Modified silk films containing glycerol

Abstract

The present invention provides for compositions and methods for preparing aqueous insoluble, ductile, flexible silk fibroin films. The silk films comprise silk fibroin and about 10% to about 50% (w / w) glycerol, and are prepared by entirely aqueous processes. The ductile silk film may be further treated by extracting the glycerol from and re-drying the silk film. Active agents may be embedded in or deposited on the glycerol modified silk film for a variety of medical applications. The films may be into 3-dimentional structures, or placed on support surfaces as labels or coatings. The glycerol modified silk films of the present invention are useful in variety of applications such as tissue engineering, medical devices or implants, drug delivery, and edible pharmaceutical or food labels.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application claims benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 61 / 104,135 filed Oct. 9, 2008, the contents of which are incorporated herein by reference in its entirety.GOVERNMENT SUPPORT[0002]This invention was made with government support under grant no. EB002520 awarded by the National Institutes of Health and No. FA9550-07-1-0079 awarded by the Air Force Office of Scientific Research. The U.S. federal government has certain rights in the invention.FIELD OF THE INVENTION[0003]The present invention provides for compositions and methods for preparing silk fibroin films containing glycerol and having improved mechanical properties.BACKGROUND[0004]Silk fibroin has excellent film-forming capabilities and is also compatible for use in the human body. Silk fibroin films, without further manipulation or treatment, are soluble in water because of dominating random coil protein structures. The structural features of ...

AI Technical Summary

Benefits of technology

[0005]The present invention provides for films comprising silk fibroin and glycerol, which have distinct properties compared with silk fibroin films lacking glycerol. More specifically, the aqueous solubility and biocompatibility are enhanced with the use or inclusion and use of glycerol as a plasticizer. Processing silk fibroin in water also enhances both biocompatibility and the potential to load bioactive compounds without loss of function, and adds “green chemistry” value to these biomaterials. For example, blends of silk fibroin and glycerol with glycerol concentrations above 30% (w / w) cast into films resulted in the conversion of silk secondary structure from random coil to a-helix, prevented silk from dissolution upon hydration, provided distinct film nanostructure morphology, improved film flexibility in either dry (as-cast film) or wet (after leaching out the glycerol) environments, and preserved cell biocompatibility. Mechanistically, glycerol may replace water in silk fibroin chain hydration, resulting in initial stabilization of helical structures as opposed to random coil or β-sheet structures. The impact of glycerol on stabilizing film structure, aqueous insolubility and function apparently occurs above a glycerol concentration of about 20 wt % glycerol. The use of glycerol in combination with silk fibroin in materials processing expands the functional features attainable with this fibrous protein, and the formation of more flexible films with potential utility in biomaterial and device applications.

[0006]The present invention provides for a silk film comprising silk fibroin and from about 10% (w / w) to about 50% (w / w) glycerol, in which the film is prepared by entirely aqueous processes, and the silk film is ductile and substantially aqueous-insoluble. Many embodiments of the silk / glycerol blend films of the present invention exhibit higher ductility than silk films lacking glycerol, optionally following methanol treatment or water-annealing. The glycerol in the silk fibroin film, without being bound by theory, appears to stabilize the α-helical structure of the silk fibroin. Thus, in one embodiment, the ductile silk fibroin film may be converted from α-helical structure to β-sheet structure by extracting glycerol from the silk film and re-drying the film.

[0007]In one embodiment, a composition comprising glycerol modified silk film may be used as a 2-dimensional or 3-dimensional construct for tissue engineering, and may further comprise at least one active agent. Such tissue engineered construct may be used for organ repair, organ replacement, or other regenerated tissue materials such as cardiac muscle or cornea tissues. A 3-dimensional tissue engineering embodiment may be made by wrapping or shaping a ductile silk / glycerol film around a device or implant, such as a dental implant, and allowing the film to dry. Silk / glycerol blends may be formed, or the films folded or shaped, into sponges or blocks or other 3-dimensional structures. Optionally, the glycerol may then be leached out from the silk. Thus, the silk film may also be used as coatings on biomedical materials such as medical devices, tissue-engineered materials or implants, by coating the surfaces of such structures with a silk / glycerol ductile film. Coating from such modified silk film provides for improved compatibility and conforms well to the contours of the substrate.

[0009]The embodiments of the prevent invention also provide for methods of preparing a silk film which is substantially aqueous-insoluble, by blending a silk fibroin solution with glycerol, wherein the concentration of glycerol in the silk fibroin / glycerol blend solution ranges from about 10% to 50% (w / w); casting the silk fibroin / glycerol blend solution onto a film-supporting surface; and drying the film. Silk films prepared by this process exhibit increased ductility compared with silk films lacking glycerol.

Problems solved by technology

Some pure silk fibroin films tend, over time, to become stiff and brittle in the dry state, however, exhibiting impressive tensile strength but low ductility.

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