This invention relates to a new scleral buckle material and more generally to a new synthetic hydrophilic polymer for eye surgery and other in vivo implants.
Synthetic materials have several applications in ophthalmic medicine, including surgical implantation to create a scleral buckle to correct a condition known as retinal detachment, and as contact lenses. Silicone materials, both rubber and sponge, are known for use in scleral buckle procedures. Synthetic organic polymers with hydrophilic properties also have been used as scleral buckle materials, and certain species are the popular materials for contact lenses. Recent developments in correcting retinal detachment with scleral buckling are described in "Sutureless Scleral Buckling", G. A. Calabria, R. C. Pruett, M. F. Refojo, and C. L. Schepens, Archives of Ophthalmology, May 1970, Vol. 83, pp. 613-618; "Further Experience With Sutureless Scleral Buckling Materials", G. A. Calabria, R. C. Pruett, and M. F. Refojo, Archives of Ophthalmology, July 1971, Vol. 86, pp. 77-81; and "Experimental Scleral Buckling With A Soft Xerogel Implant", M. F. Refojo and H. S. Liu, Ophthalmic Surgery, December 1978, Vol. 9, No. 6, pp. 43-50. Materials for contact lenses, and particularly for soft contact lenses, are described in "Contact Lens Materials", M. F. Refojo, International Ophthalmology Clinics, Spring 1973, Vol. 13, No. 1, pp. 263-277; "Contact Lenses", M. Refojo, Encyclopedia of Polymer Science And Technology, Supplement Volume 1, pp. 195-219; and "Contact Lenses", M. F. Refojo, Encyclopedia of Chemical Technology, Volume 6, Third Edition, pp. 720-742. The polymer chemistry of certain synthetic hydrogels is described in Soft Contact Lenses: Clinical And Applied Technology, M. Ruben, Editor, Published by John Wiley & Sons, Chapter 3, pp. 19-38.
Materials for these ophthalmologic applications are to be non-toxic and otherwise tolerated without causing tissue inflamation or other rejection mechanisms, and they are to be relatively nonabsorbable. The materials are also to be capable of sterilization without deterioration, and are to be permeable to oxygen, water and low molecular-weight water-soluble substances. Implant materials also are often to be non-biodegradable. Another desired property is that the implant material be capable of being cast or otherwise formed into an article of specific configuration, which the article retains. In addition, material for a scleral buckle preferably is soft, pliable and elastic; a specific objective is that it be capable of being compressed by overlying sutures without cutting through the implant or of being applied with sutureless techniques. Materials for ophthalmic surgery in addition are often desired to absorb antibiotics and other drugs for prolonged release after surgical implantation. In addition, it is desired that surgically implantable materials have pores of such small size that they do no form sites for infection by bacteria or other pathogens.
Known materials meet numerous of these properties, but all too often the fulfillment of some properties is attendant with deficiencies with regard to other properties. For example, methacrylate hydrogels known for use as scleral buckles have the disadvantage of being hard and stiff when dry; they become soft and pliable only when wet. The known silicone rubber sponges used in scleral buckle surgery is considered to have pores sufficiently large to provide a site for bacterial infection.
It is accordingly an object of this invention to provide an improved hydrophilic gel, or hydrogel, for in vivo implantation. "Implantation" and "implant" are used in this application in a broad context to include not only surgical implants but also a topical implant such as a contact lens.
A more particular object is to provide an implant hydrogel which attains the properties discussed above to a greater extent than previously available, and further to provide such a hydrogel suitable for ophthalmic use.
Another object of the invention is to provide an implant hydrogel having improved properties in terms of softness, in terms of elasticity, and in terms of resistance to tensile rupture. More specific objects are that the hydrogel be soft, pliable and elastic when dry as well as when wet, and furthermore that it be sufficiently tough, for example, to hold a surgical suture. Thus the objects of the invention include the provision of a scleral buckle hydrogel which is soft and elastic when wet as well as when dry, and which has sufficient resistance to tensile rupture to hold a suture.
It is also an object of the invention to provide a method for preparing hydrogel implant articles of the above character.
Other objects of the invention will in part be obvious and will in part appear hereinafter.
The invention accordingly comprises a composition of matter possessing the characteristics, properties and relation of constituents exemplified in the composition hereinafter described; the article possessing the features, properties, and relation of elements exemplified in the following detailed disclosure; and the several steps and the relation of one or more of such steps with respect to each of the others for the preparation of such a composition of matter and such an article; and the scope of the invention is indicated in the claims.