Dextran-based
hydrogels were obtained by polymerization of aqueous solutions of
methacrylated dextran (
dex-MA) or
lactate-
hydroxyethyl methacrylate-derivatized
dextran (dex-
lactate-
HEMA). Both nondegradable
dex-MA and degradable dex-
lactate-
HEMA disk-shaped
hydrogels, varying in initial water content and degree of substitution (DS, the number of
methacrylate groups per 100
glucose units), were implanted subcutaneously in rats. The tissue reaction was evaluated over a period of 6 weeks. The initial
foreign-body reaction to the
dex-MA hydrogels was characterized by infiltration of granulocytes and macrophages and the formation of
fibrin, and exudate, as well as new blood vessels. This reaction depended on the initial water content as well as on the DS of the
hydrogel and decreased within 10 days. The mildest tissue response was observed for the gel with the highest water content and intermediate DS. At day 21 all
dex-MA hydrogels were surrounded by a fibrous
capsule and no toxic effects on the surrounding tissue were found. No signs of degradation were observed. The initial
foreign-body reaction to the degradable dex-
lactate-
HEMA hydrogels was less severe compared with the
dex-MA gels. In general, the size of the dex-
lactate-
HEMA hydrogels increased progressively with time and finally the
gels completely dissolved. Degradation of the dex-
lactate-
HEMA hydrogels was associated with infiltration of macrophages and the formation of giant cells, both of which phagocytosed pieces of the
hydrogel. A good correlation between the in vitro and the in vivo degradation time was found. This suggests that extra-cellular degradation is not caused by
enzymes but depends only on hydrolysis of the
ester and/or
carbonate bonds present in the crosslinks of the
hydrogels. After 21 days, the degradable
hydrogels, as such, could not be retrieved, but accumulation of macrophages and giant cells was observed, both of which contained particles of the
gels intracellularly. As for the
dex-MA hydrogels, no toxic effects on the surrounding tissue were found. The results presented in this study demonstrate that
dextran-based
hydrogels can be considered as
biocompatible materials, making these
hydrogels attractive systems for
drug delivery purposes.