Biomedical Engineering Reference
In-Depth Information
Enzymatically degradable peptides may be reacted with PEG via Michael
addition in a one step process to produce hydrogels (Figure 1C). Linear PEG-
vinylsulfone that is reacted with an enzymatically degradable peptide containing
A
B
C
Fig. 1. Three routes to synthesize enzymatically degradable hydrogels. A. An enzymatically
degradable peptide is synthesized one amino acid at a time on both ends of a linear PEG. This
product is then reacted with acryloyl chloride. The diacrylamide derivative may be
photopolymerized to form a network. B. A bifunctional PEG may be reacted with an enzymatically
degradable peptide, and the product may be photopolymerized. C. An eight arm PEG-vinylsulfone
is reacted with an enzymatically degradable peptide to directly form a network.
three or more cysteine residues forms a degradable hydrogel [39]. Alternatively,
multiarm PEG-vinylsulfone may be reacted with an enzymatically degradable
peptide containing two cysteines to produce a hydrogel [35]. Reaction of
multiarm PEGs may also be performed enzymatically in a two step process.
Initially, the hydroxyl groups on multiarm PEG are activated with a good leaving
group. This leaving group is reacted with a nucleophilic amine group on a
peptide containing either lysines or glutamines. Complementary peptides on
different multiarm PEGs are then crosslinked via enzymatic catalysis with
transglutaminases [40]. By including sequences in the peptide that are
susceptible to specific proteases, enzymatically degradable hydrogels are
produced [41]. Instead of using enzymatically degradable peptides, entire
proteins can crosslink PEG. Proteins generally have multiple lysine groups that
may be used to crosslink activated linear PEG, as first described by Fortier and
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