Surgery – Means and methods for collecting body fluids or waste material – Absorbent pad for external or internal application and...
Reexamination Certificate
2001-03-30
2004-12-21
Acquah, Samuel A. (Department: 1711)
Surgery
Means and methods for collecting body fluids or waste material
Absorbent pad for external or internal application and...
C525S054100, C525S054110, C525S054400, C525S055000, C525S063000, C524S017000, C524S018000, C524S047000, C604S372000, C604S374000
Reexamination Certificate
active
06833488
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates, generally, to composite materials comprised of intercoupled biopolymers and synthetic polymers, which when in contact with aqueous media behave as hydrogels, and methods for their preparation. More precisely, the present invention relates to the method of crosslinking three-dimensional macromolecular configurations by polymer-polymer intercoupling without using micromolecular or oligomeric combination crosslinking agents or coupling agent, in liquid media containing water. Most precisely, the invention relates to reacting synthetic polymers having reactive chemical functional groups with free chemical functional groups of biopolymers to form covalent bonds, without forming secondary products. The synthesis is preformed in a liquid-liquid heterogeneous system. Particularly, the invention relates to the preparation of superabsorbent materials that are biocompatible and biodegradable for use in different applications, such as for bodily hygiene, medical biomaterials, agromaterials, drying agents and others.
BACKGROUND OF THE INVENTION
Absorbing materials for water and aqueous solutions, including fluids, screted or eliminated by the human body are known. These materials are generally polymer based in the form of powders, granules, microparticles, films or fibres. Upon contact with aqueous liquid systems they swell by absorbing the liquid phase in their structure, without dissolving it. When the swelling reaches equilibrium there is obtaining a gel, which frequently is called “hydrogel”.
These polymers (also referred to as superabsorbent polymers or hydrophilic resins) are primarily used in personal care products to absorb body fluids, for example baby diapers, adult incontinence products, feminine hygiene products, and the like. The hydrophilic resin particles quickly absorb fluids and retain such fluids to prevent leakage and give the absorbent structure a “dry feel” even when wetted.
In the applications for hygienic products, hydrophilic resin particles, as superabsorbent polymers, are incorporated into absorbent structures which contain for example, synthetic and natural fiber or paper based woven and nonwoven structures, and toughened masses of fibers, such as fluff pads. The materials used in such structures can quickly absorb aqueous fluids and distribute them over the whole absorbent structure. The structures, in the absence of hydrophilic resin particles, have limited absorption capacity, and are bulky due to the large amount of material needed to provide acceptable absorption capacity and do not retain fluid under pressure. Therefore, in order to improve the absorbency and fluid retention characteristics of such absorbent structures there are incorporated hydrophilic resin particles which imbibe fluids to form a swollen hydrogel material.
Initially, only the very high swelling capacity on contact with liquids, also referred to as free swelling capacity, had been the main factor in the development of superabsorbers; later it turned out, however, that not only the amount of absorbed liquid is of importance but also the stability of the swollen gel. As it turns out however, absorbency, also referred to as swellability or free swelling capacity, on the one hand, and gel strength of a cross-linked polymer, on the other hand, represent contradictory properties, as is known from U.S. Pat. No. Re 32,649. This means that polymers having a particularly high absorbency exhibit poor strength of the swollen gel so that the gel is deformable under pressure (e.g., the load of a body) and further liquid distribution and absorption is prevented. Therefore, a balance between absorption capacity (gel volume) and gel strength is to be aimed for to ensure liquid absorption, liquid transport, dryness of the diaper and the skin when such superabsorbers are used in a diaper structure. In this connection, not only the polymer's capability of retaining a liquid under pressure, after first swelling freely is of importance, but also that liquids be absorbed even when there exists a simultaneous pressure, i.e. while the liquid is being absorbed. This is the case in practice when a baby or person sits or lies on a sanitary article or when shear forces are exerted, such as by moving legs. This particular absorption property is referred to as absorption under load.
Furthermore, the absorbent capacity of superabsorbents for body fluids is dramatically lower than for deionised water. It is generally believed that this effect results from the electrolyte content of body fluids and the effect is often referred to as “salt poisoning”.
Water absorption and water retention characteristics of superabsorbents are due to the presence in the polymer structure of ionisable functional groups. These groups are usually carboxyl groups, a high proportion of which are in the form of salt when the polymer is dry. and undergo dissociation and solvation upon contact with water. In the dissociated state, the polymer chain will have a series of functional groups having the same electric charge and thus repel one another. This leads to expansion of the polymer structure which, in turn, permits further absorption of water molecules. This expansion is, however, subject to the constraints provided by the cross-links in the polymer structure which must be sufficient to prevent dissolution of the polymer. It is assumed that the presence of a significant concentration of electrolytes in the water interferes with dissociation of the functional groups and leads to the “salt poisoning” effect. Although most commercial superabsorbents are anionic, it is equally possible to make cationic superabsorbents with the functional groups being, for example, quaternary ammonium groups. Such materials also need to be in salt form to act as superabsorbents and their performance is also affected by the salt-poisoning effect.
Superabsorbents have not found widespread use in superabsorbent sanitary articles used to absorb blood and other serous body fluids such as sanitary napkins, surgical wipes, because these superabsorbents do not absorb blood readily, since they do not have a high capacity for blood. Low blood absorbent capacity means that large amounts of the superabsorbent material must be incorporated in blood absorbent articles, which increases the cost of such articles.
Previously known processes for the production of in-situ superabsorbent polymers have the disadvantage that large amounts of monomers are present in an unreacted form after termination of the actual polymerization. Since these monomers are usually toxic, they are removed in a subsequent step by reacting them or otherwise. If reacted, they general form linear polymer chains of mean molecular weight and not the desired cross-linked polymers. These polymer chains are soluble and cannot contribute to the water absorption, in particular under load, or to the water retention under load. Furthermore, they have the undesired property of giving a slimy feel to the polymer after water absorption.
The known synthetic absorbers are practically water-insoluble, and although they absorb multiple amount of their weight of water, urine, or other aqueous solutions, they are relatively resistant to biodegradation.
Many strategies were used to increase the performance of superabsorbent materials such as:
chemical structure: partially neutralized poly(acrylic acid) polymer (see U.S. Pat. No. 4,654,039), partially neutralized copolymer of isobutylene and maleic anhydride (U.S. Pat. No. 4,389,513), a saponification product of a vinyl acetate-acrylic acid copolymer (U.S. Pat. No. 4,124,748), a hydrolyzate of acrylamide polymer or acrylamide copolymer (U.S. Pat. No. 3,959,569), a hydrolyzate of an acrylonitrile copolymer (U.S. Pat. No. 3,935,099), polysaccharides and its derivatives (U.S. Pat. No. 4,076,663, U.S. Pat. No. 4,076,663, U.S. Pat. No. 5,847,031; U.S. Pat. No. 5,712,316; U.S. Pat. No. 5,733,576; U.S. Pat. No. 5,736,595; U.S. Pat. No. 5,453,323, U.S. Pat. No. 6,107,432), proteins (U.S. Pat. No. 5,847,089, U.S. Pat. Nos. 4,264,493
Bucevschi Mircea Dan
Colt Monica
Acquah Samuel A.
Exotech Bio Solution Ltd.
Lahive & Cockfield LLP
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