Comprehensive Physicochemical Analysis of Polyphosphate-Modified Alginate Matrices: Synthesis, Structural Analysis, and Calcium Ion Release Dynamics

The selection of cross-linking techniques is essential for the development of the alginate matrix. In this study, we investigated porous sodium alginate matrices (ALG1@in, ALG3@in, ALG5@in) synthesized by internal gelation and further functionalized with polyphosphate (PP) at concentrations of 5% and 15% (ALG3@inPP5, ALG3@inPP15). Extensive characterizations were conducted, employing scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS) for morphological and compositional analysis, Fourier transform infrared spectroscopy (FTIR-ATR) for structural elucidation, thermogravimetric analysis (TGA-DTG) for thermal stability, and porosimetry (ASAP) for surface area and pore size evaluation. Surface charge density (pH_ZPC) was determined, and Ca²⁺ release kinetics were monitored in demineralized water over 7 days and Dulbecco's phosphate-buffered saline (DPBS) over 14 days. The increase in sodium alginate concentration increases the BET surface area and pore volume, which improves adsorption and transport properties. The thermal stability of the tested matrices at 37 °C confirms their suitability for biomedical applications. The ALG3@in sample showed the best parameters, combining high BET surface area (11.02 m²/g), significant pore volume (0.08 cm³/g) and thermal stability up to 257 °C, making it a suitable candidate for applications in biology, tissue engineering and processes requiring sterilization and high temperatures. These findings underscore the potential of polyphosphate modifications to improve alginate matrices, opening avenues for future applications in areas like cell culture scaffolds or environmental chemistry solutions.