Regenerated Protein Fibers

Keywords

Hagfish slime • Protein • Dissolution • Formic acid • Mussel byssus • Mussel feet

Regenerated protein fibers were produced from the protein fibers (threads) found in hagfish slime [12Neg]. Proteins were solubilized in 98 % formic acid to obtain solutions (5, 7.5 %) that were spun into fibers and coagulated into an ethanol, methanol, or electrolyte buffer. However, fibers obtained were too weak and brittle. As an alternative approach, the protein solution was cast into films, and fibers were drawn from the films as shown in Fig. 49.1. Average fiber diameters obtained were between 46 and 137 ^m, and the length of the fibers was about 3 mm. Table 49.1 shows the tensile properties of the fibers obtained under various conditions. Tensile properties of the regenerated fibers were considerably lower compared to the properties of the natural slime threads but similar to that of the regenerated fibers produced from spider silks as seen in Table 49.2. Structural analysis using X-ray diffraction and Raman spectroscopy showed that the fibers were composed of about 67 % a-helix and 26 % p-sheet content. Drawing of the fibers was found to increase orientation but not the crystallinity of the fibers.

Proteins in mussel byssus have been extracted and regenerated into fibers [08Har, 09Har]. Proteins extracted from whole feet of mussel were dissolved in acetate buffer at various pHs (5.5-8). Fibers were hand drawn from the solution using a metal dissecting probe [08Har]. Figure 49.2 shows the formation of the fiber from the protein solution. It was found that the pH of the solution played a critical role in fiber formation. Fibers obtained had diameter in the range of 3-6 ^m, and TEM images showed alignment of filaments along the axis of the fiber. Table 49.3 provides a comparison of the tensile properties of the regenerated threads to the native distal and proximal byssal threads. As seen from the table, the regenerated protein fibers are considerably finer and have tensile strength and elongation comparable to that of the native threads. It was suggested that during drawing, the preCols align end-to-end and the histidine-rich termini or nearby preCols

Table 49.1 Mechanical properties of regenerated hagfish slime thread protein fibers produced using various conditions

Fig. 49.2 Formation of fibers by drawing between two metal probes [08Har]

(see Chap. 39) get cross-linked due to the interactions with the divalent metal ions [08Har].

In further continuation of their work, Harrington et al. extracted proteins from the four parts of the mussel feet to understand the role of the different proteins in the threads on the behavior of the threads [08Har]. Mussel feet were divided into four parts as proximal (PFP), distal (DFP), whole (WFP), and transition region. PreCols were separately purified from the PFP and DFP and the solution was used to draw

fibers. Table 49.4 provides a comparison of the properties of the fibers obtained from the PFP and DFP with the WFP protein fibers produced in an earlier research.

As seen from the table, the fibers produced from the DFP preCols have higher tensile strength but lower elongation than that of the fibers obtained from PFP preCols. The differences in the properties of the fibers obtained from DFP and PFP are mainly due to the varying contents of a — and p-sheets. It has been recognized that silks containing a high degree of antiparallel p-sheets have an extensibility of up to 50 %, whereas elastin-based materials such as spider silk can extend greater than 200 % [09Har]. Such mechanical gradient seen in byssal threads is considered to be very unique, and mimicking the byssal structure could lead to the develop­ment of new biomaterials.

References

[08Har] Harrington, M. J., Waite, J. H.: Biomacromolecules 9, 1480 (2008)

[09Har] Harrington, M. J., Waite, J. H.: Adv. Mater. 21, 440 (2009)

[12Neg] Negishi, A., Armstrong, C. L., Kreplak, L., Rheinstadter, M. C., Lim, L., Gillis, T. E., Fudge, D. S.: Biomacromolecules 13, 3475 (2012)