Flexible Optogenetics Implants Hack the Sense of Pain

Squishy optoelectronics should make longer-lasting implants

Photo: GEREAU LAB/Washington University in St.Louis
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A stretchy electronic implant as small as a your fingertip can control the feeling of pain in mice. That proof of concept could pave the way for future medical implants that hack the human nervous system and offer relief for people living with chronic pain.

The new demonstration represents a huge step forward for optogenetics technology: A futuristic field of science that hacks nerve cells by genetically changing them to become responsive to light. Until now, the rigid electronic components of such implants limited their placement inside living bodies. The newest generation of stretchy, wireless electronic implants bypasses those old limitations with flexible implants that can control pain signals in the main leg nerve and spinal cord of genetically-engineered mice.

“Our eventual goal is to use this technology to treat pain in very specific locations by providing a kind of ‘switch’ to turn off the pain signals long before they reach the brain,” said Robert W. Gereau, professor of anesthesiology and director of the Washington University Pain Center at Washington University in St. Louis, in a press release.

The new devices showed they could activate nerve cells of lab mice which had been genetically modified to express the light-sensitive proteins in their sensory nerve cells. The research was detailed in the 9 November 2015 online issue of the journal Nature Biotechnology.

That demonstration mainly showed how the optogenetic devices could activate the sensation of pain for such mice, but it could also theoretically block the sensation of pain. Eventually, gene therapy that modifies the nerve cells of humans could possibly enable optogenetics to help people suffering from chronic pain.

In this case, researchers in South Korea and the United States created a flexible device that is 0.7 millimeters thick, 3.8 millimeters wide, and 6 millimeters long. Simple sutures could hold its soft, stretchable body in place near the peripheral nerves and in the spinal cords of mice. By comparison, rigid versions of such devices had to be anchored to bone. (The study’s list of coauthors includes John Rogers, a materials scientist and engineer at the University of Illinois whose lab has pioneered many examples of biocompatible flexible electronics.)

The stretchy implant—weighing just 16 milligrams—contains a microLED to emit light signals and a radio-frequency antenna to wirelessly power the device. A polyimide and silicone elastomer casing make the whole implant flexible. Altogether, the new implants are one-fifth as thin; 10 times more stretchable; 10,000 times softer; and 10 million times more flexible than previous versions of such technology.

The technology is not ready for human clinical trials just yet. But the devices already demonstrated a certain durability and robustness during the mouse experiments that bodes well for the future. About 76 percent of the implants used in the mice were still functional after a week. Two of the devices continued to show reliable activation at least once per month for up to half a year after being implanted.

The new implants were also made using technology that is compatible with existing manufacturing methods in the electronics industry, researchers pointed out. That means it should be cost-effective to make large numbers of such devices.

Past studies have already shown how a laser or LED light can control a fly’s heart rate or artificially activate happy-memory neurons in mice to protect them from stress. But many older optogenetic devices were extremely clunky with protruding wires and bulky bodies. Earlier this year, a Stanford University lab had demonstrated a wireless but rigid version of the optogenetic technology for hacking the brains of mice.

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