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.

Description

[0001]This application is a divisional of application Ser. No. 10 / 458,277, filed Jun. 11, 2003, the entire specification and claims of which are incorporated herewith by reference.BACKGROUND OF THE INVENTION[0002]The present invention relates to a biodegradable biopolymer material, which is degraded while being decomposed by the action of an enzyme and which is thus converted into small molecules and a method for the preparation of the biodegradable biopolymer material as well as a functional material containing the material such as a metal ion-adsorbing material, a sustained release carrier for a useful substance, a biological cell-growth substrate and a biodegradable water-absorbing material.[0003]It is quite a long time since materials consisting of organic polymers and possessing biodegradability came on to the market. In the medical field, there have frequently been used materials, which are biologically decomposed and degraded through the action of an enzyme to thus form small...

AI Technical Summary

Benefits of technology

[0016]The silk fibers from domesticated silkworm and those from wild silkworm are fibrous materials produced and spun by silkworm and they have strong resistance to chemicals even to the action of, for instance, chemical agents and enzymes since they have fibrous structures as determined by the X-ray diffraction analysis. This is the reason why the silk fiber from domesticated silkworm is classified as the biologically non-absorbent material. Thus, the inventors of this invention have conducted various studies to provide a material comprising such a silk protein having good biodegradability while making the most use of the excellent biochemical properties of the silk protein and to develop a technique for preparing a novel material whose biodegradability can be controlled by using silk fibroin from domesticated silkworm as a starting material and combining the starting material with a specific secondary substance. The inventors have further inspected for the degradation behavior observed for a novel composite material obtained during the process for the development when acting an enzyme on the composite material, have found that a biopolymer material possessing biodegradability can be provided and have thus completed the present invention.

[0024]The sustained release carrier for a useful substance according to the present invention is characterized in that it consists of a biodegradable biopolymer material, which is 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 and that it can gradually release the useful substance supported on the biodegradable biopolymer material while being biodegraded by the action of a protease, chymotrypsin or a collagenase. The biodegradable biopolymer material is preferably a porous substance.

[0025]The living cell-growth substrate according to the present invention consists of a biodegradable biopolymer material, which is 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 substrate is used for effectively and economically growing living cells.

Problems solved by technology

Therefore, even when judging from the actual conditions of the use of the conventional silk sutures, the silk fiber can quite easily be sterilized, it is never biologically decomposed within a short period of time when embedded in the living body and when it is implanted in the living body, it only insignificantly causes an antigen-antibody reaction with the biological tissues.

With respect to the foregoing metal ion-adsorbing material and sustained release carrier for useful substances consisting of the aforementioned biodegradable biopolymer, there has not yet been proposed any product having satisfactory characteristic properties.

As has been discussed above in detail, poly(lactic acid) has widely been used as a biodegradable and bioabsorbable material, but it suffers from a problem in that the production cost thereof is too high.

On the other hand, it is too expensive, has high crystallizability, is too hard and is inferior in the compatibility with soft tissues.

Moreover, it also suffers from problems such that the rate of decomposition thereof cannot easily be controlled and that the control of the biodegradability thereof is likewise difficult even if this material is chemically modified.

In this respect, however, poly(lactic acid) or the like has a crystallization velocity slower than that observed for polyethylene terephthalate and fibers of, for instance, poly(lactic acid) are not sufficiently oriented and are not satisfactorily crystallized even when they are passed through the usual spinning and / or orientation steps.

For this reason, additional problems arise when putting them into practical use, for instance, the tensile strength and dimensional stability of poly(lactic acid) are insufficient.

In addition, the higher the molecular weight of the foregoing poly(oxy-acids), the slower the rate of the decomposition thereof.

In this connection, it is necessary to produce poly(lactic acid) and poly(glycolic acid) whose molecular weight is controlled for the control of the decomposition speed of these polymers, but the production of such polymers requires much labor and the use of highly advanced techniques requiring a great deal of skill.

For this reason, the use of poly(oxy-acids) has presently been limited to medical applications such as absorbent sutures and cosmetic applications and accordingly, there has strongly been desired for the establishment of a production process, which is not expensive or is economical and does not require any skilled technique.