Effective Cell and Particle Sorting and Separation in Screen-Printed Continuous-Flow Microfluidic Devices with 3D Sidewall Electrodes

Dielectrophoretic separation and purification: From colloid and biological particles to droplets

It is indispensable to realize the high level of purification and separation, so that objective particles, such as malignant cells, harmful bacteria, and special proteins or biological molecules, could satisfy the high precise measurement in the pharmaceutical analysis, clinical diagnosis, targeted therapy, and food defense. In addition, this could reveal the intrinsic nature and evolution mechanisms of individual biological variations. Consequently, many techniques related to optical tweezers, microfluidics, acoustophoresis, and electrokinetics can be broadly used to achieve micro- and nano-scale particle separations. Dielectrophoresis (DEP) has been used for various manipulation, concentration, transport, and separation processes of biological particles owing to its early development, mature theory, low cost, and high throughput. Although numerous reviews have discussed the biological applications of DEP techniques, comprehensive descriptions of micro- and nano-scale particle separations feature less frequently in the literature. Therefore, this review summarizes the current state of particle separation attention to relevant technological developments and innovation, including theoretical simulation, microchannel structure, electrode material, pattern and its layout. Moreover, a brief overview of separation applications using DEP in combination with other technologies is also provided. Finally, conclusions, future guidelines, and suggestions for potential promotion are highlighted.

Evaluating carbon-electrode dielectrophoresis under the ASSURED criteria

Extreme point-of-care refers to medical testing in unfavorable conditions characterized by a lack of primary resources or infrastructure. As witnessed in the recent past, considerable interest in developing devices and technologies exists for extreme point-of-care applications, for which the World Health Organization has introduced a set of encouraging and regulating guidelines. These are referred to as the ASSURED criteria, an acronym for Affordable (A), Sensitive (S), Specific (S), User friendly (U), Rapid and Robust (R), Equipment-free (E), and Delivered (D). However, the current extreme point of care devices may require an intermediate sample preparation step for performing complex biomedical analysis, including the diagnosis of rare-cell diseases and early-stage detection of sepsis. This article assesses the potential of carbon-electrode dielectrophoresis (CarbonDEP) for sample preparation competent in extreme point-of-care, following the ASSURED criteria. We first discuss the theory and utility of dielectrophoresis (DEP) and the advantages of using carbon microelectrodes for this purpose. We then critically review the literature relevant to the use of CarbonDEP for bioparticle manipulation under the scope of the ASSURED criteria. Lastly, we offer a perspective on the roadmap needed to strengthen the use of CarbonDEP in extreme point-of-care applications.

Flexible material formulations for 3D printing of ordered porous beds with applications in bioprocess engineering

BACKGROUND

3D printing is revolutioning many industrial sectors and has the potential to enhance also the biotechnology and bioprocessing fields. Here, we propose a new flexible material formulation to 3D print support matrices with complex, perfectly ordered morphology and with tuneable properties to suit a range of applications in bioprocess engineering.

FINDINGS

Supports were fabricated using functional monomers as the key ingredients, enabling matrices with bespoke chemistry, such as charged groups, chemical moieties for further functionalization, and hydrophobic/hydrophilic groups. Other ingredients, e.g. crosslinkers and porogens, can be employed to fabricate supports with diverse characteristics of their porous network, providing an opportunity to further regulate the mechanical and mass transfer properties of the supports. Through this approach, we fabricated and demonstrated the operation of Schoen gyroid columns with (I) positive and negative charges for ion exchange chromatography, (II) enzyme bioreactors with immobilized trypsin to catalyse hydrolysis, and (III) bacterial biofilm bioreactors for fuel desulphurization.

CONCLUSIONS

This study demonstrates a simple, cost-effective, and flexible fabrication of customized 3D printed supports for different biotechnology and bioengineering applications.

On the design, functions, and biomedical applications of high-throughput dielectrophoretic micro-/nanoplatforms: a review

As an efficient, rapid and label-free micro-/nanoparticle separation technique, dielectrophoresis (DEP) has attracted widespread attention in recent years, especially in the field of biomedicine, which exhibits huge potential in biomedically relevant applications such as disease diagnosis, cancer cell screening, biosensing, and others. DEP technology has been greatly developed recently from the low-flux laboratory level to high-throughput practical applications. In this review, we summarize the recent progress of DEP technology in biomedical applications, including firstly the design of various types and materials of DEP electrode and flow channel, design of input signals, and other improved designs. Then, functional tailoring of DEP systems with endowed specific functions including separation, purification, capture, enrichment and connection of biosamples, as well as the integration of multifunctions, are demonstrated. After that, representative DEP biomedical application examples in aspects of disease detection, drug synthesis and screening, biosensing and cell positioning are presented. Finally, limitations of existing DEP platforms on biomedical application are discussed, in which emphasis is given to the impact of other electrodynamic effects such as electrophoresis (EP), electroosmosis (EO) and electrothermal (ET) effects on DEP efficiency. This article aims to provide new ideas for the design of novel DEP micro-/nanoplatforms with desirable high throughput toward application in the biomedical community.

A one-step molded microfluidic chip featuring a two-layer silver-PDMS microelectrode for dielectrophoretic cell separation

Dielectrophoresis (DEP) is a powerful technique for label-free cell separation in microfluidics. Easily-fabricated DEP separators with low cost and short turnaround time are in extremely high demand in practical applications, especially clinical usage where disposable devices are needed. DEP separators exploiting microelectrodes made of conducting polydimethylsiloxane (PDMS) composites enable the construction of advantageous 3D volumetric electrodes with a simple soft-lithography process. Yet, existing devices incorporating microelectrodes in conducting PDMS generally have their fluidic sidewalls constructed using a different material, and consequently require extra lithography of a sacrificial layer on the semi-finished master for molding the electrode and fluidic sidewalls in separate steps. Here we demonstrate a novel microfluidic DEP separator with a 3D electrode and fluidic structure entirely integrated within silver-PDMS composites. We develop a further simplified one-step molding process with lower cost using a readily-available and reusable SU8 master, eliminating the need for the additional lithography step in existing techniques. The uniquely designed two-layer electrode exhibits a spatially non-uniform electric field that enables cell migration in the vertical direction. The electrode upper layer then offers a harbor-like region for the trapping of the target cells that have drifted upwards, which shelters them from being dragged away by the main flow streams in the lower layer, and thus allows higher operation flow rate. We also optimize the upper layer thickness as a critical dimension for protecting the trapped cells from high drag and show easy widening of our device by elongation of the digits. We demonstrate that the elongated digits involving more parallel flow paths maintain a high capture efficiency of 95.4% for live cells with 85.6% purity in the separation of live/dead HeLa cells. We also investigate the device feasibility in a viability assay for cells post anti-cancer drug treatment.

Combining 3D sidewall electrodes and contraction/expansion microstructures in microchip promotes isolation of cancer cells from red blood cells

Cell sorting from heterogeneous organisms and tissues composed of multi-type cells is of great importance in biological and clinical applications. As promising cell sorting methods, dielectrophoresis (DEP) and hydrodynamics are attracting much attention in recent years. In this paper, we report a novel strategy by coupling DEP unit (3D sidewall electrodes) and hydrodynamic unit (microchannels with contraction/expansion structures) together in one microfluidic chip. Depending on the relative positions of 3D sidewall electrodes and contraction/expansion structure, three microchips (full-coupling, semi-coupling and non-coupling) are developed and their cell sorting performance are compared by isolating lung cancer cells (PC-9 cells) from red blood cells (RBCs). Both finite element simulation and practical cell sorting prove that high cell sorting efficiency (recovery of PC-9 cells: 90.21%, recovery of RBCs: 94.35%) can be achieved in full-coupling microchip, mainly owing to the synergistic effects between DEP sorting and hydrodynamic sorting. i.e., the positive DEP force generated by 3D sidewall electrodes can simultaneously act as an additional shear gradient lift force and thus trigger secondary flow even at low flow velocity. Live/dead cell staining, hemolysis ratio, fluorescence images and CCK-8 assay prove that RBCs and PC-9 cells show no significance difference in cell viability before and after cell sorting. The proposed coupling platform for cell sorting brings on a new pathway to construct integrated microfluidic chips for effective cell sorting and separation.