Studying Cell–Surface Interactions In Vitro: A Survey of Experimental Approaches and Techniques - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 35

properties of in vitro surfaces such that growth and differentiation of the cells is
not affected—or even guided in a certain direction. There is not, however, one
ideal surface that is well-suited for all kinds of cells and for all scenarios. The most
appropriate material depends certainly on the cell type and also on the cellular
property that the in vitro surface is supposed to support and to foster, such as cell
adhesion, proliferation, differentiation, motility and expression of tissue-specific
genes, to mention just a few.
Even though some general correlations between the physico-chemical proper-
ties of a given surface and its performance as a support for cell adhesion and
growth have been established, there is no in-depth understanding of which surface
features influence which cellular function. Many more systematic studies need to
be done and they all rely on techniques capable of studying the cell-material
interface from different perspectives. This chapter summarizes the established and
some of the emerging techniques of analyzing the interface between cells and
man-made surfaces. They comprise optical, electrochemical and acoustic
approaches, which are compared and categorized at the end of the chapter.
2 Hallmarks of Cell Adhesion on In Vitro Surfaces
Cells do not interact directly with the surface of a man-made material but with a
pre-adsorbed layer of extracellular biomolecules, mostly proteins from the ECM
[ 1 ]. As a direct consequence, the adhesiveness of the surface for ECM-proteins is
the first prerequisite for cytocompatibility and mainly determines the behavior and
compliance of an in vitro surface in a physiological environment. However, when
a man-made material is brought in contact with a biological fluid (e.g. blood,
lymphatic fluid or cell culture medium), the surface initially encounters water
molecules. These bind rapidly to the surface, establishing a water mono- or
bi-layer. The specific arrangement of water molecules depends on the surface
properties on the atomic level. Highly reactive surfaces lead to the dissociation of
H 2 O and form a hydroxylated, i.e. OH-terminated surface. Less reactive surfaces
can interact with H 2 O molecules by hydrogen bonding, leaving the water as intact,
undissociated molecules. Surfaces that show either of these behaviors are termed
wetting or hydrophilic surfaces. On the other hand, surfaces with a weak tendency
for binding H 2 O are termed non-wetting or hydrophobic. After the formation of
this adsorbed water layer (adlayer), which occurs within nanoseconds, hydrated
ions such as Cl - and Na + get incorporated. The specific arrangement of these ions
and their water shells is strongly influenced by the properties of the surface.
Subsequently, proteins from the biological fluid adsorb to the surface in a
complex series of events, including initial adsorption, conformational changes and
eventually replacement of smaller proteins by larger ones. In experiments in vitro
these proteins originate from the serum-containing culture medium and/or they are
synthesized and secreted by the cells themselves. Depending on the properties of
the surface, the resulting mixture of proteins on the surface, their conformational