Silicone Hydrogel Contact Lens Formation via Protonatable Diluent
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Solution Overview
Problem
Current methods for forming silicone hydrogels used in medical devices like contact lenses often result in articles that are not clear or sufficiently wettable without additional coatings, and require complex solvent and water exchange processes due to the limited miscibility of diluents with water.
Innovation Solution
A process involving the curing of a reactive mixture containing silicone-containing components, hydrophilic components, and protonated or protonatable diluents with specific Hansen solubility parameters, followed by aqueous processing to enhance water solubility and miscibility, resulting in ophthalmic devices with advancing contact angles less than 80°, thereby achieving clear and wettable surfaces without additional surface treatments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional diluents (alcohols like n-hexanol, ethanol, n-nonanol) are used to compatibilize silicone monomers and hydrophilic monomers, then the components can be mixed and polymerized, but the resulting articles are either not clear or not sufficiently wettable without additional coatings
Solution Approach 1:
The patent changes the chemical parameters of the diluent by selecting compounds with specific Hansen solubility parameters (δp between 2-7) and Kamlet alpha values (0.05-1.0). This parameter selection resolves the contradiction by finding diluents that simultaneously provide component compatibilization and produce clear, wettable articles without additional coatings
Solution Approach 2:
The patent uses composite diluent systems combining protonated diluents (carboxylic acids, phenols) with protonatable diluents (amines) in specific ratios. This composite approach allows the diluent mixture to fulfill multiple functions: compatibilizing hydrophobic silicone and hydrophilic components while also ensuring article clarity and surface wettability
2Ease of manufacture
If primary and secondary alcohols with more than four carbon atoms are used as diluents, then silicone-containing hydrogels can be formed, but clear wettable articles cannot be obtained when internal wetting agents are included, and additional compatibilizing components are required
Solution Approach 1:
The patent identifies diluents that perform multiple functions simultaneously: they act as compatibilizers for silicone and hydrophilic components, serve as internal wetting agents, and enable clear article formation. This multi-functionality eliminates the need for additional compatibilizing components, resolving the contradiction between ease of manufacture and device complexity
3Ease of manufacture
If compounds with specific Hansen solubility parameters and Kamlet alpha values are used as diluents, then silicone hydrogels can be formed, but they are not miscible with water, requiring complicated solvent and water exchange processes
Solution Approach 1:
The patent selects diluents with specific Hansen solubility parameters (δp between 2-7) and Kamlet alpha values (0.05-1.0) that balance two requirements: enabling silicone hydrogel formation and ensuring water miscibility. This parameter optimization allows direct aqueous processing without complicated solvent exchange, resolving the contradiction between ease of manufacture and productivity
4Ease of manufacture
If conventional diluents are used in polymerization, then silicone hydrogels can be formed, but additional surface treatments are required to achieve wettable surfaces
Solution Approach 1:
The patent incorporates wetting functionality into the diluent itself before polymerization occurs. By selecting diluents with appropriate solubility parameters and alpha values that provide inherent wettability, the surface treatment step is eliminated. The diluent pre-configures the surface properties during the polymerization process, resolving the contradiction between ease of manufacture and device complexity
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 enables the production of clear, wettable, and water-miscible ophthalmic devices, such as contact lenses, with improved repeatability and without the need for additional surface treatments, enhancing their usability and manufacturing efficiency.
Implementation Method 1
contacting the ophthalmic device with an aqueous solution which is capable of changing the Hansen solubility parameter, δp of the protonated or protonatable diluent to enhance water solubility
Implementation Method 2
said aqueous solution has a pH sufficient to deprotonate the protonated diluent, and form a deprotonated diluent which is water miscible
Data Source
Figure 1
AI summary
The present invention is a process for forming ophthalmic devices such as contact lenses, comprising the steps of curing a reactive mixture comprising at least one silicone-containing component, at least one hydrophilic component and at least one protonated diluent or protonatable diluent having a Hansen solubility parameter, dp between about 2 and about 7 to form an ophthalmic device having an advancing contact angle of less than about 80°; contacting the ophthalmic device with an aqueous solution which is capable of changing the Hansen solubility parameter, dp of the protonated or protonatable co-diluent to enhance water solubility and removing said diluent(s) with said aqueous solution.