Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-01-05
2003-11-25
Zalukaeva, Tatyana (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S317100, C526S319000, C526S320000, C526S328000, C623S006110, C524S091000, C524S359000
Reexamination Certificate
active
06653420
ABSTRACT:
The present invention relates to a process for the manufacture of hydrogels with a high water content and porosity, exhibiting a surfactant-induced narrow pore size distribution and their use for various biomedical applications, especially contact lenses including extended-wear contact lenses and long-term implants.
In many applications it has been found advantageous for polymers to be porous. The degree of porosity required depends on the application. For example, membrane filtration depends on the use of microporous polymers to effect separations of various materials. Macroporous sheets of chemically resistant polymers find extensive use as cell dividers in cells for electrolysis or electricity storage. Macroporous materials (open cell foams) produced through the use of blowing agents are used as cushioning materials. Porous materials have also found use in medicine as the medium for the dispensing of medicinal compounds, in medical implants for cell encapsulation or tissue ingrowth, and to achieve certain mechanical properties such as viscoelasticity.
Pores may be formed in the polymer during the process of manufacturing an article of the desired shape or may be formed in the article after manufacture. A preferred process for the manufacture of porous polymers comprises the polymerization of a polymerizable component in the presence of an inert material often referred to as a porogen. Subsequent leaching of the porogen gives rise to interstices throughout the formed polymer material. However, this process is usually complicated by extensive extraction procedures necessary for a complete removal of the conventionally used porogens. A further possible disadvantage of this process is the difficulty of stabilising the suspension of porogen in the polymerization mixture. Unstable suspensions can lead to an non-homogeneous and unacceptable product. In many cases, extensive optimisation of the viscosity of the system and the type of porogen is needed to obtain a satisfactory result. In addition the procedure is limited in terms of the availability of porogens suitable for introducing the desired ranges of pore sizes. Beyond this, conventional porogens lead to a broad pore size distribution.
It now has surprisingly been found that specific surfactants, in particular surfactants with an inverse temperature dependent solubility, contribute to a narrow pore size distribution and greatly simplify porogen-removal after the polymerization process. Used as porogens, these surfactants offer an advantage in the preparation of porous matrices due to their unique inverse temperature dependent solubility property. With the proper choice of a porogen having a specific cloud point temperature, it is possible to achieve a system or formulation where the porogen forms a homogeneous phase with the polymerizable components before the cure. Due to their inverse temperature dependent solubility behavior, the porogens form aggregates during the cure at a temperature around the cloud point temperature of the composition. Therefore, curing of this formulation around its cloud point temperature leaves an imprint of the defined aggregation structure of the surfactants in the polymerized hydrogel membranes. These aggregates are then easily removed from the matrix polymer at a temperature below their cloud point in a suitable extraction medium that swells the polymer, leaving a porous hydrogel behind with a narrow pore size distribution created by the aggregated porogen that is now removed. In addition, different porogens impart different levels of porosity to the hydrogel membranes.
Hence, an object of the present invention is to provide a process for the manufacture of a hydratable porous polymer comprising the steps of:
(a) providing a homogeneous composition at a temperature below the cloud point temperature of the composition comprising
(i) a polymerizable component that comprises at least one polymerizable hydrophilic monomer or macromer,
(ii) a porogen having an inverse temperature dependent solubility, and
(iii) a solvent;
(b) subjecting the composition to a polymerization reaction at or above the cloud point temperature of the composition; and
(c) removing the porogen from the resulting porous polymer at a temperature below the cloud point temperature of the composition.
The polymerizable component according to step (a) may in principle contain any hydrophilic ethylenically unsaturated compound as long as the composition as a whole is homogenious at easy accessible temperatures, for example at room temperature, and the inverse temperature dependent solubility of the porogen is retained in the formulation. Examples of polymerizable hydrophilic monomers that may be part of the polymerizable component according to step (a) are, for example, (i) acrylic or methacrylic acid; (ii) a C
1
-C
18
-alkyl ester of acrylic or methacrylic acid which may be substituted in the alkyl portion by hydroxy; (iii) acrylamide or a N-mono- or N,N-di-C
1
-C
4
-alkyl acrylamide, for example N,N-dimethyl acrylamide; (iv) a 5- or 6-membered heteroaromatic or heteroaliphatic monomer having one N-atom and in addition no further heteroatom or an additional N- or O-heteroatom, or a 5 to 7-membered lactame, for example N-vinylpyrrolidon, N-vinylimidazol, N-vinyl-2-methylimidazol or N-acryloyl morpholine; (v) a sulfocontaining monomer, preferably an ethylenically unsaturated compound having from 2 to 18 C-atoms which is substituted by a sulfo group or a suitable salt thereof, for example methallyl-sulfonic acid, styrenesulfonic acid, sulfopropylmethacrylate, sulfopropylacrylate, 2-acrylamido-2-methylpropanesulfonic acid, vinyl sulfonic acid, or a suitable salt thereof, for example an alkaline salt or ammonium salt, in particular the sodium or potassium salt; or (vi) allyl alcohol, vinyl acetate or vinyl alcohol, which can be used in each case alone, or in mixtures with other ethylenically unsaturated monomers.
A suitable hydrophilic macromer that the polymerizable component may comprise is, for example, a vinylfunctionalized polyvinyl alcohol, polyalkylene oxide or N-vinylpyrrolidone homo- or copolymer. The macromer may contain one or more than one ethylenically unsaturated double bond. A preferred hydrophilic macromer is a vinylfunctionalized polyvinyl alcohol or polyethylene oxide, in particular a vinylfunctionalized polyvinyl alcohol, for example as described in U.S. Pat. No. 5,508,317, issued to Beat Müller on Apr. 16, 1996, which is incorporated herein by reference. The weight average molecular weight of the hydrophilic macromer may vary within wide limits; a suitable range is from about 2000 up to 1,000,000. Preferably, the hydrophilic macromer has a molecular weight of up to 300,000, especially up to approximately 100,000 and especially preferably from about 5000 to about 50,000.
In a preferred embodiment of the invention the polymerizable component comprises one or more different hydrophilic monomers selected from the group consisting of hydroxyethyl acrylate, hydroxyethyl methacrylate, N-vinyl pyrrolidone, acrylic acid, methacrylic acid, acrylamide, N,N-dimethyl acrylamide, N-acryloyl morpholine, vinyl acetate, vinyl alcohol, methallylsulfonic acid, styrenesulfonic acid, sulfopropylmethacrylate, sulfopropylacrylate, 2-acrylamido-2-methylpropanesulfonic acid, vinyl sulfonic acid, and a suitable salt thereof.
An even more preferred embodiment of the invention concerns a polymerizable component comprising one or more different monomers selected from the group consisting of hydroxyethyl methacrylate, N-vinyl pyrrolidone, acrylamide, N,N-dimethyl acrylamide, sodium methallylsulfonate, sodium styrenesulfonate, potassium sulfopropylmethacrylate and potassium sulfopropylacrylate.
In addition, the polymerizable component may contain a low molecular weight crosslinker. A suitable crosslinker, if present, is, for example, a low molecular weight di- or polyvinylic crosslinking agent such as ethylenglycol diacrylate or dimethacrylate, di-, tri- or tetraethylen-glycol diacrylate or dimethacrylate, allyl (meth)acrylate, a C
2
-C
8
-alkyl
Domschke Angelika Maria
Francis Vimala Mary
Gardner & Groff, P.C.
Novartis AG
Zalukaeva Tatyana
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