A Bi-Directional Acoustic Micropump Driven by Oscillating Sharp-Edge Structures.

This paper proposes a bi-directional acoustic micropump driven by two groups of oscillating sharp-edge structures: one group of sharp-edge structures with inclined angles of 60° and a width of 40 µm, and another group with inclined angles of 45° and a width of 25 µm. One of the groups of sharp-edge structures will vibrate under the excitation of the acoustic wave generated with a piezoelectric transducer at its corresponding resonant frequency. When one group of sharp-edge structures vibrates, the microfluid flows from left to right. When the other group of sharp-edge structures vibrates, the microfluid flows in the opposite direction. Some gaps are designed between the sharp-edge structures and the upper surface and the bottom surface of the microchannels, which can reduce the damping between the sharp-edge structures and the microchannels. Actuated with an acoustic wave of a different frequency, the microfluid in the microchannel can be driven bidirectionally by the inclined sharp-edge structures. The experiments show that the acoustic micropump, driven by oscillating sharp-edge structures, can produce a stable flow rate of up to 125 µm/s from left to right, when the transducer was activated at 20.0 kHz. When the transducer was activated at 12.8 kHz, the acoustic micropump can produce a stable flow rate of up to 85 µm/s from right to left. This bi-directional acoustic micropump, driven by oscillating sharp-edge structures, is easy to operate and shows great potential in various applications.

Study on the Heat Source Insulation of a Thermal Bubble-Driven Micropump with Induction Heating.

Thermal bubble-driven micropumps have the advantages of high reliability, simple structure and simple fabrication process. However, the high temperature of the thermal bubble may damage some biological or chemical properties of the solution. In order to reduce the influence of the high temperature of the thermal bubbles on the pumped liquid, this paper proposes a kind of heat insulation micropump driven by thermal bubbles with induction heating. The thermal bubble and its chamber are designed on one side of the main pumping channel. The high temperature of the thermal bubble is insulated by the liquid in the heat insulation channel, which reduces the influence of the high temperature of the thermal bubble on the pumped liquid. Protypes of the new micropump with heat source insulation were fabricated and experiments were performed on them. The experiments showed that the temperature of the pumped liquid was less than 35 °C in the main pumping channel.

A Concentration Gradients Tunable Generator with Adjustable Position of the Acoustically Oscillating Bubbles.

It is essential to control concentration gradients at specific locations for many biochemical experiments. This paper proposes a tunable concentration gradient generator actuated by acoustically oscillating bubbles trapped in the bubble channels using a controllable position based on the gas permeability of polydimethylsiloxane (PDMS). The gradient generator consists of a glass substrate, a PDMS chip, and a piezoelectric transducer. When the trapped bubbles are activated by acoustic waves, the solution near the gas-liquid interface is mixed. The volume of the bubbles and the position of the gas-liquid interface are regulated through the permeability of the PDMS wall. The tunable concentration gradient can be realized by changing the numbers and positions of the bubbles that enable the mixing of fluids in the main channel, and the amplitude of the applied voltage. This new device is easy to fabricate, responsive, and biocompatible, and therefore has great application prospects. In particular, it is suitable for biological research with high requirements for temporal controllability.

Recent Advances in MEMS-Based Microthrusters.

With the development of micro/nano satellites and formation flying, more advanced spatial propulsion technology is required. In this paper, a review of microthrusters developments that based on micro electromechanical systems (MEMS) technology adopted in microthrusters is summarized. The microthrusters in previous research are classified and summarized according to the types of propellants and the working principles they utilized. The structure and the performance including the thrust, the impulse and the specific impulse of various microthrusters are compared. In addition, the advantages and the disadvantages of these microthrusters presented in the paper are discussed.

Manipulation of micro-objects using acoustically oscillating bubbles based on the gas permeability of PDMS.

This paper presents a novel manipulation method for micro-objects using acoustically oscillating bubbles with a controllable position based on the gas permeability of polydimethylsiloxane. The oscillating bubble trapped within the side channel attracts the neighboring micro-objects, and the position of the air-liquid interface is controlled by generating temporary pressure difference between the side channel and the air channel. To demonstrate the feasibility of the method in technological applications, polystyrene microparticles of 10 µm in diameter were successfully captured, transported, and released. The influence of pressure difference on the movement speed of the air-liquid interface was demonstrated in our experiments, and the manipulation performance was also characterized by varying the frequency of the acoustic excitation and the pressure difference. Since the bubble generation and the air-liquid interface movement in our manipulation method do not need any electrochemical reaction and any high temperature, this on-chip manipulation method provides a controllable, efficient, and noninvasive tool for handling micro-objects such as particles, cells, and other entities. The whole manipulation process, including capturing, transporting, and releasing of particles, spent less than 1 min. It can be used to select the cells and particles in the microfluidic device or change the cell culture medium.