Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-08-24
2002-05-14
Pezzuto, Helen L. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S258000, C526S263000, C526S328000, C526S328500
Reexamination Certificate
active
06388035
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to coatings for surgical implants. In particular, the present invention relates to hydrophilic copolymers that are hydrophobically bound to the surface of surgical implants.
BACKGROUND OF THE INVENTION
Both rigid and foldable implantable ophthalmic lens materials are known. The most common rigid material used in ophthalmic implants is polymethyl methacrylate (“PMMA”). Foldable intraocular lens (“IOL”) materials can generally be divided into three categories: silicone materials, hydrogel materials, and non-hydrogel (“hydrophobic”) acrylic materials. See, for example,
Foldable Intraocular Lenses
, Ed. Martin et al., Slack Incorporated, Thorofare, N.J. (1993). For purposes of the present application, hydrophobic acrylic materials are acrylic materials that absorb less than approximately 5% water at room temperature.
Silicone and non-hydrogel acrylic materials used in ophthalmic implants can damage endothelial cells and perhaps other cells or tissues as well during or after the implant's insertion in the eye. These materials are generally hydrophobic and/or tacky and can pull cells off of eye tissues that contact the implant. Particularly in the case of phakic IOL's implanted between the capsular bag and the iris, there is significant potential for physical contact between the implant and surrounding cells or tissue even after the implant reaches its target location.
SUMMARY OF THE INVENTION
The present invention relates to hydrophilic coating compositions for surgical implants, particularly ophthalmic implants comprising silicone or non-hydrogel acrylic materials. More specifically, the present invention relates to a coating material for an implant where the coating material comprises a copolymer of 2-phenylethyl (meth)acrylate and N-vinyl pyrrolidone (“NVP”). The coating material is capable of absorbing from about 40 to about 90% water. Despite its relatively high water content, the coating material of the present invention is sufficiently tough to withstand folding or handling with forceps without rupturing.
The present invention also relates to a method for applying a coating comprising a copolymer of 2-phenylethyl (meth)acrylate and NVP to an implant's surface, wherein the copolymer lacks a cross-linking monomer. The method comprises dissolving the copolymer in a solvent to form a coating solution, contacting the coating solution with the implant's surface, and drying the coated implant.
DETAILED DESCRIPTION OF THE INVENTION
Unless indicated otherwise, all amounts are expressed as weight %.
The coating material of the present invention is a copolymer of 2-phenylethyl (meth)acrylate and NVP. The coating material is attached to the substrate by means of hydrophobic or “physical” (i.e., non-covalent) cross-linking. The coating material is also internally cross-linked by non-covalent cross-linking. The coating material is capable of absorbing from about 40 to about 90% water, preferably from about 65 to about 75% water. The proportion of the copolymer's monomers will depend on the desired water content, with individual concentrations generally ranging from about 25 to about 60% for 2-phenylethyl (meth)acrylate and about 40 to about 75% for NVP. Copolymers of 2-phenylethyl methacrylate (“2-PEMA”) and NVP are preferred. In the preferred case where the desired water content is about 65-75%, the copolymeric coating material comprises from about 35 to about 45% 2-PEMA and from about 40 to about 50% NVP.
The copolymeric coating material is prepared by combining the 2-phenylethyl (meth)acrylate and NVP ingredients with a polymerization initiator (generally about 2% or less) to form a coating composition and curing the coating composition. Any type of polymerization initiator may be used, including thermal initiators and photoinitiators. A preferred initiator is the benzoylphosphine oxide initiator, 2,4,6-trimethyl-benzoyldiphenylophosphine oxide (“TPO”), which is activated by blue-light. Suitable thermal initiators include the conventional peroxides t-butyl peroctoate and bis-azoisobutronitrile. Suitable UV initiators include benzoin methyl ether and Darocur 1173.
In addition to the 2-phenylethyl (meth)acrylate, NVP, and polymerization initiator, the coating copolymers optionally include one or more ingredients selected from the group consisting of UV absorbers that are copolymerizable with the 2-phenylethyl (meth)acrylate and NVP ingredients; blue-light blocking colorants that are copolymerizable with the 2-phenylethyl (meth)acrylate and NVP ingredients; reactive plasticizers to minimize haze or crazing; and chain transfer agents to minimize cross-linking within the coating copolymer.
Ultraviolet absorbing chromophores can be any compound which absorbs light having a wavelength shorter than about 400 nm, but does not absorb any substantial amount of visible light. Suitable copolymerizable ultraviolet absorbing compounds are the substituted 2-hydroxybenzophenones disclosed in U.S. Pat. No. 4,304,895 and the 2-hydroxy-5-acryloxyphenyl -2H-benzotriazoles disclosed in U.S. Pat. No. 4,528,311. The most preferred ultraviolet absorbing compound is 2-(3′-methallyl-2′-hydroxy-5′-methyl phenyl) benzotriazole. Suitable polymerizable blue-light blocking chromophores include those disclosed in U.S. Pat. No. 5,470,932. If a blue-light activated polymerization initiator is chosen and a blue-light blocking colorant is added, the polymerization initiator identity or concentration may have to be adjusted to minimize any interference.
Suitable reactive plasticizers or softening agents include polyethylene glycol (200-2000) mono(meth)acrylates and polyethylene glycol (200-2000) monomethylether mono(meth)acrylates. Methacrylates are preferred, with PEG(400)monomethylether monomethacrylate most preferred. If needed or desired, the amount of the reactive plasticizer will range from about 5 to about 25%. Depending on the implant's function and the thickness of the coating, some degree of haze or crazing may be tolerated such that a reactive plasticizer may not be required.
The chain transfer agent, if present, is typically added in an amount ranging from 0.01 to 0.4%. Many chain transfer agents are known in the art. Examples of suitable chain transfer agents include 1-dodecanethiol and 2-mercaptoethanol.
After the coating copolymer is cured, it is purified by extraction to remove water-soluble components and low-molecular weight hydrophobic components. This can be accomplished by a two-stage extraction where the first stage is an aqueous extraction and the second is a non-aqueous extraction. The resulting coating copolymer is extracted in water, typically for 12-20 hours to remove aqueous extractables, such as N-vinyl pyrrolidone or low-molecular weight polyvinyl pyrrolidone. After the coating copolymer is extracted in water, it is dissolved in an organic solvent, such as methylene chloride. The resulting solution containing the dissolved polymer is added to a bath of volatile aliphatic solvent(s), such as heptane or hexane, to precipitate the coating copolymer. The precipitated coating copolymer is collected by, for example, filtration using a scintered glass filter and then dried, preferably under vacuum at room temperature.
After the coating copolymer is purified, a coating solution is prepared by dissolving the coating copolymer in a solvent or mixture of solvents, such as a 50:50 (parts by weight) mixture of ethanol and 2-pentanone. The solvent or mixture of solvents is preferably chosen to give a clear, homogenous coating solution where the chosen solvent or solvent mixture does not evaporate so quickly that it leaves a hazy coating.
The concentration of the coating copolymer in the coating solution will depend on the desired coating thickness. Other factors that will influence the thickness of the coating include the viscosity of the coating solution, the temperature of the coating solution and the implant, and the evaporation rate of the chosen solvent(s). In general, the coatings of the present invention w
Alcon Universal Ltd.
Pezzuto Helen L.
Ryan Patrick M.
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