Patterned and switchable surfaces for biomaterial applications

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Andrew Hook – Patterned and switchable surfaces for biomaterial applicationsSUMMARYThe interactions of biomolecules and cells at solid-liquid interfaces play a pivotalrole in a range of biomedical applications and have hence been studied in detail. Animproved understanding of these interactions results in the ability to manipulatebiomolecules and concurrently cells spatially and temporally at surfaces with highprecision. Spatial control can be achieved using patterned surface chemistries whilsttemporal control is achieved by switchable surfaces. The combination of these twosurface properties offers unprecedented control over the behaviour of biomoleculesand cells at the solid-liquid interface. This is particularly relevant for cell microarrayapplications, where a range of biological processes must be duly controlled in orderto maximise the efficiency and throughput of these devices. Of particular interest aretransfected cell microarrays (TCMs), which significantly widen the scope ofmicroarray genomic analysis by enabling the high-throughput analysis of genefunction within living cellsInitially, this thesis focuses on the spatially controlled, electro-stimulatedadsorption and desorption of DNA. Surface modification of a silicon chip with anallylamine plasma polymer (ALAPP) layer resulted in a surface that supported DNAadsorption and sustained cell attachment. Subsequent high density grafting ofpoly(ethylene glycol) (PEG) formed a layer resistant to biomolecule adsorption andcell attachment. PEG grafted surfaces also showed significantly reduced attachmentof DNA with an equilibrium binding constant of 23 ml/mg as compared with 1600ml/mg for ALAPP modified surfaces. Moreover, both hydrophobic and electrostaticinteractions were shown to contribute to the binding of DNA to ALAPP. Spatialcontrol over the surface chemistry was achieved using excimer laser ablation of thePEG coating which enabled the production of patterns of re-exposed ALAPP withIV
Andrew Hook – Patterned and switchable surfaces for biomaterial applicationshigh resolution. Preferential electro-stimulated adsorption of DNA to the ALAPPregions and subsequent desorption by the application of a negative bias wasobserved. Furthermore, this approach was investigated for TCM applications. Cellculture experiments demonstrated efficient and controlled transfection of cells.Electro-stimulated desorption of DNA was shown to yield enhanced solid phasetransfection efficiencies with values of up to 30%. The ability to spatially controlDNA adsorption combined with the ability to control the binding and release of DNAby application of a controlled voltage enables an advanced level of control over DNAbioactivity on solid substrates and lends itself to biochip applications.As an alternative approach to surface patterning, the fabrication andcharacterisation of chemical patterns using a technique that can be readily integratedwith methods currently used for the formation of microarrays is also presented. Here,phenylazide modified polymers were printed onto low fouling ALAPP-PEGmodified surfaces. UV irradiation of these polymer arrays resulted in the crosslinkingof the polymer spots and their covalent attachment to the surface. Cell attachmentwas shown to follow the patterned surface chemistry. Due to the use of a microarraycontact printer it was easily possible to deposit DNA on top of the polymermicroarray spots. A transfected cell microarray was generated in this way,demonstrating the ability to limit cell attachment to specific regions and thesuitability of this approach for high density cell assays. In order to allow for the highthroughputcharacterisation of the resultant polymer microarrays, surface plasmonresonance imaging was utilised to study the adsorption and desorption of bovineserum albumin, collagen and fibronectin. This analysis enabled insights into theunderlying mechanisms of cell attachment to the polymers studied. For the systemanalysed here, electrostatic interactions were shown to dominate cellular behaviour.V
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Chapter 1 - IntroductionA number of
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CHAPTER 2.SPATIALLY CONTROLLED ELEC
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CHAPTER 3.COMPARISON OF THE BINDING
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DNA (mg/m 2 ) DNA (mg/m 2 )Andrew H
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CHAPTER 5.SURFACE PLASMON RESONANCE
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SPR signal intensity (counts)Andrew
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Reflectivity (%) Reflectivity (%)An
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Thickness (nm)Thickness (nm)Thickne
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CHAPTER 6.OVERALL CONCLUSIONS6.6An
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