Zhenan Bao, Vivian Feig, Helen Tran and Minah Lee
Faculty fellow Zhenan Bao and researchers in her group have created a stretchable, conductive material that could be used to integrate electronics with squishy biological tissue.
BY BETH MILLER
Most electronic medical implants are made of rigid metal, which creates a mechanical mismatch with the body’s squishy biological tissue, especially in delicate areas like the brain. This mismatch can damage cells or create scarring around the implant, leading to complications for the patient.
But Stanford researchers have created a new highly stretchable and conductive composite material that acts more like human tissue. The polymer has the potential to revolutionize medical devices such as the deep-brain stimulators that are used to jumpstart nerve cells in the brains of patients with Parkinson’s disease. The material was introduced in a paper in Nature Communicationsin July.
“If we want to integrate electronics long-term with the body, we need to create a new class of materials that resembles something completely different and is much more similar mechanically to us,” says lead author Vivian R. Feig, a Materials Science and Engineering PhD candidate in the lab of Professor Zhenan Bao, K.K. Lee Professor in Chemical Engineering, with courtesy appointments in Chemistry and Material Science and Engineering, and a faculty fellow in Stanford ChEM-H.
The human brain is a bustling center of biological wires that conduct electricity, so conductive materials provide opportunities to both probe and heal the brain. In creating a material, the researchers also need something that resembles biological tissue, which is stretchy and made of mostly water.
Hydrogels - a network of hydrophilic or “water-loving” molecules – are soft and easily integrated with polymers that conduct electricity. However, previous conductive hydrogels were either too inflexible or not conductive enough for many biomedical applications. Bao and Feig solved this problem by making a hydrogel network out of a conducting polymer and interweaving it with another web of non-conductive material, creating a biologically compatible, pliable composite.
Bao and Feig created the hydrogel by adding a small amount of water to a conductive polymer called PEDOT:PSS. “The conducting polymer that we use on its own can be really stiff and brittle,” Feig says, “but if you make it into a hydrogel with water, it suddenly starts to resemble biological tissue.” The new material can be carefully controlled to tune its stiffness and conductivity by modifying either of the interpenetrating polymer systems, and it can also be formed into different shapes and patterns.
Conductive hydrogel networks could prove important in the medical field for invasive procedures such as deep brain stimulation, which is used to treat patients with Parkinson’s disease who are not responsive to medication, or other medical procedures that require electrical signals such as stimulation of the heart.
PEDOT:PSS is a commercially available material, which means it can be used reproducibly by researchers across many fields. “There’s no complex chemistry involved,” Feig says. She hopes that this material can be used by medical device developers to build their own scaffolds or coat the material on implants, bringing hydrogels to an operating room near you.
