Preparation And Properties Of New Mesoporous Bioactive Glass Material Of The Morphology And Controlled Components

Tissue engineering is an interdisciplinary field that applies the principles of engineering and the life sciences toward the development of biological substitutes that restore, maintain, or improve tissue function. In typical process for the creation of new tissue, cells place on or within scaffolds at first, and then cells attached to scaffolds are implanted and become incorporated into the body. Finally, new substitute is formed with the help of scaffold and cells. During this process, scaffold with three dimensional (3D) interconnected porous structures, which is facilitate for the growth of cells, plays an important role in these tissue engineering research. The potential applications are stimulating more and more research efforts on the synthesis of scaffolds with 3D porous structure and better bone-forming bioactivities.Bioactive glasses (BGs) with excellent bone-repairing ability and biocompatibility have been widely used in a variety of clinical application. The bioactivities of BGs are related to the composition, pore size, surface area and pore volume etc. However, the pores in conventional BGs are disordered and the pore sizes are not uniformly distributed, the pore volume is also relatively low. Recently, highly ordered bioactive glasses (MBGs) have been prepared by using non-ionic block copolymers as structure-directing through an evaporation-induced self-assembly (EISA) process. MBGs are more homogeneous materials than conventional BGs. MBGs with tunable pore size, high surface area and large pore volume show superior bone-forming bioactivities in vitro. By tuning the chemical compositions, calcination temperatures, and structure-directing agents, a series of MBGs with different compositions, calcination temperature, and pore sizes were obtained. The investigations of in vitro bioactivities of these MBGs were carried out in order to understand the correlation between the bioactivities and compositions or structures profoundly. Nevertheless, how to control the morphology of MBGs precisely is still unsolved problem, which is important for enlarging the applications in clinic medicine, such as bone tissue engineering and so on. At the same time, the mechanical properties of MBGs should be enhanced significantly, which is urgent to be solved.The aim of our study is to improve the varieties of properties of MBGs. On the one hand, we manage to obtain MBGs with different morphologies through precise control of the synthesis process. On the other hand, several types of metal oxides were added into the MBGs, which are anticipated to ameliorate the mechanical properties and biocompatibilities of MBGs.Mesoporous bioactive glass (MBG) fibers have been synthesized using a sol-gel process and then a high velocity spray process which should be carried out in the rational control of composition, acidity and water content. When the molar ratio of CaO is less than 35 % and the concentration range of HCl in solution is 2-4 mol/L, the ordered MBG fibers with excellent in vitro bioactivities can be successfully synthesized. Meanwhile, spinnable sols can be obtained and uniform MBG fibers can be synthesized in the condition of the molar ratio of H₂O/TEOS equals to -2.6. It is worth to mention that a 3D macro-structure with 50-100μm interconnected macropores is formed by randomly cumulate fibers in the spraying process. Sprague-Dawley (SD) rat osteoblasts have been cultured on MBG fibers. It is found that the MBG fibers have good cell biocompatibility and the 3D macro-structure is beneficial for cell attachment. It is anticipated that MBG fibers with controlled mesostructure and superior in vitro bioactivity are good candidates for future tissue-engineering scaffolds. Otherwise, different types of morphologies of MBGs with large scale production can be synthesized during spray-drying process. Spheres, sticks, slices can be obtained by controlling the concentration of solution and temperature. At low temperature (100℃), we can easily get the hollow spheres of MBGs, which own ordered mesostrucutre. When they were immersed in stimulated body fluid (SBF) for 24 h, a lot of hydroxyapatites (HA) appeared on the surface of materials. At the same time, sticks or irregular tubes of MBGs can be obtained at 180℃. But the mestructure of materials collapsed and little HA didn't appear on the surface of materials after soaking materials in SBF for 24 h.The chemical compositions of MBGs have been changed and new metal oxides were added for the improvement of mechanical properties and biocompatibility. For one thing, ordered quaternary mesoporous bioactive glasses (SiO₂-CaO-MgO-P₂O₅ and SiO₂-ZnO-MgO-P₂O₅) have been synthesized through EISA processes and nonionic block copolymer surfactants as templates. Quaternary MBGs still obtain a two-dimensional (2D) hexagonal lattice (p6mm) with the additions of a little metal-oxide (MgO or ZnO) (molar ratio: 1-5%). The rate of formation of HA in the MBG-Mg system is retarded as the amount of MgO increased when the materials exposed to SBF. Meanwhile, a whitlockite-like phase (β-(Ca,Mg)₃(PO₄)₂) appeared together with HA phase fomed on the surface of bioactive materials. For MBG-Zn materials, HA can not been found after immersion time increased to 48 h, even including the composition of MBG-1Zn (ZnO molar ratio: 1%). It is probably that zinc phosphate came into being in the in vitro bioactivity testing firstly which prevent the formation of calcium phosphate. For another, MBGs with titania compositions also can be synthesized by a sol-gel process in the presence of block copolymer templates. Incorporation of titania into silca may accelerate the rate of hydrolysis and condensation, with that effects the self assembly of materials. When the molar ratio of TiO₂ is over 5 %, materials doesn't possessed p6mm symmetry, as no diffraction peaks can be found in its XRD pattern. The results of ultraviolet-visible (UV-vis) analysis show that Ti exists as tetrahedral and hexahedral complex coordination compound rather than aggregation. The investigations of in vitro bioactivities of MBG-Ti were carried out and HA hardly appeared on the surface of MBG-Ti after soaking in SBF for 2 days, including MBG-1Ti, due to its less ordered mesostructure.In conclusion, novel MBGs with different morphologies and compositions can be synthesized successfully. As a new family of biomaterials, MBGs with superior bioactivity and satisfactory biocompatibility may be used as important bone-repairing materials in the future.