Chemical and rheological aspects of gel formation in the California Mastitis Test

The rheological properties of the CMT gel were analysed. Data are presented to demonstrate that the gel is a non-homogenous, visco-elastic, non-Newtonian fluid with rheopectic, and rheodestructive behaviour. The fundamental chemistry of the CMT is reviewed and a modified theory of gel formation is presented. The implications of the rheological properties and modified theory of gel formation for an automatic sensor are discussed

Analogies between light and matter waves: From laser modes to phase holography

With the creation of the laser in the 1960s, optics research gained a whole new type of coherent, well-behaved light with which to experiment. Later, similar matter was created; first in the form of super-fluids and then Bose-Einstein condensates (BECs).A BEC as a whole behaves in many ways analogous to a monochromatic laser beam; the ultra-cold atoms in a BEC are the matter equivalent of photons in the laser beam. Researchers have built the BEC analogs of a number of optical components, including lenses and beam splitters. The work described in this thesis was inspired by the aim to investigate theoretically BEC analogs of effects known from laser physics and by developing a BEC analog of Fourier holography.After introductions into lasers and BECs (chapter 1) and numerical methods for solving the differential equations governing the behaviour of both light and BECs (chapter 2), this thesis comes in two parts.The first part is concerned with the BEC analogs of the formation of transverse laser modes (chapter 3) and an interferometer for sorting optical vortices (chapter 5), and a non-destructive method of Fourier-transforming a BEC (chapter 4).The second part is about optical holography and optical tweezers. It starts with a review of hologram-design algorithms (chapter 6). Originally inspired by optical Fourier holography, discussions about BEC Fourier holography counter-inspired a new algorithm for optical Fourier holography, namely a Gerchberg-Saxton algorithm for 3-dimensional light shaping (chapter 7). My work on the improvement of hologram-calculation software for optical tweezers is described in chapter 8

Optically controlled grippers for manipulating micron-sized particles

We report the development of a joystick controlled gripper for the real-time manipulation of micron-sized objects, driven using holographic optical tweezers (HOTs). The gripper consists of an arrangement of four silica beads, located in optical traps, which can be positioned and scaled in order to trap an object indirectly. The joystick can be used to grasp, move (lateral or axial), and change the orientation of the target object. The ability to trap objects indirectly allows us to demonstrate the manipulation of a strongly scattering micron-sized metallic particle

Deformability-induced lift force in spiral microchannels for cell separation

Cell sorting and isolation from a heterogeneous mixture is a crucial task in many aspects of cell biology, biotechnology and medicine. Recently, there has been an interest in methods allowing cell separation upon their intrinsic properties such as cell size and deformability, without the need for use of biochemical labels. Inertial focusing in spiral microchannels has been recognised as an attractive approach for high-throughput cell sorting for myriad point of care and clinical diagnostics. Particles of different sizes interact to a different degree with the fluid flow pattern generated within the spiral microchannel and that leads to particles ordering and separation based on size. However, the deformable nature of cells adds complexity to their ordering within the spiral channels. Herein, an additional force, deformability-induced lift force (FD), involved in the cell focusing mechanism within spiral microchannels has been identified, investigated and reported for the first time, using a cellular deformability model (where the deformability of cells is gradually altered using chemical treatments). Using this model, we demonstrated that spiral microchannels are capable of separating cells of the same size but different deformability properties, extending the capability of the previous method. We have developed a unique label-free approach for deformability-based purification through coupling the effect of FD with inertial focusing in spiral microchannels. This microfluidic-based purification strategy, free of the modifying immuno-labels, allowing cell processing at a large scale (millions of cells per min and mls of medium per minute), up to high purities and separation efficiency and without compromising cell quality

Simulated holographic three-dimensional intensity shaping of evanescent-wave fields

The size of bright structures in traveling-wave light fields is limited by diffraction. This in turn limits a number of technologies, for example, optical trapping. One way to beat the diffraction limit is to use evanescent waves instead of traveling waves. Here we apply a holographic algorithm, direct search, to the shaping of complex evanescent-wave fields. We simulate three-dimensional intensity shaping of evanescent-wave fields using this approach, and we investigate some of its limitations. (c) 2008 Optical Society of America.</p

Fourier transforming a trapped Bose-Einstein condensate by waiting a quarter of the trap period: simulation and applications

We investigate the property of isotropic harmonic traps to Fourier transform a weakly interacting Bose–Einstein condensate (BEC) every quarter of a trap period. We solve the Gross–Pitaevskii equation numerically to investigate the time evolution of interacting BECs in the context of the Fourier transform, and we suggest potential applications

Microconstriction Arrays for High-Throughput Quantitative Measurements of Cell Mechanical Properties

AbstractWe describe a method for quantifying the mechanical properties of cells in suspension with a microfluidic device consisting of a parallel array of micron-sized constrictions. Using a high-speed charge-coupled device camera, we measure the flow speed, cell deformation, and entry time into the constrictions of several hundred cells per minute during their passage through the device. From the flow speed and the occupation state of the microconstriction array with cells, the driving pressure across each constriction is continuously computed. Cell entry times into microconstrictions decrease with increased driving pressure and decreased cell size according to a power law. From this power-law relationship, the cell elasticity and fluidity can be estimated. When cells are treated with drugs that depolymerize or stabilize the cytoskeleton or the nucleus, elasticity and fluidity data from all treatments collapse onto a master curve. Power-law rheology and collapse onto a master curve are predicted by the theory of soft glassy materials and have been previously shown to describe the mechanical behavior of cells adhering to a substrate. Our finding that this theory also applies to cells in suspension provides the foundation for a quantitative high-throughput measurement of cell mechanical properties with microfluidic devices

Purifying stem cell-derived red blood cells:a high-throughput label-free downstream processing strategy based on microfluidic spiral inertial separation and membrane filtration

Cell-based therapeutics, such as in vitro manufactured red blood cells (mRBC), are different to traditional biopharmaceutical products (the final product being the cells themselves as opposed to biological molecules such as proteins) and that presents a challenge of developing new robust and economically feasible manufacturing processes, especially for sample purification. Current purification technologies have limited throughput, rely on expensive fluorescent or magnetic immuno-labelling with a significant (up to 70%) cell loss and quality impairment. To address this challenge, previously characterised mechanical properties of umbilical cord blood CD34+ cells undergoing in vitro erythropoiesis were used to develop a mRBC purification strategy. The approach consists of two main stages: (1) a microfluidic separation using inertial focusing for deformability-based sorting of enucleated cells (mRBC) from nuclei and nucleated cells resulting in 70% purity and (2) membrane filtration to enhance the purity to 99%. Herein, we propose a new route for high-throughput (processing millions of cells /min and mls of medium /min) purification process for mRBC, leading to high mRBC purity while maintaining cells integrity and no alterations in their global gene expression profile. Further adaption of this separation approach offers a potential route for processing of a wide range of cellular products