Multifunctional Nanocomposites Based on Mesoporous Silica: Potential Applications in Biomedicine

In the last decade, significant research efforts were devoted to obtaining materials with welldefined nanostructures for a wide range of applications (Hamley, 2003; Soler-Illia et al., 2002; Paul & Sharma, 2006). Mesoporous silica materials like M41S, HMS, SBAn, FSM, and MSU, among others, are a fairly new type of material that has pores in the mesoscopic range of 2–50 nm (Wan et al., 2007). The characteristic features of ordered mesoporous materials are their monodispersed and adjustable pore size in an inert and biocompatible matrix with an easily modified surface. Procedures to obtain ordered mesoporous silicates rely on the micelle-forming properties of a surfactant, whose chemical composition, size, and concentration control the structural dimensions of the final material (Zhao et al., 1998). In most cases, ionic and neutral surfactants have been employed as templates to direct mesophase formation based on the electrostatic and hydrogen-bonding interaction. Polymerization of the inorganic precursor and further removal of the surfactants result in a rigid silica shell that delimits the structural shape of the mesopores. In such processing routes, the resultant material presents an ordered hexagonal arrangement of unidirectional mesoporous channels and a high surface area, above 800 m2/g, depending on the synthesis conditions. Figure 1 shows the scheme of structure formation mediated by inorganic mesoporous structure-directing agent. The intrinsic uniform porous structure of this class of compounds with their large specific surface area and pore volume, associated with surface silanol groups, give these materials a significant potential for applications as matrices of many chemical species, such as organic molecules, metals, and polymeric materials. The combination of different materials to obtain nanocomposites is of great research interest due to their potential medical applications, such as tissue engineering, drug delivery devices, and hyperthermia, among others (Vallet-Regi et al., 2008; Souza et al., 2010). In this work, the recent developments in nanocomposites based on mesoporous materials (also referred to as hybrid materials) will be overviewed. Two categories of nanocomposites