer dissolution reactions become rate-limiting. Under this mechanism the transition time is sensitive to the nature of the conversion layer and solution conditions. These results reveal the dependence of P 2 O 5-CaO-Na 2 O glass dissolution on solution pH, and provide new insight into the dissolution mechanisms, particularly regarding the transition between the two dissolution stages.

The evolution of the structure and mechanical properties of fully bioresorbable polymer-glass composites during degradation

“…Significant differences were seen for the glasscontaining composites, demonstrating a fast pH reduction before plateauing, as a result of glass dissolution. The plateau pH was dependent on the phosphate glass composition, with the higher P 2 O 5 glass resulting in a lower pH, consistent with previous results [20]. Although the addition of PLCL-PEG had a major effect on the degradation of the unfilled matrix, the same cannot be said of the composite materials.…”

“…Composites with 15wt.% glass demonstrated similar behaviour, however the initial absorption was slower but reached a higher mass. The initial absorption stage did not appear to be heavily influenced by the glass composition, however in the later mass loss stage composites containing the faster dissolving P45Ca45 glass [20] lost mass more quickly.…”

“…As a result of glass dissolution and subsequent formation and deposition of conversion layer species [20], inorganic NaCl and Ca 2 P 2 O 7 .4H 2 O crystallites were observed in all composite samples by XRD, reaching a maximum of 3 -18wt.% after 120 days degradation (Fig 8d). These were also observed with SEM (Fig.…”

“…Phosphate glasses, with nominal composition (P 2 O 5 ) 90-x (CaO) x (Na 2 O) 10 , where x = 45 or 50, (denoted P45Ca45 and P40Ca50 respectively) were produced using a melt-quenching method described elsewhere [20]. PLLA (Ingeo 2500 HP) was supplied by Natureworks LLC, USA, and PLCL-PEG was synthesised and supplied by Ashland Specialties Ireland Ltd.…”

A technique for improving dispersion within polymer-glass composites using polymer precipitation

“…Phosphate glass, with nominal composition (P 2 O 5 ) 45 (CaO) 45 (Na 2 O) 10 was produced as described elsewhere [14]. Briefly, precursors (Na 2 CO 3 , CaCO 3 , and NH 4 H 2 PO 4 ) were melted in a vitreous silica crucible in a kiln (SBSC-1500L, Kilns and Furnaces Ltd., Stoke-on-Trent, UK) at 1250℃ and quenched by pouring onto a cooled steel plate.…”