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

Abstract

Phosphate-based glasses (PGs) are promising bioresorbable materials for controlled delivery of therapeutic species and tissue regeneration. In this work, the room-temperature, water-based method of coacervation was used for the synthesis of polyphosphate coacervate gels as precursors for the production of P2O5-CaO-Na2O-(MnO)x (x = 0, 1, 3, 5, 10 mol %) powders (PGPs) and fibres (PGFs). Both systems were obtained starting from the same gels; PGPs by vacuum drying and PGFs by electrospinning. Elemental composition of PGPs and PGFs was assessed using Energy-Dispersive X-ray spectroscopy (EDX) and their structure investigated using X-ray Powder Diffraction (XRPD), Fourier Transform Infrared (FT-IR) and Raman spectroscopy. PGPs and PGFs structures turned out to be similar for both systems and like that of PGs prepared using the high temperature, melt-quenching (MQ) technique. Released of P, Ca, Na and Mn in deionized (DI) water for up to 72 h was investigated via MP-AES (Microwave Plasma Atomic Emission Spectroscopy). Results show that the release of the therapeutic metallic ion Mn2+ is similar in PGPs and PGFs, and increases with Mn loading, up to a maximum of 45-49 µg∙mL-1 after 72 h from the systems loaded with 10 mol % of Mn2+. In-vitro biocompatibility was investigated for both systems via the MTT assay on human osteoblasts 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). PGPs and PGFs loaded with Mn2+ up to 1 mol % were not cytotoxic at all ratios considered. Therefore, preliminary bioactivity tests were 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. Results show some structural changes in the FT-IR spectra and in the XRD diffraction patterns after immersion, that along with Scanning Electron Microscopy (SEM) analysis, suggest the deposition of a disordered phase on the surface of the glass.