Silicone Hydrogel Reaction Kinetics for Clear, Low-Modulus Lenses
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Solution Overview
Problem
Existing silicone hydrogel contact lenses face challenges with poor wettability, high modulus, poor clarity, hydrolytic instability, and high cost, despite efforts to incorporate poly(N-vinylpyrrolidone) and acyclic polyamides, which require custom compatibilizing components and result in hazy polymers with low oxygen permeability.
Innovation Solution
A silicone hydrogel formulation with controlled reaction kinetics, using a reaction mixture comprising slow-reacting hydrophilic monomers and fast-reacting silicone-containing components, photocuring or ebeam irradiation to achieve a balance of properties including wettability, clarity, and oxygen permeability without surface treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If polyfunctional silicone monomers or macromers are used as crosslinking agents to improve wettability by incorporating NVP, then wettability is improved, but the modulus of the final polymer increases
Solution Approach 1:
The patent changes the reaction kinetics parameters by using a monofunctional silicone monomer with a faster reaction rate than NVP. This kinetic parameter change allows the silicone component to polymerize first, forming a network that can then incorporate NVP without requiring polyfunctional crosslinking agents, thus maintaining low modulus while achieving wettability
Solution Approach 2:
The patent applies preliminary action by having the silicone-containing monomer react first before NVP is fully incorporated. This sequential reaction approach, enabled by differential reaction rates, allows the silicone network to form initially, preventing the need for high crosslinking densities that would increase modulus
2Use of energy by moving object
If conventional silicone hydrogel formulations are used to achieve high oxygen permeability, then oxygen permeability is improved, but clarity deteriorates due to haziness
Solution Approach 1:
The patent changes the reaction kinetics parameters to control the polymerization sequence. By using a monofunctional silicone monomer that reacts faster than NVP, the system achieves a different molecular structure formation pattern that simultaneously provides high oxygen permeability through silicone network formation and good clarity by avoiding the hazy polymer structures associated with conventional formulations
3Stability of the object's composition
If polyfunctional crosslinking agents are used to form silicone hydrogels, then the polymer structure is stabilized, but the manufacturing complexity increases due to need for custom compatibilizing components
Solution Approach 1:
The patent extracts the complex polyfunctional crosslinking agents and custom compatibilizing components from the formulation. Instead, it uses a simple monofunctional silicone monomer that relies on reaction kinetics control rather than molecular structure complexity to achieve the desired polymer network formation and stability
Solution Approach 2:
The patent replaces expensive, custom-manufactured polyfunctional crosslinking agents with a commercially available monofunctional silicone monomer. This substitution reduces manufacturing complexity and cost while achieving the necessary polymer structure through kinetic control rather than molecular design
4Illumination intensity
If anionic monomers such as methacrylic acid are added to reduce haziness, then clarity is improved, but hydrolytic stability deteriorates
Solution Approach 1:
The patent converts the potential harm of using additional monomers (which could compromise hydrolytic stability) into a benefit by relying on the inherent hydrolytic stability of the silicone monomer and HEMA. The reaction kinetics control eliminates the need for anionic monomers like methacrylic acid, maintaining both clarity and hydrolytic stability simultaneously
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 process results in clear, hydrolytically stable silicone hydrogels with low modulus and high oxygen permeability, processed easily and without the need for surface modification, achieving desirable properties such as haze below 50%, advancing contact angles less than 80°, and oxygen permeability greater than 70 barrers.
Implementation Method 1
The reaction mixture is photocured to form the silicone hydrogel
Implementation Method 2
The reaction mixture is photocured via ebeam irradiation
Data Source
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AI summary
The present invention relates to a silicone hydrogel and a process for forming the silicone hydrogel.