From Nanocomposite to Blend Hybrid pHEMA/SiO<sub>2</sub> Hydrogels: The Effect of Chemical Coupling on Thermal Stability, Swelling and Bioactivity

Abstract

Hybrids of poly(2-hydroxyethylmethacrylate) (pHEMA), a polymer widely employed for biomedical applications, and silica gel, exhibiting a well-known bioactivity, were produced by in- situ sol-gel synthesis using two different procedures. Only Tetraethylortosilicate (TEOS) was used as inorganic precursor in the former, whereas both TEOS and methacrylate monomers bearing an alkoxysilyl unit, prepared by Michael addition of 2-hydroxyethylmethacrylate (HEMA) to 3-Aminopropyltriethoxysilane (APTS), were employed in the latter. A final concentration of 30% w/w of silica gel to the mass of polymer was obtained in both procedures. The samples prepared through the former route will be referred as T03, those obtained the latter route will be named as AT03. AT03 hybrids are optically transparent, whereas T03 samples show phase separation between the polymer and the silica gel. Synthesis procedure strongly affects hybrids structure: the silica phase mean diameter changes from 500 nm (T03) to about 50 nm when the coupling hybrid monomer is employed (AT03). Both hybrids keep swelling properties and show improved thermal stability than the as-prepared polymer, indeed AT03 exhibits the highest decomposition temperature and T03 show the highest swelling ratio. Moreover, silica gel has hydroxyapatite formed on both hybrids surface, when soaked in SBF.