Digital microfluidic three-dimensional cell culture and chemical screening platform using alginate hydrogels

Digital microfluidics for biological analysis and applications

Digital microfluidics (DMF) is an emerging liquid-handling technology based on arrays of microelectrodes for the precise manipulation of discrete droplets. DMF offers the benefits of automation, addressability, integration and dynamic configuration ability, and provides enclosed picoliter-to-microliter reaction space, making it suitable for lab-on-a-chip biological analysis and applications that require high integration and intricate processes. A review of DMF bioassays with a special emphasis on those actuated by electrowetting on dielectric (EWOD) force is presented here. Firstly, a brief introduction is presented on both the theory of EWOD actuation and the types of droplet motion. Subsequently, a comprehensive overview of DMF-based biological analysis and applications, including nucleic acid, protein, immunoreaction and cell assays, is provided. Finally, a discussion on the strengths, challenges, and potential applications and perspectives in this field is presented.

Contactless Micro-Droplet Manipulation of Liquid Released from a Parallel Plate to an Open Region in Electrowetting-on-Dielectric Platform

In electrowetting-on-dielectric (EWOD) platform, the transfer of droplets from the EWOD boundary region (top plate and bottom plate) to the open region is challenging. The challenge is due to the resistance-like surface tension, friction from the top-plate edge, and the so-called boundary. For this purpose, we designed the top plate to minimize the friction resistance at the boundary. The experiment focused on Gibb’s formula and successfully transferred the liquid droplet between the top plate and bottom plate boundary region under a high voltage environment. The threshold voltage for the successful transportation of the droplet between the boundary is 250 V which provides strong pressure to drive the droplet.

Polymeric Hydrogels for In Vitro 3D Ovarian Cancer Modeling

Ovarian cancer (OC) grows and interacts constantly with a complex microenvironment, in which immune cells, fibroblasts, blood vessels, signal molecules and the extracellular matrix (ECM) coexist. This heterogeneous environment provides structural and biochemical support to the surrounding cells and undergoes constant and dynamic remodeling that actively promotes tumor initiation, progression, and metastasis. Despite the fact that traditional 2D cell culture systems have led to relevant medical advances in cancer research, 3D cell culture models could open new possibilities for the development of an in vitro tumor microenvironment more closely reproducing that observed in vivo. The implementation of materials science and technology into cancer research has enabled significant progress in the study of cancer progression and drug screening, through the development of polymeric scaffold-based 3D models closely recapitulating the physiopathological features of native tumor tissue. This article provides an overview of state-of-the-art in vitro tumor models with a particular focus on 3D OC cell culture in pre-clinical studies. The most representative OC models described in the literature are presented with a focus on hydrogel-based scaffolds, which guarantee soft tissue-like physical properties as well as a suitable 3D microenvironment for cell growth. Hydrogel-forming polymers of either natural or synthetic origin investigated in this context are described by highlighting their source of extraction, physical-chemical properties, and application for 3D ovarian cancer cell culture.

A review on microfluidics manipulation of the extracellular chemical microenvironment and its emerging application to cell analysis

Spatiotemporal manipulation of extracellular chemical environments with simultaneous monitoring of cellular responses plays an essential role in exploring fundamental biological processes and expands our understanding of underlying mechanisms. Despite the rapid progress and promising successes in manipulation strategies, many challenges remain due to the small size of cells and the rapid diffusion of chemical molecules. Fortunately, emerging microfluidic technology has become a powerful approach for precisely controlling the extracellular chemical microenvironment, which benefits from its integration capacity, automation, and high-throughput capability, as well as its high resolution down to submicron. Here, we summarize recent advances in microfluidics manipulation of the extracellular chemical microenvironment, including the following aspects: i) Spatial manipulation of chemical microenvironments realized by convection flow-, diffusion-, and droplet-based microfluidics, and surface chemical modification; ii) Temporal manipulation of chemical microenvironments enabled by flow switching/shifting, moving/flowing cells across laminar flows, integrated microvalves/pumps, and droplet manipulation; iii) Spatiotemporal manipulation of chemical microenvironments implemented by a coupling strategy and open-space microfluidics; and iv) High-throughput manipulation of chemical microenvironments. Finally, we briefly present typical applications of the above-mentioned technical advances in cell-based analyses including cell migration, cell signaling, cell differentiation, multicellular analysis, and drug screening. We further discuss the future improvement of microfluidics manipulation of extracellular chemical microenvironments to fulfill the needs of biological and biomedical research and applications.

Magnetic actuation and deformation of a soft shuttle

Here, we describe the magnetic actuation of soft shuttles for open-top microfluidic applications. The system is comprised of two immiscible liquids, including glycerol as the soft shuttle and a suspension of iron powder in sucrose solution as the magnetic drop. Permanent magnets assembled on 3D printed motorized actuators were used for the actuation of the magnetic drop, enabling the glycerol shuttle to be propelled along customized linear, circular, and sinusoidal paths. The dynamics of the hybrid shuttle-magnetic drop system was governed by the magnetic force, the friction at the interface of the shuttle and the substrate, and the surface tension at the interface of the shuttle and the magnetic drop. Increasing the magnetic force leads to the localized deformation of the shuttle and eventually the full extraction of the magnetic drop. The versatility of the system was demonstrated through the propelling of the shuttle across a rough surface patterned with microfabricated barriers as well as taking advantage of the optical properties of the shuttle for the magnification and translation of microscale characters patterned on a planar surface. The integration of the system with current electrowetting actuation mechanisms enables the highly controlled motion of the magnetic drop on the surface of a moving shuttle. The simplicity, versatility, and controllability of the system provide opportunities for various fluid manipulation, sample preparation, and analysis for a range of chemical, biochemical, and biological applications.

Hydrogels as artificial matrices for cell seeding in microfluidic devices

Hydrogel-based artificial scaffolds and its incorporation with microfluidic devices play a vital role in shifting in vitro models from two-dimensional (2D) cell culture to in vivo like three-dimensional (3D) cell culture

On-chip organic synthesis enabled using an engine-and-cargo system in an electrowetting-on-dielectric digital microfluidic device

This paper presents a microfluidic chemical reaction using an electrowetting-on-dielectric (EWOD) digital microfluidic device. Despite a number of chemical/biological applications using EWOD digital microfluidic devices, their applications to organic reactions have been seriously limited because most of the common solvents used in synthetic organic chemistry are not compatible with EWOD devices. To address this unsolved issue, we first introduce a novel technique using an "engine-and-cargo" system that enables the use of non-movable fluids (e.g., organic solvents) on an EWOD device. With esterification as the model reaction, on-chip chemical reactions were successfully demonstrated. Conversion data obtained from on-chip reactions were used to characterize and optimize the reaction with regard to reaction kinetics, solvent screening, and catalyst loading. As the first step toward on-chip combinatorial synthesis, parallel esterification of three different alcohols was demonstrated. Results from this study clearly show that an EWOD digital microfluidic platform is a promising candidate for microscale chemical reactions.

Digital Microfluidic Cell Culture

Digital microfluidics (DMF) is a droplet-based liquid-handling technology that has recently become popular for cell culture and analysis. In DMF, picoliter- to microliter-sized droplets are manipulated on a planar surface using electric fields, thus enabling software-reconfigurable operations on individual droplets, such as move, merge, split, and dispense from reservoirs. Using this technique, multistep cell-based processes can be carried out using simple and compact instrumentation, making DMF an attractive platform for eventual integration into routine biology workflows. In this review, we summarize the state-of-the-art in DMF cell culture, and describe design considerations, types of DMF cell culture, and cell-based applications of DMF.

Digital microfluidic platform for dielectrophoretic patterning of cells encapsulated in hydrogel droplets

In this article, we present a method for cell patterning and culture within a hydrogel droplet on a digital microfluidic (DMF) platform.