Showing papers in "Journal of Micromechanics and Microengineering in 2011"
TL;DR: The presented results prove the CMUT as a MEMS technology for many medical diagnostic and therapeutic applications as well as the progression of developing several generations of fabrication processes.
Abstract: Capacitive micromachined ultrasonic transducers (CMUTs) have been subject to extensive research for the last two decades. Although they were initially developed for air-coupled applications, today their main application space is medical imaging and therapy. This paper first presents a brief description of CMUTs, their basic structure and operating principles. Our progression of developing several generations of fabrication processes is discussed with an emphasis on the advantages and disadvantages of each process. Monolithic and hybrid approaches for integrating CMUTs with supporting integrated circuits are surveyed. Several prototype transducer arrays with integrated front-end electronic circuits we developed and their use for 2D and 3D, anatomical and functional imaging, and ablative therapies are described. The presented results prove the CMUT as a micro-electro-mechanical systems technology for many medical diagnostic and therapeutic applications.
290 citations
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TL;DR: In this paper, the authors present a design methodology and manufacturing process for the construction of articulated three-dimensional microstructures with features on the micron to centimeter scale, and three example devices are presented.
Abstract: We present a design methodology and manufacturing process for the construction of articulated three-dimensional microstructures with features on the micron to centimeter scale. Flexure mechanisms and assembly folds result from the bulk machining and lamination of alternating rigid and compliant layers, similar to rigid-flex printed circuit board construction. Pop-up books and other forms of paper engineering inspire designs consisting of one complex part with a single assembly degree of freedom. Like an unopened pop-up book, mechanism links reside on multiple interconnected layers, reducing interference and allowing folding mechanisms of greater complexity than achievable with a single folding layer. Machined layers are aligned using dowel pins and bonded in parallel. Using mechanical alignment that persists during bonding allows device layers to be anisotropically pre-strained, a feature we exploit to create self-assembling structures. These methods and three example devices are presented.
229 citations
TL;DR: In this article, a wirelessly powered contact lens display was tested on live, anesthetized rabbits with no observed adverse effect, and the display can be powered wirelessly from ~1 m in free space and 2 cm in vivo on a rabbit.
Abstract: We present the design, construction and in vivo rabbit testing of a wirelessly powered contact lens display. The display consists of an antenna, a 500 × 500 µm2 silicon power harvesting and radio integrated circuit, metal interconnects, insulation layers and a 750 × 750 µm2 transparent sapphire chip containing a custom-designed micro-light emitting diode with peak emission at 475 nm, all integrated onto a contact lens. The display can be powered wirelessly from ~1 m in free space and ~2 cm in vivo on a rabbit. The display was tested on live, anesthetized rabbits with no observed adverse effect. In order to extend display capabilities, design and fabrication of micro-Fresnel lenses on a contact lens are presented to move toward a multipixel display that can be worn in the form of a contact lens. Contact lenses with integrated micro-Fresnel lenses were also tested on live rabbits and showed no adverse effect.
204 citations
TL;DR: In this paper, the authors reported real-time measurement results of various contact forces exerted on a new flexible capacitive three-axis tactile sensor array based on polydimethylsiloxane (PDMS).
Abstract: In this paper, we report real-time measurement results of various contact forces exerted on a new flexible capacitive three-axis tactile sensor array based on polydimethylsiloxane (PDMS). A unit sensor consists of two thick PDMS layers with embedded copper electrodes, a spacer layer, an insulation layer and a bump layer. There are four capacitors in a unit sensor to decompose a contact force into its normal and shear components. They are separated by a wall-type spacer to improve the mechanical response time. Four capacitors are arranged in a square form. The whole sensor is an 8 × 8 array of unit sensors and each unit sensor responds to forces in all three axes. Measurement results show that the full-scale range of detectable force is around 0‐20 mN (250 kPa) for all three axes. The estimated sensitivities of a unit sensor with the current setup are 1.3, 1.2 and 1.2%/mN for the x-, y- and z-axes, respectively. A simple mechanical model has been established to calculate each axial force component from the measured capacitance value. Normal and shear force distribution images are captured from the fabricated sensor using a real-time measurement system. The mechanical response time of a unit sensor has been estimated to be less than 160 ms. The flexibility of the sensor has also been demonstrated by operating the sensor on a curved surface of 4 mm radius of curvature. (Some figures in this article are in colour only in the electronic version)
165 citations
TL;DR: In this paper, a planar and printable thermoelectric energy generators were constructed using dispenser-printed thin film thermoeide materials, and a 50couple prototype with 5 mm × 640 µm × 90 µm printed element dimensions was fabricated on a polyimide substrate.
Abstract: This work presents advancements in dispenser-printed thick film thermoelectric materials for the fabrication of planar and printable thermoelectric energy generators. The thermoelectric properties of the printed thermoelectric materials were measured as a function of temperature. The maximum dimensionless figures of merit (ZTs) at 302 K for the n-type Bi2Te3-epoxy composite and the p-type Sb2Te3-epoxy composite are 0.18 and 0.19, respectively. A 50-couple prototype with 5 mm × 640 µm × 90 µm printed element dimensions was fabricated on a polyimide substrate with evaporated metal contacts. The prototype device produced a power output of 10.5 µW at 61.3 µA and 171.6 mV for a temperature difference of 20 K resulting in a device areal power density of 75 µW cm−2.
149 citations
TL;DR: In this paper, in-plane acoustic reflectors are proposed to enhance the quality factor (Q) in lateral-mode micromachined resonators, which can reduce the overall anchor loss with minimum modification in the resonator design.
Abstract: In this paper, novel in-plane acoustic reflectors are proposed to enhance the quality factor (Q) in lateral-mode micromachined resonators. Finite element coupled-domain simulation is used to model anchor loss and to estimate the relative change in the resonator's performance without and with the inclusion of acoustic reflectors. Several 27 and 110 MHz AlN-on-silicon resonators are fabricated and measured to validate the theoretical and simulated data. An average Q enhancement of up to 560% is reported for specific designs with reflectors over the same resonators without reflectors. The measured results trend well with the simulated data and support that the acoustic reflectors can reduce the overall anchor loss with minimum modification in the resonator design.
148 citations
TL;DR: In this article, an inertial power generator has been developed that can harvest traffic-induced bridge vibrations at only 2 Hz, and the generator is capable of operating over an unprecedentedly large acceleration (0.54 m s −2 ) and frequency range (up to 30 Hz) without any modifications or tuning.
Abstract: This paper discusses the development and testing of a renewable energy source for powering wireless sensors used to monitor the structural health of bridges. Traditional power cables or battery replacement are excessively expensive or infeasible in this type of application. An inertial power generator has been developed that can harvest traffic-induced bridge vibrations. Vibrations on bridges have very low acceleration (0.1‐0.5 m s −2 ), low frequency (2‐30 Hz), and they are non-periodic. A novel parametric frequency-increased generator (PFIG) is developed to address these challenges. The fabricated device can generate a peak power of 57 μW and an average power of 2.3 μW from an input acceleration of 0.54 m s −2 at only 2 Hz. The generator is capable of operating over an unprecedentedly large acceleration (0.54‐9.8 m s −2 ) and frequency range (up to 30 Hz) without any modifications or tuning. Its performance was tested along the length of a suspension bridge and it generated 0.5‐0.75 μW of average power without manipulation during installation or tuning at each bridge location. A preliminary power conversion system has also been developed. (Some figures in this article are in colour only in the electronic version)
137 citations
Journal Article•
135 citations
TL;DR: In this article, a survey of 23 ambient vibration sources in the machine room of a large building is presented, and a model is developed which uses a discretization method to accept measured arbitrary acceleration data as an input and gives harvester response as output.
Abstract: Micro-fabricated piezoelectric vibration energy harvesters with resonance frequencies of 31–232 Hz are characterized and deployed for testing on ambient vibration sources in the machine room of a large building. A survey of 23 ambient vibration sources in the machine room is presented. A model is developed which uses a discretization method to accept measured arbitrary acceleration data as an input and gives harvester response as output. The modeled and measured output from the energy harvesters is compared for both vibrometer and ambient vibration sources. The energy harvesters produced up to 43 nWrms g−2 on a laboratory vibrometer and 10 nW g−2 on ambient vibration sources typically in large buildings.
131 citations
TL;DR: The capabilities and limitations of µPIM as a micro-manufacturing technique by reviewing the latest developments in the area and by considering potential improvements are discussed and evaluated in this article.
Abstract: Micro-powder injection moulding (µPIM) is a fast-developing micro-manufacturing technique for the production of metal and ceramic components. Shape complexity, dimensional accuracy, replication fidelity, material variety combined with high-volume capabilities are some of the key advantages of the technology. This review assesses the capabilities and limitations of µPIM as a micro-manufacturing technique by reviewing the latest developments in the area and by considering potential improvements. The basic elements of the process chain, variant processes and simulation attempts are discussed and evaluated. Challenges and research gaps are highlighted, and potential areas for improvement are presented.
131 citations
TL;DR: This work takes a step toward in vitro mechanical or chemical manipulation of cells as well as controlled assembly of microcomponents in microbiorobots.
Abstract: One of the great challenges in microscale science and engineering is the independent manipulation of cells and man-made objects on the micron scale. For such work, motile microorganisms are integrated with engineered systems to construct microbiorobots (MBRs). MBRs are negative photosensitive epoxy (SU-8) microfabricated structures with typical feature sizes ranging from 1 to 100 µm coated with a monolayer of swarmer cells of the bacterium Serratia marcescens. The adherent cells naturally coordinate to propel the microstructures in fluidic environments. In this study, ultraviolet light is used to control rotational motion and direct current electric fields are used to control the two-dimensional movement of MBRs. They are steered in a fully automated fashion using computer-controlled visual servoing, used to transport and manipulate micron-sized objects, and employed as cell-based biosensors. This work is a step toward in vitro mechanical or chemical manipulation of cells as well as controlled assembly of microcomponents.
TL;DR: The intrinsic possibilities of an EWOD lab-on-a-chip as a versatile platform for homogeneous and heterogeneous bio-assays with high analytical performance are presented and a fully on-chip enzymatic assay is realized withhigh analytical performance.
Abstract: Electrowetting-on-dielectric (EWOD) lab-on-a-chip systems have already proven their potential within a broad range of bio-assays. Nevertheless, research on the analytical performance of those systems is limited, yet crucial for a further breakthrough in the diagnostic field. Therefore, this paper presents the intrinsic possibilities of an EWOD lab-on-a-chip as a versatile platform for homogeneous and heterogeneous bio-assays with high analytical performance. Both droplet dispensing and splitting cause variations in droplet size, thereby directly influencing the assay's performance. The extent to which they influence the performance is assessed by a theoretical sensitivity analysis, which allows the definition of a basic framework for the reduction of droplet size variability. Taking advantage of the optimized droplet manipulations, both homogeneous and heterogeneous bio-assays are implemented in the EWOD lab-on-a-chip to demonstrate the analytical capabilities and versatility of the device. A fully on-chip enzymatic assay is realized with high analytical performance. It demonstrates the promising capabilities of an EWOD lab-on-a-chip in food-related and medical applications, such as nutritional and blood analyses. Further, a magnetic bio-assay for IgE detection using superparamagnetic nanoparticles is presented whereby the nanoparticles are used as solid carriers during the bio-assay. Crucial elements are the precise manipulation of the superparamagnetic nanoparticles with respect to dispensing and separation. Although the principle of using nano-carriers is demonstrated for protein detection, it can be easily extended to a broader range of bio-related applications like DNA sensing. In heterogeneous bio-assays the chip surface is actively involved during the execution of the bio-assay. Through immobilization of specific biological compounds like DNA, proteins and cells a reactive chip surface is realized, which enhances the bio-assay performance. To demonstrate this potential, on-chip adhesion islands are fabricated to immobilize MCF-7 human breast cancer cells. Viability studies are performed to assess the functionalization efficiency.
TL;DR: In this paper, a finite volume method was used to investigate 3D acoustic streaming patterns produced by surface acoustic wave propagation within microdroplets, where a SAW microfluidic interaction was modelled using a body force acting on elements of the fluid volume within the interaction area between the SAW and fluid.
Abstract: This work uses a finite volume method to investigate three-dimensional acoustic streaming patterns produced by surface acoustic wave (SAW) propagation within microdroplets. A SAW microfluidic interaction has been modelled using a body force acting on elements of the fluid volume within the interaction area between the SAW and fluid. This enables the flow motion to be obtained by solving the laminar incompressible Navier–Stokes equations driven by an effective body force. The velocity of polystyrene particles within droplets during acoustic streaming has been measured and then used to calibrate the amplitudes of the SAW at different RF powers. The numerical prediction of streaming velocities was compared with the experimental results as a function of RF power and a good agreement was observed. This confirmed that the numerical model provides a basic understanding of the nature of 3D SAW/liquid droplet interaction, including SAW mixing and the concentration of particles suspended in water droplets.
TL;DR: A device with parallel deterministic lateral displacement devices for enrichment of leukocytes from blood shows capture of 98% and approximately ten-fold enrichment ofLeukocytes in whole blood.
Abstract: A disposable device for fractionation of blood into its components that is simple to operate and provides throughput of greater than 1 mL min−1 is highly sought after in medical diagnostics and therapies. This paper describes a device with parallel deterministic lateral displacement devices for enrichment of leukocytes from blood. We show capture of 98% and approximately ten-fold enrichment of leukocytes in whole blood. We demonstrate scaling up through the integration of six parallel devices to achieve a flow rate of 115 µL of undiluted blood per minute per atmosphere of applied pressure.
TL;DR: In this article, a poly(dimethylsiloxane) (PDMS)-based hot embossing process for low-cost rapid prototyping of plastic microfluidic devices is presented.
Abstract: We present a poly(dimethylsiloxane) (PDMS)-based hot embossing process for low-cost rapid prototyping of plastic microfluidic devices. Unlike the conventional hot embossing process, the process presented here uses a 2 mm thick PDMS mold, two 3/4" wide binder clips, two standard 1 mm thick 1" × 3" microscope glass slides and a standard laboratory oven. Micro-scale features were successfully replicated in 1.5 mm thick polystyrene slides from various PDMS molds. Also, the PDMS molds can be reused for many replications without any damage.
TL;DR: In this article, the authors present a piezoelectric energy harvesting system, which is able to self-tune its resonance frequency in an energy-autonomous way, in order to extend its efficient operation over a large frequency range.
Abstract: We present a piezoelectric energy-harvesting system, which is able to self-tune its resonance frequency in an energy-autonomous way, in order to extend its efficient operation over a large frequency range. The system consists of a resonant and frequency-tunable piezoelectric generator and a control unit. In predefined temporal intervals, the control unit analyzes the ambient vibration frequency, decides whether an adjustment of the generator's resonance frequency is necessary or not and delivers the appropriate voltage to a piezoelectric actuator which alters the generator's mechanical stiffness to tune its resonance frequency. The control unit has been optimized to an ultralow power consumption which means that up to 90% of the harvested energy can be fed to the powered electrical load, which could be an embedded system. With frequency-tunable generators, the application range of vibration energy harvesters can be extended to environments with a non-constant vibration frequency, like e.g. the surface of an engine with a varying number of revolutions per minute. Furthermore, the presented system opens the door to off-the-shelf solutions for environments with constant but uncommon vibration frequencies. With the smart tuning algorithm presented in this work, our system is even able to compensate typical weak points of piezoelectrically tunable harvesters, like e.g. hysteresis effects, the temperature dependence of the mechanical stiffness and aging effects.
TL;DR: In this paper, the microstructures of inkjet-printed nanosilver films sintered by intense pulsed light (IPL) were systematically analyzed and correlated with the electrical properties.
Abstract: In this work, the microstructures of inkjet-printed nanosilver films sintered by intense pulsed light (IPL) were systematically analyzed and correlated with the electrical properties. Nanosilver films with various dimensions were inkjet-printed and sintered at different light intensities to investigate the effects of the film dimension and light intensity on the sintering characteristics. For comparison purposes, the same inkjet-printed films were also thermally sintered at 210 °C for 1 h. Consecutive light pulses from a xenon lamp induced film swelling and the corresponding hollow microstructures of the inkjet nanosilver films. The resistance of IPL-sintered films was inversely proportional to the light intensity, and the resultant conductivity comparable to the thermally sintered one was achieved within just a few tens of ms, without damaging a polymer substrate. While all the thermally sintered patterns experienced shrinkage during the sintering process, the IPL-sintered ones could keep their initial dimension at a certain light intensity.
Abstract: Wrinkling patterns in shape memory polymer (SMP) sputter deposited with a thin layer (10 s nm in thickness) of gold atop are systematically investigated under various conditions. Depending on the surface condition, heating temperature and pre-straining, different patterns of micro/nano-scaled wrinkles are produced. Although elastic buckling of the gold layer is the mechanism behind all types of wrinkles, the shape memory effect (SME) and thermal expansion mismatch (TEM) are the driving force for different patterns after heating to different temperatures, i.e. the evolution of wrinkle pattern is due to the SME after heating to low temperatures and the TEM after heating to high temperatures. The flexibility and convenience in using SMP to achieve different wrinkling patterns is demonstrated.
TL;DR: In this paper, a parylene insulating/moisture barrier layers and Ti/Au electrodes were fabricated from the nanocomposite using a fabrication process designed specifically for this chemical and temperature-sensitive material.
Abstract: This paper reports the development of micromachining processes and mechanical evaluation of a stimuli-responsive, mechanically dynamic polymer nanocomposite for biomedical microsystems. This nanocomposite consists of a cellulose nanofiber network encased in a polyvinyl acetate matrix. Micromachined tensile testing structures fabricated from the nanocomposite displayed a reversible and switchable stiffness comparable to bulk samples, with a Young's modulus of 3420 MPa when dry, reducing to ~20 MPa when wet, and a stiff-to-flexible transition time of ~300 s. This mechanically dynamic behavior is particularly attractive for the development of adaptive intracortical probes that are sufficiently stiff to insert into the brain without buckling, but become highly compliant upon insertion. Along these lines, a micromachined neural probe incorporating parylene insulating/moisture barrier layers and Ti/Au electrodes was fabricated from the nanocomposite using a fabrication process designed specifically for this chemical- and temperature-sensitive material. It was found that the parylene layers only slightly increased the stiffness of the probe in the wet state in spite of its much higher Young's modulus. Furthermore, the Ti/Au electrodes exhibited impedance comparable to Au electrodes on conventional substrates. Swelling of the nanocomposite was highly anisotropic favoring the thickness dimension by a factor of 8 to 12, leading to excellent adhesion between the nanocomposite and parylene layers and no discernable deformation of the probes when deployed in deionized water.
TL;DR: In this article, the effect of two types of commonly used side-clamped, anchoring-stem geometries on the quality factor of three different laterally-driven resonator topologies was examined.
Abstract: MEMS resonators fabricated in silicon-on-insulator (SOI) technology must be clamped to the substrate via anchoring stems connected either from within the resonator or through the sides, with the side-clamped solution often employed due to manufacturing constraints. This paper examines the effect of two types of commonly used side-clamped, anchoring-stem geometries on the quality factor of three different laterally-driven resonator topologies. This study employs an analytical framework which considers the relative distribution of strain energies between the resonating body and clamping stems. The ratios of the strain energies are computed using ANSYS FEA and used to provide an indicator of the expected anchor-limited quality factors. Three MEMS resonator topologies have been fabricated and characterized in moderate vacuum. The associated measured quality factors are compared against the computed strain energy ratios, and the trends are shown to agree well with the experimental data.
TL;DR: In this paper, a generalized foundry-oriented CMOS-MEMS platform for integrated micromechanical resonators alongside IC amplifiers is developed for commercial multi-user purpose and demonstrated with a fast turnaround time of only 3 months and a variety of design flexibilities for resonator applications.
Abstract: A generalized foundry-oriented CMOS-MEMS platform well suited for integrated micromechanical resonators alongside IC amplifiers has been developed for commercial multi-user purpose and demonstrated with a fast turnaround time of only 3 months and a variety of design flexibilities for resonator applications. With this platform, different configurations of capacitively-transduced resonators monolithically integrated with their amplifier circuits, spanning frequencies from 500 kHz to 14.5 MHz, have been realized with resonator Q’s ranging between 700 and 3500. This platform, specifically featured with various configurations of structural materials, multi-dimensional displacements, different arrangements of mechanical boundary conditions, tiny supports of resonators, large transduction areas, well-defined anchors and performance enhancement scaling with IC fabrication technology, offers a variety of flexible design options targeted for sensor, timing reference, and RF applications. In addition, resonators consisting of metal-oxide composite structures fabricated by this platform offer an effective temperature compensation scheme for the first time in CMOS-MEMS resonators, showing TCf six times better than that of resonators merely made by CMOS metals. (Some figures in this article are in colour only in the electronic version)
TL;DR: In this article, the effect of meniscus curvature on the permeability of micro-post arrays was investigated using the capillary rate of rise experiment and numerical simulation, and the results obtained from the analytical model match the experimental and numerical results within the error of 5% over the range of parameters commonly found in microfluidic applications.
Abstract: This study aims to investigate the effect of meniscus curvature on the permeability of the micro-post arrays, which are widely used for applications of microfluidics. An analytical model that accounts for the meniscus curvature is developed. The model considers two common array types: quadratic and hexagonal arrays. The permeability of micro-post arrays is estimated using the capillary rate of rise experiment and numerical simulation. The results obtained from the analytical model match the experimental and numerical results within the error of 5% over the range of parameters commonly found in microfluidic applications (0.06 0.2), where d * and H * are the post-diameter and the post-height, respectively, which are normalized by the pitch. Based on the analytic results, the effects of the post-diameter, post-height and the contact angle on the permeability of post-arrays are investigated. It is shown that the previous permeability models based on the flat meniscus assumption overestimate the experimental value by 26% for the quadratic array and 24% for the hexagonal array when cos θ = 1, d * = 0.5 and H *=1. The effect of the meniscus curvature is shown to become more pronounced as the contact angle or the post-height decreases.
TL;DR: In this paper, the authors theoretically investigate their ultimate limit of detection and enunciate design rules for performance optimization of aluminum nitride (AlN) piezoelectric microcantilevers.
Abstract: Due to low power operation, intrinsic integrability and compatibility with CMOS processing, aluminum nitride (AlN) piezoelectric (PZE) microcantilevers are a very attractive paradigm for resonant gas sensing. In this paper, we theoretically investigate their ultimate limit of detection and enunciate design rules for performance optimization. The reduction of the AlN layer thickness is found to be critical. We further report the successful development and implementation in cantilever structures with a 50 nm thick active PZE AlN layer. Material characterizations demonstrate that the PZE e_(31) coefficient can remain as high as 0.8 C m^(−2). Electrically transduced frequency responses of the fabricated devices are in good agreement with analytical predictions. Finally, we demonstrate the excellent frequency stability with a 10^(−8) minimum Allan deviation. This exceptionally low noise operation allows us to expect a limit of detection as low as 53 zg µm^(−2) and demonstrate the strong potential of AlN PZE microcantilevers for high resolution gas detection.
TL;DR: In this paper, a liquid crystal polymer (LCP) membrane-based pressure sensor for flow rate and flow direction sensing applications is presented, which demonstrates a good sensitivity of 3.695 mV (ms−1)−1, large operating range (0.1 to >10 ms−1), and good accuracy in measuring airflow.
Abstract: The paper reports the design, fabrication and experimental results of a liquid crystal polymer (LCP) membrane-based pressure sensor for flow rate and flow direction sensing applications. Elaborate experimental testing results demonstrating the sensors' performance as an airflow sensor have been illustrated and validated with theory. MEMS sensors using LCP as a membrane structural material show higher sensitivity and reliability over silicon counterparts. The developed device is highly robust for harsh environment applications such as atmospheric wind flow monitoring and underwater flow sensing. A simple, low-cost and repeatable fabrication scheme has been developed employing low temperatures. The main features of the sensor developed in this work are a LCP membrane with integrated thin film gold piezoresistors deposited on it. The sensor developed demonstrates a good sensitivity of 3.695 mV (ms−1)−1, large operating range (0.1 to >10 ms−1) and good accuracy in measuring airflow with an average error of only 3.6% full-scale in comparison with theory. Various feasible applications of the developed sensor have been demonstrated with experimental results. The sensor was tested for two other applications—in clinical diagnosis for breath rate, breath velocity monitoring, and in underwater applications for object detection by sensing near-field spatial flow pressure.
TL;DR: In this article, a self-directed capillary densification method is proposed for CNT micropillar densification, where a liquid is controllably condensed onto and evaporated from the CNT forests.
Abstract: Vertically aligned carbon nanotube (CNT) ‘forest’ microstructures fabricated by chemical vapor deposition (CVD) using patterned catalyst films typically have a low CNT density per unit area. As a result, CNT forests have poor bulk properties and are too fragile for integration with microfabrication processing. We introduce a new self-directed capillary densification method where a liquid is controllably condensed onto and evaporated from the CNT forests. Compared to prior approaches, where the substrate with CNTs is immersed in a liquid, our condensation approach gives significantly more uniform structures and enables precise control of the CNT packing density. We present a set of design rules and parametric studies of CNT micropillar densification by self-directed capillary action, and show that self-directed capillary densification enhances Young’s modulus and electrical conductivity of CNT micropillars by more than three orders of magnitude. Owing to the outstanding properties of CNTs, this scalable process will be useful for the integration of CNTs as a functional material in microfabricated devices for mechanical, electrical, thermal and biomedical applications. (Some figures in this article are in colour only in the electronic version)
TL;DR: The use of electrodeformation as a method for single cell mechanical characterization in which mechanical properties of SiHa and ME180 cells (two cervical cancer cell lines) were quantified was presented.
Abstract: This paper presents the use of electrodeformation as a method for single cell mechanical characterization in which mechanical properties of SiHa and ME180 cells (two cervical cancer cell lines) were quantified. Cells were directly placed between two microelectrodes with a rectangular ac electric field applied, and cell deformation was recorded under certain experimental conditions. Numerical simulations were performed to model cell electrodeformation based on the Maxwell stress tensor formulation. In these simulations, effects of cell electrical property variations on their electrodeformed behavior were investigated. By comparing the measured morphological changes with those obtained from numerical simulations, we were able to quantify Young's modulus of SiHa cells (601 ± 183 Pa) and ME180 cells (1463 ± 649 Pa). These values were consistent with Young's modulus values (SiHa: 400 ± 290 Pa and ME180: 1070 ± 580 Pa) obtained from conventional micropipette aspiration.
TL;DR: By introducing aminosilane derivatives into CYTOP-based perfluorinated polymer film, a nano-clusters containing the organic siloxanes in the polymer electrets was observed in this paper.
Abstract: Development of high-performance electret materials is required to obtain a large power output of the electrostatic vibration-driven energy harvesters. In this study, by introducing aminosilane derivatives into CYTOP-based perfluorinated polymer film, we have successfully formed nano-clusters containing the organic siloxanes in the polymer electrets. Using small-angle x-ray scattering, tapping mode AFM and SEM analysis, the existence of such nano-clusters has been directly observed in the CYTOP film. It is suggested that the observed nano-clusters serve as the charge trap site and enhance the surface charge density and the thermal stability of the trapped charges. As a polymer electret, an extremely high surface charge potential of −1.6 kV with the 15 µm thick film has been obtained under the optimum condition of corona charging.
TL;DR: In this article, a size-dependent model for electrostatically actuated microbeam-based MEMS using strain gradient elasticity theory is presented, where the normalized pull-in voltage is shown to increase nonlinearly with the decrease of the beam height, and the size effect becomes prominent if the beam thickness is on the order of microns or smaller.
Abstract: We present a size-dependent model for electrostatically actuated microbeam-based MEMS using strain gradient elasticity theory. The normalized pull-in voltage is shown to increase nonlinearly with the decrease of the beam height, and the size effect becomes prominent if the beam thickness is on the order of microns or smaller (i.e. when the beam dimension is comparable to the material length scale parameter). Very good agreement is found between the present model and available experimental data. The study may be helpful to characterize the mechanical properties of small size MEMS, or guide the design of microbeam-based devices for a wide range of potential applications.
TL;DR: MEMS sensors, because of their small size and fine force/displacement resolution, are ideal for force and displacement sensing at the single cell level, leading to robust statistical studies.
Abstract: Forces generated by cells play a vital role in many cellular processes such as cell spreading, motility, differentiation and apoptosis. Understanding the mechanics of single cells is essential to delineate the link between cellular force generation/sensing and function. MEMS sensors, because of their small size and fine force/displacement resolution, are ideal for force and displacement sensing at the single-cell level. In addition, the amenability of MEMS sensors to batch fabrication methods allows the study of large cell populations simultaneously, leading to robust statistical studies. In this paper, we discuss various microsystems used for studying cell mechanics and the insights on cell mechanical behavior that have resulted from their use. The advantages and limitations of these microsystems for biological studies are also outlined.
TL;DR: An integrated strain array for cell culture enabling high-throughput mechano-transduction studies and proof of compatibility with basic biological assays and standard imaging equipment was accomplished.
Abstract: We have developed an integrated strain array for cell culture enabling high-throughput mechano-transduction studies. Biocompatible cell culture chambers were integrated with an acrylic pneumatic compartment and microprocessor-based control system. Each element of the array consists of a deformable membrane supported by a cylindrical pillar within a well. For user-prescribed waveforms, the annular region of the deformable membrane is pulled into the well around the pillar under vacuum, causing the pillar-supported region with cultured cells to be stretched biaxially. The optically clear device and pillar-based mechanism of operation enables imaging on standard laboratory microscopes. Straightforward fabrication utilizes off-the-shelf components, soft lithography techniques in polydimethylsiloxane and laser ablation of acrylic sheets. Proof of compatibility with basic biological assays and standard imaging equipment were accomplished by straining C2C12 skeletal myoblasts on the device for 6 h. At higher strains, cells and actin stress fibers realign with a circumferential preference.