Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
2000-01-24
2001-10-30
Wilson, James O. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C536S127000
Reexamination Certificate
active
06310188
ABSTRACT:
This invention pertains to a method for producing chitin or chitosan, particularly to a method for producing chitin or chitosan from crustacean shells.
Chitosan is a biopolymer with many uses in the health care industry. To take just a few examples, chitosan may be used as a cell delivery vehicle, in a synthetic bone graft material (e.g., a mixture of chitosan and hydroxyapatite), in spinal fusions, and in various wound healing applications. Chitosan has also been marketed for use in consumer products that are said to reduce fat and cholesterol.
Chitosan and its precursor, chitin, are typically prepared from waste shells of crustaceans, particularly decapod crustaceans such as crab, shrimp, crawfish, krill, lobster, and prawn. The conventional process for producing chitin and chitosan from crustacean shells is described, for example, in H. No et al., “Preparation of chitin and chitosan, ” pp. 475-489 in
R. Muzzarelli
et al. (Eds.),
Chitin Handbook
(1997). Crustacean shells are ground and treated with dilute sodium hydroxide and heat to remove protein (deproteinization). Calcium carbonate is removed by extraction with dilute hydrochloric acid at room temperature (demineralization). Following deproteinization and demineralization, the resulting product is predominantly chitin. An optional decolorization step may be used to bleach the chitin, for example, extraction with ethanol and ether, or bleaching with sodium hypochlorite. Removal of acetyl groups from the chitin polymer (deacetylation) produces chitosan; deacetylation is usually performed by reacting chitin with concentrated sodium hydroxide or potassium hydroxide and heat. Deacetylation need not be complete. No et al. observed that the characteristics of chitin and chitosan differ, depending on the crustacean species used for the starting material and the particular preparation method used.
Variations on the basic process for producing chitosan are disclosed, for example, in U.S. Pat. Nos. 3,862,122, 4,066,735, and 4,195,175.
Work done under the supervision of the present inventor was described in J. Bienvenu, “Development of a Process to Produce Chitosan from Crawfish Waste,” report presented at Louisiana Region I Science and Engineering Fair, Bossier City, La. (March 18-19, 1999); and at the International Science and Engineering Fair, Philadelphia, Pa. (May 1999).
Prior methods of producing chitosan are expensive, especially methods of producing high-purity chitosan. There is an unfilled need for a less expensive method for producing chitosan, particularly a chitosan of high purity that is suitable for biomedical uses.
I have discovered a method for improving the efficiency of producing chitin and chitosan, particularly chitosan of high purity that is suitable for biomedical uses. Cleaned crustacean shells are maintained at a high temperature for a sufficient time to convert most of the chitin in the shells to an amorphous form. The shells are then rapidly cooled, for example by plunging into liquid nitrogen, so that most of the chitin in the shells remains in the amorphous form. These “quenched” shells are then deproteinized and demineralized to produce chitin. The chitin may be deacetylated to produce chitosan. High purity chitin or chitosan is thereby produced more efficiently and at a lower cost than has been possible using previous methods. An optional dialysis step to remove low molecular weight compounds can further improve the purity of the chitosan. The resulting chitosan is biocompatible and can be used for the delivery of cells or bioactive agents, or for other applications.
Without wishing to be bound by this theory, it is believed that the heating followed by immediate quenching enhances the formation of chitin chains in an amorphous or a relaxed form, making the chitin more susceptible to attack by acid or alkali during, the subsequent treatment steps. Making the chitin amorphous allows the more efficient and economical production of chitosan, using lower quantities of chemicals such as hydrochloric acid and sodium hydroxide, thus making the entire process both more economical and less polluting.
REFERENCES:
patent: 3862122 (1975-01-01), Peniston et al.
patent: 4066735 (1978-01-01), Peniston et al.
patent: 4195175 (1980-03-01), Peniston et al.
No, H. et al., “Preparation of chitin and chitosan,” pp. 475-489 in R. Muzzarelli et al. (Eds.),Chitin Handbook(1997).
Caplus abstract of Signini, R. et al “Purification and characterization of commercial chitosan” Polim.: Cienc. Tecnol. vol. 8 No. 4 pp. 63-68, 1998.*
Bienvenu, J., “Development of a Process to Produce Chitosan from Crawfish Waste,” report presented at Louisiana Region I Science and Engineering Fair, Bossier City, Louisiana (Mar. 18-19, 1999); and at the International Science and Engineering Fair, Philadelphia, Pennsylvania (May 1999).
Board of Supervisors of Louisiana State University and Agricultu
Maier Leigh C.
Runnels John H.
Wilson James O.
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