Enhanced impregnation of hydrogel contact lenses with salicylic acid by addition of water in supercritical carbon dioxide

An impregnation of soft contact lenses with salicylic acid in supercritical CO2 was enhanced by addition of water. The supercritical CO2 impregnations including water were conducted at 40 °C and 11 MPa with 0.34-2.18 g L−1 of water amount. The contact lenses impregnated in supercritical CO2 including water result in the high loading-amount of salicylic acid compared with those without water. The higher amount of water in supercritical CO2 impregnation gives the slower release of salicylic acid from the lenses. The impregnation efficiency of the contact lenses with salicylic acid in supercritical CO2 including water was evaluated from the loading-amount in the lenses and the concentration in the supercritical CO2 phase. The efficiencies of supercritical CO2 impregnation including water are higher than aqueous solution impregnation. The impregnation efficiency of the lenses increases with the water amount in the supercritical CO2 impregnation processes. The amount of salicylic acid loaded in the lenses also increases with the amount of water dissolved in supercritical CO2. A release model using kinetic constant and exponent parameter was applied for modeling the release profile of salicylic acid from the contact lenses. The release modeling suggested that the release from the contact lenses resulted from the superimposition of Fickian controlled and hydrogel swelling controlled releases.