Effect of temperature and pH on contraceptive gel viscosity.

The rheological properties of four commercially available spermicidal gels (two polyacrylic acid derivatives and two carboxymethylcellulose based) and their dilutions with a vaginal fluid simulant (pH 4.2) and a semen simulant (pH 7.7) were measured at 25 degrees C and 37 degrees C over a biologically relevant range of shear rates. All four gels were shear thinning with temperature-dependent rheological properties. The two types of gels responded differently to dilution. The rheological properties of the polyacrylic acid derivative gels were strongly dependent on the type of diluent used. Their viscosities after dilution with the semen simulant were 100 times greater than after comparable dilutions with the vaginal fluid simulant, this effect being due primarily to the higher pH. The cellulose gels did not exhibit such an effect. These results suggest that the polyacrylic acid and cellulose gels interact differently with the vaginal environment in vivo. Such differences could lead to differences in the extent and durability of epithelial coating.