Artificial Xylem Chip: A Three-Dimensionally Printed Vertical Digital Microfluidic Platform

Automated Droplet Ejection from a Digital Microfluidics Sample Pretreatment Device Enables Batch-Mode Chemiluminescence Immunoassay

Digital microfluidics (DMF) features programmed manipulation of fluids in multiple steps, making it a valuable tool for sample pretreatment. However, the integration of sample pretreatment with its downstream reaction and detection requires transferring droplets from the DMF device to the outside world. To address this issue, the present study developed a modified DMF device that allows automated droplet ejection out of the chip, facilitated by a tailor-designed interface. A double-layered DMF microchip with an oil-filled medium was flipped over, with a liquid infusion port and a liquid expulsion port accommodated on the top working PCB plate and the bottom grounded ITO plate, respectively, to facilitate chip-to-world delivery of droplets. Using chemiluminescent immunoassay (CLIA) as an illustrative application, the sample pretreatment was programmed on the DMF device, and CLIA droplets were ejected from the chip for signal reading. In our workflow, CLIA droplets can be ejected from the DMF device through the chip-to-world interface, freeing up otherwise occupied electrodes for more sample pretreatment and enabling streamlined droplet microreactions and batch-mode operation for bioanalysis. Integrated with these interfacing portals, the DMF system achieved a single-channel throughput of 17 samples per hour, which can be further upscaled for more productive applications by parallelizing the DMF modules. The results of this study demonstrate that the droplet ejection function that is innovated in a DMF sample pretreatment microsystem can significantly improve analytical throughput, providing an approach to establishing an automated but decentralized biochemical sample preparation workstation for large-scale and continuous bioanalysis.

Compound Droplet Generation by a Hybrid Microfluidic Device

Microfluidic technology based on a compound droplet plays an increasingly significant role in different disciplines, such as genetic detection, drug transportation, and cell culture. Low-cost, stable, and rapid methods to produce compound droplets are more and more in demand. In this paper, a hybrid 3D-printed microfluidic device was designed to realize efficient fabrication of multicore compound droplets, where a first oil phase (O1) is cut by a water phase (W) to form pure O1 droplets, and then the W phase containing O1 droplets is cut by a second oil phase (O2) to generate multicore compound droplets. A series of experiments were conducted to determine the influence of the flow rate and viscosity on the formation dynamics of compound droplets. It is found that the number of inner cores is mainly affected by the W and O2 phases, and a W phase with higher viscosity and a higher flow rate is more likely to produce compound droplets with more inner cores. This work provides new insights into the formation dynamics of compound droplets and can contribute to the optimization of emulsion production.

A review of optoelectrowetting (OEW): from fundamentals to lab-on-a-smartphone (LOS) applications to environmental sensors

Electrowetting-on-dielectric (EWOD) has been extensively explored as an active-type technology for small-scale liquid handling due to its several unique advantages, including no requirement of mechanical components, low power consumption, and rapid response time. However, conventional EWOD devices are often accompanied with complex fabrication processes for patterning and wiring of 2D arrayed electrodes. Furthermore, their sandwich device configuration makes integration with other microfluidic components difficult. More recently, optoelectrowetting (OEW), a light-driven mechanism for effective droplet manipulation, has been proposed as an alternative approach to overcome these issues. By utilizing optical addressing on a photoconductive surface, OEW can dynamically control an electrowetting phenomenon without the need for complex control circuitry on a chip, while providing higher functionality and flexibility. Using commercially available spatial light modulators such as LCD displays and smartphones, millions of optical pixels are readily generated to modulate virtual electrodes for large-scale droplet manipulations in parallel on low-cost OEW devices. The benefits of the OEW mechanism have seen it being variously explored in its potential biological and biochemical applications. This review article presents the fundamentals of OEW, discusses its research progress and limitations, highlights various technological advances and innovations, and finally introduces the emergence of the OEW technology as portable smartphone-integrated environmental sensors.

Real-Time Image Defect Detection System of Cloth Digital Printing Machine

In order to solve the surface defects such as white silk, spots, and wrinkles on the fabrics in the process of digital printing production, a surface defect detection system for printed fabrics based on the accelerated robust feature algorithm is proposed. The image registration is mainly carried out by the speeded up robust features (SURF) algorithm; the bidirectional unique matching method is used to reduce the mismatch points, realize the accurate registration of the image, and extract the defect information through the difference algorithm. The experiment uses multiple images to verify the performance of the improved SURF algorithm. The experimental results show that the detection accuracy of the new system for surface defects of printed fabrics reaches 98%. The algorithm has higher detection rate and faster detection speed, which can meet the needs of practical industrial applications.

Particle-Based Imaging Tools Revealing Water Flows in Maize Nodal Vascular Plexus

In plants, water flows are the major driving force behind growth and play a crucial role in the life cycle. To study hydrodynamics, methods based on tracking small particles inside water flows attend a special place. Thanks to these tools, it is possible to obtain information about the dynamics of the spatial distribution of the flux characteristics. In this paper, using contrast-enhanced magnetic resonance imaging (MRI), we show that gadolinium chelate, used as an MRI contrast agent, marks the structural characteristics of the xylem bundles of maize stem nodes and internodes. Supplementing MRI data, the high-precision visualization of xylem vessels by laser scanning microscopy was used to reveal the structural and dimensional characteristics of the stem vascular system. In addition, we propose the concept of using prototype “Y-type xylem vascular connection” as a model of the elementary connection of vessels within the vascular system. A Reynolds number could match the microchannel model with the real xylem vessels.

PDMS Microfabrication and Design for Microfluidics and Sustainable Energy Application: Review

The polydimethylsiloxane (PDMS) is popular for wide application in various fields of microfluidics, microneedles, biology, medicine, chemistry, optics, electronics, architecture, and emerging sustainable energy due to the intrinsic non-toxic, transparent, flexible, stretchable, biocompatible, hydrophobic, insulating, and negative triboelectric properties that meet different requirements. For example, the flexibility, biocompatibility, non-toxicity, good stability, and high transparency make PDMS a good candidate for the material selection of microfluidics, microneedles, biomedical, and chemistry microchips as well as for optical examination and wearable electronics. However, the hydrophobic surface and post-surface-treatment hydrophobic recovery impede the development of self-driven capillary microchips. How to develop a long-term hydrophilicity treatment for PDMS is crucial for capillary-driven microfluidics-based application. The dual-tone PDMS-to-PDMS casting for concave-and-convex microstructure without stiction is important for simplifying the process integration. The emerging triboelectric nanogenerator (TENG) uses the transparent flexible PDMS as the high negative triboelectric material to make friction with metals or other positive-triboelectric material for harvesting sustainably mechanical energy. The morphology of PDMS is related to TENG performance. This review will address the above issues in terms of PDMS microfabrication and design for the efficient micromixer, microreactor, capillary pump, microneedles, and TENG for more practical applications in the future.

Continuous Droplet-Actuating Platforms via an Electric Field Gradient: Electrowetting and Liquid Dielectrophoresis

This work develops a technology for actuating droplets of any size without the requirement for high voltages or active control systems, which are typically found in competitive systems. The droplet actuation relies on two microelectrodes separated by a variable gap distance to generate an electrostatic gradient. The physical mechanism for the droplet motion is a combination of liquid dielectrophoresis and electrowetting. Investigating the system behavior as a function of the driving frequency identified the relative contribution of these two mechanisms and the optimum operating conditions. A fixed signal frequency of 0.5 kHz actuated various liquids and contaminants. Droplet actuation was demonstrated on several platforms, including linear, radial-symmetric, and bilateral-symmetric droplet motion. The electrode designs are scalable and can be fabricated on a flexible and optically transparent substrate: these key advancements will enable consumer applications that were previously inaccessible. A self-cleaning platform was also tested under laboratory conditions and on the road. This technology has significant potential in microfluidics and self-cleaning platforms, for example, in the automotive sector to clean body parts, camera covers, and sensors.