Microfluidics refers to devices and methods for controlling and manipulating fluid flows at length scales less than a millimeter. Miniaturization of a laboratory to a small device, usually termed as lab-on-a-chip, is an advanced technology that integrates a microfluidic system including channels, mixers, reservoirs, pumps and valves on a micro scale chip and can manipulate very small sample volumes of fluids. While several flow control concepts for microfluidic devices have been developed to date, here flow control concepts based on thermally responsive polymer solutions are presented. In particular, flow control concepts base on the thermally triggered reversible phase change of aqueous solutions of the polymer Pluronic will be discussed. Selective heating of small regions of microfluidic channels, which leads to localized gel formation in these channels and reversible channel blockage, will be used to control a membrane valve that controls flow in a separate channel. This new technology will allow generating inexpensive portable bioanalysis tools where microvalve actuation occurs simply through heaters at a constant pressure source without a need for large external pressure control systems as is currently the case. Furthermore, a concept for controlled cross-channel transport of particles and potentially cells is presented that relies on the continuous regeneration of a gel wall at the diffusive interface of two co-streaming fluids in a microfluidic channel.

A computer-controlled microfluidic extensional flow device is developed for trapping and manipulating micron-sized hard and soft particles. The extensional flow is generated in a diamond-shaped cross-slot that has each corner connected to a pressure-controlled liquid reservoir. By employing an imaging-based control algorithm, a particle can be made to move to an arbitrary position within the slot by adjusting the reservoir pressures and hence the fluid flow rates into/out of the slot. Thus, a soft particle can be trapped indefinitely at a point within the slot, and a known hydrodynamic force can be applied to study the dynamics of stretching and breakup of the particle. Alternatively, adhesion or coalescence dynamics of soft particles may be investigated by effecting a controlled collision between two particles. The device is validated by measuring the low interfacial tension of a compatibilized oil-water interface.

No description available.

No description available.

A computer-controlled microfluidic extensional flow device is developed for trapping and manipulating micron-sized hard and soft particles. The extensional flow is generated in a diamond-shaped cross-slot that has each corner connected to a pressure-controlled liquid reservoir. By employing an imaging-based control algorithm, a particle can be made to move to an arbitrary position within the slot by adjusting the reservoir pressures and hence the fluid flow rates into/out of the slot. Thus, a soft particle can be trapped indefinitely at a point within the slot, and a known hydrodynamic force can be applied to study the dynamics of stretching and breakup of the particle. Alternatively, adhesion or coalescence dynamics of soft particles may be investigated by effecting a controlled collision between two particles. The device is validated by measuring the low interfacial tension of a compatibilized oil-water interface.

Thesis (Ph. D.)--Auburn University, 2009. / Abstract. Vita. Includes bibliographical references (p. 168-174).

Thesis--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 78-81).

Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 61-63). Also available on the World Wide Web.

Thesis (M.Sc.Eng.) PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / Silk fibers from arthropods possess several favorable properties for biomedical applications, including high mechanical strength and biocompatibility. However, the majority of silk fiber production is currently limited to manipulation of cocoons from the Bombyxmori silkworm. The efficiency of the process can be increased by dissolving waste silk threads and using artificial spinning techniques to spin the proteins back into usable fibers. Once an artificial spinning technique has been perfected, it may be possible to use similar designs to spin recombinant silk proteins into threads with more favorable mechanical properties. The first step towards customizable silk is to artificially spin silk protein into fibers with comparable properties to naturally-derived silk threads. Current microfluidic devices are limited to spinning B. mori silk into weak, poorly-formed fibers. The incorporation of silk gland-like ion gradients and high shear stress into current and novel microfluidic devices is theorized to improve mechanical properties of resultant spun silk. To this end, ion gradients were added to the current microfluidic device. In addition, a novel microfluidic device was developed to increase shear stress. After investigating the individual effects of ion gradients and shear stress on the silk spinning process, an integrated microfluidic device was designed to investigate the combined effects. Computational models of the flow within each microfluidic device were generated and used to predict biomimetic design parameters. Measurements of fiber diameter and pH within the microfluidic devices were collected to verify the accuracy of the computational models. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and mechanical testing measurements were collected to characterize and compare resultant fibers. From these results, relationships were found between the incorporation of ion gradients and shear stress into the spinning process and the properties of the fibers produced. / 2031-01-01

Micro-devices are developed for uses in targeted drug delivery and microscale manipulation. Here we numerically and analytically study two promising devices in early stages of development. Firstly, we study Armoured Microbubbles (AMBs) which can self-propel as artificial microswimmers or facilitate microfluidic mixing in a channel when held stationary on a wall. Secondly, we study an artificial cilium, which due to its unique design, when placed in an array, easily produces a metachronal wave for fluid transportation. The Armoured Microbubble was designed by our experimental collaborators (group of Philippe Marmottant, University Grenoble Alpes) and consists of a partial hollow sphere, inside which a bubble is caught. Under ultrasound the bubble oscillates, generating a streaming flow in the surrounding fluid and producing a net force. Motivated by the AMB but considering initially a general setup, using matched asymptotic expansions we calculate the streaming flow around a spherical body undergoing arbitrary, but known, small-amplitude surface shape oscillations. We then specialise back to the AMB and consider its excitation under ultrasound, using a potential flow model with mixed boundary conditions, to identify the resonant frequencies and mode shapes, including the dependence of the resonance on the AMB shape parameters. Returning to our general streaming model, we applied the mixed boundary conditions directly to this model, calculating the streaming around the AMB, in good agreement with experiments. Using hydrodynamic images and linear superposition, this model was extended to incorporate one wall, and AMB compounds. We then study the streaming flows generated by arrays of AMBs in confined channels, by modelling each AMB as its leading order behaviour (with corrections where required) and superposing the individual flow fields of all the AMBs. We identified the importance of two confining walls on the streaming flow around the array, and compared these flows to experiments in five cases. Motivated by this setup, we theoretically considered the extension of a two fluid interface passing through an AMB array to quickly identify good AMB arrays for mixing. We then studied the second artificial micro-device: an artificial cilium. Tsumori et. al. produced a cilium of PDMS containing aligned ferromagnetic filings, which beat under a rotating magnetic field. We modelled a similar cilium but assumed paramagnetic filings, using a force model balancing elastic, magnetic and hydrodynamic forces identifying the cilium beat pattern. This agreed with our equilibrium model and asymptotic analysis. We then successfully identified that the cilium applies the most force to the surrounding fluid at an intermediate value of the two dimensionless numbers quantifying the dynamics.