The influence of calcium phosphate type on the structure and properties of injectable sodium alginate hydrogel composites for biomedical applications

The development of effective non-invasive surgical materials for treating bone tissue injuries and diseases remains a pressing issue, necessitating the search for novel biomaterials. In this study, new injectable hydrogel composites based on sodium alginate with different types of calcium phosphates were synthesized via crosslinking and characterized. Three different calcium phosphate (CaPs) powders, as synthetic hydroxyapatite (SHA), biogenic hydroxyapatite (BHA), and β -tricalcium phosphate ( β- TCP), were prepared and used as starting materials for composite hydrogels. Sodium alginate hydrogel (AlgNa hydrogel) was prepared at 2 wt.% concentration as the starting material. The prepared hydrogel composites contained calcium phosphate phases at concentrations of 1, 2, and 3 wt.% in a constant AlgNa hydrogel matrix. X-ray studies showed the preservation of the phase composition of calcium phosphate materials in the composite structure. Fourier transform infrared spectroscopy also confirmed the presence of functional groups of AlgNa and CaPs in the composite structure. The microstructure of prepared composites was investigated. Skeleton density, injectability, adsorption activity and swelling behavior of the composites were analyzed. An injectability study (the force to initiate extrusion and the force to sustain the extrusion) was conducted, which is necessary when using hydrogels as injectable materials. The adsorption activity of the composites was examined using methylene blue as a model compound. The cytotoxicity of the composites, as assessed by the MTT method, depended on the type of CPs, as well as the eluate concentration. The results demonstrated a significant structural and property variation depending on the type of calcium phosphate used. • Injectable sodium alginate hydrogel composites based on calcium phosphates were prepared • Type and content of calcium phosphate influenced microstructure formation • Equilibrium swelling degree was reached within the first 5 h for all types composites. • The lowest force extrusion demonstrated composites based on hydroxyapatite