Microscale Ultrasound Powered Neurostimulator Research

Miniature Passive Neurostimulators

Ultrasound waves carry a relatively high energy density in their transit through body tissues compared to for example, radio waves.  In addition ultrasound can be highly focused and directed to specific locations in tissue which increases the efficiency of energy delivery compared to radio frequencies.

Piezoelectric materials, particularly the plastic polyvinylidene fluoride placed in body tissues convert ultrasound energy to a high frequency electrical current. This current can then be rectified by a diode and used to power biomedical implants.

Based on these principles we are investigating a class of  potentially implantable microdevices that are powered by ultrasound energy for purposes of neurostimulation.  Short pulses of ultrasound energy are converted  correspondingly electrical pulses whose current is delivered to tissues for the purposes of evoking bioelectrical activities.

A potentially implantable neurostimulator chip approximately 1mm x 5mm.

These devices can readily fit through syringe needle lumens and potentially introduced into tissue with minimal trauma.

We find that these devices can be made compact enough to deliver to tissues through a syringe needle and provide pulsed current flows in the milliampere range when using short duty cycles typical of neurostimulation.

Ultrasound can penetrate skull and tissues and produce electrical pulses from piezoelectric materials.
Diodes integrated with PVDF plastic are placed in electrical parallel.

 

Because  ultrasound transducers and instrumentation has been highly developed for medical imaging, these kinds of approaches to power transfer to implanted microdevices in tissue have a high potential for application in bioelectronic devices and biosensors in tissues.

Towe, B.C.; Larson, P.; Gulick, D. “A microwave Powered Injectable Neural Stimulator” Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS 2012, :5006-5009.

Gulick, D.W.,  Towe, B.C., “Method of Locating Ultrasound-Powered Nerve Stimulators” Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS 2012;():887-890.

Larson, P, and Towe, B.C.,   “Miniature Ultrasonically Powered Wireless Nerve Cuff  Stimulator”,   5th International IEEE-EMBS Conference,  April 28th  on  Neural Engineering,  Cancun, Mexico, April 27, 2011.

Figure 1.  Ultrasound energy is converted into pulses ofhigh frequency current by an integral diode.
Current pulse amplitudes from piezoelectric materials depend on the tissue attentuation beam focusing, and other factors and so vary as a function of depth as seen at right.