W. Richard Bowen and Nidal Hilal 4

196 7. MICRO/NANOENgINEERINg ANd AFM FOR CELLULAR SENSINg
evidence has shown that the various interactions between a cell and different
microenvironments play crucial roles in embryonic morphogenesis,
tissue formation and maintenance of physiological functions [1]. Perturbations
of cellular microenvironments or the adhesion of cells to the ECM
can cause genetic defects, autoimmune diseases and cancers [2, 3]. It is
also well known that in cancer metastasis, malignant cancer cells are able
to break down tissue architecture and invade distant organ sites [4, 5].
The ECM is an intricate network within which biomolecules are
precisely organised [6]. Classes of structural ECM proteins, mainly, collagen,
glycoproteins and proteoglycans, form highly organised nanoscale
structures, providing cells with both biological information and physical
scaffolds for adhesion and migration. Although the regulatory functions
of soluble factors (i.e. growth factors and hormones) present in the ECM
have been well investigated, it has recently become increasingly recognised
that the physics and mechanics of the ECM also have a significant
impact on cell function and fate. Revealing the precise mechanisms underlying
these processes is intrinsically challenging – the events happen at
many dimensions from single molecules to the macrotissue level, and in a
dynamic/collective and hierarchical manner.
In order to better understand the interactions between the cells and
the ECM and subsequent responses, engineered substrates and scaffolds
are being developed to replace the native ECM. This has required inputs
from many fields, ranging from surface engineering, material science and
tissue engineering to cell biology. In this chapter, we will describe current
developments of micro- and nanoengineered ECM materials and
structures for the investigation of adhesion-associated responses of cells
to chemical and mechanical cues. These efforts will be illustrated by an
interconnected set of examples.
Importantly, as the length scales being examined in these studies have
progressively shrunk, progress in interpreting the nanoworld has become
increasingly dependent on techniques capable of nanoscale measurements
within physiologically relevant environments. In this context, atomic
force microscopy (AFM) has emerged as a powerful and multifunctional
nanoscale tool, opening exciting new possibilities to address mechanistic
questions in cell biology that may facilitate the development of efficient
therapies for human health. In the following sections, we briefly introduce
the basic biological principles for adhesion-associated cell sensing,
followed by the engineering methods involved in generating substrates
and materials to study cellular interactions, and finally the methodology
associated with AFM measurements on these systems.
7.1.1 How do Cells respond to the ECM?
First, we review two important subcellular systems that are of fundamental
importance in cell adhesion to the ECM: the cell membrane and