Effect of different water-soluble additives on water sorption into silicone rubber.

The ability of ethylene glycol; glycerin; polyethylene glycols 200, 400, and 6000; polysorbate 80; and lactose dispersed in silicone rubber, to promote water sorption into the polymer was investigated in water and in isotonic (pH 7.4) phosphate buffer. Polyethylene glycols 200 and 400, lactose, and, especially, glycerin were effective water carriers. Marked differences in the kinetics of rubber swelling were observed, depending on the carrier. The swelling patterns relative to ethylene glycol, glycerin, and polyethylene glycol 200 showed a maximum due to significant leaching of these additives from the polymer. Steady swelling degrees were afforded by polyethylene glycols 400 and 6000 and by polysorbate 80. The interdependent processes of polymer imbibition and carrier release were speeded up without altering their kinetic patterns by increasing the initial surface-volume ratio of the devices. A proportionality resulted between maximal swelling and initial carrier concentration, although the swelling patterns were substantially unaffected by this variable.