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Microstimulators and Microtransducers for Functional Neuromuscular Stimulation


Principal InvestigatorAffiliationContract NumberLink
Joe Schulman, Ph.D.A.E. Mann FoundationN01-NS5-2325


The Neural Prosthesis Program (NPP) of The National Institute of Neurological Disorders and Stroke is committed to the development of safe, reliable, and effective systems for functional neuromuscular stimulation (FNS) in spinal cord injured individuals. Multiple implantable microstimulators which selectively stimulate paralyzed muscles in a controlled fashion may permit an individual to use his or her own muscles as the motors to produce limb movement. Multiple implantable microtransducers that sense contact, grasp force, and limb position from either implanted transducers or intact sensory receptors may provide sensory feedback from an otherwise insensate limb. To produce a useful system, these sensory and motor prostheses are being developed together as standard and compatible building blocks of an integrated FNS system.

The NPP is supporting research and development of a system consisting of an extracorporeal coil and a family of implantable microstimulators and microtransducers (Loeb et. al., Injectable microstimulator for functional electrical stimulation., Med. & Biol. Eng. & Comput. 29:NS13-NS19, 1991; Troyk and Schwan, Closed-loop class E transcutaneous power and data link for microimplants., IEEE Trans. on BME 39:589-599, 1992). The system is designed to power and control up to 64 individual transducers and stimulators through a single external coil. During the past five years significant progress has been made in developing addressable, implantable microstimulators and an extracorporeal coil and transmission system. This work has progressed to the point where first generation devices are available for implantation. Work was also begun during the past 2 years on the development of implantable addressable transducers. This contract will continue the engineering development of the microstimulators and transducers. In addition, in-vivo evaluation of these devices will be initiated in an animal model.

This RFP represents a competitive renewal of an ongoing contract. Copies of progress reports from current contracts related to this work and a bibliography of Neural Prosthesis Program publications are available from the Contracts Management Branch, Room 901 Federal Bldg., 7550 Wisconsin Ave., Bethesda, MD 20892.


Independently, and not as an agent of the Government, the Contractor shall exert its best efforts to develop and test a system for functional neuromuscular stimulation (FNS) consisting of implantable receiver-stimulators and transducer-telemeters and an easily donned extracorporeal transmitter.

Specifically, the Contractor shall:

A. Design, fabricate, and test implantable receiver-stimulators, implantable transducer-telemeters, and an extracorporeal transmitter for FNS.

1. The implantable receiver-stimulators, consisting of power receiver, control receiver, stimulus and control circuitry, electrodes, and encapsulation shall meet the following specifications:

a. They shall be made as small as possible while still being compatible with the other requirements described below. The target volume of each stimulator shall be 60 cubic mm or less.

b. An individual stimulator shall initiate a stimulus pulse only in response to a properly addressed command from the transmitter. There shall be at least 64 different stimulator addresses that can be selected.

c. The stimulators shall derive their power and commands by an inductive link from a transmitter coil with field specifications as outlined below.

d. The stimulus current waveform shall have two phases of opposite polarity. The duration of the first phase shall be variable from 0 to 200 microseconds in at least 200 steps on a pulse by pulse basis.

e. The stimulus current level of the first phase of a stimulus pulse shall be adjustable and shall include levels of 1 and 10 milliamps under control of the transmitter. The current of the second phase shall guarantee long term charge balance at the electrodes under all pulsing conditions within specifications. Stimulator compliance voltage shall be at least 10 volts.

f. Stimulating electrodes shall be made of corrosion resistant and biocompatible materials (e.g. platinum, platinum-iridium, iridium, or tantalum pentoxide) and shall be stable in physiologic saline at 37 degrees C for at least 1 year at the maximum charge delivery rate.

g. The stimulator shall be encapsulated in a manner that permits stable operation in physiologic saline at 37 degrees C for at least 1 year with materials that are known to be biocompatible.

2. The implantable transducer-telemeters consisting of transduction unit, power receiver, control circuitry, digitizer, telemetry circuitry, and encapsulation shall meet the following specifications:

a. The transducer-telemeters shall not interfere with the operation of the receiver-stimulators and vice-versa.

b. The transducer-telemeter package shall occupy a volume of no more than 125 cubic mm (not including magnets, electrodes, or other passive elements which can be external to the package if they are needed for the design). Biocompatibility and life expectancy shall be as specified for the microstimulator in part 1.

c. The transducer-telemeters shall derive power and commands from the same transmitter coil as the microstimulators and shall transmit information to this coil upon command.

d. The transducer-telemeters shall be addressable with at least 64 unique addresses using an addressing scheme that is compatible with the microstimulator addressing.

e. The telemeter's digitizing and telemetry circuits shall be designed to provide at least 8 bits of digital data per sample. Signal conditioning for sensing biopotentials suitable for closed-loop control and/or sensory feedback shall be incorporated in telemeters with addresses 1 through 16.

f. A joint angle transducer-telemeter shall be designed to provide wrist joint angle information for use as a command signal with a resolution of at least 5 degree as the wrist moves through its physiological range of flexion and extension. The error of angle measurement (including drift, hysteresis, and errors due to wrist movement other than pure flexion and extension) shall not exceed 15 degrees.

3. The extracorporeal transmitter shall meet the following specifications:

a. The transmitter field shall permit specified operation of the stimulators and transducers anywhere within a cylindrical shaped volume of physiologic saline at least 9 cm. in diameter and at least 16.0 cm in length.

b. The transmitter field shall permit specified operation with up to 10 degrees of axial misalignment between the transmitter coil and the receiver coils in the stimulators and transducers.

c. The transmitter, under the control of a computer, shall be capable of powering and controlling at least 64 stimulators and/or transducers in any combination.

d. The transmitter coil shall be designed to be donned and doffed as easily as an item of clothing.

e. The transmitter shall operate reliably in the presence of electromagnetic interference commonly found in a home or work environment.

4. The Contractor shall make its best effort to deliver to the Project Officer one set of 32 receiver-stimulators each with a different address, one set of 4 joint angle transducer-telemeters each with a different address, and one transmitter with specifications as outlined above by the end of the contract period.

B. Select a suitable animal model and evaluate implanted microstimulators in this animal model.

1. Evaluate the tissue reaction to implanted stimulators placed intramuscularly and subdermally for periods of at least 3 months.

a. Evaluate the tissue reaction to active and inactive devices.

b. Evaluate the tissue reaction to any components used in making the device that might be exposed to tissue should the encapsulation fail.

2. Investigate the threshold stability and motor recruitment stability of microstimulators over a period of at least 3 months.

3. Investigate the function of implanted transducer-telemeters over a period of at least 3 months.

C. Cooperate with other investigators in the Neural Prosthesis Program to integrate this work into practical FNS systems.

Last Modified November 24, 2008