Abstract We investigated the Biogran on bone repair and metabolism at several time-intervals upon grafting into rat tibia artificial defects. The biomaterial was thoroughly characterized in vitro, and its dissolution behavior upon immersion was assessed in simulated body fluid (SBF) solution for 1, 3, 7, 14, and 30 days. Biogran was also assessed by in vitro hydroxyapatite formation in SBF solution, which is a marker for bioactive behavior. In vivo, distal and proximal bone defects were performed in the Wistar rat's right tibia and filled according to the experimental groups: I) negative control, no filling; II) positive control, 10 mg of autogenous bone; and III) 10 mg of Biogran. Animals were euthanized at 1, 2, 3, 4, 7, and 10 weeks. Bone neoformation was analyzed using histomorphometry (proximal defect), and local levels of bone morphogenetic protein 2 (BMP-2) were measured using the ELISA assay (distal defect). In vitro, the Biogran sample showed a fast dissolution rate within the first 7 days, parallel to the formation of the hydroxyapatite layer. In vivo, the sample was progressively resorbed at a higher rate within the first month until it became almost absent at week 10th. The sample presented similar or higher bone neoformation concerning the autogenous bone. BMP-2 levels were sustained in the Biogran group (around 200 pg/mg) and detected until the last experimental time with a significant difference compared with the controls. Results suggest Biogran is a candidate for hard tissue engineering even in highly active bone remodeling sites.

Bioactive glasses undergo corrosion with leaching of alkaline ions when exposed to body fluids. This results in the spontaneous formation of a layer of hydroxyapatite (HA), the mineral component of natural bone, which in turn can induce bone growth in vivo. This paper describes the different types of bioactive glasses, the characterization methods currently used, and the main factors that influence their bioactivity. Nucleation and crystallization, the main mechanisms involved in the formation of hydroxyapatite, Ca10(PO4)6(OH)2, are discussed as a function of the chemical composition and the reactivity of the surface of the material. Finally, promising applications are considered.

Samples of a commercial glass fiber FM® (Fiber Max) were used to test the efficacy of a chemical sol-gel surface treatment to enhance their bioactivity. After treatment with tetraethoxysilane (TEOS), individual fiber samples were soaked into a simulated body fluid (SBF) solution, from which they were removed at intervals of 5 and 10 days. Micrographs obtained by scanning electron microscopy (SEM) analysis of samples chemically treated with TEOS revealed the formation of a hydroxyapatite (HA) coating layer after 5 days into SBF solution. Fourier transform infrared spectroscopic (FTIR) analyses confirmed that the coating layer has P-O vibration bands characteristic of HA. The in vitro cytotoxicity was evaluated using a direct contact test, minimum essential medium elution test (ISO 10993-5) and MTT assay. Fibers immersed in SBF and their extracts exhibited lower cytotoxicity than the controls not subjected to immersion, suggesting that SBF treatment improves the biocompatibility of the fiber.

The focus of this work is to show the influence of surface charge on the bioactivity of modified collagen fiber surface. Because silica plays an important role on bone mineralization process, silica obtained by a sol-gel process was used as a surface modification agent. Zeta potential (xi) of silica-coated and non-coated samples was measured as a function of pH. It was observed a shift in xi vs. pH. The isoelectric point for silica-coated collagen was 6.8, while that of non-treated sample it was near 10. Pure silica has isoelectric point near 2, and the shift observed indicates that at least part of the silica was incorporated onto the surface during the treatment. The ability of samples exposed to biological simulated fluids (SBF) to form a hydroxyapatite layer has been used to recognize bioactive materials. The pH of these biological solutions is about 7.3. It means that treated samples acquire negative charge when in contact with the biological solution and attract ions like Ca2+, HPO4(2-), and OH- to form HA coatings. Micrographs of chemically treated samples corroborate this assumption. For treated samples, the formation of a coating layer is clear after 5-day immersion in SBF, while pure collagen remains practically unaltered. Fourier Transform Infrared Spectroscopic (FTIR) analyses confirmed that the coating layer has P-O vibration bands near 1060 cm-1 and 600 cm-1 characteristic of hydroxyapatite (HA).