Applications of LCVD Coating on Silicone Contact Lens

APPLICATIONS OF LCVD COATING ON SILICONE CONTACT LENS 

The three key features of LCVD coating ideally suited for biomaterial surface, and the important balance between the bulk properties and the surface properties, could be best illustrated by examples of nanofilms of methane plasma polymer on a contact lens made of polydimethylsiloxane elastomer. Hence, some details of processing factors and their influence on the overall properties of the product are described in the following sections. 

Liquid water on one side of a silicone contact lens permeates through the lens by a solution-diffusion mechanism and evaporates on the other side quickly according to the permeability of water, whereas the solubility of water in silicone polymer is low [1]. The high water vapor permeability was speculated to be one of the reasons causing the suction cup effect that makes the lens stationary on one spot and tenaciously stick to the cornea this may damage the corneal epithelium and result in other complications. However, the high permeability per se cannot be the reason for the suction cup effect if the exterior surface is covered by the tear film, i.e., if there is no driving force for water permeation. 

The hydrophobicity of the surface prevents the wetting by tear and tends to expose dry surface of a contact lens. Therefore, rapid dehydration of the corneal tissues could occur, which could cause the damage of corneal epithelium. However, this explanation seems to be oversimplified in light of the adsorption of protein, which makes a hydrophobic surface wettable by tear fluid, as described in Chapter 26. Moreover, the highly hydrophobic surface characteristic of silicone rubber tends to encourage the deposition of protein and mucus of the tear on the surface of the lens. Lipids and lipid-soluble materials follow the same track and eventually penetrate into the bulk phase of the contact lens. Because of these undesirable factors, the use of silicone contact lenses of various chemical compositions and with surface treatments has not been successful but rather disastrous because of the interfacial characteristics of silicone contact lens on the cornea, which cannot be oflfset by these efforts. It indicates that more profound surface modification to cope with the problems rather than mere surface treatment is needed in capitalizing on the advantageous bulk properties of silicone polymers. 

The major problems associated with silicone rubber used for contact lens stem from the surface properties. The surface is hydrophobic and hinders the spontaneous 

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