Author's School

Graduate School of Arts & Sciences

Author's Department/Program

Chemistry

Language

English (en)

Date of Award

Spring 3-21-2013

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

Joshua A Maurer

Abstract

The subsequent work describes advances in modifying the chemical properties of various substrates to tailor the surface properties for specific applications. This is achieved by making use of a molecular assembly known as self-assembled monolayers, or SAMs. SAMs are composed of tightly packed organic molecules that form a well-ordered structure on a substrate. Typically, the head group of the monomer is covalently anchored to the substrate, and monolayer order and self-assembly is achieved through van der Waals interactions between the long alkyl chains of the monomer's tail group. Monolayers containing head groups consisting of thiols, siloxanes, and phosphonates have been demonstrated on gold, glass, and metal oxides, respectively. We have expanded upon existing monolayer technology and designed monolayers with either new head group or new tail group functionalities. The resulting surfaces have been characterized by a variety of techniques including infrared spectroscopy, contact angle analysis, quartz crystal microbalance analysis, surface plasmon resonance imaging, and atomic force microscopy. We have also explored applications for these functionalized surfaces in areas ranging from microelectromechanical systems: MEMS) lubrication to platforms for studying neuronal development in vitro.

In the area of MEMS lubrication, the development of new surface coatings is critical for combating wear and increasing the device lifetime. We reported a class of arsonic acid SAMs that form readily on oxide substrates including silicon oxide, borosilicate glass, and titanium oxide. The monolayers are easily prepared using a straightforward soaking technique, which is amenable to large-scale commercial applications. We have characterized monolayer formation on borosilicate glass and titanium oxide using infrared spectroscopy. Monolayers on borosilicate glass, native silicon oxide and titanium oxide were also evaluated with contact angle measurements, and as wear measurements using nanoscratching experiments. On titanium oxide and borosilicate glass, monolayers prepared from hexadecylarsonic acid provide significantly greater surface protection than surfaces reacted under similar conditions with hexadecylphosphonic acid, a common modifying agent for oxide substrates.

To develop a platform for in vitro studies of neuronal development, we have utilized mixed-monolayers incorporating low densities of cell-adhesive peptides. The monomers feature a tetraethylene glycol moiety in the tail group to prevent the non-specific adsorption of proteins, and a low density of monomers were terminated with an azide moiety to specifically attach a laminin-derived peptide: IKVAV) terminated with an alkyne group via the copper-mediated azide-alkyne cycloaddition: CuAAC) reaction. To achieve this, a pentynoic acid molecule was appended to the N-terminus of the peptide during solid phase synthesis. Surfaces containing 0.01% and 0.1% azide-coupled peptide were determined to be resistant to the non-specific adsorption of proteins. Hippocampal neurons dissected from embryonic mice were cultured on these surfaces and the effects of the peptides on neurite outgrowth were observed. Similar neurite numbers per cell were observed on both substrates, but longer neurites were measured on the 0.1% azide-coupled peptide substrate. Unfortunately, further studies revealed that aldehyde fixation methods for immunohistochemistry did not successfully attach neuronal cells to the surface due to limited attachment points on the surface.

Many developmental cell biology experiments require downstream immunohistochemical analysis. As such, to overcome this limitation and to simplify the surface preparation, a protein-resistant intermolecular zwitterionic monolayer, which supports cell fixation, was utilized. We have shown that the intermolecular zwitterionic monolayer has well-defined, non-receptor mediated cellular attachment provided by cell-surface sugar interactions. Exploiting these properties, we have developed a monolayer stripe assay, where the interactions between neurons: cell bodies and neurites) and extracellular matrix: ECM) proteins or guidance cues can be observed and quantified. This system goes beyond current technologies and is capable of evaluating neuronal response to the extracellular matrix protein, laminin, which has previously been considered a control molecule in neuronal stripe assays.

Taken together, this work highlights advancements in the field of self-assembled monolayer chemistry with practical applications. In particular, we have focused on the functionalization of glass and oxides surfaces for applications in device lubrication. As well, we have developed two alkanethiol self-assembled monolayer approaches for generating surfaces that are both protein resistant and cell permissive, advancing the tools available for studying neuronal development in vitro.

Comments

Permanent URL: http://dx.doi.org/10.7936/K75B00HZ

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