Polyphosphate coacervate gels for manufacturing of manganese loaded glass powders and fibres: structural, cytocompatibility and surface bioactivity study

Phosphate-based glasses (PGs) are promising bioresorbable materials for controlled delivery of therapeutic species and tissue regeneration. The traditional method of synthesis of PGs involves the use of high temperatures, which limits their biomedical applications. The main goal of this work was to manufacture Mn loaded PGs for bone regeneration using an alternative, versatile and sustainable manufacturing technique. In this work, the novel room temperature, water-based method of coacervation was used for the synthesis of PGs in the system P2O5–CaO–Na2O–(MnO)x where x = 0, 1, 3, 5, 10 mol% both in powder (PGPs) and fibre (PGFs) form. PGPs were manufactured by vacuum drying polyphosphate coacervate gels and PGFs by electrospinning them. The addition of Mn2+, which plays an important role in bone mineralization, represents a clear novelty of this work as Mn loaded PGs prepared via coacervation have not been presented to date. Mn2+ release in deionized (DI) water has been shown to increase with Mn2+ loading in both PGPs and PGFs, demonstrating tailored release by modifying its content in the glass. In vitro biocompatibility was investigated for both systems via MTT assay on human osteosarcoma cells (MG-63) at three different ratios of dissolution products to cell medium after 24 h immersion in DI water (1, 3 and 5% v/v). Results have demonstrated that PGPs and PGFs loaded with Mn2+ up to 1 mol% are the most promising systems as they are not cytotoxic at all ratios investigated. Preliminary bioactivity tests performed by immersing a PGP sample containing 1 mol% of Mn2+ in both cell medium (McCoy's 5A) and Tris-buffer solution for 24 and 72 h suggest the deposition of a disordered, possibly hydroxyapatite-like phase on the surface of the glass. This study demonstrates that PGPs and PGFs, synthesised via coacervation, exhibit controlled release of the therapeutic ion Mn2+ and promising biocompatibility, making them suitable candidates for applications such as bone regeneration and controlled delivery.