The primary research aim in this thesis is to demonstrate the versatility of porous silicon based
nanomaterials for biomaterial and photonic applications. In chapter 2 of this thesis, the
suitability of porous silicon as a biomaterial was investigated by performing different surface
modifications on the porous silicon films and evaluating biocompatibility of these surfaces in
vitro. The porous silicon surfaces were characteriszed by means of atomic force microscopy
(AFM), scanning electron microscopy (SEM), diffuse reflectance infrared spectroscopy (DRIFT)
and interferometric reflectance spectroscopy (IRS). Cell attachment and growth was studied
using fluorescence microscopy and cell viability assays. Both fabrication of the porous silicon
films and subsequent surface modifications were demonstrated. Polyethylene glycol
functionalised porous silicon prevented cell attachment, whilst collagen or fetal bovine serum
coating encouraged cell attachment. Surface modifications were also performed on porous
silicon films with different pore sizes and the influence of pore size and surface modification on
primary hepatocyte growth was recorded over a course of 2 weeks by means of laser scanning
confocal microscopy (LSCM), toxicity and metabolic assays. On collagen-coated surfaces with
average pore sizes of 30 nm, multilayer cells stacks were formed. This stacking behaviour was
not observed on samples with smaller pore sizes (10 nm), or in the absence of collagen.
Hepatocytes remained viable and functional (judging by a metabolic assay) for 6 days, after
which they generally underwent apoptosis. Collagen-coated porous silicon films showed later
onset of apoptosis than porous silicon films not coated with collagen or collagen-coated flat
silicon..
In chapter 3 of this thesis, the nitrogen laser of a laser desorption/ionization (LDI) mass
spectrometer was used to selectively ablate regions on porous silicon films that had been
functionalised with a non-fouling polyethylene oxide layer, affording a microscale patterning of
the surface. Surface characterization was performed by means of AFM, SEM, LDI mass
spectrometry, DRIFT and IRS. This approach allowed the confinement of mammalian cell
attachment exclusively on the laser-ablated regions. By using the more intense and focussed
laser of a microdissection microscope, trenches in a porous silicon film were produced of up to
50 micron depth, which allowed the construction of cell multilayers within these trenches,
mimicking the organization of liver cords in vivo. Fluorescent staining and LSCM was used to
study cell multilayer organization.
To gain a better understanding of how surface topography influences cell attachment and
behaviour, porous silicon films were fabricated containing a gradient of pore sizes by means of
asymmetric anodisation (chapter 4). These gradients allowed the investigation of the effect of
subtle changes of pore size on cell behaviour on a single sample. Analysis by means of LSCM
and SEM showed that pore size can dictate cell size and area as well as cell density. In addition,
a region of pore size where cell attachment and proliferation was strongly discouraged was also
identified. This information can prove to be useful for designing non-biofouling surface
topographies.
Using the same asymmetric anodisation setup, photonic mirrors gradients were produced and
overlaid over one another to produce multidirectional lateral photonic mirror gradients that
display a series of roving spectral features (photonic stop-bands) from each gradient layer
(chapter 4). These multidirectional photonic gradients have the potential to serve as optical
barcodes or contributing to the development of graded refractive index devices such as lenses for
high quality image relay and graded-index optical fibers.
| Identifer | oai:union.ndltd.org:ADTP/229869 |
| Date | January 2009 |
| Creators | Khung, Yit Lung, y.khung@unsw.edu.au |
| Publisher | Flinders University. School of Chemistry, Physics and Earth Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.flinders.edu.au/disclaimer/), Copyright Yit Lung Khung |
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