Environmental scanning electron microscopy analysis for contact lens coating selection and manufacturing
Use of high resolution environmental scanning electron microscopy to capture images of contact lens coating layers, enabling measurement of the coating thickness and structures of the coating layer to be precisely characterized. The coating layer can be directly visualized and quantitatively measured. Furthermore, controlled environments of varying temperatures and varying levels of relative humidity can be established in environmental scanning electron microscopy, such that the dynamic changes of the coating in such conditions can be imaged and measured. The controlled environments can be set up to mimic either the manufacturing process conditions, or be set up to simulate lens-on-eye conditions.
1. A method of selecting a lens coating for a coated contact lens comprising: providing at least one preformed contact lens in a dry state;
subjecting the at least one preformed contact lens to one or more surface treatment steps to obtain at least one contact lens with coating thereon; analyzing the at least one contact lens with coating thereon using environmental scanning electron microscopy (ESEM); and selecting the desired coating material based on said ESEM, wherein the step of analyzing the at least one contact lens with coating thereon using ESEM is a determination of a water-swelling ratio (designated as WSR), wherein WSR is a ratio of L wet to L Dry times 100, L wet is an average thickness of the coating layer of the contact lens in fully hydrated state as measured with ESEM on a cross section of the contact lens in fully hydrated state and L Dry is an average thickness of the coating layer of the contact lens in dry state as measured with ESEM on a cross section of the contact lens in dry state obtained by air drying the sample at room temperature for >2 hour and then drying under vacuum (<0.01 Pa) overnight.
2. The method of claim 1 wherein a plurality of different contact lenses with coatings thereon are analyzed using ESEM.
3. The method of claim 1 wherein the step of analyzing is performed while a temperature and a humidity are changed in the ESEM to measure dynamic changes of the coating of the contact lens.
4. The method of claim 1 wherein the preformed contact lens is a silicone hydrogel contact lens.
5. The method of claim 1 , wherein the desired coating material having the water-swelling ratio of at least 110% is selected.
6. The method of claim 1 , wherein the desired coating material having the water-swelling ratio of at least 150% is selected.
7. The method of claim 1 , wherein the desired coating material having the water-swelling ratio of at least 200% is selected.
8. The method of claim 1 , wherein the desired coating material having the water-swelling ratio of at least 250% is selected.
9. The method of claim 1 , wherein the desired coating material having the water-swelling ratio of at least 300% is selected.
10. The method of claim 1 , further comprising the step of staining the coating material using a staining agent before the step of analyzing the at least one contact lens with coating thereon using ESEM.
11. The method of claim 10 , wherein the staining agent is selected from a group consisting of Ruthenium Tetroxide (RuO4), Osmium tetroxide (OsO04), Phosphotungstic acid (PTA), lead citrate, uranyl acetate, toluidine blue, sudan black, and nile red.
12. The method of claim 11 , wherein the staining agent is Ruthenium Tetroxide (RuO4) or, Osmium tetroxide (OsO4).
13. The method of claim 12 , wherein the staining agent is Ruthenium Tetroxide (RuO4).
14. The method of claim 1 , comprising providing multiple different contact lenses with various coatings thereon, analysing the contact lenses by ESEM for determining their WSR and selecting a desired coating based on said ESEM analysis.