Class II Hybrid Materials

On the basis of the sol-gel process, much more attention has been paid to silicate-containing Class II hybrids, also referred to as organically modified silicas, ormosils. In this section, the synthesis of some of the most characteristic ormosils for bone and dental applications are described. 

The sol-gel synthesis of siloxane-based hybrid organic-inorganic implants usually involves di- or trifunctional organosilanes co-condensed with metal alkoxides, mainly Si(OR)4 and Ti(OR)4. As we will see in this section, the incorporation of Ca salts is a common strategy to provide bioactivity at the systems. Each of these components has specific roles that will be reviewed and discussed. 

Poly(oxyethylene)-Si02 ormosils have been prepared as an approach to the preparation of biologically active polymer-apatite composites. For this purpose, Yamamoto et al. [72] obtained these Class II hybrids from triethoxysilyl-terminated poly(oxyethylene) (PEG) and TEOS by using the in situ sol-gel process. After being subjected to the biomimetic process to form the bone-like apatite layer, it was found that a dense apatite layer could be prepared on the hybrid materials, indicating that the silanol groups provide effective sites for CHA nucleation and growth. 

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In the last decades, silicate sol-gel chemistry has predominantly been based on alkoxysilanes, which provide substantial flexibility in preparation. Moreover, incorporation of a broad range of organic functionalities in alkoxysilanes has advanced the development of class II hybrid materials, that is, materials with a covalent link between organic and inorganic moieties. By varying the structure of this organic functionality or by combining alkoxysilanes with other... 

While polymers most commonly consist of carbon, nitrogen and oxygen, hybrid materials containing metals or other elements represent an important class of materials [76-78]. Hybrid materials too have been used as hyperbranched grafts. Two examples of such materials are described here. The first is a polysiloxane graft. The second is a dendritic coordination polymer based on a thermally and oxygen stable Pd(II) pincer complex [79]. 

Class II Tin-Based Hybrid Materials Prepared From Alkynyltin Precursors... 

Hydrolysis-condensation of organically bridged o , )-bis(trialkynyltin) compounds 2 was the second route investigated to prepare class II tin-based hybrid materials. At first, hydrolysis conditions of 2 were determined to get transparent gels. As gelling of neutral solutions is very slow, acidic or basic conditions were employed to accelerate the process. Whatever the compound 2 and the water amounts used, base-catalyzed... 

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