BackgroundIt has been difficult to find bioactive compounds that can optimize bone repair therapy and adequate osseointegration for people with osteoporosis. The nano-hydroxyapatite (nHAp)/carbon nanotubes with graphene oxides, termed graphene nanoribbons (GNR) composites have emerged as promising materials/scaffolds for bone regeneration due to their bioactivity and osseointegration properties. Herein, we evaluated the action of nHAp/GNR composites (nHAp/GNR) to promote bone regeneration using an osteoporotic model.Materials and methodsFirst, three different nHAp/GNR (1, 2, and 3 wt% of GNR) were produced and characterized. For in vivo analyses, 36 Wistar rats (var. albinus, weighing 250–300 g, Comissão de Ética no Uso de Animais [CEUA] n.002/17) were used. Prior to implantation, osteoporosis was induced by oophorectomy in female rats. After 45 days, a tibial fracture was inflicted using a 3.0-mm Quest trephine drill. Then, the animals were separated into six sample groups at two different time periods of 21 and 45 days. The lesions were filled with 3 mg of one of the above samples using a curette. After 21 or 45 days of implantation, the animals were euthanized for analysis. Histological, biochemical, and radiographic analyses (DIGORA method) were performed. The data were evaluated through ANOVA, Tukey test, and Kolmogorov-Smirnov test with statistical significance at P<0.05.ResultsBoth nHAp and GNR exhibited osteoconductive activity. However, the nHAp/GNR exhibited regenerative activity proportional to their concentration, following the order of 3% >2% >1% wt.ConclusionTherefore, it can be inferred that all analyzed nanoparticles promoted bone regeneration in osteoporotic rats independent of analyzed time.

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Nanomaterials based on graphene oxide nanoribbons (GNR) and nanohydroxyapatite (nHAp) serve as attractive materials for bone tissue engineering. Herein, we evaluated the potential of nHAp/GNR toward in vitro analysis of specific genes related to osteogenesis and in vivo bone regeneration using animal model. Three different concentrations of nHAp/GNR composites were analyzed in vitro using a cytotoxicity assay, and osteogenic potential was determined by ALP, OPN, OCN, COL1, and RUNX2 genes and alkaline phosphatase assays. In vivo bone neoformation using a well-established in vivo rat tibia defect model was used to confirm the efficiency of the optimized composite. The scaffolds were nontoxic, and the osteogenesis process was dose-dependent (at 200 μg mL–1 of nHAp/GNR) compared to controls. The in vivo results showed higher bone neoformation after 15 days of nHAp/GNR implantation compared to all groups. After 21 days, both nHAp/GNR composites showed better lamellar bone formation compared to control. We attributed this enhanced bone neoformation to the high bioactivity and surface area presented by nHAp/GNR composites, which was systematically evaluated in previous studies. These new in vivo results suggest that nHAp/GNR composites can be exploited for a range of strategies for the improved development of novel dental and orthopedic bone grafts to accelerate bone regeneration.

The results show that the physical and chemical properties of the nanomaterials are suitable for the fabrication of scaffolds intended for bone regeneration. The in vitro tests suggested a non-toxicity of the GNRs as well as improved biocompatibility and bone mineralization activity. Here, for the first time, we evaluated the potential of GNRs in remodeling and repairing bone defects in osteoporotic animal models in vivo. Interestingly, bone mineralization and the initiation of the remodeling cycle by osteoclasts/osteoblasts were observed after the implantation of GNRs, thus implying healthy bone remodeling when using GNRs. This study, therefore, has opened our perspectives and certainly calls for more attention to the use of carbon nanomaterials for a wide range of osteoporosis applications.