Year

2010

Degree Name

Doctor of Philosphy

Department

University of Wollongong. Institute for Superconducting and Electronic Materials

Abstract

Poly-di-methylsilixoxane (PDMS) thick films approximately 4 μm in thickness were spin coated onto a silicon wafer support in preparation for topological and chemical surface modification. Thorough mixing and time within a vacuum chamber ensured a bubble and defect free, homogeneous, quality PDMS elastomer film.

From these pristine quality PDMS thick films, films with three-dimensional features self-organized into coherent and semi-coherent buckling domains were then created by implanting different species of metal ions and combinations thereof, using a metal evaporation ion source, into these quality polydimethylsiloxane films. As a result of the implantation process, functionalized discrete regions of straininduced surface buckling were created, taking the forms of domains of parallel surface waves, semi-ordered regions, and disordered regions. In addition, deep, strain-induced, V-shaped cracks were observed to penetrate well into the elastomer matrix. Furthermore, it was found that controlling the localized strain by altering the metal ion species could control the frequency of the V-shaped cracks and the properties of the buckled areas.

Thus, low energy metal ion implantation has been used to combine an easy ‘bottom up’ way of creating and tuning different topographic structures on submicron to micrometer scales with the embedding of a metallic element-rich functionalised layer at the surface for a variety of scientific and technological applications. The self-organising and complex patterns of functionalised topographic structures created through strain induced buckling are highly dependent on the implanted metal ion species, variations in the geometric confinement of the buckled areas onto the larger unmodified elastomer film, and the boundary conditions of the buckled regions. Characterization and systematic investigations of the strain induced buckling and its dependencies on geometric confinement, metal ion species, and its boundary conditions have been thoroughly investigated along with possible mechanisms for the formation of the cracks and complex buckling domains.

Once it has been demonstrated that low energy metal ion implantation of PDMS films simultaneously allow for the creation of complex and tuneable surface topographical features, the surface modification effects of enhancing the biocompatibility of the surface for biological applications are investigated. PDMS thick films were implanted with Mg, Ta, and Fe at constant dose, and cellular cultures were used to test the surface modification effects on biocompatibility, along with any variation as a result of metal ion species. Cells cultured on all of the modified surfaces enjoyed an increase in viable cell count of over 450% when compared to the pristine surface, with the Fe implanted surface showing a 600% increase combined with a substantial increase in surface energy, which was reflected by the increased contact angle. This was achieved without any biochemical patterning requiring multiple processing steps, complex chemistries, or clean room facilities. The rapid prototyping and ease of creation makes this technique useful for the fabrication of selective and functionalised substrates and scaffolds for in depth bioanalytic studies, implants, and device components. The results of surface energy investigations, cross-sectional transmission electron microscopy, and compositional analysis, as well as initial biocompatibility testing are presented.

A planar micro-electrode array (pMEA) system has been set up as a potential direction in which this research work could be taken. In the planar multi-electrode array (pMEA) system, Indium Tin Oxide (ITO) conductors are covered by 3 μm of polysiloxane resin before the 64 electrodes at the centre of the plate are deinsulated and gold plated for reduced impedance. This elastomer coating is used both as an insulating material to minimise neuronal crosstalk and as a patterning material to guide growth of neuronal networks only to areas where there are electrodes present that are available for bidirectional communication. SH-SY5Y neuroblastoma cells have been cultured in a flask, trypsinised, and allowed to settle and adhere onto the electophysiologally active glass slide. The bio-electrical spike trains resulting from the live cell culture were recorded by the pMEA system and are presented in preparation for the potential continuation of this work.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.