Showing papers in "Journal of Micromechanics and Microengineering in 2018"
TL;DR: In this paper, a soft actuator embedded with two types of eutectic alloys is presented, which enable sensing, tunable mechanical degrees of freedom (DOF), and variable stiffness properties.
Abstract: This paper presents a soft actuator embedded with two types of eutectic alloys which enable sensing, tunable mechanical degrees of freedom (DOF), and variable stiffness properties. To modulate the stiffness of the actuator, we embedded a low melting point alloy (LMPA) in the bottom portion of the soft actuator. Different sections of the LMPA could be selectively melted by the Ni–Cr wires twined underneath. To acquire the curvature information, EGaIn (eutectic gallium indium) was infused into a microchannel surrounding the chambers of the soft actuator. Systematic experiments were performed to characterize the stiffness, tunable DOF, and sensing the bending curvature. We found that the average bending force and elasticity modulus could be increased about 35 and 4000 times, respectively, with the LMPA in a solid state. The entire LMPA could be melted from a solid to a liquid state within 12 s. In particular, up to six different motion patterns could be achieved under each pneumatic pressure of the soft actuator. Furthermore, the kinematics of the actuator under different motion patterns could be obtained by a mathematical model whose input was provided by the EGaIn sensor. For demonstration purposes, a two-fingered gripper was fabricated to grasp various objects by adjusting the DOF and mechanical stiffness.
75 citations
TL;DR: In this paper, the authors demonstrate fabrication, characterization, and implementation of'soft-matter' pressure and bending sensors for a soft robotic hand, which are embedded in a robot finger composed of a 3D printed endoskeleton and covered by an elastomeric skin.
Abstract: We demonstrate fabrication, characterization, and implementation of 'soft-matter' pressure and bending sensors for a soft robotic hand. The elastomer-based sensors are embedded in a robot finger composed of a 3D printed endoskeleton and covered by an elastomeric skin. Two types of sensors are evaluated, resistive pressure sensors and capacitive pressure sensors. The sensor is fabricated entirely out of insulating and conductive rubber, the latter composed of polydimethylsiloxane (PDMS) elastomer embedded with a percolating network of structured carbon black (CB). The sensor-integrated fingers have a simple materials architecture, can be fabricated with standard rapid prototyping methods, and are inexpensive to produce. When incorporated into a robotic hand, the CB–PDMS sensors and PDMS carrier medium function as an 'artificial skin' for touch and bend detection. Results show improved response with a capacitive sensor architecture, which, unlike a resistive sensor, is robust to electromechanical hysteresis, creep, and drift in the CB–PDMS composite. The sensorized fingers are integrated in an anthropomorphic hand and results for a variety of grasping tasks are presented.
72 citations
TL;DR: This review article will emphasize the basic concept and working mechanism associated with electroporation, single cell Electroporation and biomolecular delivery using micro/nanofluidic devices, their fabrication, working principles and cellular analysis with their advantages, limitations, potential applications and future prospects.
Abstract: © 2018 IOP Publishing Ltd. The ability to deliver foreign molecules into a single living cell with high transfection efficiency and high cell viability is of great interest in cell biology for applications in therapeutic development, diagnostics and drug delivery towards personalized medicine. Many chemical and physical methods have been developed for cellular delivery, however most of these techniques are bulk approach, which are cell-specific and have low throughput delivery. On the other hand, electroporation is an efficient and fast method to deliver exogenous biomolecules such as DNA, RNA and oligonucleotides into target living cells with the advantages of easy operation, controllable electrical parameters and avoidance of toxicity. The rapid development of micro/nanofluidic technologies in the last two decades, enables us to focus an intense electric field on the targeted cell membrane to perform single cell micro-nano-electroporation with high throughput intracellular delivery, high transfection efficiency and cell viability. This review article will emphasize the basic concept and working mechanism associated with electroporation, single cell electroporation and biomolecular delivery using micro/nanoscale electroporation devices, their fabrication, working principles and cellular analysis with their advantages, limitations, potential applications and future prospects.
41 citations
TL;DR: In this paper, the authors report low-actuation voltage RF MEMS switch and its reliability test and show that low voltage can improve the lifetime of the switch without any failure in the frequency range up to 60 GHz.
Abstract: Lack of reliability of radio-frequency microelectromechanical systems (RF MEMS) switches has inhibited their commercial success. Dielectric stiction/breakdown and mechanical shock due to high actuation voltage are common impediments in capacitive MEMS switches. In this work, we report low-actuation voltage RF MEMS switch and its reliability test. Experimental characterization of fabricated devices demonstrate that proposed MEMS switch topology needs very low voltage (4.8 V) for actuation. The mechanical resonant frequency, f(0), quality factor, Q, and switching time are measured to be 8.35 kHz, 1.2, and 33 microsecond, respectively. These MEMS switches have high reliability in terms of switching cycles. Measurements are performed using pulse waveform of magnitude of 6 V under hot-switching condition. Temperature measurement results confirm that the reported switch topology has good thermal stability. The robustness in terms of the measured pull-in voltage shows a variation of 0.08 V degrees C-1. Lifetime measurement results after 10 million switching cycles demonstrate insignificant change in the RF performance without any failure. Experimental results show that low voltage improves the lifetime. Low insertion loss (less than 0.6 dB) and improved isolation (above 40 dB) in the frequency range up to 60 GHz have been reported. Measured RF characteristics in the frequency range from 10 MHz to 60 GHz support that these MEMS switches are favorable choice for mm-wave 5G applications.
41 citations
TL;DR: In this article, the kinematics of the vibration assisted milling process is formulated and surface texture formation in end-to-end milling with different machining and vibration parameters is discussed.
Abstract: This paper proposes a new surface texture formation method by non-resonant vibration assisted milling. Firstly, the kinematics of the vibration assisted milling process is formulated and surface texture formation in end milling with different machining and vibration parameters is discussed. Various types of surface textures can be generated by different combinations of machining and vibration parameters. Secondly, a novel 2D non-resonant vibration stage is developed to realize the vibration during the milling process. Thirdly, vibration assisted milling experiments are carried out to verify the proposed surface texture formation method and the effects of the vibration and machining parameters on the surface texture generation. Finally, hydrophilic performance of the machined surfaces with different surface textures is investigated to demonstrate the application of the proposed method.
39 citations
TL;DR: In this article, symmetric comb-electrode structures for the electrostatic vibrational MEMS energy harvester were introduced to lower the electric constraint force attributed to the built-in electret potential, thereby allowing the harvesters device to operate in a small acceleration range of 0.05 g or lower.
Abstract: We introduce symmetric comb-electrode structures for the electrostatic vibrational MEMS energy harvester to lower the electrostatic constraint force attributed to the built-in electret potential, thereby allowing the harvester device to operate in a small acceleration range of 0.05 g or lower (1 g = 9.8 m s−2). Given the same device structure, two different potentials for the electret are tested to experimentally confirm that the output induction current is enhanced 4.2 times by increasing the electret potential from −60 V to −250 V. At the same time, the harvester effectiveness has been improved to as high as 93%. The device is used to swiftly charge a 470 µF storage capacitor to 3.3 V in 120 s from small sinusoidal vibrations of 0.6 g at 124 Hz.
37 citations
34 citations
TL;DR: A CSFH has been analyzed with both theoretical and finite element methods, in order to obtain the relation between voltage and generated torque, and showed that CSFH performs better than linear flexure hinges in terms of larger rotations and less stress for given applied voltage.
Abstract: Progress in MEMS technology continuously stimulates new developments in the mechanical structure of micro systems, such as, for example, the concept of so-called CSFH (conjugate surfaces flexural hinge), which makes it possible, simultaneously, to minimize the internal stresses and to increase motion range and robustness. Such a hinge may be actuated by means of a rotary comb-drive, provided that a proper set of simulations and tests are capable to assess its feasibility. In this paper, a CSFH has been analyzed with both theoretical and finite element (FEM) methods, in order to obtain the relation between voltage and generated torque. The FEM model considers also the fringe effect on the comb drive finger. Electromechanical couple–field analysis is performed by means of both direct and load transfer methods. Experimental tests have been also performed on a CSFH embedded in a MEMS prototype, which has been fabricated starting from a SOI wafer and using D–RIE (deep reactive ion etching). Results showed that CSFH performs better than linear flexure hinges in terms of larger rotations and less stress for given applied voltage.
32 citations
TL;DR: On-chip acoustic actuation of in situ fabricated artificial cilia is presented, illustrating one potential application wherein researchers can achieve spatiotemporal control of biological microenvironments in cell stimulation studies.
Abstract: We present on-chip acoustic actuation of in situ fabricated artificial cilia. Arrays of cilia structures are UV polymerized inside a microfluidic channel using a photocurable polyethylene glycol (PEG) polymer solution and photomasks. During polymerization, cilia structures are attached to a silane treated glass surface inside the microchannel. Then, the cilia structures are actuated using acoustic vibrations at 4.6 kHz generated by piezo transducers. As a demonstration of a practical application, DI water and fluorescein dye solutions are mixed inside a microfluidic channel. Using pulses of acoustic excitations, and locally fabricated cilia structures within a certain region of the microchannel, a waveform of mixing behavior is obtained. This result illustrates one potential application wherein researchers can achieve spatiotemporal control of biological microenvironments in cell stimulation studies. These acoustically actuated, in situ fabricated, cilia structures can be used in many on-chip applications in biological, chemical and engineering studies.
31 citations
TL;DR: In this paper, a basic study on hydrodynamic cavitation on chip is performed, in which the authors use microfluidic devices with rough surfaces and micro restrictive elements.
Abstract: The importance of the hydrodynamic cavitation phenomenon in small domains has been increasing during recent decades along with the global demand for microfluidic devices involving small-scale cavitation applications. Different characteristics of microscale hydrodynamic cavitation relative to the conventional size can be exploited in futuristic applications and improvements in the performances of new-generation microfluidic devices. Therefore, in-depth studies on the fundamentals of microscale hydrodynamic cavitation are required to reveal new physics of small-scale hydrodynamic cavitation. In this study, microfluidic devices with rough surfaces and micro restrictive elements are fabricated so that a basic study on 'Hydrodynamic Cavitation on Chip' is performed. Cavitating flows are investigated under transient and fully developed turbulent conditions within the Reynolds number range between 2962 and 8620 and cavitation number range between 2.025 and 0.72. The microfluidic devices have short restrictive elements with hydraulic diameters of 75, 66.6 and 50 mu m and lengths of 2 mm, which are connected to a bigger microchannel with a width of 900 mu m and length of 2 mm, called an 'extended channel'. Different upstream pressures up to 900 Psi are applied at the inlet. The hydrodynamic cavitation inception is recorded and analyzed for each microfluidic device. Flow patterns are characterized inside the microfluidic devices from cavitation inception to chocked flow conditions. Accordingly, it is observed that the transition from inception to choked occurs slowly in contrast to microscale hydrodynamic cavitation results in the literature under laminar flow conditions. Moreover, the comparison between microfluidic devices with roughened and plane (smooth) surfaces reveals that the roughened surface results in more intense cavitating flows, especially at higher upstream pressures relative to the plane surface.
30 citations
TL;DR: A wearable conformal in vivo eye fatigue monitoring sensor that contains an array of piezoelectric nanoribbons integrated on an ultrathin flexible substrate that may efficiently detect abnormal eyelid motions and provide feedback for assessing eye fatigue in time so that unexpected situations can be prevented.
Abstract: Eye fatigue is a symptom induced by long-term work of both eyes and brains. Without proper treatment, eye fatigue may incur serious problems. Current studies on detecting eye fatigue mainly focus on computer vision detect technology which can be very unreliable due to occasional bad visual conditions. As a solution, we proposed a wearable conformal in vivo eye fatigue monitoring sensor that contains an array of piezoelectric nanoribbons integrated on an ultrathin flexible substrate. By detecting strains on the skin of eyelid, the sensors may collect information about eye blinking, and, therefore, reveal human's fatigue state. We first report the design and fabrication of the piezoelectric sensor and experimental characterization of voltage responses of the piezoelectric sensors. Under bending stress, the output voltage curves yield key information about the motion of human eyelid. We also develop a theoretical model to reveal the underlying mechanism of detecting eyelid motion. Both mechanical load test and in vivo test are conducted to convince the working performance of the sensors. With satisfied durability and high sensitivity, this sensor may efficiently detect abnormal eyelid motions, such as overlong closure, high blinking frequency, low closing speed and weak gazing strength, and may hopefully provide feedback for assessing eye fatigue in time so that unexpected situations can be prevented.
TL;DR: In this paper, a 6 × 8 flexible piezoresistive tactile sensor array composed of a multi-walled carbon nanotube (MWCNT) and polydimethylsiloxane (PDMS) composite is presented.
Abstract: This paper reports on a 6 × 8 flexible piezoresistive tactile sensor array composed of a multi-walled carbon nanotube (MWCNT)–polydimethylsiloxane (PDMS) composite. The sensor array has properties such as high flexibility, stretchability, uniformity and sensitivity, contributing to the anomalous-shaped surface nano-composite structure on the sensing elements. The sensitivity of the tactile sensor is 16.9–5.41 in a low-pressure range ( 0.5 at 1.3 kPa for the 125 µm thick composite sensing materials. The systematic study of the pressure response of the developed tactile sensor array in terms of various composite thickness, temperature, uniformity and repeatability have been conducted. Moreover, an array scanning system has been established and the applied pressure was detected, digitalized and displayed in real-time. This work has high potential for low-range pressure detection and artificial skin applications.
TL;DR: This work proposes a hybrid actuator design with bio-inspirations from the lobsters, which can generate reconfigurable bending movements through the internal soft chamber interacting with the external rigid shells, and enables it to exactly track its bending configurations that previously posed a significant challenge to soft robots.
Abstract: Soft pneumatic actuators (SPAs) are intrinsically light-weight, compliant and therefore ideal to directly interact with humans and be implemented into wearable robotic devices. However, they also pose new challenges in describing and sensing their continuous deformation. In this paper, we propose a hybrid actuator design with bio-inspirations from the lobsters, which can generate reconfigurable bending movements through the internal soft chamber interacting with the external rigid shells. This design with joint and link structures enables us to exactly track its bending configurations that previously posed a significant challenge to soft robots. Analytic models are developed to illustrate the soft-rigid interaction mechanism with experimental validation. A robotic glove using hybrid actuators to assist grasping is assembled to illustrate their potentials in safe human-robot interactions. Considering all the design merits, our work presents a practical approach to the design of next-generation robots capable of achieving both good accuracy and compliance.
TL;DR: In this article, the design and manufacturing of composite PDMS/nanofiber actuators using soft lithography and rotary jet spinning is described, and the impact of lamina design and fiber orientation on actuator curvature, mechanical properties, and pressurization range is examined.
Abstract: Soft pneumatic actuators are promising candidates for micro-manipulation and delicate gripping due to their wide range of motion and ease of fabrication. While existing elastomer-based devices have attracted attention due to their compliant structures, there is a need for materials that combine flexibility, controllable actuation, and robustness. This paper bridges this capability gap by introducing a novel fabrication strategy for nanofiber-reinforced soft micro-actuators. The design and manufacturing of composite PDMS/nanofiber actuators using soft lithography and rotary jet spinning is described. We examine the impact of lamina design and fiber orientation on actuator curvature, mechanical properties, and pressurization range. Composite actuators displayed a 25.8% higher maximum pressure than pure PDMS devices. Further, the best nanofiber-reinforced laminates tested were 2.3 times tougher than the control PDMS material while maintaining comparable elongation. Finally, bending and bending-twisting are demonstrated using pristine and laser-patterned nanofiber sheets, respectively.
TL;DR: In this article, conformable epidermal printed electronics enabled from gallium-based liquid metals (LMs), highly conductive and low-melting point alloys, are proposed as the core to achieving immediate contact between skin surface and electrodes, which can avoid the skin deformation often caused by conventional rigid electrodes.
Abstract: Conformable epidermal printed electronics enabled from gallium-based liquid metals (LMs), highly conductive and low-melting-point alloys, are proposed as the core to achieving immediate contact between skin surface and electrodes, which can avoid the skin deformation often caused by conventional rigid electrodes. When measuring signals, LMs can eliminate resonance problems with shorter time to reach steady state than Pt and gelled Pt electrodes. By comparing the contact resistance under different working conditions, it is demonstrated that both ex vivo and in vivo LM electrode–skin models have the virtues of direct and immediate contact with skin surface without the deformation encountered with conventional rigid electrodes. In addition, electrocardio electrodes composed of conformable LM printed epidermal electronics are adopted as smart devices to monitor electrocardiogram signals of rabbits. Furthermore, simulation treatment for smart defibrillation offers a feasible way to demonstrate the effect of liquid metal electrodes (LMEs) on the human body with less energy loss. The remarkable features of soft epidermal LMEs such as high conformability, good conductivity, better signal stability, and fine biocompatibility represent a critical step towards accurate medical monitoring and future smart treatments.
TL;DR: In this paper, a MEMS electret vibration energy harvester with an embedded bistable electrostatic spring for broadband response is proposed, and the performance of harvesters with the proposed mechanism is characterized in detail for harmonic excitation, band-limited white noise, and colored noise.
Abstract: A MEMS electret vibration energy harvester with an embedded bistable electrostatic spring for broadband response is proposed. By using a vertical electret, the bistable potential can be realized without any complex structure or additional mechanism. Based on the 1D electrostatic model, a rigorous electromechanical model as well as an approximate model with reduced parameters are developed. Based on the normalized expression of the approximate model, which is identical to the velocity-damped resonant generator model, the performance of harvesters with the proposed mechanism has been characterized in detail for harmonic excitation, band-limited white noise, and colored noise. In addition, its performance has been compared with that of a conventional duffing-type bistable generator. It is confirmed that the present mechanism has advantages such as a lower frequency range, and outperforms the duffing counterpart for colored noise.
TL;DR: In this paper, a novel technology for microfabricating 3D origami-styled micro electromechanical systems (MEMS) structures with glassy carbon (GC) features and a supporting polymer substrate is reported.
Abstract: We report on a novel technology for microfabricating 3D origami-styled micro electromechanical systems (MEMS) structures with glassy carbon (GC) features and a supporting polymer substrate. GC MEMS devices that open to form 3D microstructures are microfabricated from GC patterns that are made through pyrolysis of polymer precursors on high-temperature resisting substrates like silicon or quartz and then transferring the patterned devices to a flexible substrate like polyimide followed by deposition of an insulation layer. The devices on flexible substrate are then folded into 3D form in an origami-fashion. These 3D MEMS devices have tunable mechanical properties that are achieved by selectively varying the thickness of the polymeric substrate and insulation layers at any desired location. This technology opens new possibilities by enabling microfabrication of a variety of 3D GC MEMS structures suited to applications ranging from biochemical sensing to implantable microelectrode arrays. As a demonstration of the technology, a neural signal recording microelectrode array platform that integrates both surface (cortical) and depth (intracortical) GC microelectrodes onto a single flexible thin-film device is introduced. When the device is unfurled, a pre-shaped shank of polyimide automatically comes Journal of Micromechanics and Microengineering Glassy carbon MEMS for novel origami-styled 3D integrated intracortical and epicortical neural probes
TL;DR: In this article, a 2.0 MHz resonant displacement amplifier composed of two identical clamped-clamped-beams coupled by a mechanical beam at locations where the two beams have mismatched velocities exhibits a larger displacement, up to 9.96×, on one beam than that of the other.
Abstract: This paper presents a micromechanical clamped–clamped beam (CC-beam) displacement amplifier based on a CMOS-MEMS fabrication process platform. In particular, a 2.0 MHz resonant displacement amplifier composed of two identical CC-beams coupled by a mechanical beam at locations where the two beams have mismatched velocities exhibits a larger displacement, up to 9.96×, on one beam than that of the other. The displacement amplification prevents unwanted input impacting—the structure switches only to the output but not the input—required by resonant switch-based mechanical circuits (Kim et al 2009 22nd IEEE Int. Conf. on Micro Electro Mechanical Systems; Lin et al 2009 15th Int. Conf. on Solid-State Sensors, Actuators, & Microsystems (TRANSDUCERS'09); Li et al 2013 17th Int. Conf. on Solid-State Sensors, Actuators, & Microsystems (TRANSDUCERS'13)). Compared to a single CC-beam displacement amplifier, theory predicts that the displacement amplifying CC-beam array yields a larger overall output displacement for displacement gain beyond 1.13 thanks to the preserved input driving force. A complete analytical model predicts the resultant stiffness and displacement gain of the coupled CC-beam displacement amplifier that match well with finite element analysis (FEA) prediction and measured results.
TL;DR: In this article, the authors reported the successful implementation of an aluminum nitride (AlN) piezoelectric film for the fabrication of a large-aperture MEMS scanning micromirror.
Abstract: This paper reports on the successful implementation of an aluminum nitride (AlN) piezoelectric film for the fabrication of a large-aperture MEMS scanning micromirror. To overcome the shortcoming of the relatively low piezoelectric coefficients of AlN film, a leverage amplification mechanism and resonant amplification effect are employed to amplify the scan angle of the mirror plate. Compared to conventional PZT piezoelectric micromirrors, the fabricated AlN film-based micromirror has demonstrated excellent compatibility with the current MEMS process. In particular, piezoelectric angle sensors are monolithically integrated without any additional process or material. The test results indicate the great linear actuation relationship and the good signal quality of the integrated angle sensors. Therefore, the proposed AlN micromirror will provide a new promising option for vast optical microsystem applications.
TL;DR: In this paper, a permanent structural asymmetry compensation method for fused quartz micro wineglass resonators was proposed, which demonstrated a near six times reduction of structural asymmetric (n = 2 wineglass mode), culminating in reduction of the frequency split from 41 to 7 Hz.
Abstract: We present, for the first time, a permanent structural asymmetry compensation method for fused quartz micro wineglass resonators. Using the technique, we demonstrated a near six times reduction of structural asymmetry (n = 2 wineglass mode), culminating in reduction of the frequency split from 41 to 7 Hz. This is an iterative process. In each iteration, the structural asymmetry was first identified by measuring the mode shape of the resonators. Then, directional lapping was performed with specially designed lapping fixtures to accurately control the lapping angle down to 1°. Analytical predictions and numerical simulations were conducted to study the structural asymmetry phenomenon and the effects of compensation on the quality factor of the structure, showing the ability of this process to reduce the structural asymmetry, while not affecting the overall quality factor of the resonators.
TL;DR: In this article, the authors demonstrate the concept of a high-efficient mixing microfluidic chip as a basic unit to provide rapid mixing for lab-on-a-chip applications.
Abstract: As a platform to mix the bioagents (i.e. serum, urine), we take advantage of the alternating current electrothermal (ACET) effect which is quite suitable for rapid pumping/mixing of high conductive biomicrofluids. Here we demonstrate the concept of a high-efficient mixing microfluidic chip as a basic unit to provide rapid mixing for lab-on-a-chip applications. As an active mixer, two streams are introduced into a ring-shape microchamber by a passive flow rate regulator, and then the microfluids in the chamber are actuated by a nonuniform electric field with a phase shift of 180°. It shows perfect mixing performance by arranging four arc-electrodes around the ring-shape microchamber subsequently. Taking the Joule heating and conductivity/permittivity changes into consideration, a temperature dependent fully coupled numerical model is presented. Then, the effects of applied voltages on mixing performance and temperature rise are provided to get an optimized design for ACET mixer. Moreover, the arrangement of the electrode array is analyzed to show the effects of electrode patterns on the swirls and mixing efficiencies. Since all the electrodes here are located along a ring-shape central microchamber, the ring-shape micromixer is quite suitable to function as a compact element modular for integrated microfluidic chips.
TL;DR: An inductive tactile sensor with a chrome steel ball sensing interface based on the commercially available standard complementary metaloxide-semiconductor (CMOS) process (the TSMC 0.18 µm 1P6M CMOS process) is presented in this paper.
Abstract: This study presents an inductive tactile sensor with a chrome steel ball sensing interface based on the commercially available standard complementary metal–oxide–semiconductor (CMOS) process (the TSMC 0.18 µm 1P6M CMOS process). The tactile senor has a deformable polymer layer as the spring of the device and no fragile suspended thin film structures are required. As a tactile force is applied on the chrome steel ball, the polymer would deform. The distance between the chrome steel ball and the sensing coil would changed. Thus, the tactile force can be detected by the inductance change of the sensing coil. In short, the chrome steel ball acts as a tactile bump as well as the sensing interface. Experimental results show that the proposed inductive tactile sensor has a sensing range of 0–1.4 N with a sensitivity of 9.22(%/N) and nonlinearity of 2%. Preliminary wireless sensing test is also demonstrated. Moreover, the influence of the process and material issues on the sensor performances have also been investigated.
TL;DR: In this article, a displacement amplifying mechanism with a corner-filleted flexure hinge was proposed to achieve high frequency glue jetting and improve the stability of jetting dispensers.
Abstract: This paper presents a new jetting dispenser which is applicable to high-frequency microelectronic packaging. In order to achieve high frequency glue jetting and improve the stability of jetting dispensers, we redesign a novel displacement amplifying mechanism, and a new on–off valve jetting dispenser driven by piezoelectric actuators is developed. Firstly, the core part of this jetting dispenser—the displacement amplifying mechanism with a corner-filleted flexure hinge—is proposed and a comparison with the previous structure is carried out; then the characteristic dimensional parameters of the amplifying mechanism are determined by theoretical calculation and finite element analysis. Secondly, a prototype of the dispenser with the displacement amplifying mechanism is fabricated based on the determined parameters. We use a laser displacement sensor to test the displacement of the needle, and a maximum amplifying displacement output of 367 µm is obtained under an applied 200 V to the piezoelectric actuator, which is consistent with the simulation result and meets the requirement of high displacement output. Thirdly, we build an integrated testing system. Mixed glycerol/ethanol is chosen as the experimental dispensing glue, and the experiment and analysis of a droplet diameter are conducted. A higher jetting frequency of 400 Hz and a smaller droplet diameter of 525 µm are achieved with the glycerol/ethanol mixture, and the characteristics of consistency and temperature influencing the droplet diameter are verified by experiments.
TL;DR: This biosensor utilizes the lowest analyte volume reported for TDM with microneedle technology, and presents significant avenues to improve current TDM methods for patients, by potentially eliminating blood draws for several drug candidates.
Abstract: A hollow metallic microneedle is integrated with microfluidics and photonic components to form a microneedle-optofluidic biosensor suitable for therapeutic drug monitoring (TDM) in biological fluids, like interstitial fluid, that can be collected in a painless and minimally-invasive manner. The microneedle inner lumen surface is bio-functionalized to trap and bind target analytes on-site in a sample volume as small as 0.6 nl, and houses an enzyme-linked assay on its 0.06 mm2 wall. The optofluidic components are designed to rapidly quantify target analytes present in the sample and collected in the microneedle using a simple and sensitive absorbance scheme. This contribution describes how the biosensor components were optimized to detect in vitro streptavidin-horseradish peroxidase (Sav-HRP) as a model analyte over a large detection range (0–7.21 µM) and a very low limit of detection (60.2 nM). This biosensor utilizes the lowest analyte volume reported for TDM with microneedle technology, and presents significant avenues to improve current TDM methods for patients, by potentially eliminating blood draws for several drug candidates.
TL;DR: This paper reviews recent developments of microfluidic cell culture devices for the control of gaseous microenvironments, and discusses the advantages and limitations of current devices.
Abstract: Gaseous microenvironments play important roles in various biological activities in vivo. However, it is challenging to precisely control gaseous microenvironments in vitro for cell culture due to the high diffusivity nature of gases. In recent years, microfluidics has paved the way for the development of new types of cell culture devices capable of manipulating cellular microenvironments, and provides a powerful tool for in vitro cell studies. This paper reviews recent developments of microfluidic cell culture devices for the control of gaseous microenvironments, and discusses the advantages and limitations of current devices. We conclude with suggestions for the future development of microfluidic cell culture devices for the control of gaseous microenvironments.
TL;DR: In this article, the feasibility of using direct fabrication of microscale features by additive manufacturing (AM) processes was investigated, and the results indicated the possibility of using precision AM for a rapid, easy and reliable fabrication method for functional surfaces.
Abstract: Functional surfaces have proven their potential to solve many engineering problems, attracting great interest among the scientific community. Bio-inspired multi-hierarchical micro-structures grant the surfaces with new properties, such as hydrophobicity, adhesion, unique optical properties and so on. The geometry and fabrication of these surfaces are still under research. In this study, the feasibility of using direct fabrication of microscale features by additive manufacturing (AM) processes was investigated. The investigation was carried out using a specifically designed vat photopolymerization AM machine-tool suitable for precision manufacturing at the micro dimensional scale which has previously been developed, built and validated at the Technical University of Denmark. It was shown that it was possible to replicate a simplified surface inspired by the Tokay gecko, the geometry was previously designed and replicated by a complex multi-step micromanufacturing method extracted from the literature and used as benchmark. Ultimately, the smallest printed features were analyzed by conducting a sensitivity analysis to obtain the righteous parameters in terms of layer thickness and exposure time. Moreover, two more intricate designs were fabricated with the same parameters to assess the surfaces functionality by its wettability. The surface with increased density and decreased feature size showed a water contact angle (CA) of 124° ± 0.10°, agreeing with the Cassie–Baxter model. These results indicate the possibility of using precision AM for a rapid, easy and reliable fabrication method for functional surfaces.
TL;DR: In this paper, the authors proposed a piezoelectric micromachined ultrasonic transducers (pMUTs) with etching holes to decrease thermoelastic dissipation and enhance quality factor (Q).
Abstract: Thermoelastic dissipation is one of the main dissipative mechanisms in piezoelectric micromachined ultrasonic transducers (pMUTs). In this paper, we firstly propose pMUTs with etching holes to decrease thermoelastic dissipation and enhance quality factor (Q). The etching holes effectively disturb heat flow, and thus reduce thermoelastic loss. Working mechanism based on the Zener's model is interpreted. The experiment results show that the Q of pMUT with three rows of holes is increased by 139% from 2050 to 4909 compared with the traditional one. Temperature coefficient of frequency (TCF) and vibration performance are also improved. The enhanced pMUT can be widely used in measurement of Doppler shift and relative high power applications.