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Jun 17th, 2013
New coating makes silicon circuits implantable in human tissue
Biosensors and implantable medical devices of the future will have to live in a climate that’s hostile to traditional silicon-based electronic circuits.
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Fig 1: A silicon circuit, coated with a protective layer.
Fig 1: A silicon circuit, coated with a protective layer.

Although silicon is biocompatible, our salty bodies are too conductive and interfere with bare silicon circuits. Plus, as with any other implants, there are concerns of material’s immunogenicity and toxicity.

Fig 1: A silicon circuit, coated with a protective layer and immersed in fluid that mimicks human body chemistry.

Researchers at Ohio State University have demonstrated a new coating made of aluminum oxide that can encapsulate silicon circuits to keep them dry from the electrolytes in bodily fluids. The coating is currently patent pending and researchers believe that it will soon find application in medicine, most notably in sensors that detect early signs of transplant organ rejection.

More from Ohio state about the motivations for the research:
The project began when Berger talked to researchers in Ohio State’s Department of Biomedical Engineering, who wanted to build an insertable sensor to detect the presence of proteins that mark the first signs of organ rejection in the body. They were struggling to make a working protein sensor from gallium nitride.

We already have sensors that would do a great job at detecting these proteins, but they’re made out of silicon. So I wondered if we could come up with a coating that would protect silicon and allow it to function while it directly touched blood, bodily fluids or living tissue,” Berger said. In the study, Berger’s team tested whether electrolytes could be blocked from entering silicon with a layer of aluminum oxide.

The researchers submerged the coated test sensors in fluid for up to 24 hours, removed them from the solution, and then ran a voltage across them to see if they were working properly. The tests showed that the oxide coating effectively blocked electrolytes from the solution so the sensors remained fully functional.

Once developed, a device using this technology could detect certain proteins that the body produces when it’s just beginning to reject a transplanted organ. Doctors would insert a needle into the patient’s body near the site of the implanted organ. Silicon sensors on the needle would detect the protein, and doctors would know how to tailor the patient’s dosage of anti-rejection drugs based on the sensor readings.

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