Cell Migration on Engineered Microstructured Surfaces - Innovative Approaches to Cell Biomechanics - page 121

Fig. 9.1 SEM images of substrates with ( a ) a single groove of 1.5 µm in width and 20 µm in depth,
( b ) intersecting grooves of 1.5 µm in width, 5 µm in spacing and 20 mm in depth, and ( c and d )
intersecting grooves of 4 µm in width, 5 µm in spacing and 20 µm in depth (Miyoshi et al. 2010 ).
In this chapter, the abbreviation “L-” stands for a line groove, and the number following “W”
indicates the groove width in micrometers. The abbreviation “IS-” stands for intersecting grooves,
and the number following “W” indicates the groove width in micrometers. The scale bars corre-
spond to 10 µm. The SEM images are acquired with a scanning electron microscope (Adapted with
permission from Elsevier Ltd.: [Biomaterials], copyright (2010))

micrometers. Thus, MEMS fabrication techniques are naturally integrated with
biology, medicine, and biomedical engineering (Derby 2012 ; Nikkhah et al. 2012 ;
Khademhosseini et al. 2006 ).
Lithography and etching are the basic processes of MEMS. Here, we show how
to fabricate a microgroove on silicon wafer. The silicon substrate is used in the cell
migration assay discussed later in this chapter. Figure 9.1a-d show representative
SEM images of single line groove (Fig. 9.1a ) and the intersecting grooves (Fig. 9.1b-d )
on silicon cell culture substrates which are fabricated by photolithography followed
by deep reactive ion etching.

9.2.1 Lithography

To fabricate the grooved substrates shown in Fig. 9.1 , fi rst, bare silicon wafer is spin
coated with a light sensitive polymer called photoresist. Then the photoresist layer is
selectively exposed to ultraviolet (UV) light through a patterned mask. There are vari-
ous kinds of photoresist compositions. Positive-working and negative-working are the
major ones practically used in industrial production. The main difference between
these two is that regions exposed to UV light are removed by a developer in the case
of a positive photoresist, whereas remains in the case of a negative photoresist.
The spatial resolution of the patterning is limited to be the order of the wavelength
of the light due to light diffraction. Thus, x-rays and electron beams, whose
wavelengths are much shorter than that of UV light, are more suitable for fabricating
smaller (sub-micron) features.