Page 228 - Bio Engineering Approaches to Cancer Diagnosis and Treatment

9.2 Microfluidic system 227

Table 9.2 Criterions of microfluidic cell separation technology.
Method Sample Separation Separation Throughput
way resolution
Mechanical Human Size exclusion 17 ± 1.5 µm 0.75 mL/min,
filters metastatic cells CTCs separated ∼10 cells/min
9
spiked in whole from most
blood smaller blood
components
5
Hydrodynamic Diluted blood Streamline – ∼10 cells/min
(0.3%), liver cells manipulation
2-3 × 10 /mL
6
Diluted blood
(50%)
6
Inertia Diluted blood Lift forces and ∼5 µm ∼10 cells/min
(∼2%), cells, secondary
blood and flows
bacteria
Gravity Microparticles Sedimentation ∼17 µm ∼17 µL/min
differences
Acoustic Whole blood Acoustic >1 µm 80 µL/min
radiation force 10 cells/min
8
3
Optical Silica and protein Optical lattice <0.54 µm 2.4 × 10
microparticles particles/min

9.2.1 Microfluidic devices
The pumps, micromixers, and valves are such microfluidic devices that have been
utilized for technics such as immunoassays, PCR, electrophoresis, cell counting, and
cell sorting and will be discussed in the following [22]:

9.2.1.1 Valves
Valves are integrated into the silicon microchip to control flow rates. Various pas-
sive and active micromixers have been fabricated for such applications. External
devices are used to provide the energy of active microvalve and actuation control.
For example, the hydrogels are used to active micromixer that changes in pH or
temperature causes they can polymerize. The gelling of the hydrogels in microscale
devices can be controlled by diffusion of the protons or heat convection of the stream
layer to regulate the flow [26]. Passive micromixers use a temporary flow stop device
and limit the flow to one direction. Silicon or elastomers is used in the construction
of passive one-way valves in order to direct fluid flow.
9.2.1.2 Pumps
Pressure-driven flows are generated by syringe pumps which allow molecules car-
ried in a fluid stream and diffused throughout the microchannel. For pressure regula-
tion, these pumps require special tubing and cumbersome micropump devices. The