Effect of iron on the surface, degradation and ion release properties of phosphate-based glass fibres

Phosphate-based glass fibres (PGF) have the unique characteristic of being completely soluble in an aqueous environment, releasing bioactive and biocompatible ions. They have been proposed as tissue engineering scaffolds for craniofacial skeletal muscle regeneration, where myoblasts are seeded directly onto the fibres. Studies have shown that these cells have a preference in their initial attachment to fibres of certain composition and size, which in turn control the rate of degradation. This study investigated the relationship between the surface properties, degradation properties and ion release (cationic and anionic species) by altering the chemical composition of the PGF. Iron oxide (Fe2O3) was incorporated into glasses containing P2O5 (50 mol%), CaO (30 mol%) and Na2O (20 mol%). Six glass compositions with Fe2O3 ranging from 0 to 5 mol% by replacing the equivalent Na2O mol% were investigated. Contact angle measurements showed that polar interactions occurring on the glass surfaces diminished with increasing Fe2O3 content. This behaviour was reflected in the estimated surface energies of the glasses, where the overall surface energy decreased with increasing Fe2O3 content due to the decrease in polar or acid/base component. The incorporation of up to 5 mol% Fe2O3 into PGF resulted in a significant reduction in the degradation rate (by two orders of magnitude), which can be related to the formation of more hydration resistant P-O-Fe bonds. However, the degradation rate increased with decreasing fibre diameter (comparing average diameters of 31.6 +/- 6.5 microm versus 13.1 +/- 1.3 microm) for a given mass of fibre, and this is related to the surface area to volume ratio. Taken together the results suggest that fibres with the larger diameters and containing 3-5 mol% Fe2O3 could initially be a more durable scaffold than ones with 1 or 2 mol% Fe2O3 for initial cell attachment.