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.