Digital Microfluidic System with Vertical Functionality

Development of a Microfluidic Chip Powered by EWOD for In Vitro Manipulation of Bovine Embryos

Digital microfluidics (DMF) holds great potential for the alleviation of laboratory procedures in assisted reproductive technologies (ARTs). The electrowetting on dielectric (EWOD) technology provides dynamic culture conditions in vitro that may better mimic the natural embryo microenvironment. Thus far, EWOD microdevices have been proposed for in vitro gamete and embryo handling in mice and for analyzing the human embryo secretome. This article presents the development of the first microfluidic chip utilizing EWOD technology designed for the manipulation of bovine embryos in vitro. The prototype sustains the cell cycles of embryos manipulated individually on the chips during in vitro culture (IVC). Challenges related to the chip fabrication as well as to its application during bovine embryo IVC in accordance with the adapted on-chip protocol are thoroughly discussed, and future directions for DMF in ARTs are indicated.

Integrating machine learning and digital microfluidics for screening experimental conditions

Digital microfluidics (DMF) has the signatures of an ideal liquid handling platform - as shown through almost two decades of automated biological and chemical assays. However, in the current state of DMF, we are still limited by the number of parallel biological or chemical assays that can be performed on DMF. Here, we report a new approach that leverages design-of-experiment and numerical methodologies to accelerate experimental optimization on DMF. The integration of the one-factor-at-a-time (OFAT) experimental technique with machine learning algorithms provides a set of recommended optimal conditions without the need to perform a large set of experiments. We applied our approach towards optimizing the radiochemistry synthesis yield given the large number of variables that affect the yield. We believe that this work is the first to combine such techniques which can be readily applied to any other assays that contain many parameters and levels on DMF.

Droplet Transportation through an Orifice on Electrode for Digital Microfluidics Modulations

A digital microfluidic modular interface (chip-to-chip interface) which possesses an electrode with an orifice to vertically transport core-shell droplets is presented. The electrodes were geometrically designed to promote droplet deformation and suspension. The droplets were then applied with an electrical potential for insertion into and passage through the orifice. The concepts were tested with three types of droplets at the volume of 0.75~1.5 μL, which is usually difficult to transfer through an orifice. The integration of electrowetting on dielectric (EWOD) with paper-based microfluidics was demonstrated: the droplet could be transported within 10 s. More importantly, most of the core droplet (~97%) was extracted and passed through with only minimal shell droplets accompanying it.

Photolithographic Patterning of Cytop with Limited Contact Angle Degradation

Cytop is a commercially available amorphous fluoropolymer with excellent characteristics including electric insulation, water and oil repellency, chemical resistance, and moisture-proof property, making it an attractive material as hydrophobic layers in electrowetting-on-dielectric (EWOD) devices. However, its highly hydrophobic surface makes it difficult for photoresists to be directly coated on the surface. To pattern Cytop, plasma treatment prior to applying photoresists is required to promote the adhesion between the photoresist and the Cytop coating. This approach inevitably causes hydrophobicity loss in the final EWOD devices. Thus, a damage-reduced recipe for Cytop patterning is urgently needed. In this paper, we first characterized the damage caused by two categories of surface treatment methods: plasma treatment and metal treatment. Parameters such as plasma gas source (Ar/O₂), plasma treatment time (0⁻600 s), metal target (Al/Cu/Cr/Au), metal deposition process (magnetron sputtering or e-beam evaporation) were varied. Film thickness, wettability, and roughness were quantified by ellipsometry measurements, contact angle measurements, and atom force microscope (AFM), respectively. We then evaluated the effectiveness of annealing in damage reduction. Experimental results show that: (1) annealing is necessary in restoring hydrophobicity as well as smoothing surfaces; (2) specified film thickness can be obtained by controlling plasma treatment time; (3) "Ar/O₂ plasma treatment + an AZ5214 soft mask + annealing" is a feasible recipe; (4) "an Al/Cu/Cr/Au hard mask + annealing" is feasible as well.

Droplet Velocity Measurement Based on Dielectric Layer Thickness Variation Using Digital Microfluidic Devices

In recent years, the number of interdisciplinary research works related to the development of miniaturized systems with integrated chemical and biological analyses is increasing. Digital microfluidic biochips (DMFBs) are one kind of miniaturized systems designed for conducting inexpensive, fast, convenient and reliable biochemical assay procedures focusing on basic scientific research and medical diagnostics. The role of a dielectric layer in the digital microfluidic biochips is prominent as it helps in actuating microliter droplets based on the electrowetting-on-dielectric (EWOD) technique. The advantages of using three different material layers of dielectric such as parafilm, polytetrafluoroethylene (PTFE) and ethylene tetrafluoroethylene (ETFE) were reported in the current work. A simple fabrication process of a digital microfluidic device was performed and good results were obtained. The threshold of the actuation voltage was determined for all dielectric materials of varying thicknesses. Additionally, the OpenDrop device was tested by utilizing a single-plate system to transport microliter droplets for a bioassay operation. With the newly proposed fabrication methods, these dielectric materials showed changes in contact angle and droplet velocity when the actuation voltage was applied. The threshold actuation voltage for the dielectric layers of 10⁻13 μm was 190 V for the open plate DMFBs.

Digital microfluidics for spheroid-based invasion assays

Cell invasion is a key process in tissue growth, wound healing, and tumor progression. Most invasion assays examine cells cultured in adherent monolayers, which fail to recapitulate the three-dimensional nuances of the tissue microenvironment. Multicellular cell spheroids have a three-dimensional (3D) morphology and mimic the intercellular interactions found in tissues in vivo, thus providing a more physiologically relevant model for studying the tissue microenvironment and processes such as cell invasion. Spheroid-based invasion assays often require tedious, manually intensive handling protocols or the use of robotic liquid handling systems, which can be expensive to acquire, operate, and maintain. Here we describe a digital microfluidic (DμF) platform that enables formation of spheroids by the hanging drop method, encapsulation of the spheroids in collagen, and the exposure of spheroids to migration-modulating agents. Collagen sol-gel solutions up to 4 mg mL(-1), which form gels with elastic moduli up to ∼50 kPa, can be manipulated on the device. In situ spheroid migration assays show that cells from human fibroblast spheroids exhibit invasion into collagen gels, which can be either enhanced or inhibited by the delivery of exogenous migration modulating agents. Exposing fibroblast spheroids to spheroid secretions from colon cancer spheroids resulted in a >100% increase in fibroblast invasion into the collagen gel, consistent with the cancer-associated fibroblast phenotype. These data show that DμF can be used to automate the liquid handling protocols for spheroid-based invasion assays and create a cell invasion model that mimics the tissue microenvironment more closely than two-dimensional culturing techniques do. A DμF platform that facilitates the creation and assaying of 3D in vitro tissue models has the potential to make automated 3D cell-based assays more accessible to researchers in the life sciences.

Optofluidic Device Based Microflow Cytometers for Particle/Cell Detection: A Review

Optofluidic devices combining micro-optical and microfluidic components bring a host of new advantages to conventional microfluidic devices. Aspects, such as optical beam shaping, can be integrated on-chip and provide high-sensitivity and built-in optical alignment. Optofluidic microflow cytometers have been demonstrated in applications, such as point-of-care diagnostics, cellular immunophenotyping, rare cell analysis, genomics and analytical chemistry. Flow control, light guiding and collecting, data collection and data analysis are the four main techniques attributed to the performance of the optofluidic microflow cytometer. Each of the four areas is discussed in detail to show the basic principles and recent developments. 3D microfabrication techniques are discussed in their use to make these novel microfluidic devices, and the integration of the whole system takes advantage of the miniaturization of each sub-system. The combination of these different techniques is a spur to the development of microflow cytometers, and results show the performance of many types of microflow cytometers developed recently.