Elastin-like poly

Scheme 9 Chemical structure of the modified, elastin-like poly (pentapeptide) XIV, found to exhibit photomodulated inverse temperature transition. 59 ...

Martino, M., and Tamburro, A. M. (2001). Chemical synthesis of cross-linked poly(KGGVG), an elastin-like biopolymer. Biopolymers 59, 29-37. 

Classic examples of synthetic polymers exhibiting an aqueous LCST include poly-diethyl acrylamide), poly(dimethylaminoethyl methacrylate), poly(A -acryloylpyrrolidine), poly(2-isopropyl-2-oxazoline), elastin-like artificial polypeptides, poly(vinyl methyl ether) and poly(7V-isopropylacrylamide) (PNIPAM, Scheme 1). The latter has been by far the most studied and applied thermoresponsive polymer and therefore can be considered as the gold standard in this field of research. During the last decades, several thousands of research articles and patents described the synthesis, the properties and the applications of this fascinating macromolecule. 

Elastin is an elastic insoluble protein in connective tissue, with cross-linked tropoelastin as a major component. It is responsible for the contraction of skin, lung, and vascular tissues in our body [42]. The insolubility and enhanced immune response [43] of native elastin limits its biomedical application and demands new materials for tissues. The ability of elastin to maintain minimum platelet interaction makes it a suitable material for making biological coatings for synthetic vascular grafts [44,45]. Currently used synthetic vascular biomaterials like poly(ethylene tere-phthalate) (Dacron) and poly(tetrafluoroethylene) show... 

Elamia R, Zhdan PA, Martino M, Castle JE, Tamburro AM (2004) AFM study of the elastin-like biopolymer poly(ValGIyGlyValGly). Biomacromolecules 5 1511-1518... 

Ozturk N, Girotti A, Kose GT, Rodriguez-Cabello JC, Hasirci V (2009) Dynamic cell culturing and its application to micropattemed, elastin-like protein-modified poly(JV-isopropylacrylamide) scaffolds. Biomaterials 30 5417-5426... 

Elastin-like polypeptides (ELPs) have been extensively studied due to the fact that they combine similar stimulus response properties to other artificial polymers such as poly(iV-isopropylacrylamide) (pNIPAM) with the advantages of a biologically derived material, that is, it is biocompatible, modular in its composition, and can be obtained by biological processes. ELPs are polypeptides that contain a short, repetitive peptide sequence, most commonly (VPGXG) that is derived from tropoelastin, the precursor of elastin. In this sequence, X represents any amino acid sequence except proline. Polypeptides composed of the pentapeptide repeat unit VPGXG possess a reversible lower critical solution temperature (LCST). Below the LCST, the peptide is soluble... 

In addition to the commonly used synthetic polymers such as pNIPAM and poly(N-vinylcaprolactam) (PVCL), elastin-like polymers were introduced as thermoresponsive polymers for affinity precipitation (Shimazu et al., 2003). An elastin-like polymer consists of the repeating penta-peptide, Val-Pro-Gly-Xaa-Gly (Xaa being any amino acid except proline). It undergoes reversible phase transition under temperature or salt concentration changes similar to pNIPAM (Shimazu et a/., 2003). An elastin-like polymer was used as a terminal tag for the facilitation of recombinant protein purification as attaching it to the hydrolase enzyme improves its purification. Purification, in excess of 1300-fold was achieved after two cycles of reversible changes of elastin-like polypeptide conformation precipitation induced by environmental changes (Shimazu et al., 2003). 

More often the click reaction is used in the modification of biopolymers. An example is sugar-derived imaging in live animals. Glycans in live zebrafish embryos light up when the embryos are fed azide-derived sugars and are subsequently treated with difluori-nated cyclooctyne derived probes. Elastin-like hybrid polymers, based on the reaction of azide-terminated poly (ethylene oxide) (PEG) and alkyne functionalized peptides, are also developed. These polymers are intended to grow new vocal cords . 

The protein elastin presents another opportunity to create amyloid-like fibrils from natural proteins for the purpose of developing biomaterials. Elastin is found in tissue where it imparts elastic recoil, and fibrils formed from this protein may demonstrate some of the elastic properties of the constituent elastic proteins (Bochicchio et al., 2007). Elastin typically contains the sequence poly(ZaaGlyGlyYaaGly) (where Zaa, Yaa = Val or Leu) (Tamburro et al., 2005), and short stretches of the protein retain the ability to form structures similar to the original protein. Simple proline to glycine mutations in the hydrophobic domains of elastin can induce the formation of amyloid-like fibrils (Miao et al., 2003), suggesting that fibrillar materials can be easily generated from these sequences. 

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