Micromodular implants to provide electrical stimulation of paralyzed muscles and limbs.

We describe the design, fabrication, and output capabilities of a microminiature electrical stimulator that can be injected in or near nerves and muscles. Each single-channel microstimulator consists of a cylindrical glass capsule with hermetically sealed electrodes in either end (2-mm diameter x 13-mm overall length). Power and digital control data can be transmitted to multiple implants (256 unique addresses) via a 2-MHz RF field created by an external AM oscillator and inductive coil. In vitro testing demonstrated accurate control of output pulsewidth (3-258 microseconds in 1-microseconds steps) and current (0-30 mA in two linear ranges of 16 steps each, up to 8.5 V available compliance voltage). Microstimulators were used successfully for chronic stimulation in hindlimb muscles of cats. Design and fabrication issues affecting yield and reliability of the packaging and electronics are discussed.

Structured sleeve for repair of implantable in-line connectors.

A structured miniature repair sleeve has been designed for implantable in-line connectors that develop small current leaks post-implant. The repair sleeve has been successfully utilised in one subject following the development of current leakage in connectors on an implanted joint angle sensor.

Surface examination of electrodes of removed implants.

The influence of the corrosive environment in human tissue on implantable platinum electrodes during long term electrical stimulation with monophasic voltage stimulation pulses was studied. Various anomalies caused by electrochemical reactions and/or mechanical deformations produced on the surface of the electrodes owing to electrical stimulation were identified and investigated by means of scanning electron microscopy. Since the corrosion reactions of the electrodes depend mostly on the composition of the electrode-electrolyte system, the potentials of anode and cathode during pulsing were measured in 0.9% NaCl solution and in vivo.

A custom designed chip to control an implantable stimulator and telemetry system for control of paralyzed muscles.

A custom designed chip has been developed for the control of paralyzed muscles. The system is capable of fulfilling the stimulus and telemetry needs of advanced functional neuromuscular stimulation (FNS) applications requiring multiple channels of stimulation and multiple channels for sensor or biopotential sensing. An inductive radiofrequency link provides power to the implant device as well as 2 way transcutaneous communication. An application specific integrated circuit (ASIC) decodes the commands and provides functional control within the implant, and modular circuitry provides specific implant functions. The ASIC chip provides up to 32 independent channels of stimulation with independent control of stimulus pulse duration, pulse amplitude, interphase delay, recharge phase duration, and pulse interval. It can also control up to 8 independent back telemetry analog channels with independent control of sampling rate and pulse powering parameters (amplitude and duration). The mixed analog digital chip has been fabricated in 1.2 microm n-well CMOS technology.

Treatment of drop foot using an implantable peroneal underknee stimulator.

An implantable peroneal stimulator has been developed to improve the rehabilitation of the drop foot patients who cannot use or refuse the use of conventionally applied peroneal braces. The small size promotes convenient attachment on the stimulation site after a minor surgical intervention. During the past two years twenty implants have been applied. The influence of different stimulation parameters upon the correction of anomalies during walking has been studied using clinical and computer-supported assessment. Possible noxious effects on the peroneal nerve have been studied by measuring nerve conduction velocity. The stimulator is well accepted by patients. Clinical observations show a significant correction of equinovarus and improved gait.

Improvement of some abnormal motor functions by electrical stimulation.

Clinical results obtained from electrical stimulation of muscle, nerve, spinal cord, cerebellum, and cerebrum are surveyed. Some more data are presented from our own experience with stimulating denervated muscle and cerebellum. Mechanisms which might be responsible for its clinical effects on the muscle, synapse, or nervous system are discussed.

Implantable transducer for two-degree of freedom joint angle sensing.

An implantable joint angle transducer (IJAT) was developed to provide command-control and feedback-control information for chronic use with functional neuromuscular stimulation (FNS) neuroprostheses. The IJAT uses Hall effect sensors to transduce joint angle. A titanium encapsulated array of Hall effect sensors and support circuitry is surgically implanted in one bone, and a similarly encapsulated permanent magnet in an opposing bone, across a joint. The IJAT provides consistent, reliable, high quality signals that reflect joint movement from midsized two-degree-of-freedom joints. IJAT's were implanted using a chronic in vivo dog model to demonstrate the feasibility of implantation and periodic measurement techniques, and to validate modeling techniques used for prediction of function and calibration. The flexion resolution ranged from 0.4 to 3.0 degrees over a range of 115 degrees. The maximum deviation from a linear response was 9 degrees. The resolution and linearity depend on several transducer and joint geometry parameters, and can be predicted prior to implantation and calibrated after implantation. The results of this study 1) defined the most appropriate hermetic capsule designs for the IJAT sensor and magnet, 2) defined the best orientation of the magnetic field to optimize device function, 3) provided a computer model of the IJAT to aid in placement, calibration, and evaluation of the device, 4) verified the surgical techniques used to implant the device, and 5) verified the long-term functionality and the biocompatibility of the device.