AsianScientist (May 9, 2018) – Japanese researchers have created an implantable optical device no bigger than the width of a coin that can be used to control brain patterns. Their work is published in AIP Advances.
For centuries, it has been known that chemicals can change neural behavior. With the advent of optogenetics, scientists can now use light to manipulate neural behavior as well. In fact, researchers have successfully controlled the behavior of rodents using implanted optical devices that emit specific wavelengths of light. However, the devices are often bulky, akin to wearing a football helmet or something heavier, and cause discomfort and distress to the animals.
The miniaturization of implantable devices has been hindered by a dependency on electromagnetics. In such devices, both the voltage and the current decrease with a reduction in size, thus limiting the power. On the other hand, in devices that depend on photovoltaics, voltage remains unchanged as size is reduced.
In the present study, Associate Professor Takashi Tokuda at the Nara Institute of Science and Technology (NAIST), has created a tiny implantable optical device using a complementary metal-oxide semiconductor that controls photovoltaic power.
“We integrated two sets of photovoltaic cells onto semiconductor chips. Ten cells were integrated for powering, and seven cells for biasing,” he said.
At a volume of 1 mm3 and weighing just 2.3 mg, the device is almost one order of magnitude than any other reported device, leading Tokuda to call it “the world’s smallest wireless optical neural stimulator.”
The device also includes an InGan LED chip, which causes the device to emit blue light. A distinguishing feature of the device, however, is that it can be activated with infrared light. Infrared light is used in many light therapies because it can penetrate deep in the body, whereas blue light cannot go much deeper than the surface. This means that the device can still be stimulated when implanted deep in the body.
The researchers acknowledged that their device requires further modifications before it can reach its fullest potential.
“The device can be applied only for pulse stimulations and requires a charge time for each stimulation. Most optogenetics use multiple pulses. We need to improve the power receiving and conversion efficiency,” he said.
The article can be found at: Tokuda et al. (2018) 1 mm3-sized Optical Neural Stimulator Based on CMOS Integrated Photovoltaic Power Receiver.
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Source: Nara Institute of Science and Technology.
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