The functional reanimation of paralyzed limbs has been a long-standing goal of neural prosthetic research, but clinically successful applications have been elusive. Natural voluntary limb movement requires four major elements: actuators (i.e., motor units), sensors (i.e., somatosensory afferents),
commands (i.e., cerebral cortical activity), and control (i.e., integration of the previous three elements at various levels of the neuraxis) [4]. Prosthetic equivalents of each of these elements are primitive and often cumbersome to deploy, but new technologies promise substantial improvements.
Functional neuromuscular stimulation (FNS) involves microminiature electrical stimulators that can be injected in or near nerves and muscles. Functional neuromuscular stimulation has provided individuals with the ability to initiate movements that are of functional value, such as the restoration of limited grasping functions after cervical spinal cord injury, and the restoration of ambulation by FNS alone, or in combination with orthotics. FNS has also been used to improve ventilation by stimulation of the phrenic nerve, improve bladder, bowel, and sexual function by stimulation of the sacral anterior nerve roots, and reduce spasticity [1].
Microminiature implantable electronic devices can be used in
a variety of combinations to stimulate individual nerves and muscles. These devices eliminate the donning and reliability problems of surface and percutaneous electrodes, and do not require long leads between the electrodes and the controller because the receiving and stimulating circuitry are contained within each unit. Their small size allows injection directly into the desired muscles through a hypodermic needle, providing for unlimited combination of a multiple of individually selective channels. This website explores the design and fabrication of these microminiature devices along with their biocompatibility and application to the clinical setting. Enjoy!
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