Síntese e caracterização de novo hidrogel compósito com hidroxiapatita de estrôncio para regeneração óssea

Abstract

Rapid formation of new bone is a prerequisite for aesthetic and functional restoration of lost tissue. Taking this into account, the objective of this work was to prepare a biomaterial potentially applicable for bone regeneration based on a hydrogel matrix modified with Hydroxyapatite (HA) and Strontium Hydroxyapatite (HASr) particles. For the particle’s synthesis, the wet precipitation and calcination method was used. In the case of strontium hydroxyapatite, 50 mol% of calcium was replaced by strontium nitrate in the precipitation phase. The particles were characterized by scanning electron microscopy and X-ray dispersive energy spectroscopy (SEM-EDX - morphology and chemical composition), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The hydrogels were prepared from mixtures of poly(vinyl alcohol) polymers (PVA) and chondroitin sulfate (CS) using the freeze/thaw technique. During this process, different amounts of HA or HASr (0, 5, 10 or 15% in mass) were added to the hydrogel formulation. The obtained hydrogels (with and without particles) were characterized by FTIR, MEV-EDX and computed microtomography (micro-CT - porosity of the hydrogel). In addition, in vitro tests were performed with these hydrogels in order to evaluate their mechanical properties, liquid absorption capacity and cytotoxicity. MEV-EDX confirmed a homogeneous distribution of Ca and Sr along the particle structures. The XRD analyzes showed diffraction patterns corresponding to HA and HASr. The FTIR analysis of the hydrogels showed the formation of the polymeric network of the PVA/CS hydrogel, resulting from the physical crosslinking of the PVA chains during the freezing/thawing steps. In addition, FTIR analyzes confirmed the presence of particles (HA or HASr) in hydrogel matrices. The porosity and homogeneous distribution of the particles was confirmed by MEV-EDX showing the presence of Ca2+ and Sr2+ ions in hydrogels regardless of concentration. The micro-CT exhibited a total porosity of 30% in the control hydrogel (without particles) and a tendency to reduce total porosity as the proportion of HA or HASr increased. The compressive strength of the composite hydrogel increased with the addition of particles. The cell viability test revealed that all prepared hydrogels are non-toxic and still increase the number of cells in all groups, including the control hydrogel (without particles). In conclusion, a modified hydrogel with up to 15% in mass of HA or HASr particles has been successfully synthesized with improved physicochemical properties compared to the control hydrogel, also showing promising manipulative characteristics. The next steps should include alkaline phosphatase assays to observe the ability of hydrogels to induce bone differentiation and in vivo tests for bone regeneration on critical size defects in an animal model, in an attempt to assess their future clinical application.