Cerasomes: A New Family of Artificial Cell Membranes with Ceramic Surface

Abstract

Organic–inorganic hybrid materials have attracted much attention in the field of materials science because of their great potential for use in a wide variety of applications through fusion of individual organic and inorganic properties (Schmidt, 1994; Mackenzie, 1994; Sanchez et al., 2001; Schottner, 2001). Up to the present time, various kinds of material combinations and synthetic strategies have been developed. The sol–gel method is one of the most powerful techniques to prepare hybrid materials and has provided moderate preparative conditions for the construction of inorganic oxide frameworks that are derived from hybrid materials (Sakka, 2005). In particular, the preparation of novel materials with organized nanostructures is a fascinating research subject in the field of hybrid materials (Ulman, 1996; Ozin, 2000; Dabbs & Aksay, 2000; Scott et al., 2001; van Bommel et al., 2003; Colfen & Mann, 2003). These approaches are generally based on sol–gel techniques that utilize the presence of molecular assemblies as templates, such as rod-like micelles (Yanagisawa et al., 1990; Kresge et al., 1992; Inagaki et al., 1999), block-copolymers (Kramer et al., 1998; Melosh et al., 1999; Ryoo et al., 2000), microemulsions (Sims et al., 1998; Feng et al., 2000), organogels (Ono et al., 1998), cast films of bilayer membranes (Sakata & Kunitake, 1990) and bilayer vesicles (Hubert et al., 2000). Thus, the properties of nanohybrids depend on their nanostructures, especially the structure at the interface between the inorganic and organic components. Pre-organization by employing non-covalent interactions between an organic template and an inorganic precursor is known to be very important. However, the interface between the organic and inorganic components in these hybrids seems to be structurally ambiguous and more difficult to control at the molecular level than the individual component structures. Additionally, most of these materials are composed of inorganic components alone, and the organic portions are simply employed as templates. In contrast, a novel class of layered organic–inorganic nanocomposites composed of amphiphilic molecules with a covalent bond between the silicate and the surfactant has been developed in recent years (Huo et al., 1996; Shimojima et al., 1997; Moreau et al., 2001; RuizHitzky et al., 2002; Zhang et al., 2004). These materials offer great potential because the hybrid precursors can form three-dimensional networks during the self-assembling process, whereby inorganic layers and organic moieties are covalently linked with stable Si–C bonds. We recently developed cerasomes, a novel type of organic–inorganic nanohybrid, through a combination of sol–gel reactions and self-assembling of lipidic organotrialkoxysilanes in aqueous media to form vesicles covered with silicate surfaces (Katagiri et al., 1999). A