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While modern-day healthcare continues to improve in terms of available treatments and life expectancy in many countries, increasing costs of providing medical services to aging populations place these systems under increasingly severe pressure. With continuing increases in chronic afflictions and ailments related to old age, more cost-efficient and long-term solutions are needed to meet these challenges. Regenerative medicine offers the potential for more effective long-term treatments, but is hindered by the high cost of the desired treatments in terms of development and implementation, owing to the complexity of the living materials used for such therapies. The work described in this thesis focuses on improving the level of control over the local cellular environment in order to reduce the need for costly materials (especially growth factors). Both surface topology and immobilization of growth factors have previously been shown to have an impact, and this research investigates potential interaction between these aspects. Patterning and immobilization of bio-active compounds are combined for the culture of human mesenchymal stem cells on surfaces with differently scaled patterns and concentrations of immobilized TGF-β1. Initial work focused on the creation of patterned surfaces with feature sizes ranging from 1 to 50 µm. Patterns were successfully produced in Poly (Ethylene Glycol), Polystyrene and Polycaprolactone surfaces using a microparticle-based moulding process. Further work resulted in the successful immobilization of TGF-β1 onto chemically modified surfaces, chiefly Polycaprolactone. Proteins were successfully immobilized onto Polycaprolactone surfaces at concentrations up to 4 pmol/cm2, with exact concentrations dependent on the parameters of the immobilization process. Finally, the developed methods were combined in a hybrid experiment using both patterned surfaces and growth factor immobilization. Results demonstrated a probable link between surface patterning and the effectiveness of immobilized growth factors, although further work is needed to more accurately describe any underlying processes. more...

Dielectric elastomer actuators (DEAs) have been used for artificial muscles for years. Recently the DEA-based deformable surfaces have demonstrated controllable microscale roughness, ease of operation, fast response, and possibilities for programmable control. DEA muscles used in bioinspired robotic arms for large deformation and strong force also become desirable for their efficiency, low manufacturing cost, high force-to-weight ratio, and noiseless operation. The DEA-based responsive surfaces in microscale roughness control, however, exhibit limited durability due to irreversible dielectric breakdown. Lowering device voltage to avoid this issue is hindered by an inadequate understanding of the electrically-induced wrinkling deformation as a function of the deformable dielectric film thickness. Also, the programmable control and geometric analysis of the structured surface deformation have not yet been fully explored. Current methods to generate anisotropic wrinkles rely on mechanical pre-loading such as stretching or bending, which complicates the fabrication and operation of the devices. With a fixed mechanical pre-loading, the device can only switch between the flat state and the preset wrinkling state. In this thesis, we overcome these shortcomings by demonstrating a simple method for fabricating fault-tolerant electro-responsive surfaces and for controlling surface wrinkling patterns. The DEA-based system can produce different reversible surface topographies (craters, irregular wrinkles, structured wrinkles) upon the geometrical design of electrode and application of voltage. It remains functional due to its ability to self-insulate breakdown faults even after multiple high voltage breakdowns, and the induced breakdown punctures can be used for amplification of local electric fields for wrinkle formation at lower applied voltages. We enhance fundamental understanding of the system by using different analytical models combined with numerical simulation to discuss the mechanism and critical conditions for wrinkle formation, and compare it with the experimental results from surface topography, critical field to induce wrinkles in films of different thickness, and wrinkling patterns quantitatively analysed by different disorder metrics. Based on the results, we demonstrate its wide applicability in adjustable transparency films, dynamic light-grating filter, molding for static surface patterns, and multi-stable mirror-diffusor-diffraction grating device. For DEAs used for macroscopic-scale deformation in robotic arms, the main issue that undermines the performance of DEA muscles is the trade-off between strong force and large displacement, which limits the durability and range of potential robotic and automation applications of DEA-driven devices. In this thesis, this challenge is tackled by using DEAs in loudspeaker configuration for independent scaling-up of force and displacement, developing a theoretical prediction to optimise the operation of such DEAs in bioinspired antagonistic system to maximise speed and power of the robotic arm, and designing a clutch-gear-shaft mechanical system collaborating with the muscles to decouple the displacement and output force. Therefore, the trade-off between force and displacement in traditional DEA muscles can be resolved. The mechanical system can also convert the short linear spurt to an unlimited rotary motion. Combining these advantages, continuous movement with high output force can be accomplished. more...

Electroactive polymers (EAPs) continue to gain attention for their potential to offer unique and versatile solutions in the soft robotic and flexible electronic industries. Ionic Polymer-Metal Composites (IPMCs) are a class of ionic-type EAPs which can be configured as capacitor actuators with very low voltage requirements (≤ 5 V AC or DC). Their compact, portable, and lightweight properties, coupled with a biomimetic bending actuation response make them ideal for human-machine integrated technologies such as medical implants, active skins, and artificial muscles. The Nafion-based IPMC can be described as a layered composite capacitor containing an ionic polymer core, sandwiched between chemically plated electrodes comprising of a conductive medium. Although there are reported achievements utilizing IPMCs in actuator configurations, their hydration-related sensitivity inhibits practical application in industry and makes experimental research difficult. This research sought to overcome these challenges by applying a wide range of experimental analyses, combined with theoretical modeling comparisons, to quantitatively characterize practical and standout factors impacting the actuator’s feasibility. The specific objectives investigated in this work include: (1) modifications of experimental test arrangements for practical insight; (2) investigation of IPMC degree of saturation and exposure correlations in both liquid and vapor conditions, coupled with electrical monitoring; (3) consideration of electrical field bias intensity and application arrangements on actuation behavior; and, finally, (4) practical inspection of IPMC design features and investigation of coating and geometric modification solutions for biomimetic and biocompatible applications. Investigations resulted in the development and validation of two testing configurations (contact-based and hydration-controlled) which provided reliable and repeatable testing. These systems included electrical and hydration control and monitoring which led to the identification of electrical tracking as a means to estimate IPMC performance. Additionally, optimized operation conditions were identified with special focus on the IPMC actuator’s performance variability. This work uncovered that the material’s inconsistency is a large factor inhibiting this technology from practical application. Electrical and actuation response analyses focused on the influence of the environment and voltage intensity on IPMC behavior changes with special emphasis on voltages surrounding reported electrolysis ranges unique to IPMCs. Lastly, a decision-making procedure was developed to optimize IPMC fabrication for soft-robotic biomimetic biocompatible solutions. This included emphasis on electrode deposition and patterns with quality analysis; IPMC hydrophobic coating solutions to inhibit solvent exchange; and modification of the geometric properties. All of this has culminated in a more pragmatic perspective on the potential of this technology and an identified course of action which could lead to the production of viable real-world application configurations which capitalize on the capabilities of these material arrangements. more...

Due to their high anisotropy (physical, electromagnetic, optical, mechanical), liquid crystals (LCs) serve as an ideal testing ground to study analogues of a large variety of physical phenomena at accessible size and energy scales. In this work, I focus in particular on two particular aspects of LC systems. The first is chiral induction, in which a localized breaking of a mirror symmetry propagates from a surface or interface out into the bulk. The second is the study of several manner of topological defect (TD) systems.I begin by using two independent techniques to verify the presence of chiral induction due to a novel chiral nanoparticle prepared by collaborating chemists: an electroclinic effect (ECE) and a Raynes’ Geometry experiment. I then introduce chirality into a thin, linear array of topological defects known as “oily streaks” and demonstrate that a surface ECE produces a twisting of the molecular sublayers of the nanostructure that is incommensurate with the symmetry of the system and report the relaxation mechanisms by which this twisting is ameliorated.I then use atomic force microscopy (AFM) nanolithography to design a particular pair of surface TDs that produce bulk disclination lines that are topologically equivalent in 3D. When an applied electric field projects the director into a quasi-2D space, the topological equivalence is broken and the two disclinations undergo different transformations: one remains undisturbed, while the other splits in two.By applying this AFM nanopatterning technique to the substrate of thin films of the kind in the second experiment, I report an unexpected surface topography at the LC-air interface above the patterning and explore the mechanisms behind this topography. more...

The creation of chemical micropatterns on surfaces makes it possible to add unique chemical functionality to surfaces, modifying properties such as wettability, or even adding the ability to selectively bind other molecules. The creation of biochemical surface patterning in particular is useful in a variety of fields including tissue engineering and highthroughput drug screening. There are many existing surface patterning techniques which focus on precise control over the patterned geometry, even down to submicron scale features, but they do not allow local control over chemical concentration. So the results are high resolution patterns with binary concentration. There are also existing methods to generate surface gradients of chemicals, but the focus there is to produce unidirectional concentration variation over a large surface. Normally these two methods—surface patterning and surface gradient generation—are incompatible with each other. So despite the large number of applications where simultaneous control over chemical placement and concentration would be useful, there is a dearth of options for doing so. In addition, it would be valuable to make micro patterned surfaces in a simple and approachable way, because fields where it could be most beneficial (such as tissue culture) are populated by individuals who are typically not microfabrication experts. The goal of this research is to develop an easy and low cost method for creating biochemical surface patterns with microscale feature resolution and local control over chemical concentration. The method described here leverages the force on charged protein molecules in an electric field to drive the molecules in a given direction. The speed with which these molecules move depends on the properties of the molecules themselves and the medium through which they travel. By creating a material with heterogeneous regions—in this work, a hydrogel with different mesh densities—it is possible to have local spatial control over the speed of protein movement. In this work, this concept was used to drive biomolecules (proteins) onto a target paper surface, and then local protein concentration was measured using fluorescence or intensity of a protein stain. In addition, these patterns were achieved using materials and methods that are easily accessible to individuals in most biochemical or tissue culture laboratories. more...

Chemical lift-off lithography (CLL) is a subtractive soft-lithographic technique used to pattern self-assembled monolayers (SAMs) containing functional alkanethiolates on Au surfaces. Alkanthiolate molecules, along with a single monolayer of Au, are removed in this process by oxygen-plasma activated polydimethysiloxane (PDMS) stamps. Monolayers patterned via CLL are robust, in contrast to conventional soft lithography, enabling high-fidelity patterning over a dynamic range of feature sizes (millimeter to nanometer). Recently, I have advanced CLL to pattern additional surfaces, including other coinage metals (e.g., Pt, Pd, Ag, Cu), reactive and transition metals (e.g., Ni, Ti, Al), and semiconductors (e.g., Ge). This process has a wide range of applications, including patterning of bioactive molecules and supported metal monolayers, as well as the simple, convenient fabrication of field-effect transistors (FETs). I have designed and developed FET biosensors coupled to rationally designed and chemically synthesized oligonucleotide sequences with molecular recognition capabilities, termed aptamers, for the detection of a diverse range of biologically important small-molecule targets (e.g., neurotransmitters, amino acids, sugars, lipids). Upon target capture, aptamers undergo conformational changes that redistribute charge densities on FET surfaces resulting in measurable changes in transconductance. These aptamer-FET sensors detected targets in full ionic strength biological fluids, with high specificity and selectivity, over large concentration ranges with low detection limits. Using this platform, I have developed sensors for the direct detection of the amino acid phenylalanine for potential point-of-care use for patients with phenylketonuria (PKU), a common genetic disorder that results in elevated and potentially harmful levels of phenylalanine in the blood and brain. Phenylalanine aptamer-FETs showed high sensitivity and selectivity towards phenylalanine versus similarly structured molecules, and were able to differentiate physiological phenylalanine concentrations in serum from mice treated with a phenylalanine hydroxylase inhibitor (i.e., a PKU mouse model). In parallel, I have extended this FET biosensor platform for the detection and discrimination of single base-pair mismatches in oligonucleotides towards electronic single-nucleotide polymorphism genotyping. I demonstrated the ability of DNA-functionalized FETs to distinguish hybridization between fully complementary DNA sequences, and analogous sequences with different types and locations of mismatches. Performing FET measurements under physiologically relevant conditions and elucidating sensing mechanisms is necessary for ultimate use in disease diagnostics and clinical point-of-care applications. more...

The goal of my dissertation research was to devise new strategies to combat membrane fouling, which is a major hindrance in water treatment systems. Membrane fouling refers to the blocking of pores and the build-up of material on the membrane surface. There are many types of foulants, including but not limited to bacteria, biopolymers (such as alginate), natural organic matter, oils, proteins, particles, and salts (such as gypsum). Typical ways to combat fouling include expensive pretreatment procedures, physical membrane cleaning, and chemical treatments to the membranes. Chemical treatments tend to decrease the membrane lifetime, especially for nanofiltration and reverse osmosis membranes. One common strategy in the research community is to surface modify membranes to increase their fouling resistance. Chapter 1 reviews the surface modification methods used to reduce membrane fouling. Chapter 2 presents my work on modifying ultrafiltration membranes with poly(2-((2-hydroxy-3-(methacryloyloxy)propyl)dimethylammonio)acetate) (poly(CBOH), a polymer that switches reversibly between a zwitterionic chemistry and a quaternary amine chemistry. Surface characterization showed successful membrane modification by UV-graft polymerization. Bacteria deposition studies showed that the poly(CBOH) chemistry performed better than other common anti-fouling chemistries. Biofilm studies showed that poly(CBOH) functionalized polyethersulfone membranes accumulated half the biovolume as unmodified membranes. Poly(CBOH) switches from an anti-fouling, zwitterion mode to an anti-microbial, quaternary amine mode by changing the environment pH. Studies were done to characterize the switching pH and time using poly(CBOH) modified silicon wafers. Switching pH was determined to be 1.0, with 15 min being required to switch between the zwitterion and quaternary amine chemistries. Biofilm mortality was elevated on ultrafiltration membranes once the anti-fouling poly(CBOH) zwitterion was switched to the anti-microbial, poly(CB-Ring) quaternary amine, with dead-to-live cell ratio increasing from 0.33 to 1.04. Chapter 3 describes my work to increase the fouling resistance of nanofiltration membranes by applying both a chemical coating and a nanometer sized pattern to the membrane surfaces. A line and groove nano-pattern was applied by thermal embossing directly onto a commercial polyamide thin-film composite nanofiltration membrane. Poly(ethylene glycol) diglycidyl ether (PEGDE) was reacted onto the patterned membrane surfaces by an epoxide ring opening reaction with unreacted carboxyl groups on the polyamide selective layer. Surface characterization showed successful nano-patterning and chemical modification of the membrane surfaces. Membrane performance (flux and salt rejection) was unaffected by patterning the polyamide membrane surface directly. The fouling results show that combining line and groove nano-patterning with PEGDE chemical modification yields a membrane that was more resistant to fouling than either method alone. Chapter 4 presents my work to apply a nanometer sized pattern onto numerous commercial nanofiltration and reverse osmosis polyamide membranes. There have been differing views on the ability to pattern polyamide thin-film composite (TFC) membranes directly by nanoimprint lithography. The goal of this study was to understand what factors control patternability, working towards a set of heuristics for use by the membrane community to pattern any polyamide TFC membrane. Initial results showed that each membrane patterned to a different degree. Despite completing a comprehensive set of experiments to investigate the roles played by membrane chemistry, surface properties, mechanical properties, and performance properties on pattern peak heights for thirteen commercial nanofiltration and reverse osmosis membranes, I found no correlation between the variables studied and patternability of individual membranes. I did discover significant differences in patternability between membranes grouped by polyamide class, with those prepared by interfacial polymerization of m-phenylenediame and trimesoyl chloride having the largest pattern peak heights. I further discovered that the humectant (pore filler) used for membrane preservation plays a role on the patternability of the membranes. Upon replacement of the original humectants used by the membrane manufacturers with a 15 wt% glycerol solution, the pattern peak heights approached a similar value for each class of membranes. Tests performed to elucidate the role of the glycerol on patternability were inconclusive. Thus, while the humectant clearly contributes to membrane patternability, the reason why remains unknown. Overall, my research demonstrates the ability to reduce membrane biofouling by changing surface chemistry and surface features. Results of my work contribute to our understanding of membrane fouling and can be used to develop next-generation water treatment membranes with improved fouling resistance. Such membranes could be expected to lower the operations cost of using membranes to clean water. more...

Strain energy induced self-assembly has recently been discovered in the rare earth oxides (REO)/yttria-stabilized zirconia (YSZ) systems. This dissertation aims to deepen previous mechanistic understanding of this phenomenon and to develop a cost-efficient technique that can be used to pattern a large surface with nanoscale features. In this work, a new REO source dispersion strategy was used to address the dilemma of the process simplicity and the source controllability. With this method, we investigated the growth kinetics of the nanostructures in a quantitative manner. In contrast to previous hypothesis that both the nanoislands and the nanobars have parabolic growth kinetics, we observed a parabolic relation only for the nanobars on YSZ(110). It was further discovered that the growth is anisotropic on YSZ(110), which might explain the formation of bars instead of islands.In efforts to improve the order of the nanoislands, we investigated the surface step morphology and the formation of self-assembled nanoislands on two different types of miscut yttria-stabilized zirconia (YSZ) substrates. It was found that ordered step arrays can be produced on both (001)-[110] and (001)-[100] miscut YSZ substrates via pre-annealing. These steps are subsequently used as templates for the self-assembly of the nanoislands, which results in significantly improved alignment of the islands along the step direction. Additionally, we observed a novel step faceting only on the (001)-[100] miscut YSZ substrates where the original [100]-steps decompose into -segments. Preliminary investigation indicates that this faceting is induced by doping via surface diffusion, while the elastic interaction between the faceted steps also plays a significant role.We further investigated the impact of annealing gas environment - an overlooked factor in previous studies - on the nanostructure morphology. It was found that 5% H2-95% N2 forming gas environment can promote the reactions in Eu2O3/YSZ(001) systems, which results in an improvement in nanostructure coverage. It is believed that the existence of H2 has dynamically changed the nanostructure formation. The role of H2 and its effect on other REO/YSZ systems were also explored and discussed. more...

Spatial patterning of biomolecules on a surface with nano- and micrometer precision is important in engineering biological microenvironments. Nano- and micropatterned biological arrays are useful for chemical functionalization of miniaturized biosensors, tissue engineering, high throughput drug screening, and fundamental biophysical and molecular biology studies. Despite the growing demands and applications, current surface patterning techniques are still lacking. Parylene (or poly[p-xylylene]) is a unique family of chemically vapor deposited polymer that is biocompatible, exhibits little to no swelling in aqueous solutions and is amenable to photolithography processing. These characteristics of parylene are attractive for its use as a "peel-able", high fidelity stencil for the surface patterning of biomolecular arrays. Different types of parylene coatings containing substituted functional groups have been developed for biochemical surface modification on virtually any surface. The two themes that emerge from this work are: i) the use of parylene films with nano/microfabricated openings as a stencil tool for surface patterning (Chapters 2 - 4), and ii) the application of parylene coatings to directly pattern surfaces (Chapters 5 and 6). Chapter 2 describes a new nanofabrication process to create parylene stencils with sub-100nm openings. These stencils can then be combined with inkjet printing to rapidly generate multi-component biomolecular nanoarrays on a single surface. The work in Chapter 3 elucidates the role of cell-cell interactions in tumor angiogenesis through the use of patterned tumor cell arrays. In Chapter 4, a hybrid substrate, consisting of a hydrophobic parylene stencil with hydrophilic silanized openings, is utilized to control spot drying morphology and improve microarray reproducibility. Parylene-based paper microfluidic devices and their enhanced capabilities are presented in Chapter 5. The work in Chapter 6 involves proteins covalently immobilized onto an array of reactive (aminated) parylene strips. These strips subsequently incorporated with microfluidics for the affinity-based screening and subsequent recovery of aptamers. Chapter 7 is a summary containing unpublished observations of parylene that may serve as a useful starting point for future researchers. These cumulative studies demonstrate that parylene-based surface patterning techniques are versatile for creating nano- and microarrays towards many biological applications. more...