Thesis (M.S.)--Brigham Young University. Dept. of Mechanical Engineering, 2007. / Includes bibliographical references (p. 129-132).

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xxiii, 163 p.; also includes graphics. Includes bibliographical references (p. 118-123). Available online via OhioLINK's ETD Center

Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2006. / Dr. David W. Rosen, Committee Chair ; Dr. Farrokh Mistree, Committee Member ; Dr. W. Jack Lackey, Committee Member ; Dr. Cliff Henderson, Committee Member ; Dr. Ali Adibi, Committee Member.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

The present thesis includes a series of studies on microfluidic technology from novel microfabrication methods in polymers to diverse microfluidic applications. Specifically, this study focuses on some key issues in microfluidics, regarding the development of microfluidic fabrication strategy, material selection for microfabrication, and applications, in particularly controllable reactions of novel polymer-based microfluidic devices. We have developed novel methods, which hold completely different idea/ concept with conventional approaches', for fabrication of microfluidic chips with polymer materials. While for the microfluidic applications, the thesis exhibits cell perfusion experiments with freestanding 3D microchannels made of alginate hydrogel, convenient and sensitive lead(Ⅱ) ions detection on a plastic membrane microfluidic chip which was fabricated by the proposed novel one-step strategy, as well as and microfluidic controllable synthesis of enzyme-embedded metal-organic frameworks in a laminar flow;In the first part, we proposed an inside-out fabrication strategy using a copper scaffold as the sacrificial template to create freestanding 3D microvascular structures containing branched tubular networks with alginate hydrogel. The microvascular structures produced with this method are strong enough to allow handling, biocompatible for cell culture, appropriately porous to allow diffusion of small molecules, while sufficiently dense to prevent blocking of channels when embedded in various types of gels. In addition, other materials and biomolecules could be pre-loaded in our hydrogel tubular networks by mixing them with alginate solution, and the thickness of tubule wall is tunable. Compared to other potential strategies of fabricating free-standing gel channel networks, our method is parallel processing using an industrially mass-producible template, making our method rapid, low-cost and scalable. We demonstrated cell culture in a nutrition gradient based on a microfluidic diffusion device made of agar, a hydrogel traditionally hard to microfabricate, by embedding the synthesized tubules into the agar gel. In this way, the freestanding hydrogel vascular network we produced is a universal functional unit that can be integrated with other gel-based devices to build up the supporting matrix for 3D cell culture outside the hydrogel vascular structure; allowing great convenience and flexibility 3D culture. The method is readily implementable to have broad applications in biomedicine and biology, such as vascular tissue regeneration, drug discovery, and delivery system in 3D culture.;The second part, we developed a one-step method to mass produce microfluidic chip with thermal plastic membranes. We used a perfluoropolymer perfluoroalkoxy (often called Teflon PFA) negative mold, which is very nonsticky and has ultrahigh melting point, as solid stamp to thermal-bond two pieces of plastic membranes, low density polyethylene (LDPE) and polyethylene terephthalate (PET) coated with ethylene-vinyl acetate copolymer (EVA), which have different coefficients of thermal expansion. During the short period of contact with the heated Teflon stamp, the pressed area of the membranes permanently bonded, while the LDPE membrane spontaneously rose up at the area not pressed, forming microchannels automatically. These two regions were clearly distinguishable even at micrometer scale so that we were able to fabricate microchannels with width down to 50 microns. By using thermal-bonding, the pattern of Teflon mold will be transferred to the plastic membrane forming channels while two membranes will be bonded at the same time. The method enables generation of microchannels and bonding process to accomplish in a single step without sophisticated instruments. One Teflon mold can be used to mass replicate many plastic membrane chips in a short time because each round needs only a few seconds. Our method can fabricate a plastic microfluidic chip rapidly (within 12 seconds per piece) at an extremely low price (less than 0.02{dollar} per piece). We also showed some identical microfluidic manipulations with the flexible plastic membrane chips including droplet formation, microfluidic capillary electrophoresis and squeezing-pump for quantitative injection. In addition, we demonstrated convenient on-chip detection of lead ion by a peristaltic-pumping design, as an example of the applications of the plastic membrane chips in resource-limited environment. Due to the fast production method and low-cost of plastic materials, this one-step method will hopefully lead to new opportunities for the commercial implementations of microfluidic technologies.;Finally, on the basis of preliminary study of microfluidic laminar flow synthesis of MOFs in aqueous system in Chapter 4, we successfully synthesized and investigated formation of enzyme-embedded metal-organic frameworks (MOFs) in a continuous laminar flow on a microfluidic chip. Resultant enzyme-MOF composites displayed higher enzymatic activity than enzyme-MOF composites from bulk solution synthesis. A possible reason was that the precisely controlled and yet changeable reaction conditions such as reaction time and diffusive mixing of reagents allowed the fast reaction to be isolated into controllable processes and studied with predesigned yet changing conditions. This, in return, led to distinct morphological characteristics and activities of the enzyme-MOF composites compared to those from bulk synthesis. The results indicated that the highest activity of enzyme-MOF composites was obtained when metal ions and organic ligands were first gradually mixed within a few seconds before enzyme molecules joined the gradual mixing process. We found that the crystallinity degree of as-produced enzyme-MOF composites was reduced via the microfluidic flow synthesis, containing more structural defects compared to those with high degree of crystallinity from bulk synthesis. The reduced crystallinity allowed more effective approaching of substrates with enzyme embedded in composites and therefore an increased enzyme activity compared to enzyme-MOF composites from bulk synthesis. We further demonstrated that enzyme-MOF composites showed enhanced stability against elevated temperature and protease digestion compared with free enzymes, allowing their wider utility in biotechnology.

This thesis describes the development of electrochemical analytical approaches for the investigation of sulphide detection in stagnant and fluidic environments. The project reports the use of Fourier transform large amplitude alternating current voltammetry (FTACV) as a novel analytical technique for the investigation of sulphide sensing. Novel reactor technology and FTACV measurements carried out using macro and microelectrodes in stagnant and fluidic conditions are reported for the first time. The novel strategy adopts the use of an electrocatalytic (EC') mechanism by using a redox mediator to facilitate the reaction with sulphide in aqueous solutions. In order to support the analysis of FTACV, other electrochemical analytical techniques, cyclic voltammetry (CV) and linear sweep voltammetry (LSV), were also employed to support the observations from FTACV. Chapter 3 reports the application of the CV and FTACV for the detection of sulphide in stagnant conditions at a macroscale electrode. A split wave phenomenon, which is related to the reaction with sulphide, was observed both in the CV and FTACV. By measuring the current behaviour of the split wave, sulphide content in aqueous solution can be determined. Importantly, the split wave phenomenon of the FTACV is the first documented observation using macroscale electrodes. These observations highlight the potential of FTACV to support the detection of sulphide detection. Numerical models of the system are also presented from the calculation to support the experimental interpretation of the voltammetric responses of the CV and FTACV. In Chapter 4 measurements were focused on the voltammetric response of sulphide containing aqueous solutions using microelectrodes. In conventional CV measurements, the split wave behaviour observed at macroelectode disappears from the DC signal; however, for the FTACV measurements, the split wave can still be observed in the higher harmonics providing a clear and simple strategy for detecting sulphide. The results achieved in the FTACV are the first documented observation under the steady state at microelectrodes. Again numerical simulations are reported for this case to support the experimental results. Chapter 5 extends the FTACV measurements for sulphide detection to hydrodynamic environments. The design, development and application of a microfluidic electrochemical system are reported. Split wave characteristics were for the first time detected in both dc and FTACV measurements. The results support the possibility of using dc and ac voltammetry to detect sulphide, while also being used as a guide to assess the split-wave behaviour of the EC' mechanism under fluidic conditions. Numerical models were used to support the analysis of the experimental measurements.

The increasing density of electronics within portable electronic devices provides the motivation to develop more compact power electronics, such as DC-DC converters. Typically, integrated circuits and each passive component, such as inductors, are discreetly packaged and mounted on printed circuit board (PCB), to implement the converter. Hence for further size reduction there has been growing interest for integration schemes such as Power supply in package (PwrSiP). However, the ultimate goal is the monolithic integration of the power supply solution, in an integration scheme known as Power Supply on Chip (PwrSoC). The economic effectiveness of the converter will be determined by the device footprint and number of processing steps required to fabricate the inductor. Hence, the motivation behind this thesis is the need for microinductors with large inductance density (inductance per device footprint) while maintaining low losses, which can be integrated with silicon IC. Furthermore, the need for thick layers will result in issues with yield and reliability of the fabricated device. Hence there is a need to identify, characterise and integrate materials with low residual stress into the microinductor fabrication process. A typical choice of inter-coil dielectric is the photo-definable epoxy SU-8. However, SU-8 suffers from intrinsic issues with high residual stress and adhesion. One possible replacement for SU-8 as a structural and dielectric layer is Parylene-C. The first objective of this thesis proposes a test-bed inductor process, which incorporates Parylene as a structural and dielectric layer and has a short turnaround time of one week. This fabrication process involves the filling of high aspect ratio gaps between copper structures with Parylene and subsequent chemical mechanical planarisation, and a test chip has been designed to characterise these processes. Additionally, Scotch-tape testing has been used to confirm suitable Parylene adhesion to patterned and unpatterned films used in this process. Subsequently, complete microinductors, with magnetic cores, have been fabricated, characterised and benchmarked against other inductor technologies and architectures reported in the literature. Parylene is expected to produce films with low residual stress due to its room temperature deposition process. However, the test-bed inductor process requires thermal treatments up to 140°C. Hence it was necessary to characterise the stress in Parylene films as a result of processing temperature and compare this to stress levels in SU-8 5 and 3005 films. This study has determined the spatial variation of residual stress in Parylene-C and SU-8 films, by combining automated measurements of strain indicator test structures and local nanoindentation measurements of Young’s modulus. These measurements have been used to wafer map strain, Young’s modulus, and subsequently residual stress in these films, as a result of processing parameter variation. It is well known that placing ferromagnetic material in close proximity to current carrying coils can further enhance the measured inductance value. However, the conductive magnetic core is also a source of loss for the microinductor. Hence, magnetic permeability, electrical resistivity and mechanical stress in the magnetic core influence the inductance value, eddy current losses and reliability of the fabricated microinductor, respectively. The ability to characterise these properties on wafer is essential for process control and verification measurements. This thesis details a test chip capable of routine measurements on NiFe films to characterise the spatial variation of these properties. Furthermore, wafer mapping measurements are reported to identify the correlation between high frequency permeability, electrical resistivity, mechanical strain and the chemical composition of two-component Permalloy film (NixFe(100-x)) electroplated on the surface of 100mm silicon wafers. Finally, MEMS-based inductor fabrication processes typically require a number of electrodeposition steps, which require conductive seed layers for the deposition of the coils and magnetic core material. A typical choice of seed layer is copper. However, due to copper’s paramagnetic behaviour (μ = 1) and low electrical resistivity (ρ=6.69μΩ.cm) this layer contributes to eddy current losses, while acting as a thin ‘screening layer’. It is very likely that using a magnetic seed layer, within the magnetic core, will noticeably reduce eddy current related losses. However, detailed systematic experimental studies on any such improvement have not been documented in the literature. This study involves compositional, structural, electrical and magnetic characterisation of Ni80Fe20 films electro-deposited on non-magnetic and magnetic seed layers (i.e. copper and nickel respectively). Mechanical strain test structures and X-ray analysis have been used to characterise the stress levels and structural properties of Ni80Fe20 films electro-deposited on both copper and nickel seed layers. In addition, planar spiral micro-inductors, both with and without patterned magnetic cores, have been fabricated to determine the effect of patterning on their performance. This is in addition to quantifying the improvement in the electrical performance resulting from the enhanced magnetic and resistive contribution provided by magnetic seed layers.

Recent advances in the miniaturization of biosensors and drug delivery systems have allowed for the continuous and non-invasive monitoring of patient health. While sutures are mainly used for approximating tissues in clinical practice, there has been emerging development of new suture materials for improving wound healing outcomes. We report a novel method of continuous and high-throughput fabrication of multifunctional sutures and threads which allows for control over a wide range of important microstructural and physical properties. In the proposed fabrication method, a thread or suture is spooled across a base collecting plate. The fabrication method involves direct electrospinning (ES) onto the surface of threads and sutures. ES has also been widely used within the area of biomedical and tissue engineering, given its compatibility with a range of synthetic and natural biocompatible polymers. As the thread moves beneath a syringe pump and a spinerette needle that is positively charged, electrospun nanofibers collect on the surface of the thread. The coating layer thickness and the alignment of the nanofibers with the direction of the thread is tuned by varying the spooling speed and the distance between the spinerette needle and the thread. The resulting smart sutures have applications in both passive and on-demand drug release, durable wound biosensing, and improved cell viability and attachment. These structures may be manipulated in different materials (i.e. skin, fabrics, wound dressings) and be combined using textile methods (e.g. braiding, weaving, knitting) to form three dimensional (3D) constructs. / Graduate / 2022-09-10

Current microfabrication materials include silicon, a wide variety of metals, dielectrics, and some polymers. Because of the low cost and high processing flexibility that polymers generally have, expanding the use of polymers in microfabrication would benefit the microfabrication community, enabling new routes towards goals such as low-cost 3D microfabrication. This work describes two main unconventional uses of polymers in microfabrication. The first unconventional use is as a carrier material in the self-assembly (SA) of millimeter-scale parts in which functional electronic components and electrical interconnects were cast into 5 mm cubes of Polymethylmethacrylate (PMMA). The second unconventional use is as a non-flat micromold for an alumina ceramic and as transfer material for multiple layers of micropatterned carbon nanotubes (CNTs). Both of these uses demonstrate 3D low-cost microfabrication routes. In the SA chapter, surface forces induced both gross and fine alignment of the PMMA cubes. The cubes were bonded using low-melting temperature solder, resulting in a self-assembled 3D circuit of LEDs and capacitors. The PMMA-encasulated parts were immersed in methyl methacrylate (MMA) to dissolve the PMMA, showing the possibility of using MEMS devices with moving parts such as mechanical actuators or resonators. This technique could be expanded for assembly of systems having more than 104 components. The ultimate goal is to combine a large number of diverse active components to allow the manufacture of systems having dense integrated functionality. The ceramic micromolding chapter explores micromolding fabrication of alumina ceramic microstructures on flat and curved surfaces, transfer of carbon nanotube (CNT) micropatterns into the ceramic, and oxidation inhibition of these CNTs through ceramic encapsulation. Microstructured master mold templates were fabricated from etched silicon, embossed thermally sacrificial polymer, and flexible polydimethylsiloxane (PDMS). The polymer templates were themselves made from silicon masters. Thus, once the master is produced, no further access to a microfabrication facility is required. Using the flexible PDMS molds, ceramic structures with mm-scale curvature were fabricated having microstructures on either the inside or outside of the curved macrostructure. It was possible to embed CNTs into the ceramic microstructures. To do this, micropatterned CNTs on silicon were transferred to ceramic via vacuum molding. Multilayered micropatterned CNT-ceramic devices were fabricated, and CNT electrical traces were encapsulated with ceramic to inhibit oxidation. During oxidation trials, encapsulated CNT traces showed an increase in resistance that was 62% less than those that were not encapsulated.

Les dysfonctionnements vasculaires ou les blessures induites par l'âge, le tabac, les traumatismes ou une hyperlipidémie font partie de la myriade de facteurs de risques qui contribuent à la pathogénèse de nombreuses maladies cardiovasculaires. Un objectif important de la biologie vasculaire est de comprendre les processus cellulaires qui favorisent ou protègent contre ces maladies vasculaires. Cette pathogénèse est étroitement associée avec le dysfonctionnement de la paroi interne des vaisseaux sanguins. Cette paroi est constituée par une monocouche de cellules endothéliales qui forment l'endothélium vasculaire. La réparation de l'endothélium implique le remodelage des adhésions focales (AF) et des jonctions adhérentes (JA). Des modifications dans la composition protéique de ces structures adhésives génèrent des forces qui sont à la base du remodelage et de la réparation de l'endothélium. Dans la littérature, les forces cellulaires sont étudiées sur des cellules isolées, des doublets de cellules ou des ilots de cellules en croissance mais les forces mécaniques qui s'exercent au sein d'un tissu doivent encore être caractérisées. Dans cette thèse, nous utilisons la Microscopie à Traction de Force (TFM) sur des substrats en polyacrylamide pour étudier l'équilibre mécanique entre les jonctions intercellulaires et les adhésions cellule/substrat. Nous analysons dans quel mesure la TFM peut être utilisée pour étudier des monocouches cellulaires et présentons une nouvelle approche pour extraire les forces contractiles exercées par un tissu endothéliale. Finalement, nous utilisons cette méthode pour caractériser les forces transmises par les cellules à leur substrat et les forces contractiles pour une monocouche endothéliale. Cette méthode fournit un outil intéressant pour étudier la contribution de certaines protéines des jonctions adhérentes sur les forces transmises au sein de l'endothélium. / Vascular dysfunction or injury induced by aging, smoking, inflammation, trauma, hyperlipidaemia are among a myriad of risk factors that contribute to the pathogenesis of many cardiovascular diseases. An important objective in vascular biology is to understand cellular processes that promote or protect against cardiovascular diseases. This pathogenesis is very closely associated with dysfunction of the inner face of the vessel wall. The inner face of the vessel wall is lined by a monolayer of endothelial cells forming the vascular endothelium. Reparation of the endothelium involves remodelling of focal adhesionns (FA) and adherent junctions (AJ). Modifications in the protein composition of these adhesive structures generate forces at the basis of endothelium remodelling and reparation. In the literature, cellular forces are studied on single cells, epithelial cell doublets or cell aggregates in growth but mechanical forces inside tissues remains to be characterized. In this thesis, we use traction force microscopy (TFM) on polyacrylamide substrates to study the mechanical equilibrium between intercellular junctions and cell/substrate adhesion. We analyse to which extent TFM can be used for studying monolayers and present a novel approach to extract contractile forces exerted by an endothelial tissue. Finally, we use this methodology to characterize forces transmitted to the substrate and the contractile forces of endothelial monolayers. This method provides an interesting tool to study the contribution of some proteins of the adherent junctions to force transmission within the endothelium.