Page 221 - Bio Engineering Approaches to Cancer Diagnosis and Treatment

220 CHAPTER 9 Application of microfluidics in cancer treatment

FIGURE 9.1 Classification of microfluidic platforms.

are mixed or moved small volumes of liquids in microchips [4]. These microfluidic
devices will be discussed in the following sections. Microfluidic platforms are clas-
sified into five groups according to the main liquid propulsion principle: capillary,
pressure driven, centrifugal, electrokinetic, and acoustic systems (Fig. 9.1) [1].
Characterization of the respective platforms is provided in Table 9.1 [1]. The
surface acoustic wave (SAW) as an important technology in cancer treatment is
described in the following.

9.1.1 Surface acoustic waves
SAWs are ultrasonic waves that propagate on an elastic surface. When acoustic
waves come in contact with the fluid environment, they can be coupled to the fluid
and become a fluid flow stimulus. This effect is known as acoustic streaming. The
SAWs have been employed to move droplets on chemically modified or function-
alized piezoelectric substrate (Fig. 9.2) [4]. Exciting the interdigital transducers
(IDTs) which are deposited onto the piezoelectric substrate causes droplets moving.
A certain high-frequency voltage is applied to excite the sound waves [4]. The SAW
devices are easy to construct and operate, also they are powerful platforms to direct
chemical sensing, upstream microfluidic processing and sample preparation [5].
The application of SAW technology in microfluidics which is an important
tool, originally discovered by Lord Rayleigh in 1880. He observed when an earth-
quake occurs there is a surface wave and the ground begins to roll. Transverses and