Synthesis and in vitro bioactivity of ordered mesostructured bioactive glasses with adjustable pore sizes

Four ordered mesoporous bioactive glasses (MBGs) with the same composition and hexagonal mesostructure but adjustable pore diameters (1.9, 3.4, 5.0, 6.4 nm, denoted MBGs A-D, respectively) have been prepared for the first time by using different structure-directing agents as templates. Their in vitro bioactivities have been carefully studied by investigating the formation of hydroxycarbonate apatite (HCA) on MBG surfaces. MBG A with the smallest pore diameter (1.9 nm) shows the fastest nucleation rate of HCA, however, the total amount of calcium phosphate (CaP) species deposited after immersing in SBF for 2 days is the smallest among four MBG samples under study. The in vitro bioactivity sequence of MBGs with different pore sizes is determined to be MBG C ≈ D > B > A in terms of the total amount of CaP species deposition. MBG A has the highest surface area and thinnest wall thickness, which favor the rapid release of Ca and P species from the wall framework and thus fasten the nucleation rate. Nevertheless, the small pore of MBG A may be easily blocked by the nucleates, which is disadvantageous for the subsequent ionic diffusion and crystal growth of HCA. Our results have indicated that the fast nucleation does not necessarily correlate to a high amount of HCA deposition, which is important in the evaluation of the in vitro bioactivity of BG-related biomaterials. By understanding the relationship between the pore structure and the in vitro bioactivity, it is anticipated that MBGs with controllable mesostructure and enhanced bioactivity can be designed and fabricated.