Flow behavior of regenerated wool-keratin proteins in different mediums

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Abstract

Keratin is abundantly present in nature and the major component of hair, wool, feather, nail and horns. Dissolution of keratin is often required when non-textile applications are demanded. However, the low solubility of keratin in water is the major problem. It becomes unstable and precipitated when stored for a long time. Therefore, it is necessary to find a good solvent that provides high stability and easy processibility. In this research, we used formic acid and dimethylformamide (DMF) to dissolve regenerated keratin protein films. It is shown that formic acid is a good solvent for regenerated keratin proteins for the purpose of storage. Transparent and stable regenerated keratin solution is obtained in formic acid.

Introduction

The development of good biocompatible materials is necessary for tissue engineering, since cells must be accommodated in the scaffold to substitute the function of damaged tissue. A limited number of polymers are currently used in the medical field as biocompatible polymers, which are poly (lactic acid), poly(glycolic acid) and their copolymers as synthetic polymers and collagen and chitosan as natural polymers.

We are proposing keratin as a new protein based biomaterial. Keratin is the major component of hair, wool, feather, nail, horns and other epithelial coverings, which is abundantly present in nature. In wool, keratins occupy about 50 wt.% of the cortical cells [1]. Amino acid analysis of keratin showed its extraordinary high content of half-cystine residue, which forms inter- and intramolecular disulfide bonds to provide hair or wool with tenacious property [2]. Most of these half-cystine residues are localized at the terminal regions of the proteins [3]. It is also shown that keratin film supports the growth of mouse fibroblast cells [4].

Dissolution of keratin is often required when non-textile applications are demanded in the forms of film, porous membrane, powder and gel among others. Extraction of keratins from wool has been conducted in various ways [5]. However, aqueous keratin solution becomes unstable and precipitated due to its low solubility in water when storing for a long time. As a result, it is necessary to find out a good solution system having high stability and easy processibility and it could be used as a co-solvent in order to blend keratin with other materials and polymers. While wool protein is insoluble in formic acid and dimethylformamide (DMF), the regenerated protein films are readily soluble in formic acid [6] and DMF. A few investigations have been conducted researches on wool keratin solutions, most probably due to the difficulties of preparation and handling of the unstable reduced proteins.

Section snippets

Experimental results

In this experiment; urea, 2-mercaptoethanol, sodium dodecyl sulfate (SDS), formic acid and dimethylformamide (DMF) were used without further purification. Washed, cleaned and dried wool was obtained from Orma. The cleaned wool (2 g) was mixed with 7 M urea (36 mL), SDS (1.2 g), and 2-mercaptoethanol (3 mL) and shaken at 50 °C for 24 h in a natural pH. Water was distilled prior to use. Dialysis was performed using a regenerated cellulose membrane (Slide-A-dyzer, 3500 MWCO, Pierce), and changing the

Discussion

The rheological behavior of macromolecule solutions can often be used to study the interactions between solvent and macromolecule species. To our knowledge, there has been no published, detailed study of the rheology of regenerated wool keratin proteins. Rheological properties (viscosity and shear stress) of regenerated keratin are examined in four solvents: urea-SDS-(2-mercaptoethanol) (salt); water; DMF and formic acid. Fig. 1 shows the linear increase in shear stresses as a function of shear

Conclusions

From the above investigation it is concluded that transparent and stable regenerated keratin solution can be obtained by dissolving the regenerated keratin in formic acid. It is shown that keratin molecules in DMF, as in water, tend to be easily aggregated; resulting in an unstable state of keratin solution, while keratin in formic acid is relatively stable because of its strong solvation property for the regenerated keratin. No molecular aggregation or entanglement occurred in this solution.

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Present address: Department of Mechanical & Industrial Engineering, University of Toronto, Toronto, Canada M5S 3G8.

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