Biomedical Engineering Reference
In-Depth Information
the effect of electrical/electromagnetic/magnetic stimulation have to be carefully
thought of and incorporated into the design. For example, when analyzing
changes in stem-cell differentiation, a set-up must be created that allows one to
stimulate many cells at once yet have separable sets of cells that can be analyzed
immunocytochemically. So, when designing such an apparatus, many stipulations
must be considered.
18.5.6.1 Stimulation Methodology.
First, there are many ways to stimu-
late cells with a form of electricity. One characteristic that most devices have in
common is the way in which stimulation is applied to the cells. Usually an EF is
created around growing or proliferating cells. Ironically, this is essentially a scaled
down version of the electric air bath that served no therapeutic purpose (Figure
18.3). This EF can be applied in two fashions, with electrodes submerged in the
media and electrodes that surround the chamber where the cell are grown. There
are numerous electrodes or ways to apply a direct stimulus to the media these
include: micro-wires placed on or near the cells slated for stimulation (Salimi and
Martin 2004), semiconductor-based multi-electrode arrays (Jimbo and Kawana
1992; Sisken et al. 1993; Kawana 1996; Borkholder 1998; Grumet et al. 2000; van
Bergen et al. 2003; Bieberich and Anthony 2004; Nam et al. 2004), electrically-
conducting polymers (Schmidt et al. 1997; Kotwal and Schmidt 2001), agar saline
bridges (Zhao et al. 1996), and graphite rods (Berger et al. 1994).
Furthermore, cells can be grown on a surface that is electrically conductive
and serves as one of the electrodes (working electrode). For this, most groups use
a potentiostat: an instrument that holds a constant voltage across the growth
media, by varying the current in response to changes in resistance. Two electrodes
are placed in the media, one for the potentiostat to measure the voltage change
(reference electrode) and the other to deliver the electrical stimulus (counter
electrode) to the cells via the media. The counter electrode acting as the opposing
terminal that completes the circuit with the electrically conductive surface or ref-
erence electrode (Kimura et al. 1998). Of course, the working electrode must
allow the cells to grow without any abnormality.
Others have stimulated cells without direct electrodes to media contact,
greatly reducing changes in pH, the possibility of contamination, and electrode
by-products due to electrochemical reactions, the caveat being that more power
is needed to supply a fi eld of similar strength compared to electrodes placed
directly in the growth media where the cells are maintained. One of the simplest
ways to achieve this is to use parallel metal plates (that is, stainless steal) to create
a capacitive EF that surrounds petri dishes (Hartig et al. 2000). Similarly, electro-
magnetic stimulation through a large solenoid (Grassi et al. 2004) or with
other arrangements (Walker et al. 1994; Longo et al. 1999; Lohmann et al. 2000;
McFarlane et al. 2000; Tattersall et al. 2001), and magnetic fi elds (Blackman et al.
1993; Trabulsi et al. 1996; Arias-Carrion et al. 2004) have been used.
18.5.6.2 Signal Selection.
Second, the electrical signal that is chosen
for stimulation has many variables. The stimulus can be direct current (DC—
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