Biomedical Engineering Reference
In-Depth Information
6.3 Enzyme-Triggered Hydrogels
Severalofthebenefitsthatcanbeobtainedusingenzymesinhydro-
gel formation are summarized as follows:
12
(i) Enzymes can form covalent bonds between substrates, yield-
ing bonds generally stronger and more permanent than physi-
cal cross-links.
(ii) Enzymes often exhibit a high degree of substrate speci-
ficity, potentially allowing the sparing of pendant peptides or
polysaccharide moieties meant for interactions with cell sur-
face receptors during the cross-linkingreaction.
(iii) Catalysisundermildreactionconditionswithregardtotemper-
ature,pressure,andpHensuresthesafetyofencapsulatedcells
or biomolecules.
(iv) High enantio-, regio-, and chemo-selectivity, as well as the reg-
ulation of stereochemistry, provides the development of new
reactions forfunctional compounds forpharmaceuticals.
(v) High e
ciency of enzymatic reactions provides a much lower
viscous solution than physical hydrogels, enabling easy han-
dling andhomogeneousloading of cells or biomolecules.
(vi) Enzymatic cross-linking offers the potential for kinetic control
of gel formation and the formation of homogeneous gels
in situ
via simple control of the enzyme concentration because the
amount of enzyme present is one of the key determinants of
the overall cross-linking rate. This type of kinetic control of gel
formation can greatly assist in the ability to deliver cell-based
therapies in a noninvasivemanner.
In recent years, the
in vitro
synthesis of polymers through
enzymatic catalysis (
enzymatic polymerization
) has been studied
extensively.
13
-
21
Thesestudiesshowthatmanyfamiliesofenzymes,
such as oxidoreductases, hydrolases, and transferases, can be used
in the polymerization of useful polymers. In 2002, Kaplan
et al.
reported a trial of hydrogel formation using enzymes (peroxidases)
andpoly(asparticacid).Sevenperoxidaseswereevaluatedforcross-
linking poly(aspartic acid)s, and the properties of the resulting
hydrogels,suchasgelationtime,swelling,sol-gelratio,andmechan-
Search WWH ::
Custom Search