Enzyme-triggered hydrogels

Toledano S, Williams RJ, Jayawarna V, Ulijn RV (2006) Enzyme-triggered self-assembly of peptide hydrogels via reversed hydrolysis. J Am Chem Soc 128 1070-1071... 

FIGURE 10.6 Schematic representation of selective enzyme-triggered charge-induced swelling of the enzyme-responsive hydrogels with the zwitterionic peptide linkers that are hydrolyzed by a specific enzyme. 

In another research, an approach by using proteases, enzymes that normally hydrolyze peptide bonds in aqueous medium, to perform the reverse reaction (i.e., peptide synthesis or reversed hydrolysis) to produce amphiphilic peptide hydrog-elators that self-assemble to form nanofibrous stmctures was proposed by Ulijin et al. As shown in Fig. 3.34, Fmoc-amino acids (44) and peptides (45) could reacted to form hydrogelator 46 catalyzed by thermolysin (or chymotrypsin), which was able to form transparent gels in water. The result demonstrates that a protease can be used to selectively trigger the self-assembly of peptide hydrogels via reversed hydrolysis [84]. 

Enzyme responsiveness in injectable hydrogels has also been used to render the material biodegradable such that it can be removed once it is no longer required. In this case, poly(N-isopropylacrylamide-co-acrylic acid) that included peptide-based cross-links was used as the stimuli-responsive polymer. Hydrogelation was triggered thermally, whereas the enzyme-responsive functionality is used to provide proteolytically degradable sites in the hydrogel (Kim and Healy,2003). 

Rice, M. A. and Anseth, K. S. 2007. Controlling cartilaginous matrix evolution in hydrogels with degradation triggered by exogenous addition of an enzyme. Tissue Eng 13 683-91. 

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