W. Richard Bowen and Nidal Hilal 4

206 7. MICRO/NANOENgINEERINg ANd AFM FOR CELLULAR SENSINg
about how cells sense the nanoworld, if indeed they can. For example,
most of the commonly used cell culture dishes have a certain surface
roughness, does this matter?
Random or Semi-Random Defined Nanostructures
The use of spontaneous phase separation of blended polymers or copolymers
provides an efficient way to produce different nanoscale features
of controllable depths over a large area [49, 50]. By spin coating blends
of polystyrene (PS) and poly(4-bromostyrene) (PBrS) onto silicon wafers
and varying the ratio of polymers and their concentrations, nanoislands
of heights between 13 and 95 nm were produced (Figure 7.5) and tested
using fibroblast and endothelial cell cultures [51]. It was found that an
enhanced cell response was observed on the nanostructured islands
compared to the planar PS control: 13 nm height islands increased cell
spreading and proliferation as well as a broad up-regulation of many
genes involved in proliferation and matrix synthesis [52]. However, 95 nm
high islands reduce cell spreading and proliferation [51]. Thus, by altering
only the height of nanoscale features, a different cell response could be
induced, demonstrating the significant roles that nanotopography might
exert on cells.
Although polymer demixing can reliably control the z-depth of nanofeatures,
there can be less control over the lateral dimensions. In addition, for
many systems a possible effect from the differences in the chemistry of two
FIgurE 7.5 AFM picture of an example of nanoislands made by polymer demixing
process. Image courtesy of Drs. Matthew J. Dalby and Stanley Affrossman.