Biomedical Engineering Reference
In-Depth Information
The microchip would initiate micropumps automatically to inject-controlled quantities of
drug at specified intervals or on demand. Such systems would eliminate human errors such
as skipped medications or incorrect dosage. Another variation of the same systems could
have the ability to continuously inject drugs at a constant rate for extended periods of time.
10.6.4
Automated Feedback-Controlled Therapy
Natural evolution of smart skin-interface systems would ultimately lead to a combination
of diagnostic and therapeutic systems. The interface would extract physiological data, and
medication would be provided on the basis of the response. The diagnostic part might be
either potentiometry-based electronic sensing or more complicated lab-on-a-chip device
which would extract physiological samples via microneedles. Most prevalent system of
such a type is expected to be one for diabetic patients. Microneedles would remove bioflu-
ids for glucose-level measurements and supply insulin as required.
10.6.5
Electrotherapeutic Pain Relief
Transcutaneous electrical nerve stimulation (TENS) [13] provided via surface microelec-
trodes can be used for pain relief. The electrical pulses stimulate the body's own mecha-
nism for obtaining pain relief. The method works using either of the following
physiological mechanisms—(1) Gating theory: Pain perception is regulated by a gate
mechanism in the synapses, which is controlled by separate nerve fibers. Stimulation with
pulses of high frequency (50-200 Hz) activates the gate mechanism, providing pain relief;
(2) Endorphins: The human body uses natural forms of morphine called endorphins for
pain relief, and their secretion can be provoked with low-frequency (2-4 Hz) stimulation;
(3) Vasodilation: This effect is usually associated with pain in cold extremities and results
in increase in temperature due to increased blood flow. The same effect can be elicited
using electrical stimulation.
10.6.6
Iontophoresis
Iontophoresis is a method to accelerate transcutaneous drug delivery by application of DC
current. If the drug is in ionic form, the migration velocity may be increased either by
application of long-term DC voltages of less than 5 V, or by using high-voltage pulses up
to 200 V decaying in about 1 ms. The effect is due to creation of aqueous pathways in SC.
Various therapeutic agents can be introduced in the skin in this manner, such as anesthetic
agents, antibodies, or metals such as silver or zinc (for treatment of ischemic ulcers).
10.7
Technological Merit of Skin-Interface Systems
Micromachined electrodes and needles form the technological foundation for bioengi-
neered skin interfaces. As mentioned earlier, these enabling components will be a com-
mon denominator in design of these systems. The choice of other components would be
purely application driven. The physical characteristics of microneedles/microelectrodes
provide unique technological advantages to these systems as compared to traditional
invasive methodologies. Next-generation therapeutic methods using advances in
