Biodegradable biopolymers, method for their preparation and functional materials constituted by these biopolymers

Abstract

A biodegradable biopolymer material consists of silk fibroin from domesticated silkworm; silk fibroin from wild silkworm; a composite material comprising silk fibroin from domesticated silkworm and silk fibroin from wild silkworm; or a composite material comprising either silk fibroin from domesticated silkworm or silk fibroin from wild silkworm and at least one secondary substance selected from the group consisting of cellulose, chitin, chitosan, chitosan derivatives, keratin from wool and polyvinyl alcohol. The material may be prepared by, for instance, casting an aqueous solution of domesticated silkworm silk fibroin on the surface of a substrate and then cast drying the applied solution. The biodegradable biopolymer material is effectively used as, for instance, a metal ion-adsorbing material, a sustained release substrate for a useful substance such as a medicine, a biological cell-growth substrate and a biodegradable water-absorbing material.

What is claimed is:  
     
         1 . A biodegradable biopolymer material characterized in that the material consists of silk fibroin from domesticated silkworm; silk fibroin from wild silkworm; a composite material comprising silk fibroin from domesticated silkworm and silk fibroin from wild silkworm; or a composite material comprising either silk fibroin from domesticated silkworm or silk fibroin from wild silkworm and at least one secondary substance selected from the group consisting of cellulose, chitin, chitosan, chitosan derivatives, keratin from wool and polyvinyl alcohol.  
     
     
         2 . The biodegradable biopolymer material as set forth in  claim 1 , wherein the biodegradable biopolymer material is one capable of being digestively degraded by the action of an enzyme selected from the group consisting of proteases, collagenases and chymotrypsin.  
     
     
         3 . The biodegradable biopolymer material as set forth in  claim 1 , wherein the biodegradable biopolymer material possesses a fibrous, membrane-like, powdery, gel-like or porous shape.  
     
     
         4 . The biodegradable biopolymer material as set forth in  claim 2 , wherein the biodegradable biopolymer material possesses a fibrous, membrane-like, powdery, gel-like or porous shape.  
     
     
         5 . A method for the preparation of a biodegradable biopolymer material comprising the steps of applying, onto the surface of a substrate, an aqueous solution of silk fibroin from domesticated silkworm, an aqueous solution of silk fibroin from wild silkworm, an aqueous mixed solution containing an aqueous solution of silk fibroin from domesticated silkworm and an aqueous solution of silk fibroin from wild silkworm or an aqueous mixed solution containing either an aqueous solution of silk fibroin from domesticated silkworm or an aqueous solution of silk fibroin from wild silkworm and an aqueous solution of at least one secondary substance selected from the group consisting of cellulose, chitin, chitosan, chitosan derivatives, keratin from wool and polyvinyl alcohol and then cast drying the applied solution to form a membrane-like biodegradable biopolymer material, wherein if using the mixed aqueous solution, the aqueous solutions as the constituents of the mixed solution are uniformly admixed together by stirring them such that they do not undergo any gelation, precipitation and/or coagulation reaction to thus prepare the aqueous mixed solution.  
     
     
         6 . A method for the preparation of a biodegradable biopolymer material comprising the steps of freezing an aqueous solution of silk fibroin from domesticated silkworm, an aqueous solution of silk fibroin from wild silkworm, an aqueous mixed solution containing an aqueous solution of silk fibroin from domesticated silkworm and an aqueous solution of silk fibroin from wild silkworm or an aqueous mixed solution containing either an aqueous solution of silk fibroin from domesticated silkworm or an aqueous solution of silk fibroin from wild silkworm and an aqueous solution of at least one secondary substance selected from the group consisting of cellulose, chitin, chitosan, chitosan derivatives, keratin from wool and polyvinyl alcohol and then drying the frozen aqueous solution under a reduced pressure to thus form a powdery biodegradable biopolymer material, wherein if using the mixed aqueous solution, the aqueous solutions as the constituents of the mixed solution are uniformly admixed together by stirring them such that they do not undergo any gelation, precipitation and/or coagulation reaction to thus prepare the aqueous mixed solution.  
     
     
         7 . A method for the preparation of a biodegradable biopolymer material comprising the steps of adjusting, to a level falling within the acidic range, the pH value of an aqueous solution of silk fibroin from domesticated silkworm, an aqueous solution of silk fibroin from wild silkworm, an aqueous mixed solution containing an aqueous solution of silk fibroin from domesticated silkworm and an aqueous solution of silk fibroin from wild silkworm or an aqueous mixed solution containing either an aqueous solution of silk fibroin from domesticated silkworm or an aqueous solution of silk fibroin from wild silkworm and an aqueous solution of at least one secondary substance selected from the group consisting of cellulose, chitin, chitosan, chitosan derivatives, keratin from wool and polyvinyl alcohol, and then entirely coagulating the aqueous solution to give a gel-like biodegradable biopolymer material.  
     
     
         8 . A method for the preparation of a biodegradable biopolymer material comprising the step of subjecting, to lyophilization, the gel-like biodegradable biopolymer material prepared according to the method as set forth in  claim 6  to thus obtain a porous body.  
     
     
         9 . The method as set forth in  claim 5 , wherein the concentrations of the aqueous solution of the silk fibroin from domesticated silkworm, the aqueous solution of the silk fibroin from wild silkworm and the aqueous solution of the secondary substance used in the preparation of the mixed aqueous solution range from 0.1 to 5% w/v, respectively.  
     
     
         10 . The method as set forth in  claim 6 , wherein the concentrations of the aqueous solution of the silk fibroin from domesticated silkworm, the aqueous solution of the silk fibroin from wild silkworm and the aqueous solution of the secondary substance used in the preparation of the mixed aqueous solution range from 0.1 to 5% w/v, respectively.  
     
     
         11 . The method as set forth in  claim 7 , wherein the concentrations of the aqueous solution of the silk fibroin from domesticated silkworm, the aqueous solution of the silk fibroin from wild silkworm and the aqueous solution of the secondary substance used in the preparation of the mixed aqueous solution range from 0.1 to 5% w/v, respectively.  
     
     
         12 . The method as set forth in  claim 8 , wherein the concentrations of the aqueous solution of the silk fibroin from domesticated silkworm, the aqueous solution of the silk fibroin from wild silkworm and the aqueous solution of the secondary substance used in the preparation of the mixed aqueous solution range from 0.1 to 5% w/v, respectively.  
     
     
         13 . A metal ion-adsorbing material comprising a biodegradable biopolymer material, which comprises a biodegradable biopolymer material characterized in that it consists of silk fibroin from domesticated silkworm; silk fibroin from wild silkworm; a composite material comprising silk fibroin from domesticated silkworm and silk fibroin from wild silkworm; or a composite material comprising either silk fibroin from domesticated silkworm or silk fibroin from wild silkworm and at least one secondary substance selected from the group consisting of cellulose, chitin, chitosan, chitosan derivatives, keratin from wool and polyvinyl alcohol.  
     
     
         14 . The metal ion-adsorbing material as set forth in  claim 13 , wherein the metal ions are antibacterial metal ions or metal ions present in waste water.  
     
     
         15 . A sustained release carrier for a useful substance comprising a biodegradable biopolymer material, which comprises a biodegradable biopolymer material characterized in that it consists of silk fibroin from domesticated silkworm; silk fibroin from wild silkworm; a composite material comprising silk fibroin from domesticated silkworm and silk fibroin from wild silkworm; or a composite material comprising either silk fibroin from domesticated silkworm or silk fibroin from wild silkworm and at least one secondary substance selected from the group consisting of cellulose, chitin, chitosan, chitosan derivatives, keratin from wool and polyvinyl alcohol.  
     
     
         16 . The sustained release carrier for a useful substance as set forth in  claim 15 , wherein the biodegradable biopolymer material is a porous substance.  
     
     
         17 . A substrate for growth of biological cells comprising a composite material containing silk fibroin from domesticated silkworm and silk fibroin from wild silkworm; or a composite material comprising either silk fibroin from domesticated silkworm or silk fibroin from wild silkworm and at least one secondary substance selected from the group consisting of cellulose, chitin, chitosan, chitosan derivatives, keratin from wool and polyvinyl alcohol, wherein the substrate is used for the growth of biological cells.  
     
     
         18 . A biodegradable water-absorbing material consisting of a biodegradable biopolymer material, which comprises a biodegradable biopolymer material characterized in that it consists of silk fibroin from domesticated silkworm; silk fibroin from wild silkworm; a composite material comprising silk fibroin from domesticated silkworm and silk fibroin from wild silkworm; or a composite material comprising either silk fibroin from domesticated silkworm or silk fibroin from wild silkworm and at least one secondary substance selected from the group consisting of cellulose, chitin, chitosan, chitosan derivatives, keratin from wool and polyvinyl alcohol.