Preparation Of MBG/TiO₂ Nanorod Films And Their Biological Evaluations

The surface modification technology through micro-nanostructure is adopted to effectively accelerate bone tissue growth at the interface between metal implants and the host bone tissue (osseointegration). In our previous studies, TiO2 nanorod films have shown good cellular responses, however, the structure features of nanorod films limit the loading capacity and releasing property of biological molecules. In this work, mesoporous bioglass (MBG) with good loading and releasing ability was used to be incorporated into TiO2 nanorod films in order to assemble MBG/TiO2 nanorod films with controlled exposure height of nanorods, and such films are expected to have not only excellent cellular responses but also good loading and releasing ability. The main achievements or results in this work are described as follows:MBG/TiO2 nanorod films were prepared respectively by hydrothermal method and sol-gel method, and MBG could be well incorporated into medium-density TiO2 nanorod films for building a micro-nanostructure with controlled exposure height of nanorods. When TiO2 was introduced into the compositions of MBG (T-MBG), the stability of T-MBG with tipical characteristics of mesoporous structure could be obviously improved in phosphate buffer. Moreover, the degree of MBG incorporation was effectively controlled through changing MBG precursor sol concentration so that exposure height of nanorods could be adjusted from 10 nm to 300 nm.The loading and releasing behaviors of MBG/TiO2 nanorod films were measured and analyzed in a dynamic way. MBG incorporation could obviously restrain initial burst release behaviors of small molecules (vancomycin hydrochloride), which showed that 1-hour cumulative release amount reduced from 71% to 48%. Also, MBG incorporation could effectively improve loading capacity and sustained release ability of macromolecules (human bone morphogenetic protein-2, rhBMP-2), which showed that loading amount increased nearly 3.3 times from 101 ng/cm2 to 435 ng/cm2, while release time of 90% rhBMP-2 extended from 6 days to 25 days. Furthermore, dynamic analysis indicates that improved loading and releasing behaviors are mainly attributed to existence of more biological molecules in the pore channels of MBG and difficulty in diffusion of the molecules existing in tortuous pore channels.The cellular responses of MBG/TiO2 nanorod films were evaluated. MBG incorporation could further improve cell compatibility, the proliferation of preosteoblast increased to about 1.5 times of TiO2 nanorod films. Additionally, MBG/TiO2 nanorod films with loading rhBMP-2 could effectively improve differentiation and mineralization abilities of mesenchymal stem cells, the cellular differentiation level and mineralization degree respectively were enhanced to 2 times and 1.3 times of the films without loading rhBMP-2, demonstrating that rhBMP-2 biologically functioned well. These results suggest that the surface micro-nanostructure with appropriate exposure height of TiO2 nanorods can provide a quasi-three-dimension microenvironment for cell growth, strengthen interactions of cells with the surfaces, activate BMP-2 signal pathway and finally accelerate osteogenesis differentiation.The present MBG/TiO2 nanorod films with rapid osteogenesis through the double effects of micro-nanostructure and biological molecules delivery could provide an effective way to improve the osseointegration ability of metal implants.