W. Richard Bowen and Nidal Hilal 4

Au nanoparticles with a cyclic RGD-thiol, nanoislands of RGD-ligands
are created. This novel method has enabled a series of studies, demonstrating
that cells can detect surface variations at the size of a typical protein
complex (�100 nm) and are affected dramatically by small variations
in ligand–cluster spacing (e.g. 58 and 73 nm) [39].
Although nanopatterning of adhesive molecules is ultimately valuable
to reveal molecular mechanisms underlying cellular processes, the
reliability of the information obtained depends on the accuracy of the
characterisation measurements at the nanoscale. In this context, it should
be noted that topographic features as small as 10 nm can exert dramatic
effects on a cell (more details in the next section). This type of observation
is particularly important for protein nanopatterning studies based on the
assembly of particle templates, as discussed in Spatz’s work.
7.2.2 nanotopography
7.2 ENgINEERINg THE ECM FOR PRObINg CELL SENSINg 205
In contrast to the use of micro- and nanoscale patterns of (bio)chemical
motifs described earlier, cell behaviour has also been extensively studied
on patterns of micro- and nanoscale topographic features [40].
Motivation for many of these studies comes from the observation that
although the physical form of the ECM appears as a random meshwork,
in fact, it contains enormously detailed nano- and microscale structures.
For instance, a corrugation with a period of 68 nm has been recently
observed on collagen fibres [41]. When looked at on the small scale, the
ECM possesses nanopores, micro- and nanofibres, and peaks and depressions.
Since the middle of the twentieth century, it has been increasingly
recognised that cells react to microtopography. Early evidence has shown
that cells adhere, align and move along fibres in the range of 30–100 �m
[42–44]. In recent decades, the advance in micro- and nanofabrication has
allowed intense investigations in this area and greatly push forward our
understanding.
Since the early 1960s, Curtis and his colleagues have studied the reaction
of a number of cell types with various microtopographic structures
[40, 45]. Microgrooves with a wide combination of widths and depths
have been studied, and it was found that cells react to both depth and
width. In general, on deep and narrow grooves, cells tend to bridge
between grooves, whilst on shallow grooves, they often follow the surface,
although detailed reactions are cell type dependent [46]. Substantial
evidence has been obtained, showing that adhesion or interaction with
microscale topographic structures induces changes in cell cytoskeletal
organisation, apoptosis (programmed cell death), macrophase activation
(causing inflammatory reactions) and gene expression [47, 48]. The
observed phenomena clearly demonstrated that microtopography influences
cell development, and thus triggered researchers to pose questions