Microassembly technology for modular, polymer microfluidic devices

Assembly of modular, polymer microfluidic devices with different functions to obtain more capable instruments may significantly expand the options available for detection and diagnosis of disease through DNA analysis and proteomics. For connecting modular devices, precise, passive alignment structures can be used to prevent infinitesimal motions between the devices and minimize misalignment. The motion and constraint of passive alignment structures were analyzed using screw theory. A combination of three v-groove and hemisphere-tipped post joints constrained all degrees of freedom of the two mating modules without overconstraint. Simulations and experiments were performed to assess the predictability of dimensional and location variations of injection molded components. A center-gated disk with micro scale assembly features was replicated. Simulations using a commercial package (Moldflow) overestimated replication fidelity. Mold surface temperatures and injection speeds significantly affected the experimental replication fidelity. The location of features for better replication, at each mold surface temperature, moved from the edge of the mold cavity to the injection point as the mold surface temperature increased from 100˚C to 150˚C. Prototype modular devices were replicated using double-sided injection molding for the experimental demonstration. Dimensional and location variations of the assembly features and alignment standards were quantified for an assembly tolerance analysis. Monte Carlo methods were applied to the assembly tolerance analysis to simulate propagation and accumulation of variation in the assembly. In simulations, mean mismatches with standard deviations ranged from 115±29 to 118±30 µm and from 17±11 to 19±13 µm along the X- and Y-axes, respectively. Vertical gaps with standard deviations at the X- and Y-axes were 312±37~319±37 µm, compared to the designed value of 287µm. The measured lateral mismatches were 103±7~116±11 µm and 15±9~20±6 µm along the X- and Y-axes, respectively. The vertical gaps ranged from 277±4 µm to 321±7 µm at the X- and Y-axes, respectively. The present study combined an investigation of microassembly technology with a better understanding of the micro injection molding process, to assist in realizing cost-effective mass production of modular, polymer microfluidic devices enabling biochemical analysis

MICRO AND NANO R2R EMBOSSING OF EXTRUDED POLYMERS

This dissertation presents a process for directly imprinting or embossing extruded polymers as an advancement in roll-to-roll (R2R) embossing methods that avoids the problems of converting preformed films, increases throughput, and reduces costs. A proof-of-concept R2R apparatus was designed and constructed for directly embossing extruded polymer, and experimental results were evaluated. This laboratory scale R2R apparatus employed a thin metal ribbon belt mold with micro or nano scale features in a calendering setup, with a close coupled induction heating (IH) coil to preheat the ribbon mold above glass transition temperature (Tg) of the polymer, prior to contact with the extrudate at the nip of the calender. This allowed the melted polymer to fully fill the mold patterns before starting to solidify. The thin ribbon mold rapidly conducted heat to the calender roller, providing an effective cooling stage. Microscale and nanoscale features were imprinted directly onto extruded polymer film at a rate of 10 to 12 meters per second, three to over one hundred times the throughput of current R2R processes and orders of magnitude faster than planar processes. Metal ribbon mold belts with nano features were needed to test the direct embossing of extruded polymers at the nano scale. Three different avenues were taken to make such ribbon belts. First, preset nickel alloy molds were obtained. A master mold of the Book of Leviticus with letters 6 µm in width, 6 to 9 µm tall and 60-170 nm high and a nickel alloy DVD master mold with track pitch of 740 nm and 105 nm deep Pits between 400 nm and 1900 nm long. These were welded into stainless steel ribbon belts to form belt molds. Second, a process was developed using base forms or mandrels for metal-forming nickel ribbon belt molds with test patterns that included gratings from 70 to 500 nm and pillars having diameters of 1 µm, 700 nm, 500 nm and 350 nm. Third, an investigation of metal glass (MG) as a candidate mold material was undertaken and a laboratory scale mechanism was designed and constructed to emboss metal glass surfaced rollers thermally

Characterization of shrinkage effects in micro-injection moulding (µ-IM)

This thesis characterizes the effects on shrinkage in microinjection moulding. The literature review considers four branches of investigation (material properties, processing parameters, mould design and specimen design). Two research gaps rise from the analysis of the literature review: the absence of a standardized methodology for measuring shrinkage of moulded parts at the micro-scale, and the absence of optimization stage that implements multiple quality criteria. Adequate research routes are set in order to address these gaps. The conventional standard for determining shrinkage at the macro scale is adapted to the micro-scale and this bridges the first gap. The micro-mould replicates the same design of the standard, and a preliminary stage solves some mouldability problems: the implemented mould extended the mouldability range of processing parameters for improving the reliability of results. After the micro-mould validation, the study of shrinkage at the micro-scale considers the influence of five processing parameters: the mould and melt temperature, the holding time and pressure, then the injection pressure. The design of experiment approach identifies the critical parameters that affect moulding, post-moulding and total shrinkage in parallel to and normal to the flow direction within an interval of confidence of 95% for POM and 90% for 316L feedstock. Statistical tools analyse the results, and the trends of critical factors found confirmation in the literature. This methodology at the micro-scale can fill the first gap because it is on purpose designed for the micro-scale. Moreover, the binder of feedstock is a mixture of POM based polymers, and the use of a common platform permits to compare directly the two materials and highlight the influence of powder loading. The optimization stage adopts desirability functions for achieving optimized values that simultaneously fulfil two requests: minimize shrinkage and maximize moulded part mass. The analysis of the literature review shows that few papers adopt multiple quality criteria approach as methodology for optimizing the results, and none consider jointly part mass and shrinkage. The optimized processing parameters allow moulding “optimized specimens”, and results demonstrate that their total shrinkage and part mass achieve the requests. Even if the use of desirability functions produce results thatrepresents a compromise between the requests, the results show that overall shrinkage decreases and part mass increases. This approach demonstrates its reliability and bridges the second gap. The last part of the thesis investigates the 316L feedstock behaviour for filling micro-features parallel to and normal to the flow oriented. The moulded features are investigated for studying the replication quality and the effect of the orientation of channels with dimension close to the feedstock lower mouldability value. These informations are available in the literature only for polymers, and the contribution of this part of thesis is to fill this gap by analysing a feedstock. The statistical approach permits to identify the critical factors that affect the feature replication quality. Optical investigations allow to identify the 316L feedstock lower mouldability value and to observe the influence of the orientation of features with dimensions near the lower limit

Monolithic integration of high-aspect-ratio microstructures with CMOS circuitry

This work involves developing processing techniques for monolithically integrating a high-aspect-ratio microstructures with CMOS circuitry. A microsystem comprising of a microprobe array and signal processing circuitry is utilized as a test vehicle to demonstrate this fabrication process. One potential application of this microsystem is for recording neural signals from the central nervous system. The main results include thick photoresist processing, DC and pulse electroplating to form high-aspect-ratio microprobes, microprobe sharpening and developing a post-IC monolithic integration process. SU-8 is utilized for thick photoresist application. This work focuses on realization of a deep microrecess array in thick resists rather than traditional stand-alone SU-8 columns. The former encounters more processing challenges. Several novel techniques are developed including a unique development step, which results in clean microrecesses up to 450 &181;m deep with the smallest width of 40 &181;m giving aspect-ratio of 11. Electroplating is performed in nickel sulfamate electrolyte. DC plating rate is found to depend on probe location, dimension and probe spacing. Nernst diffusion boundary layer model is utilized to estimate Ni ion diffusion coefficient to be 3.3&215;10&178;-6 cm&178;2 /s. Stress in deposit is found to change from compressive to tensile with increasing DC plating current density and with increasing deposit thickness saturating respectively at 92 MPa and 73 MPa. Stress in pulse plated Ni with long pulses saturates at 54.5 MPa, while short pulse periods produce only compressive stresses between -110 MPa and -160 MPa. Surface morphology of electroplated Ni is related to built-in stress. A one-dimensional simplified model is built to describe the pulse plating process taking fixed and moving boundary approaches. The results are utilized to determine the pulse on time for plating into deep microrecesses. Nickel wire or probe is sharpened electrochemically with wires giving sharper tips under conditions of 30 &176;C, 4 V potential in a 0.5 M sulfuric acid electrolyte. Chemicals are carefully tailored in developing post-IC monolithic integration process to avoid detrimental impact on the CMOS circuitry with processing temperature maintained below 100 &176;C to avoid circuit degradation. A unique chip-level tape-and-wire bonding technique is developed to perform chip-level monolithic integration

The Efficacy of Bionate as an Articulating Surface for Joint Hemiarthroplasty

Hemiarthroplasty procedures replace the diseased side of the joint with an implant to maximize bone preservation while maintaining more native anatomy than a total joint replacement. Even though hemiarthroplasty procedures have been clinically successful, they cause progressive cartilage damage over time due to the use of relatively stiff metallic implant materials. This work investigates the role of low moduli implant material on implant-cartilage contact mechanics and early in vitro cartilage wear. A finite element simulation was developed to assess the effect of low moduli implants in the range of 0.015-0.288 GPa on contact mechanics. Higher contact area and lower peak contact stress was quantified as the Young’s moduli decreased. Bionate implants were fabricated through microinjection moulding for three Young’s moduli of 0.020 GPa, 0.035 GPa and 0.222 GPa. An in vitro wear study was conducted using a pin-on-plate simulator to investigate the effect of these different Bionate formulations on cartilage wear. A significant decrease in cartilage wear was observed for the 0.020 GPa and 0.035 GPa Bionate implants (p\u3c0.001). In conclusion, these studies have demonstrated the desirable range of hemiarthroplasty implant moduli to reduce cartilage wear, and have shown that Bionate implants have the potential to provide improved longterm outcomes of joint hemiarthroplasty

OPTIMIZATION OF TIME-RESPONSE AND AMPLIFICATION FEATURES OF EGOTs FOR NEUROPHYSIOLOGICAL APPLICATIONS

In device engineering, basic neuron-to-neuron communication has recently inspired the development of increasingly structured and efficient brain-mimicking setups in which the information flow can be processed with strategies resembling physiological ones. This is possible thanks to the use of organic neuromorphic devices, which can share the same electrolytic medium and adjust reciprocal connection weights according to temporal features of the input signals. In a parallel - although conceptually deeply interconnected - fashion, device engineers are directing their efforts towards novel tools to interface the brain and to decipher its signalling strategies. This led to several technological advances which allow scientists to transduce brain activity and, piece by piece, to create a detailed map of its functions. This effort extends over a wide spectrum of length-scales, zooming out from neuron-to-neuron communication up to global activity of neural populations. Both these scientific endeavours, namely mimicking neural communication and transducing brain activity, can benefit from the technology of Electrolyte-Gated Organic Transistors (EGOTs). Electrolyte-Gated Organic Transistors (EGOTs) are low-power electronic devices that functionally integrate the electrolytic environment through the exploitation of organic mixed ionic-electronic conductors. This enables the conversion of ionic signals into electronic ones, making such architectures ideal building blocks for neuroelectronics. This has driven extensive scientific and technological investigation on EGOTs. Such devices have been successfully demonstrated both as transducers and amplifiers of electrophysiological activity and as neuromorphic units. These promising results arise from the fact that EGOTs are active devices, which widely extend their applicability window over the capabilities of passive electronics (i.e. electrodes) but pose major integration hurdles. Being transistors, EGOTs need two driving voltages to be operated. If, on the one hand, the presence of two voltages becomes an advantage for the modulation of the device response (e.g. for devising EGOT-based neuromorphic circuitry), on the other hand it can become detrimental in brain interfaces, since it may result in a non-null bias directly applied on the brain. If such voltage exceeds the electrochemical stability window of water, undesired faradic reactions may lead to critical tissue and/or device damage. This work addresses EGOTs applications in neuroelectronics from the above-described dual perspective, spanning from neuromorphic device engineering to in vivo brain-device interfaces implementation. The advantages of using three-terminal architectures for neuromorphic devices, achieving reversible fine-tuning of their response plasticity, are highlighted. Jointly, the possibility of obtaining a multilevel memory unit by acting on the gate potential is discussed. Additionally, a novel mode of operation for EGOTs is introduced, enabling full retention of amplification capability while, at the same time, avoiding the application of a bias in the brain. Starting on these premises, a novel set of ultra-conformable active micro-epicortical arrays is presented, which fully integrate in situ fabricated EGOT recording sites onto medical-grade polyimide substrates. Finally, a whole organic circuitry for signal processing is presented, exploiting ad-hoc designed organic passive components coupled with EGOT devices. This unprecedented approach provides the possibility to sort complex signals into their constitutive frequency components in real time, thereby delineating innovative strategies to devise organic-based functional building-blocks for brain-machine interfaces.Nell’ingegneria elettronica, la comunicazione di base tra neuroni ha recentemente ispirato lo sviluppo di configurazioni sempre più articolate ed efficienti che imitano il cervello, in cui il flusso di informazioni può essere elaborato con strategie simili a quelle fisiologiche. Ciò è reso possibile grazie all'uso di dispositivi neuromorfici organici, che possono condividere lo stesso mezzo elettrolitico e regolare i pesi delle connessioni reciproche in base alle caratteristiche temporali dei segnali in ingresso. In modo parallelo, gli ingegneri elettronici stanno dirigendo i loro sforzi verso nuovi strumenti per interfacciare il cervello e decifrare le sue strategie di comunicazione. Si è giunti così a diversi progressi tecnologici che consentono agli scienziati di trasdurre l'attività cerebrale e, pezzo per pezzo, di creare una mappa dettagliata delle sue funzioni. Entrambi questi ambiti scientifici, ovvero imitare la comunicazione neurale e trasdurre l'attività cerebrale, possono trarre vantaggio dalla tecnologia dei transistor organici a base elettrolitica (EGOT). I transistor organici a base elettrolitica (EGOT) sono dispositivi elettronici a bassa potenza che integrano funzionalmente l'ambiente elettrolitico attraverso lo sfruttamento di conduttori organici misti ionici-elettronici, i quali consentono di convertire i segnali ionici in segnali elettronici, rendendo tali dispositivi ideali per la neuroelettronica. Gli EGOT sono stati dimostrati con successo sia come trasduttori e amplificatori dell'attività elettrofisiologica e sia come unità neuromorfiche. Tali risultati derivano dal fatto che gli EGOT sono dispositivi attivi, al contrario dell'elettronica passiva (ad esempio gli elettrodi), ma pongono comunque qualche ostacolo alla loro integrazione in ambiente biologico. In quanto transistor, gli EGOT necessitano l'applicazione di due tensioni tra i suoi terminali. Se, da un lato, la presenza di due tensioni diventa un vantaggio per la modulazione della risposta del dispositivo (ad esempio, per l'ideazione di circuiti neuromorfici basati su EGOT), dall'altro può diventare dannosa quando gli EGOT vengono adoperati come sito di registrazione nelle interfacce cerebrali, poiché una tensione non nulla può essere applicata direttamente al cervello. Se tale tensione supera la finestra di stabilità elettrochimica dell'acqua, reazioni faradiche indesiderate possono manifestarsi, le quali potrebbero danneggiare i tessuti e/o il dispositivo. Questo lavoro affronta le applicazioni degli EGOT nella neuroelettronica dalla duplice prospettiva sopra descritta: ingegnerizzazione neuromorfica ed implementazione come interfacce neurali in applicazioni in vivo. Vengono evidenziati i vantaggi dell'utilizzo di architetture a tre terminali per i dispositivi neuromorfici, ottenendo una regolazione reversibile della loro plasticità di risposta. Si discute inoltre la possibilità di ottenere un'unità di memoria multilivello agendo sul potenziale di gate. Viene introdotta una nuova modalità di funzionamento per gli EGOT, che consente di mantenere la capacità di amplificazione e, allo stesso tempo, di evitare l'applicazione di una tensione all’interfaccia cervello-dispositivo. Partendo da queste premesse, viene presentata una nuova serie di array micro-epicorticali ultra-conformabili, che integrano completamente i siti di registrazione EGOT fabbricati in situ su substrati di poliimmide. Infine, viene proposto un circuito organico per l'elaborazione del segnale, sfruttando componenti passivi organici progettati ad hoc e accoppiati a dispositivi EGOT. Questo approccio senza precedenti offre la possibilità di filtrare e scomporre segnali complessi nelle loro componenti di frequenza costitutive in tempo reale, delineando così strategie innovative per concepire blocchi funzionali a base organica per le interfacce cervello-macchina

A micromachined thermo-optical light modulator based on semiconductor-to-metal phase transition

In this research, a micromachined thermo-optical light modulator was realized based on the semiconductor-to-metal phase transition of vanadium dioxide (VO2) thin film. VO2 undergoes a reversible phase transition at approximately 68 0C, which is accompanied with drastic changes in its electrical and optical properties. The sharp electrical resistivity change can be as great as five orders. Optically, VO2 film will switch from a transparent semiconductor phase to a reflective metal phase upon the phase transition. The light modulator in this research exploits this phase transition related optical switching by using surface micromachined low-thermal-mass pixels to achieve good thermal isolations, which ensures that each pixel can be individually switched without cross talking. In operation, the pixel temperature was controlled by integrated resistor on each pixel or spatially addressed thermal radiation sources. Active VO2 thin film was synthesized by thermal oxidation of e-beam evaporated vanadium metal film. The oxidized film exhibits a phase transition at ~65°C with a hysteresis of about 15°C. A transmittance switching from ~90% to ~30% in the near infrared and a reflectance switching from ~50% to 15% in the visible have been achieved. The surface microstructure was studied and correlated to its optical properties. A study on the hysteresis loop reveals that the VO2 can be repetitively switched between the on and off\u27 states. The micromachined thermal isolation pixel was a bridge-like silicon dioxide platform suspended with narrow supporting legs. The pixel design was optimized with both thermal and optical simulations. The VO2 light modulator was fabricated by surface micromachining based on dry processing. Silicon dioxide was deposited on a polyimide sacrificial layer by PECVD and patterned to form the structural pixel. Vanadium film was e-beam evaporated and patterned with lift-off process. It was thermally oxidized into VO2 at 390°C. The thermal isolation pixel was anchored on substrate by aluminum pedestals. Finally, the structure was released in an oxygen plasma barrel asher. The VO2 array was experimentally tested and its light switching and modulation ability were demonstrated. Further study shows that the surface micromachining process has no degrading effect on the optical property of VO2 thin film

Powder Injection Moulding of Tungsten Based Metal Matrix Composites

Ph.DDOCTOR OF PHILOSOPH