Injectables bioactives cements functionalized with osteogenic peptide for bone repair

The development of biomaterials that promote repair of injured tissues has been the subject of intense research. Regarding the bone tissue repair, ceramics are one of the most researched biomaterials groups due to its wide possibility of use, including cement pastes with good moldability. The mesoporous silica has high specific surface area (~1000 m2.g-1) and pore size usually around 2-30 nm attracting attention for its applications as drugs and proteins carriers. The osteogenic growth peptide (OGP) is an endogenous tetradecapeptide, whose active form acts as an anabolic agent and hematopoietic stimulator, promoting osteoblast differentiation. Thus, the aim of this study was to develop an injectable bone cement, resorbable and bioactive, mesoporous silica and osteogenic growth peptide. The peptide was synthesized by the solid phase method, purified by High Performande Liquid Chromatography (HPLC) and characterized by Mass Spectrometry. The mesoporous materials were synthesized by sol-gel method and its porosity confirmed by Adsorption-desorption of N2, Small-angle X-ray Scattering and Transmission Electronic Microscopy. Cements were prepared from calcium sulfate (CaS), calcium phosphate (CaP) and calcium aluminate (CaAl), without and with mesoporous silica, and analyzed for its physicochemical characteristics. In vitro experiments were carried out to evaluate the cements cytotoxic and genotoxic potential in CHO-K1 hamster ovary cell line and analysis of the mineralized matrix formation in MC3T3-E1 osteosblastics cell line. The in vivo study was performed in critical defects in rat calvaria, and it has analized as formation of bone tissue by histomorphometry and density of newly formed tissue by X-ray images. The cements analysis have shown that the presence of mesoporous silica particles promoted different physico-chemical behavior when compared to those without silica, such as higher ratio Liquid/Powder, higher porosity and, hence, decreases the mechanical resistance. CaP and CaAl cements showed bioactivity in vitro when immersed in Simulated Body Fluid solution. Concerning OGP liberation, the CaS cement showed the fastest release in the OGP-mesoporous silica-loaded cement release studies, releasing 80% peptide loaded in 24 hours. Regarding cell viability, CaS cements with and without silica, were not cytotoxic, but the CaP and CaAl cement showed cytotoxicity; however this behavior did not affect cell proliferation. And in mutagenicity tests, the cements did not promote significant cell damage. The tests involving MC3T3-E1 cells showed that cell viability and mineralized matrix formation capacity is independent of the OGP peptide presence and it is more sensitive to the presence of silica and the treatment time with the conditioned culture media. The test in vivo, with CaP cements, with and without mesoporous silica and OGP, demonstrated that these cements have degraded and promoted increased bone formation during the first 15 postoperative days, with approximately 30% of the defect filled by newly formed tissue as well as higher density on the defects borders when compared to the control. However, the presence of OGP peptide was significant only during the first 30 days postoperative, but there was no statistical difference with silica cement and without this peptide. Furthermore, there was no difference between experimental groups and the control in the later study periods. According to the results, it is concluded that, among the cements studied, those with mesoporous silica particles and OGP peptide are the most promising for bone tissue repair, especially in the initial stages of healing due to its osteogenic potential. (AU)