Genetic Engineering & Biotechnology NewsVol. 31, No. 7 MF3 Fosters Micro/Nanofluidic CollaborationsUCI-Based Group Aids Transition from Prototype to Mass-Produced Commercial ProductGisela Lin,Gisela Lin,Gisela Lin, Ph.D. (E-mail Address: gisela@uci.edu), is the MF3 Center development manager, University of California, Irvine. Web: www.inrf.uci.edu/mf3.Search for more papers by this authorPublished Online:1 Sep 2011https://doi.org/10.1089/gen.31.7.03AboutSectionsView articleView Full TextPDF/EPUB Permissions & CitationsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail View articleFiguresReferencesRelatedDetails Volume 31Issue 7Apr 2011 Information© 2011 by GEN PublishingTo cite this article:Gisela Lin,.MF3 Fosters Micro/Nanofluidic Collaborations.Genetic Engineering & Biotechnology News.Apr 2011.63-63.http://doi.org/10.1089/gen.31.7.03Published in Volume: 31 Issue 7: September 1, 2011PDF download

Microfluidics is an emerging technology with the potential to streamline workflows and processes in the food and health sciences. Because of extreme miniaturization, less reagent consumption and more efficient sample-to-answer protocols are not only attainable but in many cases demonstrated. In this article, we present some key examples of relevant research at the Micro/Nano Fluidics Fundamentals Focus (MF3) Center that has direct applications in food, environmental, and physiological health monitoring.

A suitable platform has been introduced to exert mechanical tension along radial glial processes between groups of neural stem cells to study the effect of tension on cerebral cortex neurogenesis. Two improvements were implemented in the clamp-and-ratchet microstructure design based on polycrystalline silicon (polysilicon) micro-electro-mechanical systems (MEMS) technology. Finite Element Analysis shows that these new designs are well within fracture limits under expected tension loading. Stretching the PDMS using the clamp-and-ratchet will produce various precise tensions in these radial extensions, which may modulate neuronal migration, a key process in neurogenesis.

We present a new micro-fabrication process to improve the yield of thin film metal strain gauges that are embedded in a poly-dimethyl-siloxane (PDMS) membrane. This work is directed towards the realization of a flexible, implantable sensor array for measuring surface strain on live bone. Although previous lift-off and peeling processes have been demonstrated to be feasible for fabricating the strain gauges in PDMS, they resulted in a very low yield, approximately 5%. Hence, we implemented a different process to improve the mechanical robustness and fabrication yield. One of the key improvements was the use of wet etching to pattern the thin metal film instead of conventional lift-off. The results demonstrated both an increase in yield to 50% and further miniaturization of the devices. Electromechanical testing results revealed that our metal thin-film gauges have greater gauge factors than commercially available ones, which will result in potentially more precise strain sensing. Various biocompatible adhesives were tested for fixing the micro strain sensor to imitation bone materials. Ultimately this strain gauge will be part of an implantable, wireless array for real-time in vivo monitoring of bone strain in the presence of disease and bone remodeling.

A clamp-and-ratchet microstructure based on poly crystalline silicon (polysilicon) microelectromechanical systems (MEMS) technology has been designed to exert mechanical tension along radial glial processes between groups of neural stem cells to study the effect of tension on cerebral cortex neurogenesis. FEA analysis shows that the design should not fail under expected loading conditions. Preliminary studies show that embryonic brain tissue survives under tension for at least six days. Neurospheres have been successfully cultured on Poly(dimethylsiloxane) (PDMS) for eight days and exhibit radial extensions which appear to support neuronal migration. Stretching the PDMS using the clamp and ratchet will produce tension in these radial extensions which may modulate neuronal migration, a key process in cerebral cortex development.

We present the design of a strain gauge embedded in polydimethylsiloxane (PDMS) that could be implanted and used for monitoring strain on surfaces of bones with high resolution. Our ultimate goal is to design and fabricate the device such that it could be used to provide real-time data of strain development in live subject. We have simulated the mechanical characteristics of thin-film metal strain gauges embedded in a flexible substrate made from polydimethyl-siloxane (PDMS) with various loading conditions using ANSYS/spl reg/ finite element analysis tool. Various gauge designs were subjected to stresses from several different directions. Linear relationships between fractional change of resistance and nominal resistance were found for both tensile and compressive stress applied on the gauges. Most significantly, the simulation demonstrated that external stresses were effectively transmitted through the PDMS layer to the thin-film metal, validating our approach.

The characteristics of the materials and surfaces in microelectromechanical systems (MEMS) and microsystems technology (MST) profoundly affect the performance, reliability, and wear of MEMS and MST devices. It is critical to measure the properties of surfaces that are in contact during microstructure movement, such as the underside of a MEMS gear and the underlying substrate. However, contacting surfaces are usually inaccessible unless the MEMS device is broken and removed from the substrate. This paper presents a nondestructive method for characterizing commercially fabricated surface micromachined polycrystalline silicon (polysilicon) devices. Microhinged flaps were designed that enable access to the upper surface, the part of a structural layer deposited last; the lower surface, the part of a structural layer deposited first; and the underlying substrate. Due to the susceptibility of surface-micromachined MEMS to adhesion failures, the surface roughness is a key parameter for predicting device behavior. Using the microhinged flaps, the RMS surface roughness for polycrystalline surfaces was measured and indicated that the upper surfaces were 3.5–6.4 times rougher than the lower surfaces. The difference in the surface roughness for the upper surface, which is easily accessed and the one most commonly characterized, and that for the lower surface reveals the importance of characterizing contacting surfaces in MEMS and MST devices.

We present micro-fabrication and device characterization results towards the realization of a flexible, implantable sensor array for measuring surface strain on live bone. Thin-film metal strain gauges were embedded in a poly-dimethyl-siloxane (PDMS) membrane. Various adhesives used to adhere the device to both imitation bone materials and cow bones were tested. The measured strain level and resolution indicates that the device is suitable for bone surface strain measurement. Ultimately this gauge will be part of an implantable, wireless array for real-time monitoring of bone disease and bone remodeling.

This report documents the results to date of the surface characterization of micromachined polycrystalline silicon structures project. In particular, polysilicon flaps fabricated in the MUMPs 36 and 37 runs at Cronos, a JDS subsidiary, were investigated. Atomic force microscopy (AFM), scanning electron microscopy (SEM), and electron dispersive spectroscopy (EDS) were used to determine the surface topography and chemical composition of the surfaces. Fabricated die were dried after the removal of the sacrificial oxide layers using two methods: air and supercritical CO2 drying. The effects of release etching on the surface roughness were also studied. The layout of the flaps on the chip and flap design will first be presented. Then, the AFM and EDS results for the air dried die will be discussed. Next, the preand post-release AFM scans of the second structural layer subject to a HF etch are shown. The AFM and EDS results for the supercritical CO2 dried sample are then described. Finally, some initial conclusions are presented.

MEMS packaging for biomedical applications can be achieved in several ways. One is complete device encapsulation. Several examples are discussed, including the encapsulation of a MEMS heart cell force transducer in which the encapsulant is composed of four different materials. The second option is a reconfigurable packaging scheme that consists of an inert protective polymer layer that can be moved or broken on command. This type of package facilitates direct sensor access to the environment and preliminary results are presented. INTRODUCTION Micro-electromechanical systems (MEMS) technology provides a relatively new, inexpensive way to make sensors. By using silicon-based integrated circuit fabrication techniques chemical, inertial, thermal, and pressure sensors have been miniaturized [l]. MEMS has tremendous growth potential especially in the biomedical sciences. Miniature MEMS biosensors have already been used to measure and interact with a variety of biomolecules, and wireless communication to and from surgically implanted biomedical MEMS devices has been demonstrated [l] [2]. However, advances in MEMS biosensor packaging are fewer in number. This often neglected but important device aspect is necessary to complete a system. Especially in wet, corrosive environments, such as biological fluid, reliable packaging of active devices is extremely challenging. Two methods of biosensor packaging can be employed: (1) complete encapsulation of active components or (2) reconfigurable encapsulation that allows the active components controlled access to the environment. Complete ncapsulation s a more straightforward approach and has proven effective for both standard and MEMS biomedical devices. However, total encapsulation inherently limits the type of sensing that can be performed. Sensors ultimately need access to the environment and will thus require a more sophisticated, interactive package that simultaneously protects the sensor while allowing the required access when needed. Both approaches will be discussed. ENCAPSULATION PACKAGING For many years, medical devices such as pacemakers consisted of electronics encased in biocompatible hard shell titanium housings to protect the device from hostile body fluids. Miniature, in-situ sensor systems operating in harsh liquid environments have also involved complete encapsulation. For example, a swallowable temperature sensor has been developed by HTI Technologies Incorporated (Figure I ) [3]. The pill is entirely coated in silcone rubber and epoxy which enables it to withstand the acidity and toxicity of the GI tract.

Three-dimensional MEMS microsystems that are commercially fabricated require minimal post-processing and are easily integrated with CMOS signal processing electronics. Measurements to evaluate the fabrication process (such as cross-sectional imaging and device performance characterization) provide much needed feedback in terms of reliability and quality assurance. MEMS technology is bringing a new class of microscale measurements to fruition. The relatively small size of MEMS microsystems offers the potential for higher fidelity recordings compared to macrosize counterparts, as illustrated in the measurement of muscle cell forces.

The MEMS Technology Group is part of the Microdevices Laboratory (MDL) at the Jet Propulsion Laboratory (JPL). The group pursues the development of a wide range of advanced MEMS technologies that are primarily applicable to NASA's robotic as well as manned exploration missions. Thus these technologies are ideally suited for the demanding requirements of space missions namely, low mass, low power consumption and high reliability, without significant loss of capability. End-to-end development of these technologies is conducted at the MDL, a 38,000 sq. ft. facility with approximately 5500 sq. ft. each of cleanroom (class 10 - 100,000) and characterization laboratory space. MDL facilities include computer design and simulation tools, optical and electron-beam lithography, thin film deposition equipment, dry and wet etching facilities including Deep Reactive Ion Etching, device assembly and testing facilities. Following the fabrication of the device prototypes, reliability testing of these devices is conducted at the state-of-the-art Failure Analysis Laboratory at JPL.

Micro-Nano Technology Visualization (MNTV) is critical to studies in MEMS reliability. The ability to see and characterize the microstructures and interfaces with high resolution at the microscale and nanoscale is invaluable. In this paper we present the motivation, paradigm and examples of visualization techniques applied to several aspects of surface micromachined polysilicon structures. High resolution cross-section imaging, using both a FIB/SEM and FIB/STEM, is used to acquire information on profile differences between fabrication facilities and grain size and orientation. The AFM is used to compare surface roughness on both sides (top and bottom surfaces) of thin film polysilicon after release etching. The data gathered will be extremely useful feedback for fabrication facilities in terms of process characterization and quality assurance. The data will also be useful for MEMS CAD tools where device and process models must be validated.

Three-dimensional MEMS microsystems that are commercially fabricated require minimal post-processing and are easily integrated with CMOS signal processing electronics. Measurements to evaluate the fabrication process (such as cross-sectional imaging and device performance characterization) provide much needed feedback in terms of reliability and quality assurance. MEMS technology is bringing a new class of microscale measurements to fruition. The relatively small size of MEMS microsystems offers the potential for higher fidelity recordings compared to macrosize counterparts, as illustrated in the measurement of muscle cell forces.

A microelectromechanical systems (MEMS) force transducer system, with a volume less than 1 mm/sup 3/ millimeter, has been developed to measure forces generated by living heart muscle cells. Cell attachment and measurement of contractile forces have been demonstrated with a commercially fabricated surface-micromachined hinged polysilicon device. Two freestanding polysilicon clamps, each suspended by a pair of microbeams, hold each end of a heart cell. When the cell contracts, the beam bend and force is determined from the measured deflection and the spring constant in the beams. The average maximal force over seven contractile experiments using a calcium solution stimulus was F/sub max/=12.6/spl plusmn/4.66 /spl mu/N. Normalizing to a cross-sectional area, F/sub max//area was 23.7/spl plusmn/8.6 mN/mm/sup 2/. These force data were also correlated to optically imaged striation pattern periodicity. Intermediate forces were also measured in response to a calcium solution gradient and showed similar behavior to those measured in other laboratories. This MEMS force transducer demonstrates the feasibility of higher fidelity measurements from muscle cells and, thus, an improved understanding of the mechanisms of muscle contraction.