Researchers from University of California, Berkeley, have just published a methods paper in Neuron (Dongjin Seo et al. Wireless Recording in the Peripheral Nervous System with Ultrasonic Neural Dust. Neuron, August 2016) describing the the function of and experiments conducted with a millimeter scale, surgically implanted sensor for picking up electrical activity from rat muscle and neurons in vivo.
The U.S. Defence Advanced Research Projects (DARPA)-funded group have identified ultra-sound as being ideal means of communication between the implanted sensor and an external power signal generator and signal converter. The sensor incorporates a piezoelectric crystal as the ultrasound sensing element, which vibrates in response to the ultrasound wavefront. This vibration, with its characteristics determined by the ultrasonic signal’s frequency and amplitude, is converted by the piezocrystal into electrical charge, which powers a transistor circuit. The transistor acts as an amplifier for amplifying voltage picked up between two electrodes connected to its terminals. This electrical signal is, in turn, sent back to the piezoelectric crystal. Here it interferes with the piezocrystal’s ultrasonic vibrational code, causing a “backscatter” on the ultrasound wavefront which gets detected by an external receiver and translated into an electrical trace.
The Berkeley group experiments showed electromyographs from rat gastrocnemius muscle and sciatic nerve
Diagram showing the components of the neural-dust mote (sensor). The entire device is covered in a biocompatible gel. (credit: Dongjin Seo et al./Neuron)
The complete sensor measured at approximately 0,8 x 3 x 1mm, but in their paper they suggest several measures for reducing its size to <500um3 in size, which will open up many opportunities for implantable electronics. The group also claim that it’s possible to steer the ultrasound beam/s in order to address several neural dust sensors independently. The project is also evolving towards using more biocompatible compounds, which may last in the body for a decade or more.
Besides the wide-ranging questions which can be answered in the lab by chronic in vivo electrical recording and stimulation, electrode implants have a long list of potential clinical applications, including treatment of disorders like Parkinsons and epilepsy, as well as implications for control of robotic prosthetics and brain-machine interfaces. Tethered devices have the limitation of being more invasive in terms of initial surgery, and leading to long term infections and unwanted movements relative to the target site.
For more information, refer to the open-access papers:
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