Abstract
The goal of this project was to develop a strategy to fabricate various nanometre and
micrometre scale structures for biocompatible poly(Cysteine methacrylate) (PCysMA) brushes
by photopatterning of 3-(2-bromoisobutyramido)propyl triethoxysilane (APTES-BIBB) film on a
silicon surface. Micrometre scale structures were formed by exposure through a mask, and
nanometre scale structures by Interference lithography. UV exposure causes debromination of
the surfaces. Surface-initiated atom transfer radical polymerization (SI-ATRP) was used to grow
the brushes from the ATRP initiators. Friction force microscopy (FFM) was used to investigate
the conformations of the brushes as a function of footprint sizes in different environments. The
friction - load relationship was found to be dependent on the conformation of the brushes,
which is then was found to be influenced by the solvent medium. In a good solvent, sublinear
friction-load relationships were acquired that were fitted with the Derjaguin-Muller-Toporov
(DMT) model of contact mechanics, for nanostructured materials the contact mechanics were
found to depend on the periodicity of the patterns. For large periods, the grafted polymer
molecules exhibit a brush conformation, but this starts to collapse when the period is reduced
below the critical value. In contrast, in poor solvent linear friction-load relationships were
acquired and the friction coefficient increased as the period increased. In a poor solvent the
polymer molecules collapse and form mushroom or pancake structures. These observations
were rationalised by considering the friction values as a sum of an interfacial (shear) and
plowing (load) dependent term.
Unpatterned brushes of controlled, but varying densities were fabricated by maskless UV
exposure of brominated films followed by SI-ATRP. By varying the exposure, the density of
initiator sites was changed. The contact mechanics were studied as a function of brush
coverage. In a good solvent, sublinear friction-load relationships were observed at high density,
but the relationship became linear as the density decreased. The change is attributed to a
change in the conformation, from brushes at high grafting density to mushrooms and the
pancakes as the density decreased. In a poor solvent, the friction-load relationship was linear
regardless of grafting density. This means that energy dissipation by molecular ploughing was
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dominate for poorly solvated brushes. The friction coefficient increased initially as the grafting
density decreased, then started to decrease as the density further reduced.
The impact of nanotopography, chemistry and utility of non-biofouling of PCysMA brushes on
the cultivation of mesenchymal stem cells (MSC) has been explored. AFM, ellipsometry, XPS,
contact Angle goniometry, and fluorescence microscopy have been utilised to characterise the
surfaces. Interference lithography (IL) was used to pattern three different types of SAM,
including 2-nitrophenylpropyloxycarbonyl-protected aminosiloxane (NPPOC-APTES),
(chloromethyl)phenyltrichlorosilane (CMPTS) and APTES-BIBB film. The patterned SAMs were
used as templates to control SI-ATRP. Uniform polymer brush structures showed excellent
resistance toward nonspecific adsorption of the cells, after 7 days of culture. The cells attached
successfully on the patterned surfaces, but their alignments and organisations were different,
depending on the feature sizes of grafted polymer lines and the chemistry of adhesive regions.
Immunocytochemical methods were used to characterise the effect of nanoscale surface cues
on cytoskeletal organisation in MSCs grown on these surfaces.
A method was developed for the fabrication of lipid bilayers supported on a PCysMA brush layer
with integral gold nanostructures, to facilitate spectroscopic characterisation using plasmonic
techniques. Gold nanostructures were formed using IL to pattern a resist consisting of SAM of
octadecanethiol on gold. Regions between nanostructures were functionalised with an
aminosilane which was brominated and used as an initiator for SI-ATRP. The polymer growth
was controlled so that swollen brushes in water had heights identical to the heights of the Au
nanostructures. Supported lipid bilayers were formed on these materials and lipid mobility was
characterised using fluorescence recovery after photobleaching (FRAP). Mobilities were
achieved that were similar to those obtained for positive control surfaces (glass).
