Coating Thickness Measurement on Hydrated Contact Lenses
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Solution Overview
Problem
Current methods for imaging and thickness determination of coatings on water gradient contact lenses are inadequate, as existing techniques either require drying the lenses or are unsuitable for edge-to-edge imaging, limiting the ability to accurately assess and optimize coating thickness.
Innovation Solution
A method involving the use of a fluorescently-labeled polycationic polymer to selectively stain negatively-charged coatings on fully hydrated contact lenses, followed by orthogonal cutting and imaging, allows for precise determination of coating thickness and optimization of coating processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a positively charged dye is used to stain the coating, then the coating can be visualized, but the dye penetrates into the lens body causing unwanted staining
Solution Approach 1:
The patent uses a polycationic polymer as an intermediary staining agent instead of small molecule dyes. The polymer's large molecular size prevents penetration into the lens body while its positive charges enable selective binding to negatively charged coating groups, achieving both visualization and prevention of unwanted penetration
Solution Approach 2:
The patent changes the molecular size parameter of the staining agent from small molecules to large polymers. This parameter change fundamentally alters the penetration behavior while maintaining the electrostatic binding capability to negatively charged coating groups
2Measurement precision
If the contact lens is dried before staining, then selective staining can be achieved, but the staining procedure becomes complicated
Solution Approach 1:
The patent extracts the drying step from the staining procedure. By using a polycationic polymer that can selectively stain coatings on hydrated lenses, the method eliminates the need for drying while maintaining selective staining capability, thereby simplifying the overall procedure
Solution Approach 2:
The patent performs preliminary selection of a polycationic polymer staining agent that inherently provides selective staining on hydrated lenses. This preliminary choice eliminates the need for subsequent drying steps and complicated procedures
3Measurement precision
If AFM is used to determine coating thickness, then thickness measurement is possible, but edge-to-edge imaging is not achievable
Solution Approach 1:
The patent employs fluorescence microscopy as a universal imaging technique that can simultaneously provide both thickness measurement and edge-to-edge imaging coverage. The fluorescently labeled polycationic polymer enables the same imaging modality to achieve multiple functions that previously required different techniques
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
Enables accurate imaging and thickness measurement of coatings on contact lenses without penetrating the lens body, facilitating the selection of candidate coating materials and optimization of coating processes to achieve desired thicknesses.
Implementation Method 1
selectively staining the coating over the lens body of the coated contact lens by immersing the coated contact lens in an aqueous solution of a fluorescently-labeled polycationic polymer
Implementation Method 2
fluorescently-labeled polycationic polymer
Data Source
AI summary
The invention provides a method for imaging and thickness determination of coatings on coated contact lenses. The method comprises selectively staining a negatively-charged-groups-containing coating over the lens body of a coated contact lens by immersing the coated contact lens in an aqueous solution comprising a fluorescently-labeled polycationic polymer and having a pH of from about 6.5 to 8.0; orthogonally cutting the selectively-stained coated contact lens; and determining the thickness of the coating on the coated contact lens. In addition, the invention provides a method for selecting a candidate coating material comprising negatively charged groups for applying a coating with a desired thickness onto silicone hydrogel contact lenses and for optimizing a coating process for producing coated silicone hydrogel contact lenses with a desired thickness coating thereon.