Photocurable siloxane polymers

Details Photocurable siloxane polymers Photocurable siloxane polymers

2002-04-29

2004-05-18

Peng, Kuo-Liang (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From silicon reactant having at least one...

C528S012000, C528S033000, C528S036000, C528S043000, C526S279000

Reexamination Certificate

active

06737496

ABSTRACT:

FIELD OF INVENTION
The present invention relates to photocurable polysiloxanes polymers (silicones) having functional acryl groups, useful in the preparation of intraocular lenses (IOLs). The invention also relates to methods for producing elastomers comprising the said polymers, as well as to methods for producing accommodating lenses in vivo, which means that the lens is formed in the capsular bag of the eye.
BACKGROUND OF THE INVENTION
Implantation of an intraocular lens (IOL) following the extraction of a cataract is now a standard ophthalmic procedure. The conventional IOL used to replace the natural lens is a fixed focus lens manufactured from a rigid plastic such as poly(methylmethacrylate), PMMA, or from an elastomer, such as silicone. The implantation of such a lens usually necessitates the patient using spectacular correction for reading. To overcome this limitation of the conventional IOL, increasing attention has been given to bifocal and multizonal lenses.
The technique of cataract explantation and lens replacement for an accommodating IOL, an accommodating capsular lens, ACL, involves the metered injection of a low viscosity liquid, through a small incision (≈1 mm diameter), into the capsular bag, followed by its polymerization under forming pressure to create a lens of the required shape, using the form of the capsular bag as the mold. To reproduce the optical performance of the natural lens, the replacement lens will require a refractive index close to 1.41. To respond to the accommodating forces of the eye, the compression modulus of IOL should be comparable to that of the natural lens which is in the range of about 1 to 5 kPa. To design materials which balance the conflicting material's requirements of the ACL requires the design of unique systems. These considerations have led a number of researchers to propose and to study the development of an ACL. An accommodative re-fill lens is an IOL formed by filling the capsular bag with the precursors of an elastomer, and causing, or allowing, the elastomer to set in the form of the natural lens. Thin-walled inflatable balloons, of silicone rubber, have also been developed which can be inserted into the capsular bag and filled with the desired system.
Most researchers of the development of the accommodative re-fill lens have used silicone-derived systems for filling the capsular bag, either in the form of silicone oils or LTV (low temperature vulcanizing) silicone elastomers. Such systems suffer from disadvantages in the context of re-fill lens formation, the dimethyl silicones have a restricted refractive index (1.40), LTVs cure slowly, up to 12 hours may be needed to complete their setting and their slow setting may result in material loss from the capsular bag through the surgical incision, further, the high viscosities of some silicone oils and intermediates make their air-bubble free injection very difficult.
Injectable formulations of polysiloxanes for making an IOL directly in the capsular bag of the human eye have been suggested in U.S. Pat. Nos. 5,278,258, 5,391,590 ('590) and U.S. Pat. No. 5,411,553 to Gerace et al as well as in U.S. Pat. No. 5,116,369 (Kushibiki et al) These patents describe mixtures of a vinyl-containing polyorganosiloxane, an organosilicone comprising hydride groups and a platinum group metal catalyst which are capable of being cured at ambient body temperature to an IOL inside the capsular bag of the eye. These compositions suffer from the general drawback of low temperature curing in that the curing process is difficult to control for the surgeon. The use of silicone fluids, demonstrating the principle of a silicone-based ACL, has been reported by Haefliger, E. and Parel, J-M. (1994) J. Refractive and Corneal Surgery 10, 550-555, but the gain in accommodation declined, probably because the system was not crosslinked.
Subsequently, the difficulties of introducing a thermally curing silicone into the capsular bag have been demonstrated. A major disadvantage of the use of a thermally curable system, such as one based on Pt-cured vinyl addition, for the “mold-in-the-bag” approach is understood from a consideration of the three characteristic phases of network formation, viz. (a) pre-gelation; (b) gelation; and (c) curing. A lens can only be molded successfully in the pre-gelation phase, and once the system has passed into its gelation phase it cannot be molded with precision. This is because the gel (polymer of infinite molecular weight) which is formed at and after the gel point has an elastic memory, and so, regardless of the forming conditions, it will always revert to its original shape with time. When molding an IOL, or ACL, this recovery process becomes evident as surface defects. such as ripples or wrinkles, which cause serious impairment of lens quality. When molding lenses from silicone systems, involving thermally induced polymerization, outside the body this phenomenon is easily regulated by adjusting the process variables of catalyst type and concentration, time, temperature and pressure. Molding an ACL within the eye during surgery imposes severe restrictions on the choice of these process variables, the molding temperature is body temperature, the molding time is the minimum compatible with the required residence time for any given patient upon the operating table, that is to say that ideally it must be variable to meet the exigencies of the surgical demands of both the ophthalmologist and the patient. In general terms, in a thermally cured silicone system, such as those based on Pt-catalysts, the durations of the pre-gelation and cure phases are coupled, a system with a short cure time has a short pre-gelation time. It is generally regarded as complicated to lengthen the pre-gelation time without lengthening the cure time.
To comply with the difficulties of controlling the thermally induced curing it would be desirable to provide systems wherein the curing is command set by the surgeon. For this purpose photocurable (i.e. photopolymerization) compositions have been contemplated. EP 0414219 describes an injectable system in which the liquid composition comprises a difunctional acrylate and/or methacrylate ester and a photoinitiator activated by light of 400-500 nm wavelength. Hettlich et al. (German J. Ophthalmol. vol. 1, 346-349, 1992) was amongst the first to propose the use of photopolymerization of a monomer system as an alternative approach to setting the material within the capsular bag. He pointed to the clinical success of blue light photocurable resins for dental applications and explored the use of such systems as injectable materials for filling capsular bags from the eyes of cadaver pigs and live rabbits. However, the systems used by Hettlich form materials with moduli too high to allow accommodative processes. Further, the introduction of acrylic monomers into the eye would be undesirable, since they are well-known to have high physiological activity.
Compositions comprising polysiloxanes with functional acrylic end groups which are curable with UV light have earlier been disclosed for the manufacture of contact lenses. Curable acrylic silicones per se have indeed been known for a considerable time in various industrial applications, as disclosed by U.S. Pat. Nos. 4,778,862 and 4,348,454. U.S. Pat. No. 5,321,108 and the Japanese patent specifications published as 3-257420, 4-159319 and 5-164995 disclose compositions of acryl-terminated polysiloxanes suitable for contact lens production. However, the compositions for making contact lenses are unsuitable for intraocular lens production directly inside the human eye, wherein specific considerations to the polysiloxanes must be taken in order to perfect an injectable lens forming material.
Consequently, there is a need for photocurable polymers and injectable compositions thereof which are adapted to be included in a composition suitable for injection into the capsular bag of the human eye. The present invention aims to perfect such polymers and compositions including them, so they meet the necessary r

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