Engineers at MIT have developed an elastic yet sturdy hydrogel material that can be used as a flexible, biocompatible wound dressing and as a “smart” delivery method for drugs or medical devices.
The material was designed to be embedded with medically-useful electronics, such as conductive wires, semiconductor chips, LED lights, and temperature sensors, according to a study published online December 7, 2015 in the journal Advanced Materials.
Electronics coated in the hydrogel could be placed not only on the surface of the skin but also inside the body—such as implanted biocompatible glucose sensors or soft, compliant neural probes, the researchers wrote.
“Electronics are usually hard and dry, but the human body is soft and wet. These two systems have drastically different properties,” said lead investigator Xuanhe Zhao, PhD, Associate Professor in MIT’s Department of Mechanical Engineering, in Cambridge, MA.
Dr. Zhao explained, “If you want to put electronics in close contact with the human body for applications such as health care monitoring and drug delivery, it is highly desirable to make the electronic devices soft and stretchable to fit the environment of the human body. That’s the motivation for stretchable hydrogel electronics.”
Current hydrogels are often brittle and made of degradable biomaterials that don’t last long, he explained. So, his team designed a hydrogel that is not only as flexible as human soft tissues, but can bond strongly to non-porous surfaces such as gold, titanium, aluminum, silicon, glass, and ceramic.
In the study, the researchers described several uses for the hydrogel:
A transparent, stretchable conductor: In experiments, the researchers encapsulated a titanium wire in the hydrogel, which they stretched repeatedly and found it maintained constant electrical conductivity. Dr. Zhao also embedded an array of LED lights in a sheet of the novel material. The array continued working even when stretched across highly deformable areas such as the knee and elbow.
A smart wound dressing: The group implanted temperature sensors and tiny drug reservoirs within a sheet of hydrogel, along with tiny tubes and pathways for drugs to flow through the matrix. They placed the dressing over various regions of the body and found that, even when highly stretched, the dressing continued to monitor skin temperature and release drugs according to the sensor readings.
An immediate application of this technology may be as a stretchable, on-demand treatment for burns or other skin conditions. “It’s a very versatile matrix,” said Hyunwoo Yuk, a graduate student in Dr. Zhao's lab. “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.”
Biocompatible delivery material. Dr. Zhao is currently exploring hydrogel’s potential as a biocompatible casing for miniature electronic devices, such as glucose sensors and neural probes. Conventional implanted glucose sensors typically provoke a foreign-body immune response, which covers the sensors with dense fibers, requiring the sensors to be replaced often. While various hydrogels have been used to coat glucose sensors and prevent such a reaction, the hydrogels are brittle and can detach easily with motion. Dr. Zhao said the hydrogel-sensor system his group is developing would likely be robust and effective over long periods.
A similar concept could be used for neural probes. “The brain is a bowl of Jell-O,” Dr. Zhao said. “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.”
Dr. Zhao explains and demonstrates the hydrogel in this MIT video.