A sheet of hydrogel is bonded to a matrix of polymer islands (red) that can encapsulate electronic components such as semiconductor chips, LED lights, and temperature sensors. (Image courtesy of Melanie Gonick/MIT.)

Built on previous research on a conductive hydrogel adhesive, a stretchable hydrogel material could be the future of medical wound dressings.

The “smart wound dressing” can release medicine in response to sensor input and can be designed to indicate if medicine levels are running low.

The sticky, gel-like material can incorporate temperature sensors, LED lights or other miniaturized electronics, as well as drug delivery reservoirs or channels.

Because it is highly flexible, the material will stretch with movement. This makes it ideal for use on elbows, knees and other joints.

Building a Stretchable, Flexible Gel Material

The hydrogel matrix is rubbery and mostly composed of water. The material is also designed to bond strongly to surfaces such as gold, titanium, aluminum, silica, glass and ceramic.

Many currently used synthetic hydrogels are brittle, offer weak adhesion and barely stretch.

When the team of MIT engineers created the stretchy hydrogel, they developed a design for a robust material by mixing small amounts of selected biopolymers with water.

This created a soft, stretchy material with a stiffness of 10 to 100 kilopascals, similar to the range of human soft tissues.

Demonstrating the stretch of a new hydrogel material. (Image courtesy of Melanie Gonick/MIT.)

The team also worked to develop a method for their hydrogel to bond strongly with various non-porous surfaces.

Their most recent research revolves around demonstrating different applications for the hydrogel. For example, they encapsulated a titanium wire within the hydrogel to form a transparent and stretchable conductor.

In tests, the team found they could stretch the encapsulated wire multiple times while it retained its electrical conductivity.

They also created an array of LED lights embedded in a sheet of hydrogel. The array continued working even when flexed over a highly deformable area such as a knee or elbow.

The “Smart Wound Dressing”

These tests led the team to work on their main application for the hydrogel – a “smart wound dressing” for medical treatment.

The team embedded various electronic components into a sheet of hydrogel, regularly spacing temperature sensors and tiny drug reservoirs. They created pathways for drugs to flow through the hydrogel by either inserting patterned tubes or drilling tiny holes in the gel matrix.

A stretchable, smart wound dressing includes temperature sensors and drug-delivery channels and reservoirs, embedded in a robust hydrogel matrix. Mock drugs can be released at various locations on demand, based on the measured temperatures. (Image courtesy of MIT.)

When the research team placed their dressing on various regions of the body, they found that the dressing monitored skin temperature and released the drugs according to sensor readings even when highly stretched.

Theoretically, in the future this information could be captured and sent to patients, nurses and doctors using IoT framework or other digital connectivity.

“It’s a very versatile matrix,” said Hyunwoo Yuk, a graduate student involved in the project. “The unique capability here is, when a sensor senses something different, like an abnormal increase in temperature, the device can on demand release drugs to that specific location and select a specific drug from one of the reservoirs, which can diffuse in the hydrogel matrix for sustained release over time.”

Not Just for External Medical Treatment

The team envisions their hydrogel in applications such as stretchable, on-demand medical treatment for burns and other skin conditions.

But they also see potential for it to act as a biocompatible vehicle to deliver electronics inside the body.

For instance, they are currently exploring the potential of the hydrogel being a carrier for glucose sensors and neural probes.

Because conventional glucose sensors implanted in the body spark a foreign-body response from the immune system, the sensors become covered with dense fibres. This means that the sensors need to be removed and replaced frequently.

While hydrogels have previously been used to coat glucose sensors, the gels are brittle and detach easily due to motion.

The MIT team believes that their hydrogel-sensor system would be more robust and therefore more effective over long periods of time. A similar case could be made for use with neural probes.

“The brain is a bowl of Jell-O,” said Xuanhe Zhao, lead researcher and associate professor in MIT’s department of mechanical engineering. “Currently, researchers are trying different soft materials to achieve long-term biocompatibility of neural devices. With collaborators, we are proposing to use robust hydrogel as an ideal material for neural devices, because the hydrogel can be designed to possess similar mechanical and physiological properties as the brain.”

The new research on MIT’s hydrogel and its applications is published in the journal Advanced Materials.