Editorial for the Special Issue on Micro/Nano-Chip Electrokinetics

Micro/nanofluidics-based lab-on-a-chip devices have found extensive applications in the analysis of chemical and biological samples over the past two decades. Electrokinetics is the method of choice in these micro/nano-chips for transporting, manipulating and sensing various analyte species (e.g., ions, molecules, fluids and particles, etc.) [1,2]. This Special Issue in Micromachines is aimed to provide the recent development in the field of Micro/Nano-Chip Electrokinetics. It consists of 15 papers, which cover both fundamentals and applications, original research and review

Micro/Nano-Chip Electrokinetics

Micro/nanofluidic chips have found increasing applications in the analysis of chemical and biological samples over the past two decades. Electrokinetics has become the method of choice in these micro/nano-chips for transporting, manipulating and sensing ions, (bio)molecules, fluids and (bio)particles, etc., due to the high maneuverability, scalability, sensitivity, and integrability. The involved phenomena, which cover electroosmosis, electrophoresis, dielectrophoresis, electrohydrodynamics, electrothermal flow, diffusioosmosis, diffusiophoresis, streaming potential, current, etc., arise from either the inherent or the induced surface charge on the solid-liquid interface under DC and/or AC electric fields. To review the state-of-the-art of micro/nanochip electrokinetics, we welcome, in this Special Issue of Micromachines, all original research or review articles on the fundamentals and applications of the variety of electrokinetic phenomena in both microfluidic and nanofluidic devices

From Cleanroom to Desktop: Emerging Micro-Nanofabrication Technology for Biomedical Applications

This review is motivated by the growing demand for low-cost, easy-to-use, compact-size yet powerful micro-nanofabrication technology to address emerging challenges of fundamental biology and translational medicine in regular laboratory settings. Recent advancements in the field benefit considerably from rapidly expanding material selections, ranging from inorganics to organics and from nanoparticles to self-assembled molecules. Meanwhile a great number of novel methodologies, employing off-the-shelf consumer electronics, intriguing interfacial phenomena, bottom-up self-assembly principles, etc., have been implemented to transit micro-nanofabrication from a cleanroom environment to a desktop setup. Furthermore, the latest application of micro-nanofabrication to emerging biomedical research will be presented in detail, which includes point-of-care diagnostics, on-chip cell culture as well as bio-manipulation. While significant progresses have been made in the rapidly growing field, both apparent and unrevealed roadblocks will need to be addressed in the future. We conclude this review by offering our perspectives on the current technical challenges and future research opportunities

Microdevices and Microsystems for Cell Manipulation

Microfabricated devices and systems capable of micromanipulation are well-suited for the manipulation of cells. These technologies are capable of a variety of functions, including cell trapping, cell sorting, cell culturing, and cell surgery, often at single-cell or sub-cellular resolution. These functionalities are achieved through a variety of mechanisms, including mechanical, electrical, magnetic, optical, and thermal forces. The operations that these microdevices and microsystems enable are relevant to many areas of biomedical research, including tissue engineering, cellular therapeutics, drug discovery, and diagnostics. This Special Issue will highlight recent advances in the field of cellular manipulation. Technologies capable of parallel single-cell manipulation are of special interest

A novel electrical conductive resin for stereolithographic 3D printing

L'abstract è presente nell'allegato / the abstract is in the attachmen

Construction of artificial skin tissue with placode-like structures in well-defined patterns using dielectrophoresis

During embryonic development of animal skin tissue, the skin cells form regular patterns of high cell density (placodes) where hair or feathers will be formed. These placodes are thought to be formed by the aggregation of dermal cells into condensates. The aggregation process is thought to be controlled by a reaction-diffusion mechanism of activator and inhibitor molecules, and involve mechanical forces between cells and cells with the matrix. In this project, placode formation in chicken embryonic skin cells was used as a model system for the study of the mechanism by which the placodes are formed. Artificial aggregates of chicken embryonic skin cells were created by suspending them in a 300 mM low conductivity sorbitol solution and attracting them by positive dielectrophoresis to high field regions within microelectrode arrays by applying a 10 - 20 Vpk-pk 1 MHz signal across the microelectrodes. It was demonstrated that using this method aggregates can be produced in a large variety of patterns and that the distance between the aggregates and aggregate size and shape within the pattern can be controlled effectively. Custom-built image analysis tools were developed in LabVIEW to analyze the patterns formed. The formation of aggregates by dielectrophoresis was followed by an immobilization phase of the resulting patterns inside a gel matrix, forming an artificial skin. Nutrients and oxygen were supplied externally. Long-term incubation of the artificial skin shows that embryonic skin cells in the aggregates were viable and showed behavior similar to that of developing embryonic skin, including further aggregation of the cells and the formation of cell condensates. The domain size was shown to have an influence on the condensation process, with cells in small aggregates forming only one condensate near the centre of the aggregate, and several condensates in larger aggregates. Whilst the distribution of cell condensates within the aggregates in round large aggregates is predominantly random, some line formation could be observed in linear aggregations, indicating some self-organization may be occurring

An Integrative Approach to Elucidating the Governing Mechanisms of Particles Movement under Dielectrophoretic and Other Electrokinetic Phenomena

Dielectrophoresis (DEP) has been a subject of active research in the past decades and has shown promising applications in Lab-on-Chip devices. Currently researchers use the point dipole method to predict the movement of particles under DEP and guide their experimental designs. For studying the interaction between particles, the Maxwell Stress Tensor (MST) method has been widely used and treated as providing the most robust and accurate solution. By examining the derivation processes, it became clear that both methods have inherent limitations and will yield incorrect results in certain occasions. To overcome these limitations and advance the theory of DEP, a new numerical approach based on volumetric-integration has been established. The new method has been proved to be valid in quantifying the DEP forces with both homogeneous and non-homogeneous particles as well as particle-particle interaction through comparison with the other two methods. Based on the new method, a new model characterizing the structure of electric double layer (EDL) was developed to explain the crossover behavior of nanoparticles in medium. For bioengineering applications, this new method has been further expanded to construct a complete cell model. The cell model not only captures the common crossover behavior exhibited by cells, it also explains why cells would initiate self-rotation under DEP, a phenomenon we first observed in our experiments. To take a step further, the new method has also been applied to investigate the interaction between multiple particles. In particular, this new method has been proved to be powerful in elucidating the underlying mechanism of the tumbling motion of pearl chains in a flow condition as we observed in our experiments. Moreover, it also helps shed some new insight into the formation of different alignments and configurations of ellipsoidal particles. Finally, with the consideration of the Faradic current from water electrolysis and effect of pH, a new model has been developed to explain the causes for the intriguing flow reversal phenomenon commonly observed (but not at all understood) in AC-electroosmosis (ACEO) with reasonable outcomes