Biomedical Engineering Reference
In-Depth Information
can be obtained in real-time, with the main potential problems related to
the handling and lifetime of the living cells.
47
11.6 Biosensors in tissue engineering
The fi eld of tissue engineering has the potential to be of widespread clinical
use in the replacement or regeneration of diseased tissues in the cardiovas-
cular system. Myocardial tissue, heart valves and vascular grafts are of
particular interest in cardiac tissue engineering. Siepe
et al.
53
review types
of stem cells that can be used for the purpose of engineering cardiac tissues.
The engineering of such tissue generally involves an
in vitro
step; the
growth of cells on a scaffold matrix or in monolayers. The vessel in which
this is performed is known as a bioreactor, and depending on the form of
the tissue required can be a simple Petri dish for growing sheets of cells,
up to a bottle containing a scaffold structure for a 3-D tissue. In some cases,
mechanical agitation will take place to provide the physical stimuli for cell
growth. Chemical stimuli are provided through the culture medium sup-
plied to the cells. Consideration must also be given to gas exchange and
temperature regulation. The conditions required for successful tissue for-
mation are precise, often challenging to obtain, and vary among cell types.
Control of the physical and chemical environment is important, and the
formation of tissue
in vitro
can benefi t from sensing technologies.
54
The
most important chemical species to monitor in bioreactors are dissolved
oxygen, glucose, pH and
p
CO
2
.
55
The functionality of the growing tissue can
be indicated by monitoring such parameters of metabolic activity. Various
biosensor types can be incorporated into the bioreactor systems to provide
these monitoring functions. Catheter-type or microelectrode probe sensors
such as those discussed above can be introduced into the culture, though
care has to be taken with regards to achieving and maintaining sterility.
Regular re-calibration of such invasive sensors is often required, to prevent
loss of sensitivity due to protein adsorption. Sensors based on electrochemi-
cal and optical technologies have been used.
55
Measurements can be made
in the culture media or with the sensor in contact with the cells or scaffold,
depending on the requirements. Sensors positioned in a shunt allow inter-
mittent sampling of the culture media to take place, which allows more
elaborate sensors to be used. Non-invasive monitoring of the bioreactor
can also be achieved, particularly using optical methods, which circumvent
the problem associated with invasive sensors.
11.7 Biosensors and nanotechnology
The development of biosensors has been enhanced in recent years by com-
bination with nanotechnology, as reviewed by Jianrong
et al.
56
and Wang.
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