Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
  • G02B1/04—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of organic materials, e.g. plastics
  • G02B1/041—Lenses
  • G02B1/043—Contact lenses
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
  • A61L27/14—Macromolecular materials
  • A61L27/16—Macromolecular materials obtained by reactions only involving carbon-to-carbon unsaturated bonds
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L2430/00—Materials or treatment for tissue regeneration
  • A61L2430/16—Materials or treatment for tissue regeneration for reconstruction of eye parts, e.g. intraocular lens, cornea

Definitions

• the present invention relates generally to polymer compositions and their use in optical lenses. More particularly, the present invention is directed to deformable intraocular lenses made from copolymers of methacrylate esters.
• the natural eye contains an internal crystalline lens, which focuses images on the retina. Either through disease or other naturally occurring processes, or mutations, this lens may fail to function properly. For instance, the lens may be cloudy at birth or become cloudy over time. This clouding of the lens is known as a cataract, which inhibits the transmission of visual information through the lens to the retina.
• the removal of diseased natural lenses has, prior to the advent of intraocular lenses, required a large incision into the eye at the junction of the cornea and the sclera in order to remove the lens. The healing time in such an operation was substantial and the pain was severe. No lens was inserted in place of the natural lens and eyeglasses or external-type contact lenses were employed to help restore vision to the patient.
• Intraocular lenses are now well-known replacements for natural crystalline lenses which have been surgically removed. Such intraocular lenses are generally surgically implanted directly into the eye and are intended to replace the damaged or diseased natural lens of the eye in order to restore a patient's vision.
• a small incision is made into the eye in order to first remove the natural lens. It is desirable to keep this incision as small as possible.
• the average minimum size for the incision is typically from about 5 millimeters (mm) to about 6 mm.
• Such large incisions can give rise to various wound-related problems, including infection, wound leak and astigmatism.
• PMMA poly(methylmethacrylate)
• PMMA is relatively light weight polymer which possesses excellent optical properties and is generally considered to be relatively inert when implanted into the eye, thereby avoiding adverse tissue reactions and thus is biocompatible.
• PMMA comprises a plastic matrix which, when formed into the shape of a lens, possesses high rigidity and cannot be deformed by folding, rolling, compression, etc. Accordingly, the use of PMMA lenses requires a relatively large incision in the ocular tissue sufficient to accommodate the entire diameter of the lens body which is typically six millimeters or larger, together with the accompanying lens support structures.
• foldable IOLs were more recently introduced to overcome the problems associated with implantation of the rigid IOLs.
• a deformable IOL is designed to be implanted into a small incision (from about 3.5 mm to about 4.0 mm) while a hard PMMA lens typically requires a much larger incision (about 6.0 mm).
• the primary medical benefit of these foldable IOLs is that the large incisions associated with the rigid IOLs are no longer necessitated.
• these soft IOLs are deformable and can be folded in half, these soft IOLs typically require substantially smaller incision sizes for implantation as compared to the incision size for implantation of the rigid IOLs having the same or comparable optical power.
• the patient benefits from the use of a deformable IOL requiring the smaller incision size since this will result in an overall safer surgical procedure and reduce the likelihood of post-operative complications such as infections, postoperative astigmatism and also substantially reduce patient rehabilitation time.
• These foldable IOLs can be made from various soft, deformable resilient biocompatible polymeric materials, such as silicone or other elastomers.
• silicone or other elastomers.
• Mazzocco U.S. Pat. No. 4,573,998 discloses a deformable intraocular lens that can be rolled, folded, or stretched to fit through a relatively small incision. The deformable lens is inserted while it is held in its distorted configuration, then released inside the chamber of the eye, whereupon the elastic property of the lens causes it to resume its molded shape.
• Suitable materials for the deformable lens, disclosed by Mazzocco includes polyurethane elastomers, silicone elastomers, hydrogel polymer compounds, organic or synthetic gel compounds and combinations thereof.
• foldable IOLs can be simple to manufacture and use, there are problems associated with the use of these IOLs made from silicones and hydrogel materials. Lenses made from various silicones can have relatively low refractive indices. Therefore, in order to provide a lens of proper refractive power, foldable IOLs derived from silicones must be relatively thick. The thicker the lens, the more difficult it can be to deform or distort the lens into a shape that is capable of fitting into a small incision.
• the distortion required to force such a thick lens through a small incision may exceed the IOL's elastic properties so when released, the IOL will tend to snap back or regain its unfolded shape too rapidly, resulting in the lens breaking and possibly damaging the integrity of the endothelial cell layer of the eye.
• the long-term stability of UN-absorbing silicone formulations is uncertain.
• hydrogels it has been found that hydrogel materials when hydrated vary in composition including water content from lot to lot. Such variability induces a corresponding variability in the refractive power of IOL lens bodies formed of hydrogel material. Therefore, hydrogel IOLs need to be hydrated in order to determine their refractive power in an implanted state.
• deformable IOLs manufactured form silicones and hydrogels
• deformable IOL materials have been developed which combine a higher refractive index with a lower elasticity.
• acrylic polymers have been used extensively because of their ease in preparation, high level of atacticity ensuring low crystallinity, good processing characteristics, high optical quality and long term stability to ultraviolet (UN) wavelengths of light.
• deformable IOLs made of acrylic materials have a tendency to be too rigid and brittle for use at room temperature, which can result in cracking of the IOL if it is folded too quickly.
• these soft acrylic materials can have other undesirable properties for use in deformable IOL applications, such as tackiness and/or stickiness.
• surface tackiness can create handling problems by hindering deformation of the IOL to a sufficiently small size for insertion through the narrow opening of the incision.
• the addition of surface energy lowering agents or plasma treatment processes have been used. However, this additional step cannot only be costly but could also alter the properties such as the biocompatibility of this IOL.
• an intraocular lens and lens material having the aforementioned properties and for the lens to also have appropriate elasticity, elastic memory, mechanical properties and possess a non-sticky surface and/or have reduced tackiness.
• the present invention includes polymeric materials, which are useful in the production of deformable lenses, including but not limited to intraocular lenses (IOL's), refractive intraocular contact lenses, and standard contact lenses, the latter type being useful for correcting aphakia, myopia and hypermetropia.
• IOL's intraocular lenses
• refractive intraocular contact lenses refractive intraocular contact lenses
• standard contact lenses the latter type being useful for correcting aphakia, myopia and hypermetropia.
• R and R' are independently selected from the group consisting of n- alkyl, .sec-alkyl, ⁇ o-alkyl, tert-alkyl and other isomeric alkyl radicals, substituted alkyl radicals containing oxygen and substituted alkyl radicals containing nitrogen.
• MMA methylmethacrylate
• R methacrylate ester
• third monomers include, but are not limited to, hydroxyethyl methacrylate, hydroxypropyl methacrylate, 2-aminoethyl methacrylate.
• a cross-linking monomer having a plurality of polymerizable ethylenically unsaturated groups, for instance ethylene glycol dimethacrylate.
• an ultraviolet absorbing material with a polymerizable functional group, such as 2-[3-(2 H-benzotriazol- 2-yl)-4-hydroxyphenyl]-ethylmethacrylate is also included in the composition.
• These methacrylate copolymers can be used to form intraocular lenses that have an essentially tack- free surface, a glass transition temperature (T g ) below about 37°C and more preferrably, below 20°C, a tensile strength from about 100 psi to about 1000 psi, and a refractive index from about 1.47 to about 1.49.
• T g glass transition temperature
• tensile strength from about 100 psi to about 1000 psi
• refractive index from about 1.47 to about 1.49.
• the present invention describes a biocompatible, intraocular lens and lens materials, which have superior optical characteristics and balanced physical properties. These properties include a relatively high refractive index, optical clarity, and sufficient characteristics and properties to provide a flexible intraocular lens, which is adequately deformable for insertion through a small incision.
• the intraocular lens and lens materials of this invention also have the appropriate elasticity, elastic memory, mechanical properties and possesses a non-sticky surface with reduced tackiness.
• a copolymer includes a mixture of polymers and statistical mixtures of polymers which include different weight average molecular polymers over a range.
• biocompatible is intended to mean that no acute physiological activity is observed in response to the presence of the material or substance described as possessing such a property. Examples of unacceptable physiological activity would include surface irritation, cellular edema, etc.
• polymer refers to materials formed by linking atoms or molecules together in a chain to form a longer molecule, i.e., the polymer.
• the polymers used in the present invention are preferably biologically inert, biocompatible and non-immunogenic.
• the particularly preferred polymeric materials are copolymers which, are biocompatible, non-immunogenic and not subject to substantial degradation under physiological conditions.
• glass transition temperature T g refers to the temperature at which the amorphous domains of a polymer take on the characteristic properties of the glassy state-brittleness, stiffness, and rigidity. At the glass transition temperature, the solid, glassy polymer begins to soften and flow (see Encyclopedia of Polymer Science and Engineering, 2 nd edition, vol. 7, pp. 531-544).
• deformable IOLs play an integral role in the effectiveness of the device.
• the deformable IOL should have sufficient structural strength, elasticity and elongation to allow the lens to be folded without fracturing.
• the IOL must also be small enough to permit adequate deformation for insertion through a small incision (less than about 3.5 mm). After insertion, the lens should regain its original shape at a controlled rate. The slow return allows the surgeon adequate time to locate the folded IOL in the eye before the lens body returns to its original shape and resolution and insures that the unfolding of the lens will not damage or otherwise traumatize surrounding ocular tissue.
• the IOL should also have sufficient structural integrity to retain such shape under normal use conditions.
• the thinner the deformable IOL the smaller the incision that is typically required.
• the lens in order for the IOL to function as desired after implantation, the lens must have sufficient optical refractory power.
• the refractive power of a lens is a function of its shape and the refractive index of the material from which it is made. A lens made from a material having a higher refractive index can be thinner and provide the same refractive power as a lens made from a material having a relatively low refractive index.
• Intraocular lenses which are designed to be rolled or folded for insertion through a small incision, have a thinner cross-section and are inherently more flexible. Because of the high refractive index of the copolymers from which the flexible IOLs of this invention are made, such IOLs can be manufactured with a thinner lens made from a polymer or copolymer with a lower refractive index, such as silicone. Accordingly, the IOLs of the present invention have thinner cross- sections than known silicone IOLs, and therefore permit the use of a smaller incision. Selection of Polymeric Materials for Deformable IOLs
• a primary object of this invention is to define a new soft methacrylate copolymer composition suitable for deformable IOL fabrication. It is also an object of the present invention that the polymer backbone structure of the soft methacrylate copolymer include a methyl group in order to structurally mimic the backbone of PMMA. It is a further object of this invention that the side chain ester group attached to the polymer backbone is selected to be structurally similar to a methyl group, as in other R-alkyl groups. Additionally, selection of the side chain ester group should result in a methacrylate ester copolymer which has a glass transition temperature (T g ) less than body temperature (i.e. 37°C), and preferably less than 20°C.
• T g glass transition temperature
• the methacrylate ester copolymer composition of this invention be essentially tacky- free through the appropriate selection of starting co-monomers, thereby, eliminating the use of surface energy lowering agents or using a plasma surface modification process.
• the polymers of the present invention are prepared by generally conventional polymerization methods (see Encyclopedia of Polymer Science and Engineering, Second Edition, Volume 1, pages 265-276, John Wiley & Sons, 1985.)
• the methacrylate copolymer composition used for the preparation of the foldable IOLs is derived from a variety of methacrylate ester monomers comprising a general formula of:
• R can independently be «-alkyl, .seoalkyl, -so-alkyl, tert-alkyl, or other isomeric alkyls, or R may be substituted alkyls which contain heteroatoms, such as oxygen or nitrogen.
• Suitable monomers include, but are not limited to, methyl methacrylate, ethyl methacrylate, butyl methacrylate, hexyl methacrylate, lauryl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxylhexyl methacrylate and N,N-dimethylethyl methacrylate.
• the soft, methacrylate ester copolymer composition of the present invention is preferably crosslinked with suitable crosslinkers comprising copolymerizable cross- linking monomers having a plurality of polymerizable ethylenically unsaturated groups.
• suitable crosslinkers include, but are not limited to, ethylene glycol dimethacrylate, 1,3-propanediol dimethacrylate, 1 ,4-butanediol dimethacrylate, 1,6- hexanediol dimethacrylate and allyl methacrylate.
• the co-polymerization reaction can be induced by traditional free radical initiators, such as azobisisobutyronitrile (AIBN), benzoylperoxide, as well as other free radical initiators.
• AIBN azobisisobutyronitrile
• an ultraviolet absorber with a polymerizable functional group is also included in the copolymer composition.
• Ultraviolet absorbers useful for IOL fabrications are, for example: 2-[3-(2 H-benzotriazol-2-yl)-4-hydroxyphenyl]ethyl- methacrylate.
• IOLs made of silicone-based polymeric materials have refractive indices which are generally about 1.46 or less. Consequently, the center or thickness of these IOLs is substantially greater than IOLs composed of materials having higher refractive indices.
• polymers of acrylate esters tend to have lower glass transition temperature (T g ), thus, these polymers can be soft and sticky (or tacky) while polymers of methacrylate esters generally tend to have higher glass transition temperature, and therefore can be hard, resulting in their inability to fold at room temperature.
• polymers of methacrylate esters can be less sticky or nonsticky compared to acrylate esters.
• copolymers engineered from the combination of acrylate esters with methacrylate esters can have a glass transition temperature below body temperature. Therefore, IOLs made of this type of copolymer can provide flexibility so that the lens can be folded requiring a small incision. On the other hand however, such a copolymer can be sticky (or tacky), which can be an undesirable property for IOL manipulation.
• copolymer compositions of the present invention are selected from monomeric methacrylate esters wherein the combination of methacrylate ester monomers is such that the resulting copolymer material will have a T g below 37°C. With this approach, the undesired tackiness of the IOL material is avoided while maintaining the needed flexibility of the IOL material.
• methacrylate esters for the present invention provides a copolymer with a refractive index in the range of about 1.47 to about 1.49.
• a refractive index in the range of about 1.47 to about 1.49 can also be sufficient for lenses designed for cataract patients. Accordingly, for the present invention, it is therefore undesirable for the refractive indices of the copolymers to fall below about 1.46.
• a methacrylate ester-based copolymer should provide similar desirable properties as that of PMMA since both polymers are a methacrylate ester- based polymer composition, which contain identical polymer backbone structures in terms of the incorporation of an appended methyl group off the tertiary carbon atom.
• the only structural alteration from PMMA is the nature of the R group(s) appended from the ester side chains of the second and possibly the third methacrylate ester monomers.
• a copolymer of methacrylate esters can be made non-sticky if appropriately substituted monomers of the methacrylate esters are selected in such a way that the T g of the copolymer is lower than body temperature. It would also be desirable for the first monomer of the methacrylate ester copolymer to be methyl methacrylate (MMA).
• MMA methyl methacrylate
• the selection of the R group in the copolymer is preferably limited to alkyl or substituted alkyl groups.
• this new soft, methacrylate ester copolymer composition has a structure which resembles as closely as possible the structure of a PMMA.
• the biocompatibility of this new soft, methacrylate ester lens mirrors that of the PMMA lens due to the close structural similarities.
• IOLs made from this new methacrylate ester copolymer composition are soft so they can be easily folded thereby requiring only a small incision for insertion.
• this new soft methacrylate copolymer composition is not sticky or tacky.
• this methacrylate-based lens will have balanced properties of optical clarity, high refractive index, flexibility, elasticity, elastic memory, mechanic properties, and a nonsticky surface. All of these properties are required for a deformable IOL.
• the general method for forming a biocompatible deformable intraocular lens comprises the steps of: (1) mixing suitable methacrylate esters; (2) partially polymerizing the methacrylate esters with an appropriate free radical initiator to form the pre-polymer; (3) forming a lens body with the polymer from step (2); and (4) curing the product of step (3).
• This process will produce a polymeric material, which has an essentially tack-free surface, a glass transition temperature (T g ) below about 37°C, a tensile strength from about 100 psi to about 1000 psi, and a refractive index from about 1.47 to about 1.49.
• T g glass transition temperature
• MMA methylmethacrylate
• lauryl methacrylate 15 grams
• lauryl methacrylate 15 grams
• ethylene glycol dimethacrylate 0.02 grams
• benzoyl peroxide 0.02 grams
• the flask is purged with nitrogen gas for about two minutes and subsequently maintained under positive N 2 atmosphere.
• the reaction mixture is then heated to about 100-110°C in a silicone oil bath with occasional stirring. After approximately 20 minutes, evolution of gas is observed, indicating decomposition of the benzoylperoxide initiator to form benzoyloxy radicals initiating the polymerization reaction.
• the reaction mixture becomes obviously viscous, indicating the polymerization and crosslinking reaction has occurred.
• the mixture is transferred to a glass plate with a Teflon gasket.
• a second glass plate is placed over the reaction mixture in order to sandwich the reaction mixture in between the two glass plates.
• the glass plates are clamped together and placed in a preheated oven at 110°C overnight (about 15 hours). The temperature is then raised to about 130°C for approximately 3 hours.
• the glass plates are subsequently removed from the oven and opened while still warm.
• a transparent, non-tacky elastic sheet (approximately 3.5 inch x 4.5 inch) is obtained.
• a lens can be made in a similar manner when a stainless steel mold is used instead of the glass plate.
• the mechanical properties of the resulting elastic copolymer are measured by standard ASTM test methods: tensile strength 150 psi; elongation 450%.
• the glass transition temperature is 0°C and refractive index is 1.48.
• the hardness, as measured by durometer Shore A is 20.
• the component composition of Example 1 is summarized in Table 1.
• Example 2 The same procedure as in Example 1 is followed with the exception of the reactants:
• Example 2 The same procedure as in Example 1 is followed with the exception of the reactants: 10.3 g of methylmethacrylate is combined with 9.2 g of lauryl methacrylate, 0.02 grams of benzoyl peroxide and 0.07 g of the crosslinker ethylene glycol dimethacrylate, is also added to the reaction mixture. The co-polymerization is initiated by benzoyl peroxide.
• the component composition is summarized in Table 3.
• the mechanical properties of the resulting elastic copolymer are: refractive index: 1.486; glass transition temperature (T g ): 28°C; hardness (Shore A): 88.
• Example 4 The same procedure as in Example 1 is followed with the exception of the reactants: 7.8 g of methylmethacrylate is combined with 13.2 g of lauryl methacrylate, 0.02 grams of benzoyl peroxide, 0.2 g of the crosslinker ethylene glycol dimethacrylate, and 0.3 g 2-[3-(2 H-benzotriazol-2-yl)-4-hydroxyphenyl]ethyl methacrylate, as a UN absorber.
• the co-polymerization is initiated by benzoyl peroxide.
• Table 4 summarizes the composition.
• the elastic copolymer has the following properties: refractive index: 1.485; tensile strength: 725psi; elongation 324%; hardness (Shore A): 46; T g : 9°C. Table 4
• Example 5 The same procedure as in Example 1 is followed with the exception of the reactants: 4.8 g of methylmethacrylate is combined with 15.2 g of hexyl methacrylate, 0.02 grams of benzoyl peroxide, and 0.07 g of the crosslinker ethylene glycol dimethacrylate. The co-polymerization is initiated by benzoyl peroxide. Table 5 summarizes the composition.
• the elastic copolymer has the following properties: refractive index: 1.482; Durometer (Shore A): 47; glass transition temperature: 23°C; tensile strength: 579 psi; elongation: 444%.
• Example 2 The same procedure as in Example 1 is followed with the exception of the reactants: 8.8 g of methylmethacrylate is combined with 15 g of lauryl methacrylate. and 0.02 grams of benzoyl peroxide. A transparent, non-sticky rubbery material is formed.
• glass plates cannot be used due to strong adhesion between the resulting copolymer and the glass surface. This adhesion problem can be resolved by using Teflon plates instead of glass plates. Table 6 summarizes the composition.

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