Page 275 - Advances in Textile Biotechnology

256 Advances in textile biotechnology

to the development of new peptide-based polymers as molecular devices
and materials.
The expansion of molecular biology has allowed the design of complex
bioengineered ELPs as well-defi ned polymers (Girotti et al., 2004, Martino
et al., 2002, Meyer and Chilkoti, 2002, Welsh and Tirrell, 2000). The most
well known members within the ELP family are based on the pentapeptide
VPGVG (or its permutations), and a wide variety of polymers with the
general formula (VPGXG), where X represents any natural amino acid
except proline, have been (bio)synthesized (Gowda et al., 1994, Martino
et al., 2002, Urry, 2005). All polymers with this general formula that have
been reported display functional properties such as acute stimuli-respon-
sive behavior.

The first elastin-mimetic protein fibers were produced from a genetically

engineered ELP (Huang et al., 2000). Various morphological patterns, such
as beaded fibers, thin filaments, or broad fibres with a ribbon-like appear-

ance, were obtained by varying the solution concentration. Chemically

crosslinked fibers were also prepared from two different ELPs containing

glutamic acid and lysine residues, respectively, confirming their reversible
anisotropy in swelling behavior and showing a fast response time upon
temperature changes (Lee et al., 2001). In another study, electrospinning of

ELP copolymer solutions in water and 2,2,2-trifluoroethanol provides fi bers
ranging from 100 nm to 3 μm showing the importance of the solvent during

the fiber spinning (Nagapudi et al., 2005).
Currently, the most often used method for laboratory scale production
of ELPs is E. coli shake cultures that give typical yields of approximately
−1
300 mg l . Other hosts that have been used for expression of ELPs or
natural elastin sequences in which the ELP is produced and recovered from
inside the cells are tobacco cell cultures, cultures of Aspergillus nidulands,
transgenic tobacco plants and Saccharomyces cerevisiae. Finally, the yeast
Pichia pastoris has been succefully used for secreted expression of ELPs
(Schipperus et al., 2009).
In biosynthesis using recombinant DNA techniques to combine poly-
peptide sequences derived from silkworm silk and mammalian elastin,
silk-elastin-like proteins (SELPs) allow diverse physical, mechanical, and
biological features to be abtained (Ferrari and Capello, 1997). Recently,
genetically engineered silk-elastin-like protein copolymer (SELP) contain-
ing tandemly repeated amino acid sequence blocks from silk, GAGAGS,

and elastin, GVGVP, was spun into clean microdiameter fibers using a wet-

spinning technique. Hydrated SELP-47K fibers were mechanically weak

but displayed large strains to failure. This was modified by chemical cross-
linking with glutaraldehyde enhancing their strength until 20 MPa and
deformability of 200–700% showing potential applications in tissue engi-
neering (Qiu et al., 2009).

© Woodhead Publishing Limited, 2010