Biomedical Engineering Reference
In-Depth Information
lab-on-a-chip devices, wireless communication capability, complex information process-
ing capability, data archiving, etc. There is no limit to the versatility of smart skin sys-
tems. This section highlights few significant applications that could potentially
revolutionize the biomedical industry.
While such systems offer immense scope and opportunity,
it should be noted that some
of the applications involve safety-critical systems
.
Also
,
certain systems intend
(
or at least pro-
vide the option
)
to remove human intervention from their functionality
,
thus demanding more
stringent precision requirements
.
Such features open up an assortment of technical, ethical
,
and
legal issues
.
A discussion on these issues is beyond the scope of this chapter
.
However, they would
need to be addressed when this technology is put in application
.
10.6.1
Bioimpedance and Bioelectricity Measurement
Bioimpedance measurements at a macroscale have routinely been used for analyzing tis-
sue quality and health monitoring in wide-ranging applications including the freshness of
fish, analysis of skin [5,6,11], and electrocardiogram (ECG). Bioimpedance measurements
give information about electrochemical processes in the tissue and can hence be used for
characterizing the tissue or for monitoring physiological changes. The difference in the
bioimpedance characteristics of different tissues and their condition (healthy or
unhealthy) form the basis of electrical impedance tomography, a standard technique in
medicine (currently being used to measure pulmonary ventilation and gastric emptying).
Determination of skin conductance enables the evaluation of the hydration state of the
upper portion of SC [12]. The technique is now being used for many new applications and
methods, for example, in areas like body composition, cell micromotion, organ viability,
and skin pathology. When coupled with long-term monitoring capability, it can be used for
searching heart arrhythmia or epileptic spikes. Along with finding new applications, basic
research is going on to provide a better understanding of such basic questions as—is living
tissue a purely ionic conductor; are there also local electronic or semiconductor mecha-
nisms; what is the conduction mechanism, for example, in keratinized tissue or DNA [13]?
10.6.2
Electrochemical Sensing
Potentiometry using microelectrodes is a highly sensitive technique of electrochemical
detection capable of detecting zepto molar concentrations in nanoliter solution volume.
Potentiometric sensors respond to the presence of analyte by a change in electrochemical
potential. The most widely used sensors in this category are the ion-selective electrodes
(ISE). Instrumentally, an ISE is designed to observe the potential of a membrane that inter-
acts selectively with a particular chemical, for example pH meter. The selectivity of this
kind of sensor depends entirely upon the membrane design. The number of chemicals that
can be determined by this method are limited only by one's ability to design a membrane
with sufficient sensitivity and selectivity for the analyte in question. Integrated sensor
arrays are capable of detecting ions, properties of fluids, and dissolved gases that are col-
lected from the skin (from sweat to interstitial fluids). Some of the analytes that can be
detected via this method are pH, Na
, K
, O
2
, CO
2
, and NH
3
[14].
10.6.3
Programmed Drug Delivery
Advanced drug-delivery systems will be able to deliver fixed quantities of drug at certain
time intervals automatically. Such systems would comprise a microneedle interface
attached to a MEMS device consisting of a drug reservoir, a microchip, and micropumps.
