Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carbohydrate or derivative as a reactant
Reexamination Certificate
2001-01-23
2002-11-26
Cooney, Jr., John M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carbohydrate or derivative as a reactant
C521S064000, C521S084100, C521S094000, C521S097000, C521S182000, C521S184000, C521S185000, C521S187000, C521S189000
Reexamination Certificate
active
06486285
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a water-swellable polymer gel and a process for preparing the water-swellable polymer gel. More particularly, the present invention relates to a water-swellable polymer gel which is excellent in safety for human bodies, water absorbability, transparency and mechanical properties, and a process for preparing the same.
2. Discussion of the Related Art
A water-swellable hydrogel obtained by chemically crosslinking a polysaccharide has been widely utilized in the fields such as industry, agriculture, food and medicine. The applications of the water-swellable gel in the medical field include, for instance, wound dressings, adhesion-preventing materials, dialysis membranes, hemostatic materials, adhesive materials, sealants, contact lenses, materials for tissue regeneration, microcapsule materials, drug delivery systems (DDS), and the like.
The chemical crosslinking of the polysaccharide can be carried out by a chemical reaction, e.g. gelation with a polyfunctional reagent; crosslinking using a coordinate bond, e.g. gelation by calcium ions of alginic acid; crosslinking using a hydrophobic bond, e.g. gelation by heating methyl cellulose or hydroxypropyl cellulose; crosslinking using intermolecular association, e.g. cooling of agar or carrageenan to cause the gelation, or the like. Among them, the crosslinking by a chemical reaction has an advantageous merit in that water absorbability and strength of the resulting polysaccharide gel can be easily controlled depending upon its purposes.
The crosslinking of the polysaccharide by a chemical reaction can be carried out by treating a polysaccharide solution with a crosslinking reagent having at least two functional groups. However, there are some defects in the crosslinking such that the crosslinking cannot be efficiently progressed in water, because many of the polysaccharides are substantially dissolved only in water.
As a process for crosslinking a polysaccharide by a chemical reaction, there has been known a process comprising crosslinking a polysaccharide with a bifunctional low-molecular weight reagent in an aqueous solvent (hereinafter simply referred to as “low-molecular weight crosslinking agent process”). Among them, as a process for crosslinking a water-soluble polysaccharide by a chemical reaction, there have been known a process comprising crosslinking a polysaccharide with an epoxy compound in an aqueous, acidic or basic solution (Japanese Examined Patent Publication No. Hei 6-69490 and Japanese Unexamined Patent Publication No. Hei 11-509256); a process comprising crosslinking a polysaccharide with divinyl sulfone in an aqueous basic solution (Japanese Patent Laid-Open No. Hei 2-138346), and the like.
However, there are some defects in the low-molecular weight crosslinking process such that the resulting gel is extremely brittle, while the gel tends to exhibit a relatively high water absorption, and that there is necessitated a complicated procedure for thoroughly washing the polymer gel after its preparation in order to remove a crosslinking agent and a catalyst remaining in large amounts in the internal of the gel.
Therefore, the low-molecular weight crosslinking agent process cannot be necessarily considered to be a useful process from the viewpoints of physical properties and productivity of the hydrogel.
Recently, there has been developed a process comprising crosslinking a polysaccharide with a polyfunctional high-molecular weight crosslinking agent (hereinafter simply referred to as “high-molecular weight crosslinking agent process”).
As the high-molecular weight crosslinking agent process, there have been known a process comprising crosslinking an ester of a carboxyl group-containing polysaccharide, for instance, propylene glycol alginate (hereinafter simply referred to as “PGA”), with a water-soluble polymer having amino group such as gelatin to cause insolubilization as disclosed in British Patent No. 962483; Japanese Unexamined Patent Publication No. Hei 8-508933; S. B. Mohamed and G. Stainsby,
Food Chemistry,
13, 241 (1984); J. E. McKay, G. Stainsby, E. L. Wilson,
Carbohyd. Polym.,
5, 223 (1985), and the like.
According to the above-mentioned process, it is thought that the gelation is caused via the aminolysis (amidation) of &egr;-amino group derived from lysine residue of a polyamino acid (protein) with an ester moiety of the PGA in water.
However, there are some defects in the gel made from PGA and a protein such as gelatin, such that water absorbability of the gel is low, because a protein solution having a high concentration is required for the preparation of the gel, so that a large amount of the protein is inevitably contained in the gel. In addition, there is also a defect in this gel such that the gel cannot be formed in a neutral aqueous solution which is suitable for materials for medical use.
Also, it has been proposed that a synthetic high-molecular weight compound having amino groups as repeating units, such as a polyethyleneimine, is used as a crosslinking agent for the PGA as disclosed in British Patent No. 962483. However, this process necessitates a treatment with a basic substance for the formation of a gel. Therefore, there are some defects in this process that pinholes are apt to be generated in the resulting gel, as well as some practical problems that the water absorbability and strength of the gel are remarkably low.
An object of the present invention is to provide a water-swellable polymer gel having high water absorbability and gel strength, the essential component of which comprises a natural ingredient, and a foam of a water-swellable polymer gel.
Another object of the present invention is to provide a process for readily preparing a water-swellable polymer gel in an aqueous solvent in high productivity and safety for human bodies.
These and other objects of the present invention will be apparent from the following description.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a water-swellable polymer gel prepared by reacting an ester of a carboxyl group-containing polysaccharide with a compound having at least two &agr;-amino groups, which is derived from a natural amino acid, and a foam made thereof.
In addition, the present invention provides a process for preparing a water-swellable polymer gel, comprising reacting an ester of a carboxyl group-containing polysaccharide with a compound having at least two &agr;-amino groups, which is derived from a natural amino acid.
DETAILED DESCRIPTION OF THE INVENTION
The ester of a carboxyl group-containing polysaccharide (hereinafter simply referred to as “esterified polysaccharide”) means a compound formed by bonding at least one of the carboxyl groups of the carboxyl group-containing polysaccharide, preferably at least two of the carboxyl groups of the carboxyl group-containing polysaccharide, with hydroxyl groups of an alcohol to form ester bonds. Among the esterified polysaccharides, those substantially water-soluble are preferable.
The alcohol includes aliphatic alcohols, aromatic aliphatic alcohols, cyclic aliphatic alcohols and heterocyclic alcohols. Among them, in consideration of the water-solubility of the esterified polysaccharide, there can be cited, for instance, aliphatic alcohols having 1 to 16 carbon atoms such as methanol, ethanol and propanol; and polyhydric alcohols having at least two hydroxyl groups and 2 to 16 carbon atoms such as ethylene glycol, propylene glycol and glycerol. As to the polyhydric alcohol, it is required that only one of hydroxyl groups of the polyhydric alcohol forms an ester bond together with carboxyl group of the carboxyl group-containing polysaccharide.
The carboxyl group-containing polysaccharide includes, for instance, carboxyl group-containing polysaccharides, such as alginic acid, xanthane gum, gellan gum, hyaluronic acid, and their physiologically acceptable artificial derivatives; artificial derivatives of polysaccharides which do not usually have any carboxyl groups, suc
Cooney Jr. John M.
Kuraray Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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