Hydroxyapatite-alginate biocomposite promotes bone mineralization in different length scales in vivo (original) (raw)

Tissue engineering is a multidisciplinary research area that aims to develop new techniques and/or biomaterials for medical applications. The objective of the present study was to evaluate the osteogenic potential of a composite of hydroxyapatite and alginate in bone defects with critical sizes, surgically made in the calvaria region of rats. The rats (48 adult males), Rattus norvegicus Wistar, were divided into two groups: control (without composite implantation) and experimental (with composite implantation) and analyzed by optical microscopy at the biological time points 15, 45, 90 and 120 d, and transmission electron microscopy 120 d after the implantation of the biomaterial. It was observed that the biomaterial presented a high degree of fragmentation since the first experimental points studied, and that the fragments were surrounded by new bone after the duration of the project. These areas were studied by analytical transmission electron microscopy using an energy dispersive X-ray spectrometer. Three regions could be distinguished: (1) the biomaterial rich in hydroxyapatite; (2) a thin contiguous region containing phosphorus but without calcium; (3) a region of initial ossification containing mineralizing collagen fibrils with a calcium/phosphorus ratio smaller than the particles of the composite. The intermediate region (without calcium or containing very low amounts of calcium), which just surrounded the composite had not been described in the literature yet, and is probably associated specifically to the biocomposite used. The high performance of the biomaterial observed may be related to the fact that alginate molecules form highly anionic complexes and are capable of adsorbing important factors recognized by integrins from osteoblasts. Regions of fibrotic tissue were also observed mainly in the initial experimental points analyzed. However, it did not significantly influence the final result. In conclusion, the biomaterial presents a great potential for application as bone grafts in the clinical area.