2.4.2 pH responsive swelling and degradation of hydrogel
Due to the presence of dynamic β -aminoacrylate bond, which can
breaks in response to changes in pH[43], we tested
the pH responsive swelling and degradation properties of hydrogel.
Hydrogels with hydrophilic nature are able to absorb water or exudate
from the wound tissue and regulate the humidity of the wound surface. As
shown in Figure 3C, the swelling kinetics increased and reached the
plateau after 6 h. The swelling capacity decreased as pH decrease in
acidic environment, due to the occurrence of degradation. The swelling
ratio of the hydrogel is also an important parameter to control the
release kinetics of the drug. It is closely related to the diffusion of
the drug into the surrounding media by regulating the rate of drug
penetration and drug diffusion/dissolution within the hydrogel. Based on
the results shown in Figure 3D, the release ratio of THB@ANVs was
evaluated in alkaline, neutral, and acidic environments. There was no
indication of a burst release during this period, and over 80% of the
THB@ANVs can be released from hydrogel after 3 d. The release kinetics
in an acidic environment were faster compared to neutral or alkaline pH,
which may be related to the degradation of β -aminoacrylate bond
in hydrogel under acidic conditions. It can be clearly observed in
Figure 3E that the CMC-DA gel will first swell within a certain time and
then degrade gradually. Thus, we hypothesis that on infected wounds with
lower pH, the release of THB@ANV will be accelerated, and the hydrogel
can slowly breakdown on the wound surface. By testing the release of
vesicular protein from hydrogel, it can be found that hydrogel can
protect the protein and keep the release process stable (Figure S13).
These results proved the hydrogel a promising material for drug delivery
and tissue engineering applications.