W. Richard Bowen and Nidal Hilal 4

7.2 ENgINEERINg THE ECM FOR PRObINg CELL SENSINg 207
polymers cannot be completely ruled out. Consequently, an alternative way
for fast and low cost of fabrication of nanoscale topographic features has
been sought through the use of colloidal lithography. Monodispersed and
nanosized colloids made using wet chemistry techniques are commercially
available. They can self-assemble into a monolayer on a substrate, with the
spacing between each tailored by their surface charge or functional linker
groups. The resulting colloid assembly is effectively a ‘photoresist’ pattern
whose lateral dimensions are determined by the colloid size and spacing.
Using this approach, nanocolumns of 160 nm height, 100 nm in diameter
and 230 nm spacing have been produced in a bulk poly(methyl methacrylate)
(PMMA) polymer [53, 54]. In comparison to the non-structured control,
nanocolumns reduced focal adhesions of cells, but significantly increased
density of filopodia formation. As discussed earlier, filopodia formation is
associated with focal complexes, indicating the involvement of nanotopographic
features on integrin cluster formation.
The fact that many of the ECM proteins are present as nanofibres is
driving intensive research on engineered nanofibres as replacements for
ECM components. Carbon nanofibre compactions have been investigated
for osteoblast culture with potential application as orthopedic/dental
implants [55]. When compared with using conventional carbon fibres
(diameter �100 nm), osteoblasts proliferate faster and deposit more extracellular
calcium (indicating osteoblastic bone formation) on the carbon
nanofibre compactions (diameter �100 nm). In other studies, synthetic
and natural polymeric nanofibres have also long been regarded as promising
analogues of the ECM. Here, a vast selection of well-established
methods can be used to tailor their chemistries to match those found in
the native ECM. To produce the polymeric nanofibres themselves, electrospining
has become perhaps the simplest and most efficient technique for
producing materials which can be assembled into 2D and 3D non-woven
fibrous mesh (see review by Pham) [56]. Interestingly, cell culture on these
nanofibre matrixes demonstrated better attachment and increased proliferation
compared to that on substrates made from larger size fibres.
Nanofibre meshes have also been found to stimulate cells to develop
phenotypical behaviour [57, 58]. For example, NIH 3T3 fibroblasts and
normal rat kidney cells grown on a polyamide nanofibre matrix displayed
in vivo-like morphology and breast epithelial cells on the same matrix
underwent morphogenesis into multicellular spheroids [58].
All the above-mentioned examples provide evidence which suggest that
nanotopography has a significant influence on cell adhesion, cytoskeletal
organisation and morphogenesis. However, the mechanisms involved are
poorly understood: We do not know whether the less well-defined lateral
dimensions of nanoislands made by either polymer mixing or colloidal
lithography play any significant role in cellular behaviour; the nanofibre
matrix may provide a large surface to volume ratio structure that could