Biomedical Engineering Reference
In-Depth Information
of such devices could be exploited is in the measurement of infl ammatory
biomarkers during and after surgery. The infl ammatory reaction is known
to contribute to post-operative complications, and pro-infl ammatory cyto-
kines TNF
, Il-6 and IL-8 in particular have been associated with negative
outcomes post-surgery.
16,33
This is of particular importance to cardiopulmo-
nary bypass-induced infl ammation.
α
11.3.2 Lab-on-a-chip
TAS (micro total analytical solutions) are terms used to
describe biosensor devices which integrate a number of sensor functions,
including sample handling and preparation, mixing, separation, lysing of
cells and detection functions.
34
Such devices can be used to sample and
detect DNA, proteins and small molecules, and are also frequently employed
for drug development.
35
DNA microarrays and protein immunoassays are
frequently employed as the sensing element. The Biosite Triage Cardiac
panel discussed above employs a protein biochip.
36
The sensing technology
is an immunoassay, using fl uorescent labelling and capable of the simultane-
ous measurement of a hundred different proteins in 15 minutes. The chip
also employs microfl uidic technology. Microfl uidics describes the technol-
ogy required for fl uid handling on the micro-scale, such as that required by
the current miniaturised lab-on-a-chip devices. Microfabrication is required
to manufacture the capillaries, channels and reservoirs on the chip surface.
Various types of fl uid propulsion, valves and mixing methods are avail-
able.
37
Flow design is particularly important at this scale, and in order to
maintain reliability, must also consider the surface deposition of proteins
and lipids.
38
Lab-on-a-chip or
μ
11.4
In vivo
sensors
11.4.1 Temporary
in vivo
biosensors
Catheter-based biosensors are available for the intravascular measurement
of
p
O
2
,
p
CO
2
and pH from companies such as Edwards LifeSciences and
Hospira, and during cardiac surgery these are the devices used most fre-
quently for making
in vivo
measurements.
30,39-41
Both electrochemical and optical sensor types are used to detect these
parameters. Electrochemical oxygen partial pressure sensors are based on
the classic amperometric Clarke electrode, with oxygen being reduced at
platinum, gold or silver electrodes. Electrochemical pH and
p
CO
2
sensors
are usually potentiometric, using metal oxide or polymer membrane pH
methods. The development of optical fi bre-based technology in particular
has allowed the three types of sensor to be fi tted into the lumen of a single
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