Indications exist that paramagnetic calcium phosphates may be able to promote regeneration of bone faster than their regular, diamagnetic counterparts. In this study, analyzed was the influence of paramagnetic cobalt-substituted hydroxyapatite nanoparticles on osteoporotic alveolar bone regeneration in rats. Simultaneously, biocompatibility of the material was tested in vitro, on osteoblastic MC3T3-E1 and epithelial Caco-2 cells in culture. The material was shown to be biocompatible and nontoxic when added to epithelial monolayers in vitro, while it caused a substantial decrease in the cell viability as well as deformation of the cytoskeleton and cell morphology when incubated with the osteoblastic cells. In the course of 6 months after the implantation of the material containing different amounts of cobalt, ranging from 5 to 12 wt%, in the osteoporotic alveolar bone of the lower jaw, the following parameters were investigated: histopathological parameters, alkaline phosphatase and alveolar bone density. The best result in terms of osteoporotic bone tissue regeneration was observed for hydroxyapatite nanoparticles with the largest content of cobalt ions. The histological analysis showed a high level of reparatory ability of the nanoparticulate material implanted in the bone defect, paralleled by a corresponding increase in the alveolar bone density. The combined effect of growth factors from autologous plasma admixed to cobalt-substituted hydroxyapatite was furthermore shown to have a crucial effect on the augmented osteoporotic bone regeneration upon the implantation of the biomaterial investigated in this study.

Pure and cobalt-exchanged hydroxyapatite (HAp and CoHAp) powders were synthesized by hydrothermal method. X-ray diffraction (XRD), Raman spectroscopy, particle size analysis, inductively coupled plasma (ICP) emission spectroscopy, and scanning electron microscopy (SEM) were used to study the microstructural and unit cell parameters, average particle size, particle size distribution, chemical composition, and morphology of the synthesized powders. XRD and Raman spectroscopy confirmed that the samples were free from impurities and other phases of calcium phosphates. It has been found that the increase in the cobalt amount in the crystal structure of HAp reduces unit cell parameters, as well as average crystallite size (from XRD measurements). All of the powders were nano-sized with narrow particle distribution (from particle size analyses). SEM investigations indicated that nano-sized particles were organized in soft micro-sized agglomerates, whose sizes increased with the increase in the content of Co in HAp crystal structure.