Contact Lens Oxygen and Water Permeability Control
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Solution Overview
Problem
Contact lenses made of silicone rubber (PDMS) experience 'sticking' issues due to high water permeability, leading to adherence to the cornea, which is not effectively addressed by current designs or surface treatments, and no material has been found that balances high oxygen transmission with low water transmission for comfort and safety.
Innovation Solution
A contact lens with a predetermined thickness or layered configuration to reduce water transmissibility while maintaining minimum oxygen transmissibility, using materials like polydimethylsiloxane and Amorphous Teflon in a 'sandwich' configuration to optimize oxygen and water vapor permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PDMS material is used for contact lens, then oxygen permeability is improved (more than twice the permeability of competitive materials), but water transmissibility is too high causing lens sticking and adherence to cornea
Solution Approach 1:
The lens is divided into multiple functional layers: a PDMS layer for high oxygen permeability and a hydrophilic polymer layer for controlled water transmissibility. This segmentation allows each layer to perform its specialized function, resolving the contradiction between oxygen transmission and water management.
Solution Approach 2:
The invention uses composite materials combining PDMS (for oxygen permeability) with hydrophilic polymers (for water control and surface wetting). This composite structure achieves both high oxygen transmission and controlled water transmissibility, preventing lens sticking while maintaining corneal health.
2Reliability
If lens thickness is reduced to support corneal health, then oxygen transmissibility is improved, but lens durability and handling are worsened
Solution Approach 1:
The composite structure combines thin PDMS layer (for oxygen transmission) with hydrophilic polymer layer (for mechanical strength and durability). This allows the lens to be thin enough for adequate oxygen transmissibility while the hydrophilic layer provides the necessary mechanical properties for handling and durability.
3Reliability
If lens thickness is reduced in hydrogel lenses, then oxygen transmissibility is improved, but dehydration occurs leading to lens shrinkage and poor wetting
Solution Approach 1:
The lens is segmented into a PDMS layer (for oxygen permeability) and a hydrophilic polymer layer (for water retention). The hydrophilic layer maintains lens hydration and prevents dehydration even when the overall lens is thin, while the PDMS layer ensures adequate oxygen transmission to the cornea.
4Ease of operation
If surface treatment is applied to reduce wetting angle, then lens comfort is improved, but the underlying water transmissibility issue remains unresolved
Solution Approach 1:
The invention extracts the water transmissibility control function from the surface treatment and places it in the bulk hydrophilic polymer layer. This addresses the root cause of lens adherence by controlling water transmission through the lens structure itself, rather than just modifying the surface, while surface treatment still provides comfort benefits.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces water transmissibility to prevent lens adherence while maintaining sufficient oxygen delivery for corneal health, addressing the long-standing issue of 'sticking' and dehydration in PDMS lenses.
Implementation Method 1
D being diffusivity (cm2/sec), a measure of how fast the oxygen moves through the material
Implementation Method 2
PDMS has extremely high permeability to oxygen and water vapor
Data Source
AI summary
A contact lens constructed to limit the water transmissibility of at least one area of the lens while maintaining at least a minimum oxygen transmissibility. The water transmissibility maximum and oxygen permeability minimum are achieved by a predetermined lens thickness of a single lens material or by the use of two or more material layers.