Method of manufacturing silicone hydrogel contact lenses having reduced rates of evaporation
A wettable silicone hydrogel contact lens having a low ionoflux and low evaporation is manufactured by curing a silicone hydrogel polymerizable composition in a contact lens mold comprising front and back lens-forming surfaces, where one of the lens-forming surfaces has a higher polarity than the other lens-forming surface.
1. A method of manufacturing a silicone hydrogel contact lens comprising:
a providing a contact lens mold comprising a first lens-forming surface to mold one side of said hydrogel contact lens and a second lens-forming surface to mold opposite side of said hydrogel contact lens, wherein the first lens-forming surface has a polarity that is at least 15 percentage points higher than the second lens-forming surface, and wherein the first lens-forming surface molds the back-posterior surface of the silicone hydrogel contact lens and the second lens-forming surface molds the front-anterior surface of the silicone hydrogel contact lens;
b curing a polymerizable composition comprising at least one siloxane monomer and at least one hydrophilic monomer in the contact lens mold to form a polymeric lens body;
c hydrating the polymeric lens body to provide a silicone hydrogel contact lens having a first surface formed by the first lens-forming surface of the contact lens mold and a second surface formed by the second lens-forming surface of the contact lens mold; and
d sealing the silicone hydrogel contact lens in a package,
wherein the silicone hydrogel contact lens has a lower ionoflux and/or a lower evaporation rate than a control contact lens manufactured by an identical method except that the second lens-forming surface has the same polarity as the first lens-forming surface.
2. The method of claim 1 , wherein the first lens-forming surface has a contact angle that is at least 20° lower than the contact angle of the second lens forming surface.
3. The method of claim 1 , wherein the first lens-forming surface is polar and the second lens-forming surface is non-polar.
4. The method of claim 1 , wherein the first lens-forming surface comprises a non-polar thermoplastic material coated with a hydrophilic coating, and wherein the second lens-forming surface comprises the non-polar thermoplastic material in the absence of any polarity-enhancing surface coating or treatment.
5. The method of claim 1 , wherein the at least one hydrophilic monomer is a hydrophilic vinyl-containing monomer.
6. The method of claim 1 , wherein the polymerizable composition comprises a total amount of hydrophilic vinyl-containing monomer of about 20 wt. % to about 60 wt. % based on the total weight of all polymerizable ingredients in the polymerizable composition.
7. The method of claim 5 , where the at least one hydrophilic vinyl-containing monomer is selected from N-vinylacetamide, N-vinyl-N-methylacetamide (VMA), N-vinyl-N-ethylacetamide, N-vinyl-2-pyrrolidone (NVP), N-vinylformamide, N-vinyl-N-ethylformamide, N-vinyl isopropylamide, N-vinylcaprolactam, N-vinyloxycarbonyl-L-alanine, 1,4-butanediol vinyl ether, ethylene glycol vinyl ether, diethylene glycol vinyl ether, a poly(ethylene glycol) vinyl ether, or any combination thereof.
8. The method of claim 7 , wherein the hydrophilic vinyl-containing monomer is VMA, or NVP, or a combination of both VMA and NVP.
9. The method of claim 1 , wherein the polymerizable composition comprises a total amount of siloxane monomer of about 30 wt. % to about 60 wt. % based on the total weight of all polymerizable ingredients in the polymerizable composition.
10. The method of claim 1 , wherein after the curing step the polymeric lens body is subjected to a surface modification treatment to increase wettability of the second surface of the silicone hydrogel contact lens.
11. The method of claim 10 , wherein the surface modification treatment is selected from air plasma, or UV-ozone, or corona discharge.
12. The method of claim 1 , wherein the contact lens has an equilibrium water content (EWC) of at least 40%.
13. The method of claim 1 , wherein the contact lens has an ionoflux of less than 0.5×10 −3 mm 2 /min, and the control contact lens has an ionoflux of at least 1×10 −3 mm 2 /min.
14. The method of claim 1 , wherein the contact lens has a lower evaporation rate from 2 to 4 hours than the control lens, wherein the evaporation rate measured at 48-50% RH and 21° C. to 23° C.
15. The method of claim 14 , wherein the evaporation rate is less than 15 mg/h.
16. The method of claim 1 , wherein the first surface of the contact lens has a sessile drop contact angle that is less than that of the second surface of the contact lens.
17. The method of claim 1 , wherein the contact lens has a back surface having a contact angle of less than 45°.