Page 67 - Read Online

Page 10 of 23 Du et al. Soft Sci 2024;4:35 https://dx.doi.org/10.20517/ss.2024.31

advances, its applications can extend to challenging deep areas such as the heart, lungs, and brain. The
hydrogel actuator releases drug molecules into the surrounding tissue environment, achieving a therapeutic
effect.

HYDROGEL ACTUATORS FOR THERAPEUTICS
The unique properties make hydrogel actuators promising for biomedical and drug delivery applications.
These hydrogels can load various drugs and release them in response to specific external stimuli to achieve
targeted functions. In this section, we summarize the typical diseases treated using hydrogel actuators as
therapeutic methods [Table 2].

Skin diseases
Wound healing
As a barrier between the human body and the outside world, the skin is highly susceptible to injury.
Modern clinical development of wound dressings has increasingly focused on combining excellent
antibacterial properties with enhanced wound healing capabilities . The functions of wound dressings
[108]
include protecting wounds, reducing bacterial presence, and promoting healing. Hydrogels, with their
beneficial properties, can simulate the ECM environment, allow sufficient gas exchange, absorb wound
[109]
exudates, maintain a moist environment, and minimize the risk of bacterial infection . Therefore,
hydrogels are ideal for wound dressings. Furthermore, hydrogels can serve as a drug reservoir, enabling on-
demand drug release and exchange of wound exudates in response to environmental stimuli to meet various
demands . Hydrogel actuator dressings can be applied to the skin, exerting contraction forces in response
[110]
to temperature changes to promote wound closure. The hydrogel’s inherent viscosity allows for rapid stress
[65]
transfer to the wound edges . In addition, drugs or other therapeutic agents can be incorporated into the
hydrogel, promoting drug release through active contraction and facilitating wound healing.

Blacklow et al. developed an active adhesive dressing composed of a thermoresponsive adhesive hydrogel
with high tensile strength, toughness, tissue adhesion, and antibacterial properties [Figure 3A]. These
[93]
dressings adhere to the skin, respond to skin temperature, and exert sufficient contraction forces to facilitate
wound closure. The hydrogel’s viscosity allows for rapid and effective transfer of these forces to the wound
edges. This mechanical therapy provides a novel approach to traditional wound healing. Additionally,
hydrogels themselves have inherent biological functions that promote wound healing. In vitro and in vivo
studies have demonstrated their effectiveness in promoting skin wound contraction and wound healing.

Yang et al. developed a new NIR photoresponsive dressing material [Figure 3B] based on dodecyl-modified
and chitosan (CS) hydrogel, photothermal agent, and antimicrobial drug (ciprofloxacin) . The
[94]
nanocomposite dressing is injectable, adaptive, and capable of rapid molding. Unlike traditional drug
delivery strategies, the light stimulation response switch allows for precise control of drug release at the
infection site, maintaining sufficient drug concentration for effective bacterial infection treatment. Under
NIR light irradiation, WS nanosheets generate significant heat, triggering the release of antibiotics at the
2
wound site on demand. In vitro antibacterial tests and infected mouse wound models verified its excellent
bactericidal effect. This synergistic therapy combines the photothermal effect and spatiotemporal control of
drug release, effectively avoiding the disadvantages of two separate treatment modes and achieving the
synergistic effect of antibacterial action and wound healing promotion in the dressing.

However, since hydrogel actuators apply contraction force based on temperature changes to promote
wound closure, more temperature factors need to be considered. For instance, in cold environments,
additional heating methods may be required. Additionally, the skin temperature of different parts of the