Silicone Hydrogel Contact Lens Surface Modification via Two-Stage Polymerization
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Solution Overview
Problem
Existing methods for manufacturing silicone-containing copolymers with hydrophilic surfaces face challenges such as the need for post-processing like plasma treatment or graft polymerization, and the use of high-molecular-weight hydrophilic polymers, which complicate the manufacturing process and may lead to reduced hydrophilicity due to solvent extraction, especially when using polypropylene molds.
Innovation Solution
A method involving a two-stage polymerization process using a monomer solution with specific silicone, hydrophilic, and crosslinkable monomers, along with a polymerization initiator with a 10-hour half-life temperature between 70°C and 100°C, within a polypropylene mold to create a hydrophilic surface without the need for high-molecular-weight hydrophilic polymers or post-processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a polypropylene mold is used for manufacturing silicone-containing copolymer contact lenses, then the manufacturing cost is reduced and ease of molding is improved, but the lens surface becomes highly hydrophobic causing lipid adhesion and reduced water wettability
Solution Approach 1:
The patent applies preliminary action by incorporating a hydrophilic monomer into the monomer solution before polymerization. This hydrophilic monomer preferentially orients toward the mold surface during the polymerization process, forming a hydrophilic surface layer on the lens before it is even removed from the mold. This pre-establishes the desired surface property without requiring subsequent post-processing steps.
2Manufacturing precision
If post-processing methods like plasma treatment or graft polymerization are applied to impart hydrophilic property to the lens surface, then water wettability is improved, but the manufacturing process complexity and number of steps increase
Solution Approach 1:
The patent merges the formation of the contact lens with the formation of its hydrophilic surface into a single integrated polymerization process. By incorporating the hydrophilic monomer into the base monomer solution before molding, both the lens structure and surface property are created simultaneously in one step, eliminating the need for separate post-processing operations.
Solution Approach 2:
The patent extracts the surface modification step from the overall manufacturing process. Instead of applying plasma treatment or graft polymerization after lens formation, the hydrophilic surface is created inherently during the initial polymerization by selecting appropriate monomer composition, effectively removing the need for complex post-processing equipment and steps.
3Manufacturing precision
If high-molecular-weight hydrophilic polymer is incorporated into the material as internal moisturizer, then surface hydrophilicity is achieved without post-processing, but the polymerization process becomes more complex and solvent extraction may remove the hydrophilic polymer
Solution Approach 1:
The patent applies parameter changes by carefully controlling the molecular weight, concentration, and chemical structure of the hydrophilic monomer used. By optimizing these parameters, the hydrophilic monomer remains sufficiently small to be incorporated into the polymer network without being extracted by solvents, while still providing adequate surface hydrophilicity. This differs from using high-molecular-weight polymers that are more susceptible to extraction.
4Reliability
If alcohol extraction is performed to remove unpolymerized monomer and oligomer from the polymer, then extraction efficiency is improved, but high-molecular-weight hydrophilic polymer may be extracted along with unreacted monomer
Solution Approach 1:
The patent applies parameter changes by optimizing the molecular weight and chemical structure of the hydrophilic monomer to fall within a specific range that balances two competing requirements: being small enough to resist extraction by alcohol solvents, yet large enough to provide sufficient hydrophilic functionality. This parameter optimization ensures that standard alcohol extraction procedures effectively remove unreacted monomers while leaving the hydrophilic monomer intact in the polymer matrix.
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 method achieves a silicone-containing copolymer with a hydrophilic surface directly from a polypropylene mold, enhancing water wettability and avoiding complex post-processing, while maintaining mechanical strength and oxygen permeability.
Implementation Method 1
a polymerization initiator with a 10-hour half-life temperature between 70°C and 100°C
Implementation Method 2
the hydrophobic monomer ends up orienting toward the portion coming into contact with the mold surface
Implementation Method 3
the oxygen permeability of conventional lenses depends on the water content of the lens
Data Source
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AI summary
The present invention provides a silicone-containing copolymer molded article having a hydrophilic surface by means of the cast molding method and without employing a high-molecular-weight hydrophilic polymer even when employing a polypropylene mold. The silicone-containing copolymer molded article having a hydrophilic surface is prepared by polymerizing a monomer solution containing (a) a silicone monomer comprising a (meth)acryloyl group; (b) a hydrophilic monomer comprising a vinyl group; (c) a crosslinkable monomer; and (d) a polymerization initiator in a cavity of a mold having a hydrophobic cavity surface. The polymerization initiator has a 10-hour half-life temperature (T10) of 70 °C or higher and 100°C or lower, and the polymerization is conducted by means of a step P1 of maintaining a temperature within a range of from the T10 of the polymerization initiator contained in the monomer solution to 35°C below T10 for one hour or more; and a step P2 of maintaining a temperature higher than the T10 of the polymerization initiator contained in the monomer solution for one hour or more.