Contact Lenses: Silicone Hydrogels

Contact lenses that have the ability to maintain a continuous clear film, sustain normal hydration, high permeability to oxygen and ion movement, and are comfortable for the user are in high demand within the ocular environment. Oxygen permeability in a contact lens is derived from the air, due to the fact that the cornea has no direct blood supply; reduced oxygen from contact lenses can result in serious eye irritation and sight threatening complications.

Current work in Bio-materials is focusing on utilizing silicone hydrogels as the design of contact lenses, due to the high oxygen permeability of polysiloxanes, along with their hydrophobic and rubbery characteristics. Through incorporating siloxane groups with large R groups into a polymer network, significant free volume can be created, to allow a high permeability to oxygen and gases. In addition, PDMS, a siloxane group with an n value greater than 5, serves as cross linking agents, linking the polymer chains together, which increases the modulus of the hydrogel proportionally to the number of cross links and the distance between cross links. 

This topic is interesting to me because I am currently conducting research in a Bio-materials lab on producing tear bacteria resistant silicone contact lenses through developing and utilizing a standard formulation of silicone contact lenses and then applying protein resistant polymer coatings to the hydrogel. 

Link to the paper: 

Contact Lenses: Silicone Hydrogels Paul C. Nicolson, Jurgen Vogt, Encyclopedia of Biomaterials and Biomedical Engineering

http://www.tandfonline.com/doi/abs/10.1081/E-EBBE-120007274#.UnHaDflDW6w