Rapid Prototyping of Microfluidic Devices:Realization of Magnetic Micropumps, Fuel Cells and Protein Preconcentrators

With the growing importance of miniaturized energy applications and the development of micro Total Analysis Systems (μTAS), we have realized microfluidic devices, namely, magnetic micropumps, microfluidic fuel cells and membrane-based protein preconcentrators, all having high application potential in future. The choice of rapid prototyping microfabrication technologies and the selection of affordable materials are important aspects, when thinking of commercialization. Thus, we have employed powder blasting, polymer molding and assembly technologies during devices fabrication throughout the thesis. The first type of microfluidic device that we present is a poly(methyl methacrylate) (PMMA) ball-valve micropump with two different designs of the electromagnetic actuator, as optimized by the finite element method. The integration of a permanent magnet in a flexible polydimethylsiloxane (PDMS) membrane, which is clamped into PMMA structure, is proposed for providing a large stroke of the pumping membrane, making the micropump bubble-tolerant and self-priming Focusing on low power consumption for μTAS integration, another type of magnetic micropump with active valves is realized. It consists of a microfluidic chamber structure in glass that is assembled with a PDMS sheet, which comprises two valving membranes and a central actuation membrane, having each an integrated permanent magnet that is peristaltically actuated by a rotating arc-shaped permanent magnets assembly. A lumped circuit model is developed to predict and describe the frequency-dependent flow rate behavior for this type of pump. Powder blasting and PDMS molding rapid prototyping technologies are employed for realization of these two types of micropumps. Fuel cells with fluid delivery and removal options, having chemical reaction sites and electrode structures that can be realized in a microfluidic format, have high potential for applications. Therefore, microfluidic direct methanol fuel cells with embedded ion- permselective medium are studied and such type of fuel cell is realized by integrating a narrow Nafion strip in a molded elastomeric structure. A mechanical clamping assembly technology enables leakage-free operation and stable performance. The characterization reveals its output power density, using H2O2-based oxidant, is among the high-performance direct methanol fuel cells in microscale. Re-using the technology of the fuel cell chip, with its particular ion-permselective Nafion membrane and assembly method, we also have developed a protein preconcentrator with high purification performance. Our device can preconcentrate negatively charged biomolecules located at the anodic compartment side of the Nafion strip within only a few minutes with a high preconcentration factor. Moreover, a complex microfluidic finite element model is proposed to study and understand the physics of the preconcentration effect. Finally, we conclude the thesis with an outlook on future developments based on our work of the project and on the assembly technologies for microfluidic device integration

Towards rapid 3D direct manufacture of biomechanical microstructures

The field of stereolithography has developed rapidly over the last 20 years, and commercially available systems currently have sufficient resolution for use in microengineering applications. However, they have not as yet been fully exploited in this field. This thesis investigates the possible microengineering applications of microstereolithography systems, specifically in the areas of active microfluidic devices and microneedles. The fields of micropumps and microvalves, stereolithography and microneedles are reviewed, and a variety of test builds were fabricated using the EnvisionTEC Perfactory Mini Multi-Lens stereolithography system in order to define its capabilities. A number of microneedle geometries were considered. This number was narrowed down using finite element modelling, before another simulation was used to optimise these structures. 9 × 9 arrays of 400 μm tall, 300 μm base diameter microneedles were subjected to mechanical testing. Per needle failure forces of 0.263 and 0.243 N were recorded for the selected geometries, stepped cone and inverted trumpet. The 90 μm needle tips were subjected to between 30 and 32 MPa of pressure at their failure point - more than 10 times the required pressure to puncture average human skin. A range of monolithic micropumps were produced with integrated 4 mm diameter single-layer 70 μm-thick membranes used as the basis for a reciprocating displacement operating principle. The membranes were tested using an oscillating pneumatic actuation, and were found reliable (>1,000,000 cycles) up to 2.0 PSIG. Pneumatic single-membrane nozzle/diffuser rectified devices produced flow rates of up to 1,000 μl/min with backpressures of up to 375 Pa. Another device rectified using active membrane valves was found to self-prime, and produced backpressures of up to 4.9 kPa. These devices and structures show great promise for inclusion in complex, fully integrated and active microfluidic systems fabricated using microstereolithography alone, with implications for both cost of manufacture and lead time

Implantable Microsystem Technologies For Nanoliter-Resolution Inner Ear Drug Delivery

Advances in protective and restorative biotherapies have created new opportunities to use site-directed, programmable drug delivery systems to treat auditory and vestibular disorders. Successful therapy development that leverages the transgenic, knock-in, and knock-out variants of mouse models of human disease requires advanced microsystems specifically designed to function with nanoliter precision and with system volumes suitable for implantation. The present work demonstrates a novel biocompatible, implantable, and scalable microsystem consisted of a thermal phase-change peristaltic micropump with wireless control and a refillable reservoir. The micropump is fabricated around a catheter microtubing (250 μm OD, 125 μm ID) that provided a biocompatible leak-free flow path while avoiding complicated microfluidic interconnects. Direct-write micro-scale printing technology was used to build the mechanical components of the pump around the microtubing directly on the back of a printed circuit board assembly. In vitro characterization results indicated nanoliter resolution control over the desired flow rates of 10–100 nL/min by changing the actuation frequency, with negligible deviations in presence of up to 10× greater than physiological backpressures and ±3°C ambient temperature variation. A biocompatibility study was performed to evaluate material suitability for chronic subcutaneous implantation and clinical translational development. A stand-alone, refillable, in-plane, scalable, and fully implantable microreservoir platform was designed and fabricated to be integrated with the micropump. The microreservoir consists two main components: a cavity for storing the drug and a septum for refilling. The cavity membrane is fabricated with thin Parylene-C layers, using a polyethylene glycol (PEG) sacrificial layer. The septum thickness is minimized by pre-compression down to 1 mm. The results of in vitro characterization indicated negligible restoring force for the optimized cavity membrane and thousands of punctures through the septum without leakage. The micropump and microreservoir were integrated into microsystems which were implanted in mice. The microtubing was implanted into the round window membrane niche for infusion of a known ototoxic compound (sodium salicylate) at 50 nL/min for 20 min. Real-time shifts in distortion product otoacoustic emission thresholds and amplitudes were measured during the infusion. The results match with syringe pump gold standard. For the first time a miniature and yet scalable microsystem for inner ear drug delivery was developed, enabling drug discovery opportunities and translation to human

HIGH PERFORMANCE PIEZOELECTRIC MATERIALS AND DEVICES FOR MULTILAYER LOW TEMPERATURE CO-FIRED CERAMIC BASED MICROFLUIDIC SYSTEMS

The incorporation of active piezoelectric elements and fluidic components into micro-electromechanical systems (MEMS) is of great interest for the development of sensors, actuators, and integrated systems used in microfluidics. Low temperature cofired ceramics (LTCC), widely used as electronic packaging materials, offer the possibility of manufacturing highly integrated microfluidic systems with complex 3-D features and various co-firable functional materials in a multilayer module. It would be desirable to integrate high performance lead zirconate titanate (PZT) based ceramics into LTCC-based MEMS using modern thick film and 3-D packaging technologies. The challenges for fabricating functional LTCC/PZT devices are: 1) formulating piezoelectric compositions which have similar sintering conditions to LTCC materials; 2) reducing elemental inter-diffusion between the LTCC package and PZT materials in co-firing process; and 3) developing active piezoelectric layers with desirable electric properties. The goal of present work was to develop low temperature fired PZT-based materials and compatible processing methods which enable integration of piezoelectric elements with LTCC materials and production of high performance integrated multilayer devices for microfluidics. First, the low temperature sintering behavior of piezoelectric ceramics in the solid solution of Pb(Zr0.53,Ti0.47)O3-Sr(K0.25, Nb0.75)O3 (PZT-SKN) with sintering aids has been investigated. 1 wt% LiBiO2 + 1 wt% CuO fluxed PZT-SKN ceramics sintered at 900oC for 1 h exhibited desirable piezoelectric and dielectric properties with a reduction of sintering temperature by 350oC. Next, the fluxed PZT-SKN tapes were successfully laminated and co-fired with LTCC materials to build the hybrid multilayer structures. HL2000/PZT-SKN multilayer ceramics co-fired at 900oC for 0.5 h exhibited the optimal properties with high field d33 piezoelectric coefficient of 356 pm/V. A potential application of the developed LTCC/PZT-SKN multilayer ceramics as a microbalance was demonstrated. The final research focus was the fabrication of an HL2000/PZT-SKN multilayer piezoelectric micropump and the characterization of pumping performance. The measured maximum flow rate and backpressure were 450 μl/min and 1.4 kPa respectively. Use of different microchannel geometries has been studied to improve the pumping performance. It is believed that the high performance multilayer piezoelectric devices implemented in this work will enable the development of highly integrated LTCC-based microfluidic systems for many future applications

Towards rapid 3D direct manufacture of biomechanical microstructures

The field of stereolithography has developed rapidly over the last 20 years, and commercially available systems currently have sufficient resolution for use in microengineering applications. However, they have not as yet been fully exploited in this field. This thesis investigates the possible microengineering applications of microstereolithography systems, specifically in the areas of active microfluidic devices and microneedles. The fields of micropumps and microvalves, stereolithography and microneedles are reviewed, and a variety of test builds were fabricated using the EnvisionTEC Perfactory Mini Multi-Lens stereolithography system in order to define its capabilities. A number of microneedle geometries were considered. This number was narrowed down using finite element modelling, before another simulation was used to optimise these structures. 9 × 9 arrays of 400 μm tall, 300 μm base diameter microneedles were subjected to mechanical testing. Per needle failure forces of 0.263 and 0.243 N were recorded for the selected geometries, stepped cone and inverted trumpet. The 90 μm needle tips were subjected to between 30 and 32 MPa of pressure at their failure point - more than 10 times the required pressure to puncture average human skin. A range of monolithic micropumps were produced with integrated 4 mm diameter single-layer 70 μm-thick membranes used as the basis for a reciprocating displacement operating principle. The membranes were tested using an oscillating pneumatic actuation, and were found reliable (>1,000,000 cycles) up to 2.0 PSIG. Pneumatic single-membrane nozzle/diffuser rectified devices produced flow rates of up to 1,000 μl/min with backpressures of up to 375 Pa. Another device rectified using active membrane valves was found to self-prime, and produced backpressures of up to 4.9 kPa. These devices and structures show great promise for inclusion in complex, fully integrated and active microfluidic systems fabricated using microstereolithography alone, with implications for both cost of manufacture and lead time.EThOS - Electronic Theses Online ServiceEngineering and Physical Sciences Research Council (EPSRC)GBUnited Kingdo

Déformation contrôlée d'une membrane par actionnement piézoélectrique : application au refroidissement de composants électriques à forte dissipation

La maîtrise de la température des composants à forte dissipation, notamment dans les systèmes électroniques nomades, constitue un verrou à leurs développements. Que ce soit pour l'électronique de puissance ou les calculateurs, les densités de puissance requièrent l'utilisation de systèmes de refroidissement de plus en plus performants, en particulier dans le cas des microprocesseurs qui associent miniaturisation et augmentation des fréquences d'horloge. Les conséquences sont multiples, limitation des performances, augmentation de la consommation et du taux de défaillance. C'est dans ce contexte que le projet CANOPEE, réunissant un consortium de partenaire industriel et académique, propose de développer et démontrer les avantages d'une solution technologique active récemment brevetée et appelée OnduloTrans. Elle consiste en un dispositif échangeur-pompe, permettant à la fois d'obtenir un excellent transfert thermique et d'assurer le pompage du fluide caloporteur. OnduloTrans est une solution active de refroidissement basée sur la déformation dynamique d'une paroi d'un canal. Le dispositif est fixé directement à l'aplomb du composant à refroidir. Le canal est déformé suivant une onde progressive pour créer un pompage péristaltique. L'intensification des transferts est obtenue lorsque les variations dynamiques des dimensions du canal viennent perturber la couche limite à l'interface conduction/convection. Le travail de la thèse consiste à concevoir et développer une solution d'actionnement intégrée permettant de mouvoir la paroi souple. Il s'accompagnera d'essais concrets témoignant des performances thermiques de cette solution. L'actionnement mis en oeuvre doit respecter les contraintes hydrauliques et thermiques de l'application embarquée visée, tout particulièrement le faible encombrement et une consommation électrique minimale. La difficulté réside dans les critères antagonistes que sont la production d'une onde progressive de grande amplitude dans un milieu aux dimensions centimétriques. Le manuscrit s'articule en trois parties. Dans un premier temps les solutions d'actionnement envisageables seront explorées. Pour ce faire, la solution OnduloTrans est d'abord décrite. Un état de l'art des solutions de conversion électromécanique, puis des micropompes péristaltiques est entrepris. Les phénomènes hydrauliques propres au micropompage péristaltique sont abordés pour cerner la problématique du développement de l'actionnement. Ensuite les deux chapitres suivants détaillent l'étude de deux solutions piézoélectriques distinctes. Une première solution piézoélectrique à onde discrète est développée dans le second chapitre. Elle consiste en une répartition d'actionneurs flextensionnels le long de la paroi souple. Une méthodologie de prédimensionnement basée sur des modèles mécaniques simples est présentée. L'onde progressive créée étant très particulière, une méthode analytique de calcul du débit, validée par simulations numériques, permet d'étudier l'influence de la commande des actionneurs. Un prototype est finalement réalisé avec l'aide des partenaires. De nombreux essais sont ensuite réalisés afin de valider les différentes hypothèses et déterminer les premières performances hydrauliques et thermiques du dispositif. Le troisième chapitre aborde une solution à onde progressive continue et actionnement intégré à la membrane. Le but est ici de prouver le concept de pompage péristaltique par flexion contrôlée d'une plaque intégrant une couche piézoélectrique. Un modèle de dimensionnement 1D constitué de tronçons piézoélectriques répartis à la surface est tout d'abord présenté. La répartition des segments piézoélectriques fait ensuite l'objet d'une étude paramétrique afin de définir judicieusement leur disposition, ceci en vue de maximiser le débit théorique. Cette étude paramétrique est finalement couplée à une optimisation des commandes électriques, évaluée par les résultats d'un prototype