Effect of temperature, pressure and depressurization rate on release profile of salicylic acid from contact lenses prepared by supercritical carbon dioxide impregnation

• Temperature and pressure in supercritical impregnation affect loading amount of salicylic acid.
• Salicylic acid loaded-amount has strong correlation with solubility in supercritical CO2.
• Slower depressurization after impregnation results in higher loaded-amount of salicylic acid.

Supercritical CO2 was used for the impregnation of a contact lens with salicylic acid. The supercritical CO2 impregnations were conducted at 308, 313 and 318 K from 9.0 to 15.0 MPa. The effects of the temperatures and pressures in the impregnation processing on the loaded amount of salicylic acid in the contact lenses were investigated. The loaded amounts of salicylic acid increase with the decrease of temperature and increase of pressures. It is found that the loaded amounts of salicylic acid in the lenses are correlated with the solubilities in supercritical CO2. The release profile of the salicylic acid from the contact lenses into the aqueous solution at 310 K for 8 h was studied by the released amounts measured using ultraviolet-visible spectroscopy. The higher temperature and lower pressure in the impregnation processing lead to the slow release rate of salicylic acid from the contact lenses. The release profiles were investigated by changing the depressurization rate from 0.06 to 0.18 MPa min−1. The lower depressurization rate results in the higher release rate of the salicylic acid from the lenses. The release profile of salicylic acid from the lenses into the aqueous solution is modeled by using kinetic constant and release exponent parameter. The modeled results suggest that the release from the lenses occurred by the superimpositions of Fickian controlled and swelling controlled releases.