192 research outputs found
Ant tracheal measurements by synchrotron
No full textData for ant abdominal tracheal radii from Levels 1 (closest to spiracle) to level 3. Code for the analysis also provided as used in the R package. The data all used for this work:<div><br></div><div><p><a>Tracheal
branching in ants is area-decreasing, violating a central assumption of network
transport models</a></p>
<p> </p>
<p>Ian
J. Aitkenhead, Grant A. Duffy, Citsabehsan Devendran,
Michael R. Kearney, Adrian Neild and Steven L. Chown</p><br></div>
Ant tracheal measurements by synchrotron tomography
No full textData for ant abdominal tracheal radii from Levels 1 (closest to spiracle) to level 3. Code for the analysis also provided as used in the R package. The data all used for this work:<div><br></div><div><p><a>Tracheal
branching in ants is area-decreasing, violating a central assumption of network
transport models</a></p>
<p> </p>
<p>Ian
J. Aitkenhead, Grant A. Duffy, Citsabehsan Devendran,
Michael R. Kearney, Adrian Neild and Steven L. Chown</p><br></div>
Ant tracheal measurements by synchrotron
No full textData for ant abdominal tracheal radii from Levels 1 (closest to spiracle) to level 3. Code for the analysis also provided as used in the R package. The data all used for this work:Tracheal
branching in ants is area-decreasing, violating a central assumption of network
transport models
Ian
J. Aitkenhead, Grant A. Duffy, Citsabehsan Devendran,
Michael R. Kearney, Adrian Neild and Steven L. Chown</div
Ultrasonic air-coupled capacitive arrays
Get PDFA model is developed which is capable of predicting the pressure field of a rectangular source, as measured by a finite-sized receiver. This novel method treats the problem in a new way, which allows an integration to be performed over the area of the receiver. Previously it has only been possible to model two circular transducers coaxially aligned. The model is used to identify a receiver, which can be used to measure the highly focussed pressure field from a phased array, with only a negligible effect due to the receiver size. Productions from the model are compared to experimental data, and show a good correlation.
A parabolic mirror used to focus the field from a circular device in air has been studied, and a model developed to predict the pressure field produced by this device. This is done by an approximation of the mirror surface to a grid of finely spaced points. The model correlates well with measured results. In addition, an image of a defect in a solid sample was produced.
Arrays are then used to image solid samples in air. This is done using three techniques. The first is a combined phased source and receiver, which is shown to locate a wire accurately and to measure a step in the surface of a sample. A 2-D array is shown to image a defect in a composite plate, and the potential for a fast through-transmission air-coupled system is indicated. In addition, two post-processing techniques are used on data recorded using an array receiver, to locate an object in air. Of these two techniques, ellipse crossing is shown to have better results for large signal to noise ratios, and SAFT for lower ratios.
The combination of theoretical modelling and experimental observations has indicated that the transducers and arrays constructed for use in air are well-understood, and that their characteristics can be predicted
Acoustophoresis in open fluidic films
No full textAcoustic particle manipulation (acoustophoresis) is a rapidly developing technology in the field of microfluidics, which uses small fluid samples for the purposes of biological or chemical based testing. Microfluidics is often aimed at producing Lab-on-a-Chip based systems, particularly useful for testing in remote locations where standard laboratory techniques are not available. Acoustophoresis holds advantages over many other particle manipulation methods as it only alters the fluid pressure to displace the non-homogeneous elements within the fluid. Other methods typically require application of a potential difference to the fluid, which may damage sensitive biological cells; or direct contact with the particles, which may also cause damage or cross-contamination with repeated trials. Common uses for acoustophoresis are the filtering of particles from fluid by displacing them to a location and then splitting the fluid flow (an acoustic filter), or creating arrays of particle clumps for drug testing purposes (bioassays). The actuating mechanism for these devices is typically a piezoelectric transducer (PZT), which vibrates upon application of an alternating current, attached to a carrier which is in turn coupled with the particulate fluid. This work seeks to adapt established acoustophoresis devices for novel uses. The key to the setup presented is the vertical offset between the PZT and carrier glass, which allows the carrier to be partially submerged while under actuation. The device then utilises two novel methods of acoustophoresis, the first has the fluid bounded by the edge of the glass carrier during actuation. The second method is for a partially submerged carrier that applies standing waves to an open and stationary fluid volume many times the size of the carrier itself. The advantage of the device itself is that the two piece system allows for ease of use, repetition and easily adjustable spatial parameters. The first method presented has the advantage of requiring only a small fluid volume and no external mechanisms. For a known fluid volume the actuating frequency is varied and the horizontal wavelength (determined by the distance between the lines the particles relocate to), is calculated and compared to theoretical expectations. The frequency against horizontal wavelength analysis is conducted for the open fluid method as well, in addition to recording the effect of variation in the fluid thickness layer on the acoustic wave. The open fluid setup has the advantage of the particle arrays being highly accessible and is examined compared to other acoustic methods using enclosed chambers. Both methods presented have experimental techniques adapted to exploit the advantages of the novel setup, as well as 2 dimensional COMSOL finite element models. The work produced succeeds in utilising the device presented for two alternate modes of particle manipulation, both of which present advantages over current methods of acoustophoresis
Manipulation in microfluidic systems using surface acoustic waves (SAW)
No full textLab-on-a-chip microfluidic systems hold substantial promise for a wide range of diagnostic and therapeutic applications. By shrinking down conventional laboratory processes and replicating their functions on-chip, the size, cost, required time, and amount of reagent and sample needed can be drastically reduced. However, because these devices operate at length scales orders of magnitude smaller than conventional fluid processes different physical phenomena become dominant, meaning new forces and techniques must be developed to perform them. Acoustic forces have the potential to be useful at small length scales, though, their use has for the most part been limited by the relatively small force magnitudes and low frequencies at which they have been generated, thereby limiting the promise of rapid acoustic manipulation on microfluidic scales. However, a developing technology relying on the application of surface acoustic waves (SAW) has shown the potential to overcome these limitations, especially due to the high frequencies (10-2000 MHz) and correspondingly small length scales (2-300 µm), on the order of the bacteria and eukaryotic cells, that are characteristic of this method. In this thesis, SAW is used in a range of applications that emphasize these advantages, specifically with respect to the large and localized forces that can be generated on interfaces, both between two immiscible phases and on particles within a single fluid phase. In the studies presented here, SAW is used to (1) actuate a fluid-air interface for the production of water-in-air droplets with tunable diameters in the range of ~0.5-50 µm for the purpose of targeted nebulization therapy, (2) actuate a water-oil interface for the tunable production of picoliter-sized water-in-oil droplets with simultaneous particle pre-concentration and encapsulation for application in digital microfluidic systems, (3) perform controlled concentration and release of particles using a novel microfabricated channel structure and (4) deterministically sort particles over a large size range, demonstrated between 0.3-7 µm with potential application in cell sorting systems where high sorting efficiency or sorting based on only small size differences is required. Finally the case is made that acoustic fields, especially those produced by SAW, are optimal for many, if not most, applications where manipulation of microfluidic species is required
Developing advanced particle manipulation techniques in microfluidic systems
No full textAdvanced particle manipulation techniques with synergistic effects of low cost, high degrees of controllability, precision, and delicateness have been developed. In particular, the one-dimensional pressure fields in a microfluidic channel device driven by a piezoelectric plate have been investigated. Particles lines were observed along the channel when corresponding resonant frequencies applied. The more complex two-dimensional pressure fields excited by one electrode in the microfluidic channel were also investigated. Single array of particles clumps have been achieved by switching between two frequencies. Additionally, two arrays of particles clumps were observed by sweeping frequency rapidly. Furthermore, particles levitation was observed under certain excitation frequency. Based on the knowledge gained from the microfluidic channel, a microfluidic chamber was conducted in the development of ultrasonic technique. Cavitation bubbles driven by the standing wave generated in the chamber have been studied. Various oscillation modes of the bubbles were also studied. Additionally, the vibrating bubbles as size-based particle selective mechanism were examined. Size varied particles either been attracted (larger particles dominated by Bjerknes force) or repelled (smaller particles dominated by drag force) by the bubble were achieved. As an alternative to the ultrasonic particle manipulation methods, the development of particles forming in lines by capillary flow due to water evaporation has also been demonstrated in this thesis. Particles behaviour has been investigated in a capillary cell formed by a parallel glass slide and a glass cover slip. Particles remaining in hydrated while assembled and harvested in batches were shown. Finally, the establishment of advanced strategies for using the float-sink scheme to selecting single fragile particles has been conducted. A droplet dispensed directly above the selected particle floating on the liquid surface was demonstrated to cause the particle to sink even when the particle was within a floating cluster
Nanoparticle manipulation and forced spreading within microscale acoustofluidic droplet systems
No full textLab-on-a-chip and micro-total-analysis systems are vital analytical tools used in both the biotechnology and nanotechnology industries. One of the most important aspects of this type of system is the ability to reliably control and manipulate the system itself or the sub-components located within the system such as cells. Audible frequency acoustofluidic actuation can provide a number of potential benefits for microfluidic procedures and is thusly investigated within this thesis. This thesis concentrates on two fundamental facets of manipulation of a microscale droplet system. The first aspect involves a previously undiscovered mechanism allowing manipulation of particles sized down to the nanoscale. The oscillatory motion of the fluid causes a time averaged linear relationship between particle and fluid flow. The intricate interplay between the hydrodynamic focussing and steady streaming effects must be controlled to optimise particle handling. The reduction in particle size has been achieved by minimising the strength of the acoustic streaming function and optimising the multiple-pass hydrodynamic focusing that acts on the particles. The magnitude of the scale reduction presented is quite significant, as particles as small as 190nm in diameter have been manipulated. The other aspect elucidates the harmonic fluidic motion’s ability to modify the wettability of a microscale droplet. The research conducted for this thesis has found that the forced spreading mechanism can be linked to the change in contact angle over an oscillation cycle. Over an oscillation period the temporal contact angle will spend more time in the advancing or receding segment depending on the direction of spreading. Consequently, this single oscillation period effect can result in droplet spreading over hundreds or thousands of oscillation cycles. The connection between the amplitude and the degree of spreading is via the oscillation mode. The behaviour of spreading changes when the droplet reaches larger accelerations. Distinct regions are defined each having different degrees of spreading. Moreover, the work conducted for this thesis has found that a droplet experiencing extremely large oscillations can spread so much that the drop can exceed its hysteretic limits. This mechanism can compel multiple droplets to evenly spread over a desired area and, subsequently, aid imaging of those drops. This thesis aims to highlight the prospective advantages that audible frequency actuation has over ultrasonic methods. These benefits include simpler instrumentation, higher transmission of particles, negligible temperature variation and synchronised manipulation of multiple samples
Ultrasonic manipulation of microparticles and cells using microfluidic devices
No full textCritical to the development of lab-on-a-chip (LOC) devices is the ability to accurately manipulate microparticles and cells within microfluidic volumes. In real fluid samples, the analyte of interest usually coexists in low concentration amongst a myriad of other constituents, resulting in the need for pre-analytical preparation procedures. Consequently, much research attention has been directed towards concentrating and/or isolating the analyte of interest from the other constituents within microfluidic volumes. The central theme of this thesis is the ultrasonic manipulation of particles and cells within microfluidic systems. Acoustically driven mechanisms for particle and cell manipulation are particularly advantageous as these techniques generally exhibit high throughput, have negligible physiological effects on cells, and are highly portable. Comprising both experimental and theoretical investigations, the studies presented herein focus on the selective concentration and isolation of one particle type from another. Both bulk acoustic wave (BAW) and surface acoustic wave (SAW) devices provide physical platforms for the microfluidic manipulation techniques. Specifically, three related studies are included: (1) selective particle concentration and isolation within a droplet, (2) particle and cell clustering at air–liquid interfaces, and (3) selective particle trapping using oscillating bubbles. These studies illustrate the intricate interplay of physics between fluid drag and acoustic forcing on the particles, where parameters such as frequency, particle size and device geometry have been exploited to achieve such results. Furthermore, these findings demonstrate the possibility and benefits of using acoustic actuation methods as a platform for microfluidic LOC devices
Applied mechanics and bio-microfluidic applications for open microfluidic systems
No full textMicrofluidics is attractive in many aspects and advancement of technology on these micron-scales have led to the development of devices often used in industries such as clinical and forensic analysis; micro-reaction engineering; surface patterning; and optical engineering. Despite its popularity, traditional microfluidic applications however, are known to have large dead volume; awkward chip-to-world interfaces; difficulty in exchanging solutions; and limited parallelization. Recent progresses in open microfluidic systems have shown great potential in addressing the aforementioned limitations. The aim of this thesis is to expand our understanding regarding fluid behaviour and interaction in the micro-domain scale of an open environment. Knowledge obtained through these studies could then be implemented in developing systems involving microfluidic components and bio-microfluidic applications. As a prelude to the main body of work, a basic theoretical framework on the background of microfluidics and the physics of the micro-scale is presented. The research can be divided into two major components, Part I: Open Microchannels and Part II: Microdroplets. These components were then further sub-categorized according to their applications including microfluidic pumping; mixing; liquid transfer; cell lysis; and concentration gradient generation. In all these, an open environment allowing for external interaction and manipulation was implemented. In Part I, flows on open channels and films was investigated. The open structures include a straight open channel defined by a narrow strip of solid surface and a wider structure allowing for multiple inputs and outputs. Computational models were also developed for fluid flow and the findings used to describe the factors affecting the stability of the system in both structures. The system can be seen as either a self-contained open fluidic device, or an open section in an otherwise enclosed system. Following on, the mixing mechanism of a Y-junction open raised channel was examined. The open nature of the channel employed allowed introduction of external shear stresses on the interfacial surface to aid in the mixing process, while maintaining the simplicity of the system as a whole. This mode of mixing provides a versatile platform where alterations can be made to the open system to accommodate mixing without the added complexities. In Part II, investigation was first carried out on two different mechanisms of vertical liquid transfer. The first is through the formation and detachment of a liquid bridge and the second is through the liquid jet formed upon rupture of an encapsulated bubble within a microdroplet. Both mechanisms demonstrated selective transfer of discrete volumes of fluid, a process that will prove useful in many droplet-based microfluidic applications. From the results gathered, the role of the bubble in inducing cell lysis in a controlled and repeatable environment was explored. The fluid jet was then presented as a method capable of causing effective 100% cell lysis of a droplet of suspended cells. Apart from that, a method using microdroplets administered on a planar surface to produce a gradient of droplet concentrations over an array of open wells is presented. The system was tailored to generate concentration gradients in a close quantitative agreement to a two-fold dilution system akin to routine pipetting operations. The findings presented in this thesis are unique in their nature as the methods and applications demonstrated were able to extract the advantages of open microfluidics. Benefits include and are not limited to minimal fabrication and consequently lower production costs involved; small sample volume requirements; selectivity; rapid operation time; and greater control. It is hoped that these results would promote the use of open microfluidics and encourage further exploration of this topic in the future
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