Protein-Based Thermoplastic Elastomers

Abstract

Investigations of high molecular weight recombinant protein triblock copolymers demonstrate unique opportunities to systematically modify material microstructure on both nano-and mesolength scales in a manner not been previously demonstrated for protein polymer systems. Significantly, through the biosynthesis of BAB-type copolymers containing flanking, plastic-like end blocks and an elastomeric midblock, virtually cross-linked protein-based materials were generated that exhibit tunable properties in a manner completely analogous to synthetic thermoplastic elastomers. Through the rational choice of processing conditions that control meso-and nanoscale structure, changes of greater than 3 orders of magnitude in Young's modulus (0.03-35 MPa) and 5-fold in elongation to break (250-1300%) were observed. Extensibility of this range or magnitude has not been previously reported for virtually cross-linked copolymers that have been produced by either chemical or biosynthetic approaches. We anticipate that these versatile protein-based thermoplastic elastomers will find applications as novel scaffolds for tissue engineering and as new biomaterials for controlled drug release and cell encapsulation.

Peptide-based biopolymers in biomedicine and biotechnology

“…Wright et al and Nagapudi et al have reported systematic rheological studies of genetically synthesized self-assembling elastin-mimetic triblock polypeptides [153,154,201,202]. The copolymers composed of a plastic domain (its consensus repetitive sequence: VPAVG) as the end blocks and an elastomeric domain (its consensus repetitive sequence: VPGVG) as the middle block.…”

“…Rheological measurements of an aqueous triblock copolymer solution as a function of temperature showed that the copolymers would be well-suited for biomedical applications. The loss modulus (G″) is higher than the storage modulus (G′) below the LCST, and G′ is higher than G″ above the LCST, indicating that above the LCST the solution converts from liquid-like to solid-like viscoelastic behavior [70,153,201,202]. They found that changing the length or hydrophilicity of the middle largely affected the viscoelastic and mechanical behavior of the copolymers when the same plastic domain was used [202].…”

“…They also used different solvent environments, such as mixtures of trifluoroethanol (TFE) and water, to change the secondary structure of the proteins. When the protein solution was electrospun to form nanofiber scaffolds, using solvent mixtures resulted in varied microstructures and mechanical properties [70,201,202]. As florinated alcohols are known to form strong solid-state complexes with polyamides, TFE is a good solvent for all three blocks of the copolymer.…”

Production of renewable polymers from crop plants

“…Well-known fibrous proteins are silk, collagen, elastin, mussel adhesive proteins, keratin, wheat glutenin and resilin (Kiick, 2007). By combining repeat sequences of the various natural fibrous proteins or even completely synthetic sequences, and changing the linker elements between the repeat sequences, a tremendous combinatorial range is available (Holland et al, 2007;Nagapudi et al, 2005). Obviously, this could also include sequences optimized for production in plants.…”

Deformation Responses of a Physically Cross-Linked High Molecular Weight Elastin-Like Protein Polymer

“…Recently, we have reported the synthesis of high molecular weight recombinant protein block copolymers using an approach, which affords significant flexibility in the selection and assembly of blocks of diverse size and structure. [7][8][9][10][11] This has led to the synthesis of a new class of BAB protein triblock copolymer composed of large polypeptide block sequences ranging from 400 to 1200 amino acids in length. This class of protein block copolymers are derived from elastin-mimetic polypeptide sequences in which identical endblocks of a hydrophobic, plastic-like sequence are separated by a central hydrophilic, elastomeric block.…”