Biomaterials for MEMS

MEMS in the Nervous System 75

In addition to effects on movement disorders, DBS appears able to elicit

strong emotional responses as well. In one patient being treated for Parkinson’s

related movement disorders, stimulation of a certain electrode elicited a case

of severe depression, which stopped upon cessation of stimulation.

57

In other

patients, stimulation of Broadmann’s area 25 (subgenual cingulated region) al-

leviated depression in patients unresponsive to traditional pharmaceutical and

behavioral therapies.

52

DBS used in the nucleus acumbens has been suggested as a

treatment for patients with obsessive compulsive disorder that does not respond to

conventional treatments.

58

There is evidence that DBS can also help patients who

have had a traumatic brain injury recover some functionality.

59

4.2.5 Peripheral Prosthetic Devices

One of the most common reasons for interfacing MEMs with the human body

are prosthetic devices. Prosthetics range from artificial limbs to retinal and

cochlear implants. They span a wide range of applications, from supplying

sensory feedback to recording and interpreting motor commands. Artificial limbs

with integrated microelectrodes may one day be capable of supplying a patient

with bio-mimetic closed-loop control, effectively mimicking natural function of an

artificial limb. Sensors in the prosthetic device could monitor information, perhaps

about pressure and temperature, and relay that back to the person so they could

module their actions accordingly. This next generation of prosthetic devices could

function essentially just like the lost limb.

Peripheral nerve electrodes are used to monitor and stimulate nerves in the

PNS. There are several varieties of peripheral nerve electrodes. Cuff electrodes

wrap around a peripheral nerve and stimulate it to generate a muscular response.

Polyamide substrates with platinum electrodes have been used to elicit activity

from rat muscle fibers.

60

Such electrodes could be used to evoke muscular activity

in a patient where communication from the spinal cord to the muscle is discon-

nected. A flexible substrate material is highly desirable in this situation, as it allows

the electrode to be curved around the nerve of interest quite easily. Sieve electrodes

contain holes and are placed between regenerating neurons to allow fibers to grow

through the holes. Electrodes around or near the holes allow for electrical stim-

ulation and recording.

61,62

Severed nerves are capable of physically regenerating

through silicon sieve electrodes

62

and have shown electrophysiological signals for

over one year.

63

Flat interface nerve electrodes (FINE) consist of a silicone tube

with electrical contacts in it; the FINE electrode flattens peripheral nerve to make

the central portion of it more accessible for stimulation and recording.

64

This is

not an exhaustive list of peripheral electrodes but rather just a sampling of what is

currently used.

4.2.6 Visual Prosthetics

Visual prosthetics are devices have the potential to help the visually impaired

regain sight or some aspects of it. Blindness can occur at several levels in the

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