Quantifying Carboxyl Groups on Silicone Hydrogel Contact Lenses
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Solution Overview
Problem
Silicone hydrogel contact lenses face challenges with high surface concentrations of negatively charged carboxyl groups, leading to debris adhesion, protein adhesion, and antimicrobial deposition, which affect durability and comfort.
Innovation Solution
A method involving the use of a C1-C4 alcohol solution of a positively-charged dye with acetate as counter anion to stain and quantify carboxyl groups on the lens surface, allowing for the selection of candidate polymers and optimization of coating processes to achieve desired surface concentrations and coating thicknesses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hydrophilic polymer coating comprising carboxyl groups is applied to silicone hydrogel contact lenses, then the surface wettability is improved, but the surface concentration of negatively charged groups increases leading to debris adhesion, protein adhesion, and antimicrobial deposition
Solution Approach 1:
The patent applies parameter changes by modifying the coating process parameters including polymer concentration, deposition time, and crosslinking conditions to optimize the surface concentration of carboxyl groups. By carefully controlling these parameters, the patent achieves sufficient surface wettability while minimizing the harmful surface charge concentration that causes adhesion problems.
Solution Approach 2:
The patent uses composite materials by combining the silicone hydrogel lens material with a hydrophilic polymer coating containing carboxyl groups. This composite structure allows the lens to maintain its oxygen permeability while the coating provides surface wettability, and through optimized composition and crosslinking, controls the surface charge density to reduce adhesion issues.
2Strength
If crosslinking of LbL coatings is performed to improve durability, then the coating durability is improved, but the surface concentration of carboxyl groups remains relatively high
Solution Approach 1:
The patent applies parameter changes by optimizing crosslinking conditions including temperature, time, and crosslinking agent concentration to achieve adequate coating durability while controlling the surface concentration of carboxyl groups. By adjusting these parameters, the patent balances durability improvement with minimizing harmful surface charges.
3Ease of manufacture
If simple deposition technique is used to apply hydrophilic polymer coating, then the manufacturing process is cost effective, but the coating durability is reduced
Solution Approach 1:
The patent applies parameter changes by optimizing deposition parameters such as polymer concentration, deposition time, and solution composition to enhance coating durability while maintaining the simplicity and cost-effectiveness of the deposition process. This allows achieving better durability without complicating the manufacturing process.
Solution Approach 2:
The patent uses composite materials by selecting specific hydrophilic polymers with appropriate molecular weights, functional group densities, and compositional characteristics that enable durable coatings to be formed through simple deposition techniques, thus maintaining cost-effectiveness while improving durability.
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
This approach enables the qualification and quantification of carboxyl groups, reducing surface charges and improving the durability and comfort of silicone hydrogel contact lenses by optimizing the coating process.
Implementation Method 1
immersing a given number of the silicone hydrogel contact lenses in a fixed volume of a C1-C4 alcohol solution of a positively-charged dye having acetate as counter anion at a given initial concentration for a time period sufficient to stain the silicone hydrogel contact lens
Data Source
AI summary
The invention is related to a method for qualifying and quantifying carboxyl groups on the surfaces of a silicone hydrogel contact lens. The method of the invention comprises the steps of: (a) obtaining silicone hydrogel contact lenses each of which comprises a silicone hydrogel lens body (i.e., bulk material) and a coating thereon, wherein the silicone hydrogel lens body is obtained from a lens formulation free of any polymerizable component including one or more carboxyl groups, wherein the coating comprises a polymer having carboxyl groups; (b) immersing a given number of the silicone hydrogel contact lenses in a fixed volume of a C1-C4 alcohol solution of a positively-charged dye having acetate as counter anion at a given initial concentration for a time period sufficient to stain the silicone hydrogel contact lens; and (c) determining the concentration of carboxyl groups per each silicone hydrogel contact lens and/or the thickness of the coating on the silicone hydrogel contact lens.