Mesoporous MCM-41 materials seem adequate for their use as bioactive materials since they exhibit high specific surfaces constituted by siloxane and silanol groups, and present a high porosity, which are important conditions for bioactivity. Even though, no signs of bioactivity are shown after 2 months of in vitro assays, revealing the need of some other element such as cations that can act as defect generators, promoting the apatite layer nucleation. The addition of a small amount of glass to a MCM-41 material induce the formation of an apatite-like layer starting from the glass surface, covering after 7 days of assay the whole surface of the biphasic material MCM-41-glass.