Dong Tian

Biodegradable and biocompatible inorganic–organic hybrid materials. I. Synthesis and characterization†

The hydroxyl or vinyl end-groups of linear or three-arm star-shaped poly(e-caprolactone) (PCL) chains have been derivatized into triethoxysilane groups reactive in the sol-gel process. New transparent hybrid materials that combine tetraethylorthosilicate (TEOS) and PCL known for biodegradability and biocompatibility have accordingly been prepared. The sol-gel process is, however, limited by the early vitrification of the reactive system. However, thermal posttreatment can overcome these diffusional and/or kinetic limitations as assessed by a set of analytical methods. The thermal stability of PCL is improved by incorporation into the silica network. Conversely, the thermal stability of the ceramer depends on the effective PCL content. The extent of PCL incorporation into the silica network depends on PCL molecular weight, number, and reactivity of the PCL functional groups. IR spectroscopy has shown that hydrogen bonding occurs between the ester groups of PCL and residual OH groups of the silicate component.

A new poly(ε-caprolactone) containing hybrid ceramer prepared by the sol-gel process

A new inorganic-organic hybrid material, known as ceramer, has been prepared by the sol-gel process. α, ω-Hydroxyl poly(e-caprolactone) (PCL) has been used as an organic reagent, as such or after conversion of the hydroxyl end-groups into triethoxysilane end-groups. The novelty has to be found in the biocompatibility and biodegradability of the organic constitutive component. Since the hydroxyl end-groups of PCL are less reactive than the triethoxysilane counterparts, the preliminary reaction of the hydroxyl end-groups with 3-isocyanatopropyltriethoxysilane is recommended for decreasing the gelation time and the amount of PCL extractable from the final hybrid material. In this respect, it has been observed that the amount of PCL incorporated into the network is limited by the early vitrification of the reactive system. This drawback can be alleviated by curing the sample at a high enough temperature (100°C). TEM observations have shown that the organic and inorganic phases are intimately mixed when the weight composition in SiO2 and PCL is close to 50%.

Biodegradable and biocompatible inorganic-organic hybrid materials : 4. Effect of acid content and water content on the incorporation of aliphatic polyesters into silica by the sol-gel process

Abstract The extent of poly e-caprolactone (PCL) incorporation into silica networks prepared by the sol-gel process depends on the HCl:tetraethoxysilane (TEOS) molar ratio and the H2O:TEOS molar ratio, as well. The PCL incorporation increases with the concentration of the acid used as the catalyst. Dynamic mechanical analysis (DMA) indicates that increasing the acid concentration or decreasing the water content results in a higher glass transition temperature for the organic component in the hybrid materials, whereas the modulus does not change significantly. Small-angle X-ray scattering (SAXS) data agree with a nanoscopic phase separation of the two constitutive components: the organic polymer and the silica network. The characteristic length of this two-phase structure increases with acid content (except for the lower HCl:TEOS molar ratio of 0.05) and with water content (except for the higher H2O:TEOS molar ratio of 2.0). The structure of the PCL/SiO2 interface is mass fractal and the structure is more open when the acid content is lower or the water content higher.

Biodegradable and biocompatible inorganic-organic hybrid materials. 2. Dynamic mechanical properties, structure and morphology

Abstract Dynamic mechanical properties, structure and morphology of tetraethoxysilane/poly(e-caprolactone) (TEOS/PCL) hybrid materials have been analysed by dynamic mechanical spectroscopy, small-angle X-ray scattering, transmission electron microscopy, and image analysis. The experimental observations agree with a microscopic phase separation of the two constitutive components: the organic polymer and the silica network. The effect of the PCL functional end-groups, the number of functional end-groups per PCL chain, the PCL molecular weight and content, and the curing conditions have been studied on the structure and properties of the hybrid materials. Finally, phase morphology has proved to be co-continuous, at least when the weight composition is close to 50% for each component (SiO2 and PCL), with a characteristic length between the PCL and silica phases of ca. 5 nm, as estimated by image analysis of transmission electron micrographs.

Porous Silica Obtained from Biodegradable and Biocompatible Inorganic-Organic Hybrid Materials

Porous silicas have been successfully prepared from poly(ε-caprolactone) (PCL)-silica hybrid materials based on the template approach. The final texture of the porous silica can be tailored by the PCL template, i.e., molecular weight and molecular weight distribution, content, type and number of reactive end-groups per chain. Porosity has been investigated by nitrogen adsorption-desorption technique and small angle X-ray scattering (SAXS).