Biomedical Engineering Reference
In-Depth Information
applieddextrantothesamesystemasKurisawa'sstudies.
39
Dextran
has been used in a range of hydrogels for drug delivery and tissue
engineering, due to the good solubility in water, ease of chemical
modification,andbiocompatibility.Theyalsodemonstratedthatthe
properties of the dextran hydrogels, such as gelation time, degra-
dation time, swelling ratio, and elasticity, could be controlled by
the concentrations of HRP, hydrogen peroxide, and polymers. This
meansthatenzyme-triggeredhydrogelshaveconsiderablepotential
as injectable biomaterials for tissue regeneration. In a subsequent
study, researchers applied chitosan to a HRP-triggered system.
40
Chitosan was modified with glycolic acid and successively phloretic
acid, followed by hydrogel characterization. The chitosan hydrogel
was finally tested as a cellular matrix by chondrocyte encapsula-
tionandculture,demonstratingcellviabilityfortwoweeks.Sakai
et
al.
also suggested a novel derivative of chitosan, conjugated with 3-
(
p
-hydroxyphenyl) propionic acid, which was soluble at neutral pH
and
in situ
cross-linkable by an HRP reaction. The properties of chi-
tosan hydrogels and their effect on cells were characterized.
41
The
researchers prepared alginate derivatives for the HRP-triggering
system.
42
Alginate is a natural polymer undergoing ionic gelation
with divalent cations (e.g., calcium ion) and has a biocompatible
nature. Alginate was modified with hydroxyl phenyl groups and
characterized for hydrogel properties containing volume changes,
mechanicalproperties,andgelationtimes.Thealginatederivativeis
bothionicallyandenzymaticallycross-linkable.Sakai'sstudieswere
extended to carboxymethylcellulose-based hydrogels. The hydrogel
was characterized in the same manner as other hydrogels, and in
particular,thecytotoxicitywastestedusingCrandellReesfelinekid-
ney (CRFK) cells.
43
Gelatin was also applied to the HRP-triggerable
system for hydrogels formed
in situ
by Sakai's group.
44
In their
study, gelatin was conjugated with TA and the gelatin time and
mechanicalpropertieswerecharacterized.Thegelatinhydrogelwas
tested by a cell culture and injected subcutaneously into mice to
test its feasibility as an injectable biomaterial for tissue engineer-
ing and drug delivery. The results showed that the coated and
injected hydrogels are biocompatible and feasible for a cellular
matrix. Recently, our group prepared a novel multiarm, amphiphilic
copolymer derivative (Tetronic-TA) that was cross-linkable
in situ
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