Colloid systems and wetting agents; subcombinations thereof; pro – Continuous or semicontinuous solid phase – The solid phase contains organic material
Reexamination Certificate
2000-02-15
2001-10-30
Brunsman, David (Department: 1755)
Colloid systems and wetting agents; subcombinations thereof; pro
Continuous or semicontinuous solid phase
The solid phase contains organic material
C530S402000, C530S409000, C530S410000, C106S124300, C106S155200, C106S156220, C106S156230, C106S156300, C106S156310
Reexamination Certificate
active
06310105
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to protein hydrogels. More specifically, the present invention relates to chemically modified protein hydrogels which are capable of absorbing a large amount of water or other liquid per unit mass.
BIBLIOGRAPHIC CITATIONS
Complete bibliographic citations to the numbered references discussed herein are contained in the bibliography section, directly preceding the Claims.
DESCRIPTION OF THE RELATED ART
Beginning in the early 1970's, and continuing to the present day, there has been a growing awareness that the continued widespread use of non-biodegradable, petroleum-based polymeric materials may pose serious environmental concerns. These concerns are heightened by production statistics showing the enormous and still-growing volume of non-biodegradable plastics produced annually, the vast majority of which are ultimately interred in landfills. This raises concerns not only as to the amount of space available for solid waste disposal (which is disappearing at an increasingly rapid pace), but also raises equally serious concerns that the leaching of toxic monomers and oligomers from landfilled plastics will contaminate ground water, thereby causing health problems in humans and animals.
In addition to concerns regarding human health and the environment, the world-wide depletion of petroleum reserves, in combination with wildly fluctuating petroleum prices due to political and economic conflicts, indicates that less dependence on petroleum-derived products might be prudent. Therefore, the development of alternative, and renewable, resources for industrial products is needed.
Because of the factual and/or perceived economic, environmental, and public health concerns accompanying non-biodegradable, petroleum-based products, a non-petroleum-based, environmentally safe, biodegradable, and renewable source for industrial products is needed. As evidenced by the following references, several types of useful products have been fabricated from renewable sources of starting materials.
For instance, Mann, U.S. Pat. No. 2,729,628, describes a process for increasing the intrinsic viscosity of a long chain polypeptide, particularly natural proteins such as fish, peanut protein, soybean protein, casein, egg albumin, and blood albumin by acylating the protein with terephthalyl dichloride. Here, the protein is reacted with the terephthalyl dichloride using the Schotten-Baumann method at a temperature of from about 0° to 30° C.
Young etal., U.S. Pat. No. 2,923,691, describe the polymerization of animal proteins to improve their characteristics for use as animal glue. Young et al. introduce aldehydes to an animal glue protein so as to modify the viscosity and jelly characteristics of the glue product without solidifying or insolubilizing the protein. Here, Young et al. are interested in increasing the viscosity and jelly strength of last run animal glues, which tend to be of inferior quality. The process described by Young et al. includes two steps: first, a cyanic acid salt is reacted with the protein material; second, an aldehyde, such as formaldehyde or glucose, is added to the protein material.
Two patents to Miller (U.S. Pat. Nos. 3,685,998 and 3,720,765), and assigned to the Monsanto Company, describe improved protein feed materials for ruminants. In the Miller patents, protein feeds are rendered resistant to digestive breakdown in the rumen, but not in the abomasum and intestines, by treating protein-containing feed material with a polymerized unsaturated carboxylic acid or anhydride. For instance, the proteinaceous feedstuff is treated with a polyanhydride such as poly(maleic anhydride). This renders the protein feedstuff substantially indigestible in the fluid medium of the rumen, yet still digestible in the acidic media of the abomasum and the intestines. In this manner the proteins of the feedstuff are spared breakdown in the rumen, and are available for absorption in the subsequent digestive organs.
Three patent references to Battista (U.S. Pat. Nos. 4,264,493; 4,349,470; and 4,416,814) describe the formation of protein hydrogel structures formed from natural proteins having molecular weights not exceeding 100,000 by dissolving the protein in an aqueous acidic solution, crosslinking the protein, and air drying the solution to a moisture content not exceeding 10 percent. The Battista patents are largely drawn to the formation of clear products such as soft contact lenses, ophthalmological films, and the like.
Although Battista refers to the compositions described therein as hydrogels, that term is defined within the Battista references as meaning “a crosslinked protein polymer of natural origin having an average molecular weight of about 100,000 or less, capable of being swollen by water over a wide range of water contents ranging from as low as 30 percent to 1,000 percent and higher while possessing useful rheological control properties for specific end product uses.” (See for instance, U.S. Pat. No. 4,264,493, column 1, lines 19-27.) The hydrogels described by Battista are not designed to be superabsorbent. Rather, they are designed to be optically clear and to have sufficient mechanical integrity to function as soft contact lenses.
The protein hydrogel structures described in the Battista patents are made from natural protein raw materials that form clear solutions in water. The protein raw material is first dissolved in an acidic aqueous solution of from pH 3.5 to about pH 5.5. A crosslinking agent is then added to the acidic protein solution. Battista's preferred crosslinking agent is Formalin (37 percent formaldehyde); however, Battista describes other suitable crosslinking agents which may be used, including glutaraldehyde. It must be noted, however, that the Battista patents do not describe acyl-modification of the protein starting material. Nor do the Battista patents describe a superabsorbent protein hydrogel. The protein hydrogels described in the Battista references are designed to have increased wet strength capabilities, thereby enabling their use in soft contact lenses.
Many disadvantages which accompany synthetic hydrogels (such as non-biodegradability) can be overcome by using hydrogels derived from natural polymer sources. In addition to chemically-crosslinked protein hydrogels, such as those described by Battista, many proteins can be thermally induced to form gels. The most critical requirements for any type of biopolymer hydrogel are that the gel should have the capacity to absorb a large amount of water relative to its mass upon rehydration, and that the gel material itself should resist dissolution.
However, conventional thermally-induced protein hydrogels do not swell to their original gel volume after they have been dehydrated. This decreased swelling capacity is related to increased hydrogen bonding, as well as electrostatic and hydrophobic interactions which occur in the dehydrated protein. The loss of swelling of thermally-induced protein hydrogels limits their range of industrial applicability.
U.S. Pat. No. 5,847,089 to Damodaran et al. describes a protein hydrogel which is superabsorbent, reversibly swellable, biodegradable, and capable of binding cations. The protein hydrogel described in Damodaran et al. is made by treating a protein with an acylating agent and crosslinking the acylated protein with a bifunctional crosslinking agent to form a protein hydrogel. A shortcoming of Damodaran et al. is that residual crosslinking agent can remain in the gel, thereby making the gel less desirable for some applications in which residues from crosslinkers, such as gluteraldehyde, are a concern.
In view of this, there is a clear need for a protein hydrogel which is highly absorbent, biodegradable, reversibly swellable, and which is substantially free of residual crosslinkers used to produce such hydrogels. The present invention provides such a protein hydrogel.
Perhaps the most desirable of renewable production materials is agricultural biomass. This is due, in large part, to the tremendous amount and vari
Brunsman David
DeWitt Ross & Stevens S.C.
Leone, Esq. Joseph T.
Wisconsin Alumni Research Foundation
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