Degradable semiconductor developed at Stanford

A team of researchers at Stanford University has created a flexible electronic device that can easily degrade just by adding a weak acid like vinegar.

"In my group, we have been trying to mimic the function of human skin to think about how to develop future electronic devices," said Zhenan Bao, a professor of chemical engineering and materials science and engineering, who had previously created a stretchable electrode modeled on human skin.

While skin is stretchable, self-healable and biodegradable, "we have achieved the first two, so the biodegradability was something we wanted to tackle," Bao said in a news release on Monday, when her team reported creating the new device in the Proceedings of the American Academy of Sciences.

Acknowledging that creating a robust material that is both a good electrical conductor and biodegradable was a challenge, considering traditional polymer chemistry, Bao said "we have been trying to think how we can achieve both great electronic property but also have the biodegradability."

"This is the first example of a semiconductive polymer that can decompose," said lead author Ting Lei, a postdoctoral fellow working with Bao.

The team found that by tweaking the chemical structure of the material, it would break apart under mild stressors.

"We came up with an idea of making these molecules using a special type of chemical linkage that can retain the ability for the electron to smoothly transport along the molecule," Bao said. "But also this chemical bond is sensitive to weak acid -- even weaker than pure vinegar."

The result was a flexible material that could carry an electronic signal but break down without requiring extreme measures.

The team also developed a degradable electronic circuit and a new biodegradable substrate material for mounting the electrical components. When the electronic device is no longer needed, the whole thing can biodegrade into nontoxic components.

The substrate, which carries the electronic circuit and the polymer, was created from cellulose, which is the same substance that makes up paper.

But unlike paper, the cellulose fibers were altered so the "paper" is transparent and flexible. The thin film substrate allows the electronics to be worn on the skin or even implanted inside the body.

In addition, while electronic components are usually made of gold, components for this device were made from iron. Bao noted that iron is an environmentally friendly product and is nontoxic to humans.

"We envision these soft patches that are very thin and conformable to the skin that can measure blood pressure, glucose value, sweat content." A person could wear a specifically designed patch for a day or week, then download the data.

According to Bao, this short-term use of disposable electronics seems a perfect fit for a degradable, flexible design. Endit