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Microfluidics is both a science and a technology offering great and perhaps even revolutionary capabilities to impact the society in the future. However, due to the scaling effects there are unknown phenomena and technology barriers about fluidics in microchannel, material properties in microscale and interactions with fluids are still missing. A systematic investigation has been performed aiming to develop "A Customer Programmable Microfluidic System". This innovative Polydimethylsiloxane (PDMS)-based microfluidic system provides a bio-compatible platform for bio-analysis systems such as Lab-on-a-chip, micro-total-analysis system and biosensors as well as the applications such as micromirrors. The system consists of an array of microfluidic devices and each device containing a multilayer microvalve. The microvalve uses a thermal pneumatic actuation method to switch and/or control the fluid flow in the integrated microchannels. It provides a means to isolate samples of interest and channel them from one location of the system to another based on needs of realizing the customers' desired functions. Along with the fluid flow control properties, the system was developed and tested as an array of micromirrors. An aluminum layer is embedded into the PDMS membrane. The metal was patterned as a network to increase the reflectivity of the membrane, which inherits the deformation of the membrane as a mirror. The deformable mirror is a key element in the adaptive optics. The proposed system utilizes the extraordinary flexibility of PDMS and the addressable control to manipulate the phase of a propagating optical wave front, which in turn can increase the performance of the adaptive optics. Polydimethylsiloxane (PDMS) has been widely used in microfabrication for microfluidic systems. However, few attentions were paid in the past to mechanical properties of PDMS. Importantly there is no report on influences of microfabrication processes which normally involve chemical reactors and biologically reaction processes. A comprehensive study was made in this work to study fundamental issues such as scaling law effects on PDMS properties, chemical emersion and temperature effects on mechanical properties of PDMS, PDMS compositions and resultant properties, as well as bonding strength, etc. Results achieved from this work will provide foundation of future developments of microfluidics utilizing PDMS.

The objective of this research is to develop a three-dimensional (3-D) microfluidic/ electronic interface system for sustaining and monitoring 3-D neuronal networks. This research work is divided into two parts. One is the development of a 3-D multi-electrode array (MEA) with integrated microfluidic channels. The other is a microneedle array with embedded microelectrodes and microfluidic channels. The 3-D MEA is composed of three elements that are essential for the development and monitoring of 3-D cultures of neurons. These components consist of scaffolds for cellular growth and structural stability, microfluidic channels for cell maintenance and chemical stimulation, and electrodes for electrical stimulation and recording. Two kinds of scaffold structures have been fabricated. The first scaffolding scheme employs a double exposure technique that embeds SU-8 towers into an SU-8 substrate. The second scaffolding mechanism introduces interconnects between towers for the purpose of mechanically supporting 3-D cell cultures and facilitating 3-D synaptic connections. Microfluidic channels are combined for fine control of the cellular microenvironment by means of diffusive and convective fluidic processes. Hollow towers with three-layer side ports were developed by using double exposure techniques and excimer laser ablation. The electrodes are combined into an integrated system that is capable of monitoring electrical activities and the cellular impedances of neurons which are attached to the electrodes. The second part of this research is to fabricate a microneedle array for monitoring brain slices, which will directly detect electrical signals from living brain slices. Although the microneedle array is targeting different 3-D neuronal networks, it also has three components and the fabrication steps are the same as those for the 3-D MEA. To generate the sharp tip, isotropic reactive ion etching (RIE) is performed on tapered SU-8 towers. High aspect ratio tower structures can be effectively generated with SU-8 and tapered shapes are created by backside exposure. The resulting systems will enable a new field of neurobiological research, in which the collective properties of 3-D neuronal circuits can be observed and manipulated with unprecedented detail and precision, and at a level of control not possible in living animals.

This study develops and demonstrates a microfluidic module for investigating the mechanism of inorganic fouling caused by the precipitation of calcium sulfate (CaSO4) on nanofiltration membranes. The developed microfluidic module enables sensitive system responses, rapid detection and real time observation of inorganic fouling commonly encountered in water treatment industries. For this development, CaSO4 is selected as the model salt due to its unique fouling characteristics. The effect of the operating conditions, such as pressure and permeate flux, was on the fouling behavior is investigated. A plate-frame type microfluidic chip was fabricated and employed in a dead-end filtration mode for constant-flux fouling experiments. The nanofiltration chip module has a dimension of 50 mm ¡Ñ 25 mm ¡Ñ 12 mm. It is consisted of a polymeric nanofilter, a pressure acquisition unit, a C.C.D., and micro electrodes on the nanofilter for investigating the relationships among trans-membrane pressure, conductivity on membrane surface and permeate fluxes. With the microfluidic system, real-time concentration polarization, bulk nucleation of CaSO4 and surface crystal accumulation were observed in terms of the variations of pressure and conductivity on membrane surface, which were verified with scanning electron micrographs to confirm the corresponding fouling stage. It is found that membrane surface conductivity increases with trans-membrane pressure before bulk crystallization of CaSO4, then slightly decreases after the formation of bulk nuclei due to the removal of solute in the aqueous phase. The conductivity remains relatively constant during cake formation stage while trans-membrane pressure steadily increases. This study successfully integrates microfluidic technology with pressure and electrical measurements for detecting the dynamic transition during CaSO4 fouling, and reports for the first time the experimental measurement of the initiation of inorganic cake formation.

Human organoids have potential to revolutionize in vitro disease modeling by providing multicellular architecture and functional that are similar to those in vivo. Nonetheless, organoid-based, high-throughput screening (HTS) of compounds is challenged by lack of easy-to-use fluidic systems that are compatible with relatively large organoids. Therefore, we first fabricated a pillar plate, which was coupled with a complementary deep well plate and a perfusion well plate for static and dynamic culture via injection molding. We established various cell loading methods in hydrogels on the pillar plate. In addition, we investigated the effect of flow on the necrotic core of spheroids in the pillar/perfusion plate. Finally, we developed microarray three-dimensional (3D) bioprinting technology using the pillar and perfusion plates for human organoid culture and analysis. High-precision, high-throughput stem cell printing and encapsulation techniques were demonstrated on a pillar plate, which was coupled with a complementary deep well plate and a perfusion well plate for static and dynamic organoid culture. Bioprinted cells and spheroids in hydrogels were differentiated into organoids for in situ functional assays. The pillar/perfusion plates are compatible with standard 384-well plates and HTS equipment, and thus may be easily adopted in current drug discovery efforts.

Capillary electrophoresis chip has gradually ripe along with the development of MEMS technology. However, such these electrophoresis chips was design closed-channel form whose process including the micro-channel forming and chip bonding and so on, so the cost is higher. In addition, if these chips use repeated will cause some pollution problems such as obstruction or difficult to clean in the closed-channel. Therefore, to fabricate a non-closed microfluidic chip system will resolve the issues above listed. In this study has successful developed a convenient and low-cost thread microfluidic system, the thin polyester thread is instead of the traditional closed separation channel. And to avoid the cross contaminations that the separation channel can free replace a new electrophoresis separation channel by the roller equipment. Thread microfluidic systems can take advantage of capillary action to move, as a disposable chromatography flow channel, and the electric field is applied to this system for electrophoresis separation and electrochemical detection in the backend. This research develop an novel process technology, the hot embossing technology shape from concave embossing and metal coating procedure in PMMA, the salient pillow-electrode structure has be produced in PMMA board, the salient electrode structure set up the polyester fiber thread, the polyester fiber thread is as the electrophoresis separation channel, and electrochemical detect samples in back-end. In this study take plasma treatment to improve wettability and surface roughness of the polyester fiber thread, in order to improve the operational effectiveness of the thread microfluidic systems. The cyclic voltammetry measure potassium ferricyanide samples and the results showed that the performance of thread microfluidic system significantly increase after the plasma treatment, the measuring current value is 10 times greater than without the plasma treatment, and the estimated detection limit of potassium ferricyanide is around 6.25 £gM in the plasma treatment one. In addition, the thread microfluidic devices with plasma treatment has successful separation and detection the mixing samples of 0.3 mM chlorine, bromine and iodine ions, and the signal of the S/N ratio is 6 times higher than the without plasma treatment one, and the number of theoretical plates of electrophoresis separation also enhance to 28% in the plasma treatment one. In addition, in order to further enhance the detection sensitivity of the thread microfluidic systems, the study design and fabricate the concave-shaped three-dimensional electrode structure, and to achieve greater contact area between thread and the electrode. Thread microfluidic system with plasma treatment detect in concave-shaped three-dimensional electrode and flat electrode respectively, the results showed that concave-shaped electrodes in the potassium ferricyanide detection limit that measured current value is 10 times greater than flat electrode, and a mixture of dopamine and catechol sample are electrophoresis separated that concave-shaped 3D electrode whose measured S/N ratio is 5 times higher than flat electrode, and the number of theoretical plates is 1.5 times higher than the flat electrode. This study develops a novel thread microfluidic system that will provide a simple process and low-cost, and can solve the shortcomings of conventional closed-channel electrophoresis chips. In future, in this study develop the thread microfluidic system architecture will have contribute for fast electrophoresis separation and detection.

The miniaturization of chemical and biological sensors has received considerable attention in recent years for medical diagnostics, environmental monitoring, pharmaceutical screening, military applications, etc. One interesting area of development in microfluidic system is detecting dielectric properties of MUT (Material Under Test) using IDC (Interdigital Capacitor) electrodes. The IDC chemical sensor has been investigated by many researchers because they are cheap to manufacture and can be easily integrated with other sensing components and signal processing electronics. This dissertation presents the design, fabrication, and testing of an IDC (interdigital capacitor) electrode sensor for a fluid property monitoring component that can be integrated into a microfluidic system. One practical point of this research is the analytical evaluation of the interdigital electrode capacitance for the detection of conductivity and permittivity of the aqueous solutions, which is not apparently analyzed in other chemical sensor applications. In addition, a new noble methodology of remotely accessing the IDC sensor by wireless inductive coupling similar to EAS (Electronic Article Surveillance) tags is presented. / text

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The diploma thesis deals with measuring pressure in microfluidic systems. The theoretical part of the work is devoted to microfluidics, pressure in liquids, pressure measurement, distribution of pressure sensors, and their specifications. Then follows the hardware and software solution of the measuring system for measuring the pressure in the microfluidic system using microprocessor technology. The practical part covers the hardware and software implementation of the measuring system.