A Study on the Manufacturing of Photochromic Contact Lenses using Spiropyran Derivatives

Abstract

Purpose: The purposes of this study are to synthesize spiropyran derivatives for the development of photochromic contact lens using both casting-mould and sandwich processes and to investigate their photochromic and physical properties. Methods: The casting-mould method was performed by a manufacturing process in which monomers including spiropyran, HEMA, EGDMA, NVP and MMA were introduced into a solid mold and polymerized to solidify. The sandwich process producing triple-layered structures started with the 1st-copolymerization of HEMA, EGDMA, NVP and MMA. The resulting substrate was coated with a mixture of binder and spiropyran derivative, followed by 2nd-copolymerization with the same monomer ratio as the 1st-copolymerization process. The water content, contact angle, and optical properties of the manufactured lenses were investigated. The photochromic properties of the lenses such as color change behavior and absorbance were investigated under UV-light exposure for 1 min or in dark-room for 10 min. Results: The contact lenses prepared by casting-mould method showed water content of 35.21% and contact angle of 70.80° with a non-photochromic property. For the sandwich process, the lenses exhibited water content of 35.21% and contact angle of 70.80° with a good photochromic property. The lenses showed deep purple in color after exposure of UV light while they became colorless in dark-room. Conclusions: The contact lenses prepared by casting-mould method showed a non-photochromic property. The application of sandwich process exhibited a photochromic behavior without changes in the water content and contact angle of the lenses, suggesting that this method has practical and potential applications in contact lens industry.