Toray Develops Breakthrough Hydrophilic Coating for Contact Lenses

Toray Industries Inc. has developed a hydrophilic coating that improves the wettability¹ of silicone materials by more than 20 times. This breakthrough enables silicone to be made durably hydrophilic for contact lenses and numerous other medical device applications.

Manufacturers employ silicone materials extensively in medical devices such as contact lenses and catheters due to their flexibility and biocompatibility. The downside is that silicone is hydrophobic, limiting its use in applications requiring wettability or lubricity. In contact lenses, this can cause dryness and foreign-body sensations. In catheters, it can impair maneuverability and increase blockages. Although approaches to improving the hydrophilicity of silicone through surface modification or material redesign have been explored, these approaches can complicate manufacturing and pose challenges in achieving sufficient hydrophilicity and clinical durability.

Toray overcame these challenges by tapping its proprietary polymer molecular design and precision polymerization technologies to innovate a hydrophilic polymer with a high affinity for silicone. The polymer’s self-assembly² properties make it easy to form a highly durable, nanometer-scale hydrophilic coating on silicone surfaces.

The thin layer imparts hydrophilicity while minimizing the impact on the silicone’s inherent physical properties. By bringing the hydrophilic polymer into contact with the surface of a commercially available hydrophilic silicone hydrogel and applying heat, a hydrophilic coating layer approximately 20 nanometers thick can be formed. As a result, wettability improved by more than 20 times compared with uncoated surfaces, with the coefficient of friction decreasing by approximately 90%. The coating also demonstrates high durability even after rubbing.

Applying this hydrophilic coating to contact lenses is expected to improve comfort during extended wear. In addition, the coating has been shown to suppress the adhesion of biological substances on silicone elastomers,³ and its application to stents and catheters is anticipated to reduce blockage while improving maneuverability through enhanced lubricity. Toray will actively promote this coating material and expand its application to a wide range of medical device materials.

References
¹ Wettability is the time between lifting a material from a phosphate-buffered solution and breaking part of the liquid film on a surface. Toray’s coating delivers more than 20 times the wettability of commercially available silicone hydrogels.
² In the self-assembly process, polymers aggregate to form stable structures.
³ RJ Cho et al., “Implantation of a Hydrophilic Polymer Coated Silicone Airway Stent Improves Airway Injury and Mucostasis in a Porcine Model: A Pilot Study.” Archives in Respiratory & Pulmonary Medicine. 1(1): 2022.