Page 238 - Bio Engineering Approaches to Cancer Diagnosis and Treatment

9.3 Microfluidic systems in cancer 237

FIGURE 9.9 The schematic of the flow configuration for the acoustophoresis cell separation.

cytoskeleton strength, membrane stiffness, and the biomechanical properties occur
by a sudden change in pressure. By contrast, if a pressure pump is used in a con-
stant pressure mode, alteration of the backpressure causes pressure supply and it is
maintained constant. A variation of the flow occurs because of trapped cells in the
microchannel but excessive pressure is avoided that results to not impose additional
mechanical stress on the cells. In a microfluidic system with a low Reynolds number,
the constant pressure mode will apply constant mechanical force on the cell mem-
brane. Due to the fact that CTC capture and enrichment depends on biomechanical
attributes and CTCs properties, a gentle change in both pressure and flow rate is
required. In CTC-HTECH device programmable pressure pump was used in order
to provide constant pressure to the blood samples at the inlet of device that caused a
low-stress environment for CTC trapping and enrichment [62].
Size is a main biophysical property of cells that has been used to CTC separation
from blood cells. Different microfluidic chips in PDMS and the other biocompatible
polymers have been designed and fabricated to separate larger epithelial tumor cells
from smaller blood cells [71]. In size-based trapping method, attainment to favor-
able efficiency and purity of CTC trapping depends on the selection of geometry and
dimension. In microfilters, for example, the array of small holes with a size around
8 µm allows most blood cells to pass through but captures CTCs [72].
Recently, S. Lee’s group has studied a flow-restricted microfluidic channel with
an array of trapping cavities. They have reached a 97% trapping rate with single
MDA-MB-231 cells spiked in mouse blood [73]. The spiked MDA-MB-231 cells
staying in the trapping channel were kept by the continuous blood flow in their deliv-
ery channel because their pressure was less than the force is needed that cancer cells
can pass through the constriction regions. However, clogging is possible when more
CTCs are trapped in the same constriction and it is a drawback to microchannel array.
The CTC-HTECH device is a label-free, low-cost, and size-dependent that
enables effectively enrichment of sample in a prostate cancer cell line in blood
samples. CTCs enumeration obtained by this method is important because it is a