Page 224 - Bio Engineering Approaches to Cancer Diagnosis and Treatment

9.1 Introduction 223

Applying mechanical vibration as a unique property in SAW introduced a variety
analytical technologies. For example, a SAW sensor is used to analyse and detect
the changes in the environment. Also SAW-induced microfluidics is used to actuate
a liquid on the surface of the piezoelectric substrate, and this actuation is used for
various processes [5].

9.1.3 Application of SAW

Regard to the recent researches, SAWs can be an effective means of fluid control
and as a particle in lab-on-a-chip devices [10]. SAW technology onto lab-on-a-
chip platforms has opened a new frontier in microfluidics. These advantages cause
SAW microfluidics to get involved in various biology, chemistry, engineering, and
medicine application [11]. An efficient actuation of fluids on the microscopic scale
such as mixing, pumping, atomizing and driving, as well as the dexterous manipula-
tion of micro-objects (cells, droplets, particles, nanotubes, etc.) such as separation,
sorting, trapping, concentration, merging, patterning, and focusing in open (sessile
droplets) and confined spaces (microchannels/chambers) are required to realization
of microscale total analysis systems (µTASs) and lab-on-a-chip technologies. The
powerful acoustofluidic technics based on high frequency (10–1000 MHz) SAWs are
used to achieve this objective. The SAW-based miniaturized microfluidic devices are
best known for their noninvasive properties, low costs, and the ability to manipulate
micro-objects in a label-free manner. Acoustofluidic technics are classified according
to the use of traveling SAWs (TSAWs) or standing SAWs (SSAWs). The schematic
of these waves is shown in Fig. 9.4. TSAWs are used to actuate fluids and manipulate
micro-objects via the acoustic streaming flow (ASF) as well as the acoustic radiation
force (ARF). The SSAWs are mainly used for micro-object manipulation and are
rarely employed for microfluidic actuation [12].
TSAWs are used to achieve fluid mixing, fluid translation in open space, micro-
fluidic pumping in enclosed channels, jetting and atomization, particle/cell concen-
tration, droplet, and cell sorting, and reorientation of nano-objects. It shows that
TSAWs are a key component for many emerging on-chip applications.
In SSAW-based devices, instead of harnessing the acoustic streaming, the primary
ARFs which act on particles via the surrounding fluid are used. The SSAW-based
devices apply these primary ARFs to focus a flow stream of particles into a single-file
line, separate a flow stream of particles based on particle properties, actuate a single
particle/cell moving with a flow stream, pattern a group of particles in stagnant fluid,

FIGURE 9.4 The schematic of the traveling SAWs (TSAWs) and standing SAWs (SSAWs).