Microsystems technology: objectives

This contribution focuses on the objectives of microsystems technology (MST). The reason for this is two fold. First of all, it should explain what MST actually is. This question is often posed and a simple answer is lacking, as a consequence of the diversity of subjects that are perceived as MST. The second reason is that a map of the somewhat chaotic field of MST is needed to identify sub-territories, for which standardization in terms of system modules an interconnections is feasible. To define the objectives a pragmatic approach has been followed. From the literature a selection of topics has been chosen and collected that are perceived as belonging to the field of MST by a large community of workers in the field (more than 250 references). In this way an overview has been created with `applications¿ and `generic issues¿ as the main characteristics

Responsive liquid crystal networks

Responsieve polymeren zijn interessant voor een groot aantal toepassingen, omdat de eigenschappen van deze materialen over een breed bereik ingesteld kunnen worden en het bovendien mogelijk is om ze tegen lage kosten en op grote schaal te fabriceren. Vloeibaar-kristallijne netwerken vormen een platformtechnologie voor deze responsieve materialen. Een groot aantal stimulusgevoelige moleculen kunnen worden toegevoegd om het polymeer gevoelig te maken voor warmte, licht, pH, waterdamp of biologische stimuli. De vloeibaar-kristallijne kernen van het polymere netwerk versterken de stimulus, wat snelle en grote responsies tot gevolg heeft. De responsies kunnen zowel mechanische als optische veranderingen zijn, en zijn naar wens reversibel of irreversibel te maken. In dit werk wordt het gebruik van deze materialen in microsystemen, zoals lab-on-a-chip, onderzocht. Actuatie met licht wordt gekozen omdat dit compatibel is met een natte omgeving en van afstand aangestuurd kan worden.Theoretische en experimentele resultaten laten zien dat door een optimalisatie van de moleculaire ordening in een ‘splaybend’ orientatie, de prestaties van buigende actuatoren sterk verbeterd kan worden. Daarnaast is er theorie ontwikkeld die de beweging van de actuator onder invloed van aansturing met licht beschrijft en deze theorie wordt door experimentele resultaten bevestigd. Voor toepassing in microfluidische systemen worden actuatoren ontworpen die gebaseerd zijn op cilia in natuurlijke organismen. Deze actuatoren kunnen dienen als pompen en mixers, maar daarvoor is het noodzakelijk dat de beweging van de cilia asymmetrisch in de tijd is. Verschillende manieren voor het genereren van deze asymmetrische beweging zijn onderzocht. Eén manier maakt gebruik van actuatoren bestaande uit verschillende delen die elk reageren op een andere kleur licht. Een andere manier maakt gebruik van een gradient in compositie van de actuator door de dikte van het materiaal, waardoor een sterk niet-lineaire responsie ontstaat. Verschillende methodes voor het miniaturiseren van deze actuatoren zijn verkend, waaronder lithografie en inkjet printen. Het is aangetoond dat met inkjet printen, actuatoren kleiner dan een millimeter gemaakt kunnen worden, zonder dat de prestaties van de actuatoren daaronder te leiden heeft. Behalve de toepassing van vloeibaar-kristallijne netwerken als actuatoren is de toepassing als sensor ook onderzocht. Als het materiaal een cholesterische ordening heeft, kan dit een gedeelte van het licht reflecteren. Als de reflectieband in het zichtbare gedeelte van het licht ligt, lijkt het materiaal een kleur te hebben. Net als bij de actuatoren kan het netwerk gedeformeerd worden door de moleculaire ordening te verstoren of door het te laten zwellen of krimpen, hetgeen een zichtbare verschuiving van de reflectieband tot gevolg kan hebben. Het is aangetoond dat door gebruik te maken van waterstofbruggen in het netwerk, cholesterische sensoren kunnen reageren op vluchtige amines, pH of temperatuur. Als alternatief voor de licht gestuurde actuatoren zijn magnetisch gedreven, ferromagnetische systemen onderzocht. Magnetische velden zijn net als licht compatibel met een nat milieu en kunnen van afstand aansturen. Twee methodes zijn onderzocht om kunstmatige magnetische cilia te maken: ‘glancing angle’ depositie van nikkel op PDMS scharnieren en electrolytisch gegroeid nikkel in een membraan. De beste resultaten werden bereikt met electrolytische gegroeide staafjes die vrij in een kanaal ronddreven. Toepassingen van de actuatoren uit dit onderzoek liggen in medische applicaties zoals lab-on-a-chip systemen, maar ook in andere toepassingen zoals mechatronica en textiel. Omdat de materialen in een continu proces aan de lopende band verwerkt kunnen worden, hebben ze de potentie om in goedkope systemen zoals slimme verpakkingen of wegwerp applicaties toegepast te worden

Three-dimensional printing of multifunctional nanocomposites: Manufacturing techniques and applications

The integration of nanotechnology into three-dimensional printing (3DP) offers huge potential and opportunities for the manufacturing of 3D engineered materials exhibiting optimized properties and multifunctionality. The literature relating to different 3DP techniques used to fabricate 3D structures at the macro- and microscale made of nanocomposite materials is reviewed here. The current state-of-the-art fabrication methods, their main characteristics (e.g., resolutions, advantages, limitations), the process parameters, and materials requirements are discussed. A comprehensive review is carried out on the use of metal- and carbon-based nanomaterials incorporated into polymers or hydrogels for the manufacturing of 3D structures, mostly at the microscale, using different 3D-printing techniques. Several methods, including but not limited to micro-stereolithography, extrusion-based direct-write technologies, inkjet-printing techniques, and popular powder-bed technology, are discussed. Various examples of 3D nanocomposite macro- and microstructures manufactured using different 3D-printing technologies for a wide range of domains such as microelectromechanical systems (MEMS), lab-on-a-chip, microfluidics, engineered materials and composites, microelectronics, tissue engineering, and biosystems are reviewed. Parallel advances on materials and techniques are still required in order to employ the full potential of 3D printing of multifunctional nanocomposites

Capillary Microfluidic Chips for Point-of-Care Testing:from Research Tools to Decentralized Medical Diagnostics

Research on microfluidic devices for biological analysis has progressed sufficiently to be developed into point-of-care diagnostics products. The goal of this thesis is to improve multiple aspects of capillary-driven microfluidic devices. In particular, the objective is to provide devices with a fast time to result, that are simple to use (one-step), that can be portable, that accept a variety of samples, that operate reliably, that provide a range of detection signals, that are mass manufacturable at lost cost, and that are able to detect medically relevant biological molecules. First, we survey the evolution of microfluidic research into portable medical diagnostic devices. By looking at several gaps and opportunities in current medical diagnostics, we provide an overview of research topics that have the potential to shape the next generation of point-of-care diagnostics. Specifically we explain technologies in the order of sample interacting with different components of a device. We investigate the materials, surface treatments, sample processing, microfluidic elements (such as valves, pumps and mixers), receptors and analytes and the integration of these components into a device that might conceivably leave the laboratory for the hands of consumers. The knowledge of what is important in a point-of-care diagnostics device was used to develop a proof of concept. One of the main challenges is to make microfluidics easy to use by incorporating reagents and microfluidic elements. We integrated a number of functional elements on a chip such as a sample collector, delay valves, flow resistors, a deposition zone for detection antibodies (dAbs), a reaction chamber sealed with a polydimethylsiloxane (PDMS) substrate, and a capillary pump and vents. We further incorporated capture antibodies (cAbs), detection antibodies (dAbs) and analyte molecules for making one-step immunoassays. The integrated microfluidic chip requires only the addition of sample to trigger a sequence of events controlled by capillary forces to detect C-reactive protein (CRP), a general inflammation and cardiac marker, at a concentration of 1 ng mL-1 within 14 min using only 5 µL of human serum. The proof-of-concept is extended to easily modify several assay parameters such as the flow rates and the volumes of samples for tests, and the type of reagents and receptors for analytes. The multiparametric microfluidic chip is capable of analyzing 20 µL of human serum in 6 parallel flow paths in a range of flow rates with filling times from 10 minutes to 72 minutes. The asymmetric release of dAbs in a stream of human serum is compensated by a Dean flow mixer. Sample is equally split into 6 reaction chambers connected to flow resistances that vary flow rates, and the kinetics of capture of analyte-dAb complexes. The increased incubation time leads to a fourfold increase in detection signal in the reaction chamber with the longer incubation time. Furthermore, integrating reagents and controlling their release is essential for simple and accurate point-of-care diagnostic devices. We developed reagent integrators (RIs) to release small amounts of dried reagents (ng quantities and less) into microliters of sample. Typical RIs are composed of an inlet splitting into a central reagent channel, with a high hydraulic resistance, and two diluter channels. Reagents spotted in the central channel reconstitute in sample during filling and merge at the end of the RI with a dilution factor corresponding to the relative hydraulic resistance of the channels forming the RI. RIs are simple to integrate in lateral flow assays and provide a great degree of control over reagent integration and dissolution. Finally, the one-step capillary-driven microfluidic chips have the ability to not only detect a variety of proteins, but also to detect nucleic acids for molecular diagnostics. These devices, especially if manufactured in low cost plastic and used with portable fluorescence readers, have the potential to identify a wide variety of health conditions and to enable truly decentralized medical diagnostics

Fabrication and Application of Flexible Sensors

A transfer printing method was developed to transfer carbon nanotubes (CNTs) from polyethylene terephthalate (PET) film to poly(dimethyl siloxane) (PDMS) polymer. Carbon nanotubes are composed of carbon atoms arranged in a honeycomb lattice structure, which are electrically conducting. When embedded in a nonconducting polymer, carbon nanotubes impart electrical conductivity to the nanocomposite, thus forming a nanocomposite that has potential applications in highly sensitive strain and pressure sensors. Several printing methods have been studied to deposit carbon nanotubes onto PDMS, including inkjet printing. Inkjet printing is a desirable deposition method since it is low-cost, simple, and allows the processing of aqueous-based inks. However, directly inkjet printing carbon nanotubes onto PDMS has been a challenge because the printed film becomes non-uniform due to the uneven drying of the droplets. Therefore, a method of transfer printing was developed to embed carbon nanotubes uniformly in PDMS. The transfer printing method consists of first inkjet printing patterns of carbon nanotubes onto a PET film, which quickly absorbs the aqueous ink and allows uniformity of the printed carbon nanotube patterns. The next step is spin-coating PDMS on the PET film to cover the carbon nanotube patterns, followed by curing the PDMS. The following step is thermally treating the PET film to promote the transfer of carbon nanotubes to PDMS, and finally peeling off PDMS from PET film to complete the transfer of carbon nanotube patterns. The transferred patterns had widths as small as 125 µm, while the obtained PDMS thickness was as low as 27.1 µm, which enabled the fabrication of highly sensitive force and pressure sensors. The transfer printing method was employed to fabricate a two-dimensional force sensor, which was composed of lines of carbon nanotubes in the x and y directions. The transduction mechanism lies in the generation of strain on the carbon nanotube pattern. When strain is produced, the resistance of the pattern changes due to the increase or decrease of the number of conduction paths in the carbon nanotube pattern. The practical application as a two-dimensional sensor was shown by monitoring the touch force exerted by multiple objects on the sensor. Due to the flexibility and stretchability of PDMS, fabricated air pressure sensors were capable of detecting small pressure differences. The sensors were composed of a circular diaphragm containing inkjet-printed carbon nanotube patterns. When air pressure increased on one side of the diaphragm, the deflection caused a strain on the CNT line, thus changing its resistance. Pressure sensors with a diaphragm diameter of five millimeters, diaphragm thickness of 27.1 µm showed sensitivity of 10.99 percent change in resistance per kilopascal (%/kPa) and limit of detection of 3.1 Pa. The pressure sensor has potential applications in monitoring minute air pressure differences such as those generated by the breathing pattern. The application of the highly sensitive and biocompatible pressure sensor was shown through the measurement of the pressure generated by a 3D-printed respiratory system

Arrayed microfluidic actuation for active sorting of fluid bed particulates

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2004.Includes bibliographical references (p. 227-237).Fluidic actuation offers a facile method to move large quantities of small solids, often referred to as fluid-bed movement. Applications for fluid bed processing are integral to many fields including petrochemical, petroleum, chemical, pharmaceutical, biochemical, environmental, defense, and medical. Thermal vapor microbubbles have been shown to be a low power input with high work output fluidic actuation technique with demonstrated commercial applications in ink jet printing and optical switching. This thesis further develops microbubble actuation (BA) as an arrayed particulate actuation technology for active sorting in particulate fluid beds. Numerical and analytical models of flows, forces, and fields affecting a tBA-based system are presented. The design and fabrication of an arrayed pBA-powered device are delineated with notation of specifications that may focus future design iterations. Performance testing and characterization of CpBA technology, including over a hundred in-plane and out-of-plane nucleation site geometries, serve as the impetus for the technical guidelines that are presented, which include a detailed comparison of in-plane and out-of-plane nucleation site geometry performance.by Antimony L. Gerhardt.M.Eng

Development of a light-powered microstructure : enhancing thermal actuation with near-infrared absorbent gold nanoparticles.

Development of microscale actuating technologies has considerably added to the toolset for interacting with natural components at the cellular level. Small-scale actuators and switches have potential in areas such as microscale pumping and particle manipulation. Thermal actuation has been used with asymmetric geometry to create large deflections with high force relative to electrostatically driven systems. However, many thermally based techniques require a physical connection for power and operate outside the temperature range conducive for biological studies and medical applications. The work presented here describes the design of an out-of-plane bistable switch that responds to near-infrared light with wavelength-specific response. In contrast to thermal actuating principles that require wired conductive components for Joule heating, the devices shown here are wirelessly powered by near -infrared (IR) light by patterning a wavelength-specific absorbent gold nanoparticle (GNP) film onto the microstructure. An optical window exists which allows near-IR wavelength light to permeate living tissue, and high stress mismatch in the bilayer geometry allows for large actuation at biologically acceptable limits. Patterning the GNP film will allow thermal gradients to be created from a single laser source, and integration of various target wavelengths will allow for microelectromechanical (MEMS) devices with multiple operating modes. An optically induced temperature gradient using wavelength-selective printable or spinnable coatings would provide a versatile method of wireless and non-invasive thermal actuation. This project aims to provide a fundamental understanding of the particle and surface interaction for bioengineering applications based on a “hybrid” of infrared resonant gold nanoparticles and MEMS structures. This hybrid technology has potential applications in light-actuated switches and other mechanical structures. Deposition methods and surface chemistry are integrated with three-dimensional MEMS structures in this work. The long-term goal of this project is a system of light-powered microactuators for exploring cells\u27 response to mechanical stimuli, adding to the fundamental understanding of tissue response to everyday mechanical stresses at the molecular level

Low-Cost Microfabrication Tool Box.

Microsystems are key enabling technologies, with applications found in almost every industrial field, including in vitro diagnostic, energy harvesting, automotive, telecommunication, drug screening, etc. Microsystems, such as microsensors and actuators, are typically made up of components below 1000 microns in size that can be manufactured at low unit cost through mass-production. Yet, their development for commercial or educational purposes has typically been limited to specialized laboratories in upper-income countries due to the initial investment costs associated with the microfabrication equipment and processes. However, recent technological advances have enabled the development of low-cost microfabrication tools. In this paper, we describe a range of low-cost approaches and equipment (below £1000), developed or adapted and implemented in our laboratories. We describe processes including photolithography, micromilling, 3D printing, xurography and screen-printing used for the microfabrication of structural and functional materials. The processes that can be used to shape a range of materials with sub-millimetre feature sizes are demonstrated here in the context of lab-on-chips, but they can be adapted for other applications. We anticipate that this paper, which will enable researchers to build a low-cost microfabrication toolbox in a wide range of settings, will spark a new interest in microsystems