General properties of silated hydroxyethylcellulose for potential biomedical applications

The general properties of hydroxyethylcellulose (HEC) grafted with 3-glycidoxypropyltrimethoxysilane (GPTMS) or 3-glycidoxypropylmethyldiethoxysilane (GPDMS) were studied for potential biomedical applications. The graft involved a Williamson reaction between the free hydroxyl function of HEC and the epoxy function of the two silanes. As the grafted silanes are in ionic form (sodium silanolate), this product remains in gel form at basic pH (>12.3) in aqueous solution. When pH decreases, sodium silanolate is transformed into silanol (2 or 3 silanol functions are carried by silicon, depending on the silane grafted). The silanols interreact, and the gel is transformed into a cross-linking form at room or body temperature. Studies were conducted to optimise this product for specific uses. Steam sterilization was used to compare self-hardening as a function of the silane grafted. Our previous work indicated that HEC grafted with GPTMS has good reactivity, but requires high pH for dissolution, whereas dissolution occurs at lower pH with GPMDS. The rate of silanol condensation for silated HEC was then determined as a function of pH, temperature, type of silane, and the percentage grafted. Condensation rates were ascertained by the viscosity method, and gels were neutralized by different solutions to obtain buffered forms at various pH. The time required to obtain 10(5) mPa x s, with an initial state of 2500 mPa x s, was then calculated. Condensation was catalysed in acid or basic medium at a lower rate at pH 5.5-6.5, and a temperature rise increased the condensation rate, regardless of the pH or silane studied. Silanetriol was more reactive than silanediol. However, as HEC lost considerable viscosity after sterilization, further studies will be conducted to develop new polysaccharides grafted with silane.