25 research outputs found
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:<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
Microfluidic batch process platforms for lab on a chip applications using acoustofluidics
No full textThe inception of microfluidics, utilising borrowed technology from the microelectronics industry, has enabled a wide range of applications in various fields ranging from engineering to biochemistry. Advancements in terms of microfabrication and micro-scale fluid control has led to the rise of Lab on a Chip. These systems aim to replicate the results of conventional laboratory procedures in miniaturised systems. Lab on a Chip systems, offer immense potential for a wide range of diagnostic and therapeutic tools. Furthermore, when sample volumes are extremely scarce, rendering conventional diagnostic methods and continuous flow micro fluidic techniques impractical, other methods need to be established. To this end, microfluidic batch process systems offers a solution, although relatively underdeveloped. Batch process systems are a single or multi-stage process in which a certain quantity of inputs are processed to achieve the desired outcome one sample set at a time. It should be noted, as these systems operate at a much smaller scale, some conventional forcing techniques, such as centrifugation are no longer practical. Therefore, different actuation mechanisms need to be developed to replicate the results of their larger scale conventional laboratory and continuous flow counterparts. Acoustic excitation is a potential actuation mechanism which enables the handling of micron-sized particles and cells. Here, we look at different acoustic excitation methods and the underlying principles that allow acoustofluidic systems to manipulate particles for sample preparation and as point- of-care diagnostic tools. In this thesis, three systems are developed to perform particle manipulation both in liquid and air based batch process systems. Firstly, an open bulk acoustic wave system, allowing the ease of external gripping mechanisms is developed to perform size-deterministic separation of 3 μm and 10 μm particles. The task of particle separation is further explored using a different underlying principle and actuation method, and separation of 3.1 μm and 5.1 μm is achieved utilising surface acoustic waves, a different excitation mechanism that enables operation at relatively higher frequencies. Finally, optimisation of an acoustic resonator in air is carried out and serves as a building block for a complete 3-dimensional (3D) acoustic trapping microgripper to be used for individualised particle transport and inspection. Throughout this thesis, a case is made for acoustic based methods to be utilised in developing essential batch process systems for sample preparation and diagnostics
Acoustic tweezing of particles using decaying opposing travelling surface acoustic waves (DOTSAW)
No full textSurface acoustic waves offer a versatile and biocompatible method of manipulating the location of suspended particles or cells within microfluidic systems. The most common approach uses the interference of identical frequency, counter propagating travelling waves to generate a standing surface acoustic wave, in which particles migrate a distance less than half the acoustic wavelength to their nearest pressure node. The result is the formation of a periodic pattern of particles. Subsequent displacement of this pattern, the prerequisite for tweezing, can be achieved by translation of the standing wave, and with it the pressure nodes; this requires changing either the frequency of the pair of waves, or their relative phase. Here, in contrast, we examine the use of two counterpropagating traveling waves of different frequency. The non-linearity of the acoustic forces used to manipulate particles, means that a small frequency difference between the two waves creates a substantially different force field, which offers significant advantages. Firstly, this approach creates a much longer range force field, in which migration takes place across multiple wavelengths, and causes particles to be gathered together in a single trapping site. Secondly, the location of this single trapping site can be controlled by the relative amplitude of the two waves, requiring simply an attenuation of one of the electrical drive signals. Using this approach, we show that by controlling the powers of the opposing incoherent waves, 5 μm particles can be migrated laterally across a fluid flow to defined locations with an accuracy of ±10 μm.</p
Trapping and patterning of large particles and cells in a 1D ultrasonic standing wave
No full textThe use of ultrasound for trapping and patterning particles or cells in microfluidic systems is usually confined to particles which are considerably smaller than the acoustic wavelength. In this regime, the primary forces result in particle clustering at certain locations in the sound field, whilst secondary forces, those arising due to particle-particle interaction forces, assist this clustering process. Using a wavelength closer to the size of the particles allows one particle to be held at each primary force minimum. However, to achieve this, the influence of secondary forces needs to be carefully studied, as inter-particle attraction is highly undesirable. Here, we study the effect of particle size and material properties on both the primary and secondary acoustic forces as the particle diameter is increased towards the wavelength of the 1-dimensional axisymmetric ultrasonic field. We show that the resonance frequencies of the solid sphere have an important role in the resulting secondary forces which leads to a narrow band of frequencies that allow the patterning of large particles in a 1-D array. Knowledge regarding the naturally existent secondary forces would allow for system designs enabling single cell studies to be conducted in a biologically safe manner.</p
Cell adhesion, morphology and metabolism variation via acoustic exposure within microfluidic cell handling systems
No full textAcoustic fields are capable of manipulating biological samples contained within the enclosed and highly controlled environment of a microfluidic chip in a versatile manner. The use of acoustic streaming to alter fluid flows and radiation forces to control cell locations has important clinical and life science applications. While there have been significant advances in the fundamental implementation of these acoustic mechanisms, there is a considerable lack of understanding of the associated biological effects on cells. Typically a single, simple viability assay is used to demonstrate a high proportion of living cells. However, the findings of this study demonstrate that acoustic exposure can inhibit cell attachment, decrease cell spreading, and most intriguingly increase cellular metabolic activity, all without any impact upon viability rates. This has important implications by showing that mortality studies alone are inadequate for the assessment of biocompatibility, but further demonstrates that physical manipulation of cells can also be used to influence their biological activity.</p
Huygens-Fresnel acoustic interference and the development of robust time-averaged patterns from travelling surface acoustic waves
No full textPeriodic pattern generation using time-averaged acoustic forces conventionally requires the intersection of counterpropagating wave fields, where suspended micro-objects in a microfluidic system collect along force potential minimizing nodal or antinodal lines. Whereas this effect typically requires either multiple transducer elements or whole channel resonance, we report the generation of scalable periodic patterning positions without either of these conditions. A single propagating surface acoustic wave interacts with the proximal channel wall to produce a knife-edge effect according to the Huygens-Fresnel principle, where these cylindrically propagating waves interfere with classical wave fronts emanating from the substrate. We simulate these conditions and describe a model that accurately predicts the lateral spacing of these positions in a robust and novel approach to acoustic patterning.</p
Surface acoustic wave enabled pipette on a chip
No full textMono-disperse droplet formation in microfluidic devices allows the rapid production of thousands of identical droplets and has enabled a wide range of chemical and biological studies through repeat tests performed at pico-to-nanoliter volume samples. However, it is exactly this efficiency of production which has hindered the ability to carefully control the location and quantity of the distribution of various samples on a chip – the key requirement for replicating micro well plate based high throughput screening in vastly reduced volumetric scales. To address this need, here, we present a programmable microfluidic chip capable of pipetting samples from mobile droplets with high accuracy using a non-contact approach. Pipette on a chip (PoaCH) system selectively ejects (pipettes) part of a droplet into a customizable reaction chamber using surface acoustic waves (SAWs). Droplet pipetting is shown to range from as low as 150 pL up to 850 pL with precision down to tens of picoliters. PoaCH offers ease of integration with existing lab on a chip systems as well as a robust and contamination-free droplet manipulation technique in closed microchannels enabling potential implementation in screening and other studies
The importance of travelling wave components in standing surface acoustic wave (SSAW) systems
No full textThe use of ultrasonic fields to manipulate particles, cells and droplets has become widespread in lab on a chip (LOC) systems. There are two dominant actuation methods, the use of bulk acoustic waves (BAW) or surface acoustic waves (SAW). The development of BAW actuated systems have been underpinned by a robust understanding of the link between the ultrasonic field and forces which can be generated. In this work, we examine this link for standing surface acoustic waves (SSAW) comparing the relative strengths of streaming induced drag and acoustic radiation forces on suspended particles. To achieve this we have employed boundary conditions which accurately capture the travelling wave components of the pseudo-standing wave field, describe the key features of the acoustic radiation force fields and the acoustic streaming fields which can be generated, and finally we show that the relative importance of these two mechanisms is spatially dependant within a fluid chamber. The boundary condition used models the SSAW as two counter-propagating travelling waves, rather than assuming a standing wave directly. This allows the accurate inclusion of energy decay as the SAW couples into the fluid chamber and the resulting travelling wave component. This study shows that this previously neglected complexity of the SAW field is a critical factor in the nature of the resultant streaming field, as it gives rise to strong streaming rolls at the channel walls, which we validate experimentally. These rolls result in spatial variations of the dominant forces which in turn varies particle migration patterns spatially across the fluid domain.</p
