Bioactive and biostable hyaluronic acid-pullulan dermal hydrogels incorporated with biomimetic hydroxyapatite spheres

In this study, hyaluronic acid-pullulan injectable hydrogels were incorporated with biomimetic hydroxyapatite spheres and were modified using silane coupling agents in order to improve the physicochemical, mechanical, and biological performance of hydrogels. So the biomimetic hydroxyapatite spheres were synthesized through immersion of gelatin-siloxane microspheres in the simulated body fluid. The results of field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction spectra confirmed the formation of hydroxyapatite on the surface of hybrid spheres. The morphology observation of the prepared hydrogels confirmed the uniform distribution of hydroxyapatite spheres in gel structure. The chemical characterization proved the possible interactions between the polymers and the created complex with a silane coupling agent to provide more durability. Improvement of storage modulus and viscosity indicated the positive role of hydroxyapatite spheres on the stability and long-lasting durability of hydrogels. A slight reduction was observed in the absorption capacity and water retention in hybrid hydrogels; even though, the great resistance to enzymatic biodegradation led to higher durability of hydroxyapatite-contained gels. Improvement in L-929 fibroblast cell adhesion and spreading especially around the biomimetic hydroxyapatite spheres along with higher cell viability demonstrated the initial potential of hydrogels for further pre-clinical and clinical studies in order to recommend the gels for dermal rejuvenation applications.