We report a flexible and versatile microcontact printing process using a micromachined elastomeric PDMS (poly-dimethylsiloxane) stamp with two-dimensional arrays of pyramidal tips. The PDMS stamp was molded from a bulk-etched single-crystalline silicon master. By changing the contact pressure, arrayed dot patterns with different dot sizes (from submicron to a few microns) were obtained controllably with one single PDMS stamp. Variable density of dot patterns was also achieved in a 'step-print' manner by conducting multiple printing on a transitional stage. This technique is expected to be useful in many nano- and biotechnology applications, including single cell and neuron studies.

This paper describes a new technology permitting a hybrid integration of silicon chips in polymer (PDMS and SU8) microfluidic structures. This two-step technology starts with transferring the silicon device onto a rigid substrate (typically PCB) and planarizing it, and then it proceeds with stacking of the polymer-made fluidic network onto the device. The technology is low cost, based on screen printing and lamination, can be applied to treat large surface areas, and is compatible with standard photolithography and vacuum based approaches. We show, as an example, the integration of a thermal sensor inside channels made of PDMS or SU8. The developed structures had no fluid leaks at the Si/polymer interfaces and the electrical circuit was perfectly tightproof.

Combustion behavior in a radial microchannel with a gap of 2.0 mm and a diameter of 50 mm was experimentally investigated. In order to simulate the heat recirculation, which is an essential strategy in microscale combustion devices, positive temperature gradients along the radial flow direction were given to the microchannel by an external heat source. A methane–air mixture was supplied from the center of the top plate through a 4.0 mm diameter delivery tube. A variety of flame patterns, including a stable circular flame and several unstable flame patterns termed unstable circular flame, single and double pelton-like flames, traveling flame and triple flame, were observed in the experiments. The regime diagram of all these flame patterns is presented in this paper. Some characteristics of the various flame patterns, such as the radii of stable and unstable circular flames, major combustion products and combustion efficiencies of all these flame patterns, were also investigated. F...

A simple micromolding method for fabricating PLGA (poly(lactic- co-glycolic acid)) microstructures made up of microchannels with a circular cross-section is presented. The thermal reflow technique is adopted to fabricate the semi-cylindrical photoresist master. The PLGA solution is prepared by dissolving PLGA polymer in acetone and then casting the solution onto the semi-cylindrical photoresist master to produce PLGA microstructures. Two PLGA membranes are bonded together to form microstructures consisting of circular microchannels. A microvessel scaffold suitable for tissue engineering was fabricated using the proposed method, and bovine endothelial cells were cultured into the scaffold by semi-dynamic seeding. The cell stain Calcein-AM was used to overcome the problem of the PLGA scaffolds becoming opaque, which in the past had made it difficult to effectively monitor the progress of cell seeding.

This paper presents a novel 3D porous micromixer fabricated using a selective ultrasonic foaming technique. The 3D porous structure can split, stretch, fold and break the mixing flows effectively and thus dramatically improves the mixing efficiency of microfluidic flows. In the paper, we report on the fabrication and performance of the 3D porous micromixer. The effects of flow rate, mixing length and pore size were studied using flow visualization experiments. It is shown that the proposed micromixer performs very well for flows with a wide range of Reynolds numbers. Sufficient mixing results can be achieved with a short mixing length for flows with Reynolds numbers as low as 0.1.

In this paper we present a 3D nonlinear dynamic model which describes the transient mechanical analysis of an ohmic contact RF MEMS switch, using finite element analysis in combination with the finite difference method. The model includes real switch geometry, electrostatic actuation, the two-dimensional non-uniform squeeze-film damping effect, the adherence force, and a nonlinear spring to model the interaction between the contact tip and the drain. The ambient gas in the package is assumed to act as an ideal and isothermal fluid which is modeled using the Reynolds squeeze-film equation which includes compressibility and slip flow. A nonlinear contact model has been used for modeling contact between the microswitch tip and the drain electrode during loading. The Johnson–Kendall–Roberts (JKR) contact model is utilized to calculate the adherence force during unloading. The developed model has been used to simulate the overall dynamic behavior of the MEMS switches including the swi...

In this paper, trends from the last 10 years of inertial micro-generator literature are investigated and it is shown that, although current generator designs are still operating well below their maximum power, there has been a significant improvement with time. Whilst no clear conclusions could be drawn from reported fabricated devices with respect to preferred transducer technology, this paper presents operating charts for inertial micro-generators which identify optimal operating modes for different frequencies and normalized generator sizes, and allows comparison of the different transduction mechanisms as these parameters vary. It is shown that piezoelectric generators have a wider operating range at low frequency than electromagnetic generators, but as generator dimensions increase, the frequency to which piezoelectric transducers outperform electromagnetic transducers decreases.

We have investigated the influence of the microfabrication processes for microelectromechanical systems (MEMS) on the degradation in the ferroelectric and piezoelectric properties of Pb(Zr,Ti)O ₃ (PZT) thin films. Multilayers of Pt/Ti/PZT/Pt/Ti/SiO ₂ were deposited on silicon-on-insulator (SOI) wafers. The multilayers were fabricated into piezoelectric micro cantilevers through a MEMS microfabrication process. The positive and negative remanent polarizations were reduced to 56% and 35% of the initial value after the microfabrication process. The results indicated that the top interface between PZT and Pt sustained more damage than the bottom interface. We have also found that wet etching of PZT thin films especially degrades the ferroelectric property. The butterfly curve for the displacement of the fabricated cantilevers displayed an asymmetric shape. This reflects the greater damage to the top interface between the PZT and Pt thin films. The transverse piezo...

Manipulation and characterization of individual biological cells require cellular forces to be precisely measured in real time. This paper presents a computer vision-based cellular force measurement platform that allows for the use of a single vision sensor (CCD/CMOS camera) to simultaneously obtain two forms of feedback (i.e., vision and force). A novel silicone elastomer-based cell holding device and a sub-pixel visual tracking algorithm are developed. Deflections of elastic, low-stiffness structures are visually tracked, and material deflections are subsequently transformed into cellular forces. Experimental results demonstrate that the current vision-based force sensing system is capable of performing robust cellular force measurements at a full 30 Hz with a 3.7 µN resolution. Importantly, the vision-based cellular force sensing framework established in this study is not scale- or cell-line-dependent. The device design, visual tracking algorithm, and experimental technique fo...

A novel design for hingeless out-of-plane microstructures is presented. These structures can be assembled to 90° by a single-point actuation, which can be provided by, for example, a microelectronics wirebonder or a microprober station. Both wirebonders and microprober stations are commonly available to microfabrication facilities, and therefore the assembly method described here introduces a practical and economical approach to the creation of out-of-plane structures. The microstructure designs can be used in many types of microfabrication processes, and in particular have been fabricated using both PolyMUMPs and an SU-8 technology developed at Simon Fraser University. In addition to the fabricated devices, we will present the results of finite element analysis (FEA). Also reported here are tests for positional repeatability and reliability.