Neuromuscular microstimulators

Implantable medical devices have been widely used to restore body functions, improve the quality of life, or save lives. Experts estimate that 8 to 10 percent of all Americans (some 20 million to 25 million people) [1], or about 1 in 17 people in industrialized countries [2], carry some form of implanted device. Many medical devices, such as the implantable cardiac defibrillator, cochlear implant, artificial vision prosthesis, neuromuscular microstimulator, and the like contain sophisticated electronic circuits. Such long-term implantable medical devices are susceptible to damage by body fluids over time. Hermetic packaging is required to protect the electronic circuitry of the implant from the harsh environment of the human body. 

Fig. 1 Photograph depicting three neuromuscular microstimulators (BIONs) in different packages. The diameters of three BIONs are 2.0 mm from AMl-Alfred Mann Institute at University of Southern California, 2.5 mm from AMF - Alfred Mann Foundation, and 3.3 mm from ABC -Advanced Bionic Corp. (Reprinted from [33] with permission of the American Association of Neurological Surgeons)...

Sometimes a ceramic-to-metal seal is the preferable design, as in the AMF neuromuscular microstimulator, where no feedthrough pin is needed. Pure iridium and platinum-iridium components attached to the titanium metal parts act as electrodes interfacing with living tissue. 

Fig. 4 The package of the first-generation neuromuscular microstimulator. (Reprinted from [71] with permission of Springer)...

In 2006, Loeb et al. reported that among a total of 80 neuromuscular microstimulators that were implanted in 35 participants in five different clinical trials, four unresponsive implants were visibly broken as determined by X-ray analysis [71]. Two of the four failures occurred in adjacent neuromuscular microstimulators in... 

For many applications it is desirable that the implantable medical devices remain benign in the subject for the rest of the subject s life to avoid a secondary removal surgery. The intent is to leave the implanted neuromuscular microstimulator in the subject s body for the rest of his/her lifetime, which could be up to 80 or more years [15]. The cochlear implant is now the treatment of choice for children with profound and severe congenital and neonatal hearing loss [84, 85]. The long-term stability of the package for both of these devices is very important. 

Ziaie, B., Nardin, M.D., Coghlan, A.R., and Najafi, K., A single channel implantable microstimulator for functional neuromuscular stimulation, IEEE Trans. Biomed. Eng. BME-44 909-920, 1997. 

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