Selective Coatings for Hydrophobic Surfaces

Abstract

Compositions for rendering a hydrophobic surface hydrophilic and methods for applying them to objects such as contact lenses. A hydrophobic binder, typically a silicone compound such as a siloxane, selectively attaches hydrophilic solution-produced nanoparticles to the surface, such as hydrophobic regions of a silicone contact lens. Hydrophilic regions are preferably unmodified. The binder attaches to the particles via functional groups in solution and can autoadhere to the hydrophobic surface. A coating of the composition can be deposited from solution at ambient or room temperature, allowing coating of temperature sensitive substrates. Such coatings can withstand heating (such as for sterilization) in acidic solutions or heat sensitive solutions, retaining their hydrophilic properties.

Claims

1. A composition comprising hydrophilic nanoparticles comprising first functional groups and a hydrophobic binder comprising second functional groups, the first functional groups bound to the second functional groups.

2. The composition of claim 1 wherein the hydrophobic binder comprises a silicone compound.

3. The composition of claim 2 wherein the silicone compound comprises a siloxane oligomer.

4. The composition of claim 1 wherein the second functional groups are each selected from the group consisting of a hydride, amino, amine, hydroxyl, epoxy, vinyl, acrylate, and mercapto group.

5. The composition of claim 1 wherein the nanoparticles are derived from a metal alkoxide precursor comprising the first functional groups.

6. The composition of claim 5 wherein the metal alkoxide is a silicon alkoxide.

7. The composition of claim 1 wherein each first functional group is selected from the group consisting of an epoxy, carboxylic acid, vinyl, acrylate, or amino group.

8. The composition of claim 1 wherein the first functional groups comprise an epoxy comprising 3-glycidylpropylsiloxane.

9. The composition of claim 1 wherein the first functional groups are bound to hydrophilic tails of the nanoparticles.

10. The composition of claim 1 wherein the nanoparticles are between approximately 10 nm and 200 nm in size.

11. An article comprising a coating comprising hydrophilic nanoparticles, the hydrophilic nanoparticles comprising first functional groups and a hydrophobic binder comprising second functional groups, the first functional groups bound to the second functional groups.

12. The article of claim 11 comprising a contact lens.

13. The article of claim 11 wherein the coating has a thickness less than approximately one micron.

14. The article of claim 12 wherein the coating has a thickness between approximately 50 and 500 nm.

15. The article of claim 11 wherein the coating is bound only to first regions of the article.

16. The article of claim 15 wherein the first regions were hydrophobic prior to coating with the coating.

17. The article of claim 15 wherein the hydrophilic nanoparticles in the coating are bound to the first regions via the hydrophobic binder.

18. The article of claim 17 wherein the hydrophobic binder adheres to the first regions via diffusion of polymeric chains across the interface and entanglement of the chains.

19. The article of claim 15 wherein surfaces of the first regions comprise a siloxane.

20. The article of claim 19 wherein the siloxane comprises polymethylsiloxane resin.

21. The article of claim 15 wherein regions of the article other than the first regions are hydrophilic both prior to and after coating with the coating.

22. The article of claim 15 wherein the coating was deposited on the first regions from solution.

23. The article of claim 15 wherein the coating was deposited on the first regions at no higher than ambient temperature.

24. The article of claim 23 wherein the article would be damaged if heated to a temperature above ambient temperature.

25. The article of claim 11 capable of being stored in an acidic solution.

26. The article of claim 25 wherein the acidic solution comprises low pH distilled water or low pH saline.

27. The article of claim 25 wherein the coating remains substantially unmodified when heated to above ambient temperature in the acidic solution.

28. The article of claim 27 wherein the coating remains substantially unmodified when heated to about 120 C. in the acidic solution.

29. The article of claim 25 wherein a contact angle of the coating increases by less than approximately 5 degrees after heating in the acidic solution.

30. The article of claim 11 wherein the nanoparticles are between approximately 10 nm and 200 nm in size.

31. The article of claim 11 wherein the coating is optically clear.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings, which are incorporated into and form a part of the specification, illustrate several embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating a preferred embodiment of the invention and are not to be construed as limiting the invention. In the drawings:

[0013] FIG. 1 is a schematic representation of surface properties of regions of a contact lens.

[0014] FIG. 2 shows a schematic of a nanoparticle comprising hydrophilic tails and hydrophobic binders.

[0015] FIG. 3A shows the nanoparticles of FIG. 2 binding to hydrophobic regions of a contact lens.

[0016] FIG. 3B shows a hydrophilic coating bound to hydrophobic regions of a contact lens

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0017] Embodiments of the present invention are compositions for the production of hydrophilic coatings on a hydrophobic substrate, such as a contact lens comprising a hydrogel and a siloxane, the compositions comprising at least one hydrolyzed metal alkoxide comprising a functional group reacted with at least one functionalized siloxane oligomer or polymer capable of reacting with the alkoxide functional group. The alkoxide can be functionalized with an epoxy, carboxyl acid, vinyl, acrylate, or amino group. The siloxane can be functionalized with a hydride or with an amino, hydroxyl, epoxy, vinyl, acrylate, or mercapto group.

[0018] Embodiments of the present invention are based on solution-produced silica nano-coatings as shown in FIG. 2, preferably comprising nanoparticles 30 comprising hydrophilic tails 40, which preferably comprise functional groups F2, and reactive binder 50, which preferably comprises functional groups F1 which bind to functional groups F2 through a chemical reaction in solution. The chemically reacted binder binds the particles specifically to the hydrophobic siloxane regions of the lens, preferably via a physical interaction of the preferably silicone-based binder and silicone-based sections of the lens, as shown in FIG. 3A. The particles preferably coalesce together to form a substantially continuous coating 60 on the hydrophobic surfaces, as shown in FIG. 3B. The coatings of the present invention are preferably submicron in thickness, more preferably having a thickness between 50 and 500 nanometers, and are synthesized in solution, enabling the addition of modifiers to the finished solution-produced particles. The reaction of functional groups F2 such as epoxy moieties with the binder enables it to bind to the hydrophilic tails of the particles prior to deposition of the coating on the article surface. More specifically, the hydrophobic silicone-based binder selectively bonds to the hydrophobic silicone-based sections of the contact lens due to the unique interaction between the two compounds. Silicones, for example siloxanes, while often liquid are still high-molecular weight polymeric materials. As such, their interaction with other materials is not just governed by typical liquid-solid parameters like contact angle but also by the ability to undergo true adhesion with other silicone materials. This autoadhesion is typically governed by diffusion of polymeric chains across the interface and entanglement of chains in both materials. This imparts hydrophilic properties specifically to the hydrophobic siloxane surfaces, while leaving the hydrophilic hydrogel regions of the lens surface unmodified.

[0019] Embodiments of the present coatings preferably rely on the chemical similarity between solid polydimethylsiloxane resins incorporated into the contact lens and oligomeric liquid precursor siloxanes of the binder with functional groups. After binding to the nanoparticles, the siloxanes preferably deposit the nanoparticles only on the siloxane polymer portions of the lens and provide the anchoring force for the solution-produced coating. Liquid siloxanes are available with a wide variety of both terminal and perpendicular bound functional groups, including amino, hydroxyl, epoxy, hydride, vinyl, acrylate, and mercapto groups. Corresponding functional modifiers on metal alkoxide precursors used to form the nanoparticles include epoxy, carboxylic acid, vinyl, acrylate, and amino groups. The precursors preferably comprise one or more epoxy-carrying silicon alkoxides.

[0020] Silica nano-coatings can be produced by first hydrolyzing a mixture of the desired metal alkoxides, typically a silicon alkoxide, with an excess amount of water in a mildly acidic solution until partial or approximately full hydrolysis has occurred. By changing the pH of the solution to mildly basic, polymerization is promoted and nanoparticle growth is initiated and continued for varying times until a test sample, which is preferably spun-coated onto a substrate, has a contact angle of 20 or less. At this point the solution is neutralized to stabilize the growth process at the desired stage. The resulting nanoparticle sizes typically range from 10 to 200 nm, and the solution appears optically clear. Spun-coated test coatings typically show a thickness of 20-200 nm and are optically clear.

[0021] The major advantage of this synthesis method lies in the ease of application of the coatings on a variety of substrates. As all chemical processes of the present invention preferably occur in solution, high heat is not required to form the coatings. In some embodiments of the present invention, the formation of the coating is performed at ambient temperatures. This enables use on substrates that are typically incompatible with silica nano-coatings, like plastics, fabrics or other temperature sensitive materials.

[0022] To produce coatings on highly hydrophobic materials it is preferable to add a reactive binder in solution to produce a good bond between the hydrophobic substrate and the overlying hydrophilic coating. The reactive binder is typically chosen from materials comprising a chain that is hydrophobic or otherwise compatible with the substrate and a reactive moiety that binds to the hydrophilic tails on the nanoparticles. In embodiments of the present invention, the compatible chain preferably comprises a siloxane oligomer and a reactive moiety such as an amine (F1) which binds to the functional groups F2, which preferably comprises an epoxy based on 3-glycidylpropylsiloxane incorporated into the solution.

[0023] An enhanced bonding effect can be also achieved by adding reactive chains to the siloxane resin of the lens. These reactive chains preferably comprise either two identical groups capable of reacting with the hydrophilic particles, or one group capable of reacting with the hydrophilic particles and one group capable of reacting with the bulk resin functionalities. Either leads to the formation of reactive bonds on the surface of the lens, which then react with reactive groups on the hydrophilic particles to bond chemically to the lens surface. This effect can be achieved using the same functionalities described above.

[0024] Coatings made using the compositions disclosed above are preferably stable at room temperature in both phosphate-buffered saline (PBS) solution (at a typical pH of 7.3) and a Tris(hydroxymethyl)aminomethane buffered saline (TBS) solution. A mixture of Tris-HCl and its conjugate base, at pH 7.0 to 9.2, is typically used in biochemistry and molecular biology, due to its heat sensitive nature, as a constituent of buffer solutions and to maintain pH within a set range. TBS is preferably used for storage of contact lenses to avoid irritation of the eye when the lens is used due to solution remaining on the lens. The concentration of the TBS solution is preferably between approximately 10 to 500 mM, more preferably between approximately 25 to 250 mM, and even more preferably between approximately 50 to 60 mM. The solution preferably comprises at least one surfactant, such as a tetrafunctional block copolymer (which preferably terminates in primary hydroxyl groups), and at least one biopolymer composite, such as a cellulose derivative.

[0025] In commercial processing of lenses for customer use, the lenses are typically heated to autoclave temperatures of 121 C. in TBS in order to sterilize them prior to sale. The pH of the TBS solution is preferably within a useful range to prevent corneal damage, between approximately 6.5 to 9.0, more preferably between approximately 6.9 to 7.5, and even more preferably between approximately 7.0 to 7.3. Generally speaking, low pH environments prove beneficial to the survival of the coatings made using the compositions disclosed above. The pK.sub.a of the TBS solution advantageously decreases approximately 0.03 units per every increase in degree C. and returns to the initial pK.sub.a after achieving ambient temperature. The favorable decrease in pK.sub.a during heating prevents destruction of the coating of the present invention. To further prevent destruction of the coating, the pH of non-heat sensitive solutions are preferably lowered to a pH from approximately 1-7, more preferably between approximately 3-6.5, and even more preferably between approximately 3.5-4.5. Solutions that can be used in accordance with this embodiment of the present invention include but are not limited to low pH distilled water or low pH saline. Coatings of the present invention can withstand such heating at such lower pH.

[0026] Coatings of the present invention can be applied by various methods. The coating is preferably applied to a finished contact lens by dipping the wet lens into the coating solution and subsequently washing retained coating on the lens in an aqueous solution. As indicated above, autoadhesion of the hydrophobic silicone-based binder to the hydrophobic silicone-based surface portions of the contact lens occurs due to the unique interlinkage between the two, and results in a coating that does not need to undergo drying, evaporation or any type of chemical reaction or alteration once applied.

[0027] To integrate the application of coatings of the present invention into a commercial manufacturing process it is desirable to not add additional steps to the existing process. Current contact lens manufacture results in a dry lens which is subjected to a series of extraction, hydration, and rinsing steps.

[0028] The coating solution of the present invention is preferably used in between two of these steps, most preferably after the last alcohol-based rinse step and prior to the aqueous media rinse step. Thus the coating is preferably applied during contact lens manufacture by addition of the coating solution to one of the solutions employed to hydrate and purify the newly molded lens.

[0029] Coating is achieved by preferably depositing in-mold and hydrating contact lenses into a coating bath for approximately 30 seconds. The length of time for the lenses to be in the coating bath is dependent on the manufacturing process and can last from 1 second to 24 hours. The coating bath is a bath comprising hydrophilic particles preferably comprising functional groups F2, which are preferably chemically reacted in solution prior to coating of the lens to functional groups F1 of a binder. Upon application of the coating solution to a contact lens, the hydrophobic binder autoadheres to the hydrophobic sections of the contact lens and the hydrophilic particles amalgamate over the hydrophobic surfaces of the lens to form a distinct coating. This amalgamation of hydrophilic nanoparticles imparts complete hydrophilic performance across the lens while preferably leaving the hydrogel regions on the lens unmodified. The in-mold and hydrated lenses, once coated, can proceed through the hydration process without the need for additional steps to evaporate the solvent, fortify, cure or modify the coating. The deposition of the coating of the present invention is a truly one-step process and is stabilized by the strong foundation of the siloxane-siloxane interaction of the hydrophobic silicone-based sections of a lens and the hydrophobic silicone-based binder reacted with the hydrophilic nanoparticles. This consequently renders surface modification or treatment unnecessary, pre or post application of the coating solution, to promote coating adhesion to the article.

[0030] Contact lenses are commonly produced by injecting resin into disposable lens molds followed by resin cure using thermal or radiative cure methods. In an alternative embodiment of the present invention, modified sol-gel coatings are applied to a mold for the production of contact lenses prior to molding or casting of the contact lens. In this embodiment, the hydrophobic silicone chains on the coating entangle with chains of the siloxane resin of the lens, leading to a more stable bond.

EXAMPLES

Example 1

[0031] A silica solution containing 80% hydrolyzed tetraethoxy silane and 20% hydrolyzed 3-glycidoxypropyltrimethoxysilane in an ethanol solution at 2% solids content, prepared according to the methodology disclosed herein, was blended with an equimolar amount of aminopropyl-terminated siloxane (1000 cSt), and allowed to react for 30 min. A commercially packed siloxane-containing contact lens was rinsed in DI water for 1 min, immersed into the modified nanogel solution for 1 min, transferred to a clean deionized water solution for 1 min, and then transferred to a buffer solution.

Example 2

[0032] A siloxane-containing contact lens was immersed into an ethanol solution of poly (aminopropyl-methyl-co-dimethyl siloxane (120 cSt) for 1 min. A nanogel containing 90% hydrolyzed tetraethoxy silane and 10% hydrolyzed 3-glycidoxypropyltrimethoxysilane in an ethanol solution with 1% solids content is added in an equimolar amount to the aminopropyl group on the siloxane, and allowed to react for 5 min. The lens was then transferred to a clean deionized water solution for 1 min, and then transferred to a buffer solution.

Example 3

[0033] A nanogel containing 90% hydrolyzed tetraethoxy silane and 10% hydrolyzed methacryloxpropyl trimethoxysilane in an ethanol solution at 2% solids content, prepared according to the methodology disclosed herein, was blended with an equimolar amount of methacryloxpropyl-terminated siloxane (70 cSt). A siloxane-containing contact lens was immersed into the modified nanogel solution for 1 min, transferred to a clean deionized water solution for 1 min, and then transferred to a solution containing 0.01% AIBN. The solution was irradiated with a medium pressure mercury lamp for 30 sec to crosslink the coating.

Example 4

[0034] A nanogel containing 90% hydrolyzed tetraethoxy silane and 10% hydrolyzed methacryloxpropyl trimethoxysilane in an ethanol solution at 2% solids content, prepared according to the methodology disclosed herein, was blended with an equimolar amount of methacryloxpropyl-terminated siloxane (70 cSt). A siloxane-containing contact lens was immersed into the modified nanogel solution for 1 min, transferred to a clean deionized water solution for 1 min, and then transferred to a solution containing 0.01% AIBN. The solution was then heated to 120 C for 30 min to crosslink the coating and sterilize the content.

Example 5

[0035] A coated contact lens as prepared in Example 1 was heated to 120 C. for 30 minutes in 2.5 mL deionized (DI) water comprising 1 drop (1N) HCl. The measured contact angle did not change after heating.

Example 6

[0036] A coated contact lens as prepared in Example 1 was heated to 120 C. for 30 minutes in 2.5 mL DI water comprising 5% NaCl and 1 drop (1N) HCl. The measured contact angle did not change after heating.

Example 7

[0037] A coated contact lens as prepared in Example 1 was heated to 120 C. for 30 minutes in 2.5 ml 50 mmol TRIS buffer. The measured contact angle did not statistically change after heating.

Example 8

[0038] A contact lens shape was produced by blending 1% aminopropoxy-terminated dimethoxysilane with a conventional siloxane resin, adding to a mold, and curing. The contact lens was then added to a nanogel containing 80% hydrolyzed tetraethoxy silane and 20% hydrolyzed 3-glycidoxypropyltrimethoxysilane in an ethanol solution at 2% solids content and allowed to react for 1 h, resulting in a hydrophilic contact lens.

Example 9

[0039] A contact lens shape was produced by blending 1% aminopropoxy-dimethoxysilane-methacrylate with a conventional siloxane resin, adding to a mold, and curing. The contact lens was then added to a nanogel containing 80% hydrolyzed tetraethoxy silane and 20% hydrolyzed 3-glycidoxypropyltrimethoxysilane in an ethanol solution at 2% solids content and allowed to react for 1 h, resulting in a hydrophilic contact lens.

Example 10

[0040] A freshly molded and cured contact lens shape was swelled in an ethanol-based nanoparticle solution as described in Example 1. The coated lens was washed twice with isopropanol, once with a 50:50 mixture of isopropanol and water, followed by deionized water, and transferred into a buffer solution.

Example 11

[0041] A freshly molded and cured contact lens shape was swelled in isopropanol, rinsed with isopropanol, and then immersed into an isopropanol-based solution using the method described in Example 1. The coated lens was washed with a 50:50 mixture of isopropanol and water, followed by deionized water, and transferred into a buffer solution.

Example 12

[0042] A nanogel containing 80% hydrolyzed tetraethoxy silane and 20% hydrolyzed 3-glycidoxypropyltrimethoxysilane in an ethanol solution at 2% solids content, prepared according to the methodology disclosed herein, was blended with an equimolar amount of aminopropyl-terminated siloxane (1000 cSt), and allowed to react for 30 min. The resulting solution was coated onto a contact lens mold and allowed to dry. Silicone resin was added to the mold and cured, resulting in a hydrophilic contact lens shape.

[0043] Note that in the specification and claims, about or approximately means within twenty percent (20%) of the numerical amount cited. As used herein, the singular forms a, an, and the include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a functional group refers to one or more functional groups, and reference to the method includes reference to equivalent steps and methods that would be understood and appreciated by those skilled in the art, and so forth.

[0044] Although the invention has been described in detail with particular reference to the disclosed embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover all such modifications and equivalents. The entire disclosures of all patents and publications cited above are hereby incorporated by reference.