Preparation and Characterization of Bombyx mori Silk Fibroin and Wool Keratin Yesim Iridag, 1 Murat Kazanci 2 1 Department of Textile Engineering, Istanbul Technical University, Gumussuyu 34439, Istanbul, Turkey 2 Max-Planck-Institute of Colloids and Interfaces, Department of Biomaterials, 14424 Potsdam, Germany Received 23 August 2003; accepted 17 November 2005 DOI 10.1002/app.23810 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Silk and wool are well-known protein-based fibers. Their environmental stability, biocompatibility, and unique mechanical properties provide an important basis for using these natural proteins in biomedical applications. To use them as biomaterials in the form of fibers, films, or membranes, it is necessary to characterize these proteins in their solution and solid states because structural character- istics and morphological features have a great influence on the physical and mechanical properties of these new regen- erated protein forms. Therefore, in the present study, silk fibroin and wool keratin were dissolved and their solution behaviors and secondary structures are analyzed and com- pared, using particle size distribution, molecular weight distribution (SDS-PAGE), Fourier transform infrared, and X-ray diffraction techniques. It was shown that keratin is more stable in solution and more amorphous in the solid state. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4260 – 4264, 2006 Key words: proteins; silk fibroin; wool keratin; FTIR, XRD, particle size distribution INTRODUCTION Naturally occurring fibrous proteins fall into one of two categories: highly extensible fibers such as the -keratins (wools, hair, and other mammalian external appendages such as quills and horns); and fibroin fibers (various silks and spider webs). Among them, silk and wool, which are both high-quality natural protein fibers, have been widely used as high-quality textile materials. Silk has been used as a textile fiber for thousands of years because of its unique gloss, handle, and mechanical properties. Silk contains a fibrous protein termed fibroin that forms the tread corn and gluelike proteins termed sericin that sur- round the fibroin fibers to cement them together. Fi- broin is a highly insoluble protein 90% of which are the amino acids glycine, alanine, and serine, leading to antiparallel -pleated sheet formation in the fibers. 1 Once the silk fiber is solidified from the silkworm through a spinning process, it becomes a well-oriented and highly crystallized polymer. Silk fiber behaves like a thermoset polymer, although it is not all crosslinked. Therefore, concentrated chaotropic salts, which destabilize proteins in solution and increase their solubility, are required to dissolve B. mori silk fiber. 2 Keratins are fibrous proteins found in hair, wool, feathers, nail, horns, and other epithelial cover- ings. In wool, keratins occupy about 50 wt % of the cortical cells. At a molecular level, the most distinctive feature of keratins is the high concentration of half- cystine residues. Keratins may thus be regarded as three-dimensional polymers interlinked by SOS bonds between reduced keratin-monomeric units. 3 The relative environmental stability of these fami- lies of natural proteins, in comparison to globular proteins, in combination with their biocompatibility, unique mechanical properties, and options for genetic control to tailor sequences, provides an important ba- sis for exploiting them for biomedical applications. 4–6 To engineer these fibers for specific biomedical appli- cations, they must be regenerated in such desirable forms as solutions, powders, films, gels, and filaments, depending on the preparation conditions and the field to which they will be applied. 7 To avoid problems with the conformational transitions of these protein fibers during solubilization and reprocessing from aqueous solution to generate new fibers and films, they should be characterized in their solution state Structural characteristics and morphological features, which greatly influence the physical and mechanical properties of these new regenerated protein forms, should be considered when these proteins are used as a biomaterial. Most previous studies were of films cast from pro- tein solutions so that the conformation of the protein molecules may have depended on the conditions of casting, for instance, casting temperature and concen- Correspondence to: M. Kazanci (Murat.Kazanci@ mpikg-golm.mpg.de). Journal of Applied Polymer Science, Vol. 100, 4260 – 4264 (2006) © 2006 Wiley Periodicals, Inc.