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Title: Development of a battery-free ultrasonically powered functional electrical stimulator for movement restoration after paralyzing spinal cord injury
Authors: Alam, M 
Li, S 
Ahmed, RU 
Yam, YM 
Thakur, S
Wang, XY
Tang, D
Ng, S
Zheng, YP 
Issue Date: 2019
Source: Journal of neuroEngineering and rehabilitation, 8 Mar. 2019, v. 16, 36, p. 1-14
Abstract: Background Functional electrical stimulation (FES) is used to restore movements in paretic limbs after severe paralyses resulting from neurological injuries such as spinal cord injury (SCI). Most chronic FES systems utilize an implantable electrical stimulator to deliver a small electric current to the targeted muscle or nerve to stimulate muscle contractions. These implanted stimulators are generally bulky, mainly due to the size of the batteries. Furthermore, these battery-powered stimulators are required to be explanted every few years for battery replacement which may result in surgical failures or infections. Hence, a wireless power transfer technique is desirable to power these implantable stimulators.
Methods Conventional wireless power transduction faces significant challenges for safe and efficient energy transfer through the skin and deep into the body. Inductive and electromagnetic power transduction is generally used for very short distances and may also interfere with other medical measurements such as X-ray and MRI. To address these issues, we have developed a wireless, ultrasonically powered, implantable piezoelectric stimulator. The stimulator is encapsulated with biocompatible materials.
Results The stimulator is capable of harvesting a maximum of 5.95mW electric power at an 8-mm depth under the skin from an ultrasound beam with about 380mW/cm(2) of acoustic intensity. The stimulator was implanted in several paraplegic rats with SCI. Our implanted stimulator successfully induced several hindlimb muscle contractions and restored leg movement.
Conclusions A battery-free miniature (10mm diameter x4mm thickness) implantable stimulator, developed in the current study is capable of directly stimulating paretic muscles through external ultrasound signals. The required cost to develop the stimulator is relatively low as all the components are off the shelf.
Keywords: Functional electrical stimulation
Wireless power
Publisher: BioMed Central
Journal: Journal of neuroEngineering and rehabilitation 
EISSN: 1743-0003
DOI: 10.1186/s12984-019-0501-4
Rights: © The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0International License (, which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link tothe Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver( applies to the data made available in this article, unless otherwise stated.
The following publication Alam, M., Li, S., Ahmed, R. U., Yam, Y. M., Thakur, S., Wang, X. Y., ... & Zheng, Y. P. (2019). Development of a battery-free ultrasonically powered functional electrical stimulator for movement restoration after paralyzing spinal cord injury. Journal of neuroengineering and rehabilitation, 16(1), 36, 1-14 is available at
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