Biomedical Engineering Reference
In-Depth Information
(A)
(B)
1
2
3
4
ARC
1. 8 mm
Figure 19.1
Sensor design [15]. (A) The sensor carries four sensing elements comprising an overall
size of 15 mm × 18 mm. (B) A single element of 1.8 mm × 2 mm is composed of interdigitating fingers
with both a width and a gap of 50 μm. Reproduced from Reitinger
et al
., 2012 with permission from
Elsevier.
a frequency range of 62.5-64 kHz. During the > 2 weeks of monitoring, the impedance of
noninduced cells leveled off as the plate reached confluency, while osteogenesis and adipo-
genesis, which were induced by commercially available differentiation mediums, were char-
acterized, respectively, by a steady increase and gradual fall in
Z
*. More detailed statistical
analysis indicated that the impedance of osteo-induced cells was significantly higher than
that of the adipo-induced cells as early as 12 h post induction in a 4-16 kHz frequency
interval and continued for the full 2-week differentiation period. Moreover, using a three-
parameter model developed by Giaever and Keese [14], it was reported that this difference in
impedance is due to the fact that: (i) osteo-induced cells established intercellular junctions
over the course of 48 h after induction as opposed to ADSCs undergoing adipogenesis; and
(ii) the cell-membrane capacitance of osteo-induced cells was significantly lower than that of
ADSCs undergoing adipogenesis.
Similarly, Reitinger
et al
. adopted a radiofrequency identification-based sensing platform
to characterize the proliferation and differentiation of human bone-marrow-derived multi-
potent stem cells (bmMSCs) over periods from several days to weeks [15]. In particular,
ECIS was achieved by fabricating electrodes comprised of two comb-shaped interdigitated
gold electrodes onto glass substrates (placed in six-well culture plates) (Figure 19.1).
Continuous measurements could then be collected using a sinusoidal voltage of 35 mV at a
frequency of 10 kHz. In agreement with Bagnaninchi and co-workers, Reitinger
et al
.
observed that impedance increased significantly as bmMSCs adhered and spread. In
addition, upon differentiation into osteogenic or adipogenic lineages there was a steady rise
(Figure 19.2A and B) and gradual fall in impedance, respectively (Figure 19.2C and D).
Importantly, the authors emphasized that the differentiation could be validated in the
bmMSC culture within a few days and monitored continuously for weeks at a time. In con-
trast, conventional protocols are end-point assays that require several weeks of cultivation
before they can be evaluated.
Finally, Öz and co-workers used an 8W10E+ ECIS Cultureware assay (Applied Biophysics),
which contained forty 250-μm gold electrodes per well, and could be measured on an ECIS
Model 1600 (Applied Biophysics) at 45 kHz for the screening of cancer drug therapies [16].
Specifically, the purpose of this work was to monitor the differentiation of cancer stem cells
