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Strong hydrogel adhesive comes painlessly off sensitive skin

Bandages made with the adhesive detach gently from skin when chilled and accelerate wound healing in rats

by Prachi Patel, special to C&EN
June 14, 2022

Credit: ACS Nano
A polyphenol-gelatin hydrogel sticks firmly to infant rat skin and, after cooling with an ice pack, peels off easily without pulling or irritating skin, unlike commercial medical tape.

Ripping a Band-Aid off provides a stinging lesson in medical adhesives: they are designed to stick strongly to healthy human skin. But for people with fragile or sensitive skin—such as infants, older adults, and people with diabetes—these adhesives can cause irritation or stick so strongly that they cause trauma during removal.

Now, researchers have developed a hydrogel adhesive that sticks strongly to skin but comes off painlessly when chilled with an ice pack (ACS Nano 2022, DOI: 10.1021/acsnano.2c00662).

Hydrogels are attractive materials for adhesives and wound dressings because they can mold to skin and be tailored at the molecular level to, for example, repair themselves if torn or promote wound healing. Recently designed soft hydrogel adhesives can detach in response to electrical signals, chemicals, or heat, but these triggers can also be harsh on sensitive or wounded skin.

Lu Han of Ocean University of China, Xiong Lu of Southwest Jiaotong University, and their colleagues wanted to design a hydrogel that detaches with a gentler trigger. They made the new hydrogel with intertwined strands of a polyphenol compound, poly(gallic acid), and a cross-linkable biopolymer, gelatin methacryloyl (GelMA). Polyphenols are known to be strong adhesives. Meanwhile, GelMA’s biocompatibility and ability to cross-link in response to heat and light make it promising for tissue engineering and drug delivery applications, but it has historically suffered from being stiff and brittle.

Adding poly(gallic acid) to GelMA loosens up the GelMA chains, making the material softer. Body heat from skin then can provide enough energy to break hydrogen bonds between the chains and further disentangle them. This makes the hydrogel pliable so that it conforms and sticks to skin. But when it is cooled, the GelMA chains re-entangle, and the hydrogel becomes rigid again and comes off easily.

The researchers used the hydrogel to attach wireless medical devices to the skin of infant rats. The hydrogel’s adhesion to skin matched that of commercial adhesives, and the sensors remained on the animals as they moved around. But unlike commercial medical tape, the hydrogel detached when cooled with ice and did not pull or irritate the rats’ skin or remove hair.

In another demonstration, the team applied the hydrogel patch to open wounds in a rat model of diabetes, which are typically difficult to heal. The covered wounds almost fully healed after 25 days unlike untreated ones. The researchers credit the accelerated healing to the poly(gallic acid)’s antioxidant and anti-inflammatory properties and to the hydrogel’s tight seal on wounds.

This is an “outstanding advance in soft and adhesive hydrogels for intimate contact with skin and to promote wound healing,” says Jun Fu, a polymer chemist at Sun Yat-sen University. The mechanism of attachment and detachment triggered by mild, easily accessible temperatures is “highly clinic relevant,” he says. “It will improve the experience of patients and medical professionals.”


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