Special Issue "Microfluidics for Soft Matter and Mechanobiology"

A special issue of Micromachines (ISSN 2072-666X).

Deadline for manuscript submissions: 10 November 2019.

Special Issue Editor

Guest Editor
Dr. Sung Sik Lee Website E-Mail
Scientific Center for Optical and Electron Microscopy, ETH Zürich, Zürich, Switzerland
Interests: soft matter; viscoelastic microfluidics; droplet microfluidics; mechanobiology; single cell analysis; bio-printing; hydrogel; rheology

Special Issue Information

Dear Colleagues,

Microfluidics has served as a useful platform to understand the material properties and technical applications of soft matter, including hydrogels, polymer solutions, emulsions, and colloidal suspensions. The study of the characteristics of soft matter, like viscoelasticity, non-Newtonian fluid mechanics, and deformation has greatly benefitted from using microfluidics to accurately control conditions in time and space. Under constrained microfluidic conditions, the dynamics of soft matter are monitored by direct visualization or by microrheology to track and quantify the movement of probes.

Microfluidics has also served as a useful platform to study biological cell and tissues systems, including mechanobiology. Using microfluidics, external mechanical stress is regulated in physiologically-relevant systems for studying cells, tissues and organisms to understand how mechanical cues are sensed and transduced into biochemical and electrical signals that influence mechano-transduction in processes such as cell proliferation, migration and fate determination. Furthermore, the characteristics of soft matter are exploited when combined with microfluidic platforms to mimic in-vivo microenviroments like extracellular matrix to directly test the influence of mechanical cues such as softness and elasticity. In addition, microfluidics platforms enable us to measure the mechanical properties of cells by establishing defined flow or confined microstructures through viscoelastic particles/cells focusing and droplet microfluidics. Finally, the 3D bio-printing of soft matter via microdevices has become widely employed.

In this Special Issue, we highlight recent progress in microfluidics with research papers, short communications, and review articles that focus on novel methodological developments and applications of microfluidics devices for soft matter and mechanobiology, as well as emerging intriguing phenomena of soft matter in microfluidics.

Dr. Sung Sik Lee
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Soft matter
  • Viscoelastic microfluidics
  • Droplet microfluidics
  • Hydrogel
  • Rheology
  • Microrheology
  • Bio-printing
  • Mechanobiology
  • Deformability
  • Mechano-transduction

Published Papers (7 papers)

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Research

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Open AccessArticle
Scalable Production of Monodisperse Functional Microspheres by Multilayer Parallelization of High Aspect Ratio Microfluidic Channels
Micromachines 2019, 10(9), 592; https://doi.org/10.3390/mi10090592 - 10 Sep 2019
Abstract
Droplet microfluidics enables the generation of highly uniform emulsions with excellent stability, precise control over droplet volume, and morphology, which offer superior platforms over conventional technologies for material synthesis and biological assays. However, it remains a challenge to scale up the production of [...] Read more.
Droplet microfluidics enables the generation of highly uniform emulsions with excellent stability, precise control over droplet volume, and morphology, which offer superior platforms over conventional technologies for material synthesis and biological assays. However, it remains a challenge to scale up the production of the microfluidic devices due to their complicated geometry and long-term reliability. In this study, we present a high-throughput droplet generator by parallelization of high aspect ratio rectangular structures, which enables facile and scalable generation of uniform droplets without the need to precisely control external flow conditions. A multilayer device is formed by stacking layer-by-layer of the polydimethylsiloxane (PDMS) replica patterned with parallelized generators. By feeding the sample fluid into the device immersed in the carrying fluid, we used the multilayer device with 1200 parallelized generators to generate monodisperse droplets (~45 μm in diameter with a coefficient of variation <3%) at a frequency of 25 kHz. We demonstrate this approach is versatile for a wide range of materials by synthesis of polyacrylamide hydrogel and Poly (l-lactide-co-glycolide) (PLGA) through water-in-oil (W/O) and oil-in-water (O/W) emulsion templates, respectively. The combined scalability and robustness of such droplet emulsion technology is promising for production of monodisperse functional materials for large-scale applications. Full article
(This article belongs to the Special Issue Microfluidics for Soft Matter and Mechanobiology)
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Open AccessFeature PaperCommunication
A Toolbox for Organelle Mechanobiology Research—Current Needs and Challenges
Micromachines 2019, 10(8), 538; https://doi.org/10.3390/mi10080538 - 16 Aug 2019
Abstract
Mechanobiology studies from the last decades have brought significant insights into many domains of biological research, from development to cellular signaling. However, mechano-regulation of subcellular components, especially membranous organelles, are only beginning to be unraveled. In this paper, we take mitochondrial mechanobiology as [...] Read more.
Mechanobiology studies from the last decades have brought significant insights into many domains of biological research, from development to cellular signaling. However, mechano-regulation of subcellular components, especially membranous organelles, are only beginning to be unraveled. In this paper, we take mitochondrial mechanobiology as an example to discuss recent advances and current technical challenges in this field. In addition, we discuss the needs for future toolbox development for mechanobiological research of intracellular organelles. Full article
(This article belongs to the Special Issue Microfluidics for Soft Matter and Mechanobiology)
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Open AccessArticle
Effects of Ionic Strength on Lateral Particle Migration in Shear-Thinning Xanthan Gum Solutions
Micromachines 2019, 10(8), 535; https://doi.org/10.3390/mi10080535 - 15 Aug 2019
Abstract
Viscoelastic fluids, including particulate systems, are found in various biological and industrial systems including blood flow, food, cosmetics, and electronic materials. Particles suspended in viscoelastic fluids such as polymer solutions migrate laterally, forming spatially segregated streams in pressure-driven flow. Viscoelastic particle migration was [...] Read more.
Viscoelastic fluids, including particulate systems, are found in various biological and industrial systems including blood flow, food, cosmetics, and electronic materials. Particles suspended in viscoelastic fluids such as polymer solutions migrate laterally, forming spatially segregated streams in pressure-driven flow. Viscoelastic particle migration was recently applied to microfluidic technologies including particle counting and sorting and the micromechanical measurement of living cells. Understanding the effects on equilibrium particle positions of rheological properties of suspending viscoelastic fluid is essential for designing microfluidic applications. It has been considered that the shear-thinning behavior of viscoelastic fluid is a critical factor in determining the equilibrium particle positions. This work presents the lateral particle migration in two different xanthan gum-based viscoelastic fluids with similar shear-thinning viscosities and the linear viscoelastic properties. The flexibility and contour length of the xanthan gum molecules were tuned by varying the ionic strength of the solvent. Particles suspended in flexible and short xanthan gum solution, dissolved at high ionic strength, migrated toward the corners in a square channel, whereas particles in the rigid and long xanthan gum solutions in deionized water migrated toward the centerline. This work suggests that the structural properties of polymer molecules play significant roles in determining the equilibrium positions in shear-thinning fluids, despite similar bulk rheological properties. The current results are expected to be used in a wide range of applications such as cell counting and sorting. Full article
(This article belongs to the Special Issue Microfluidics for Soft Matter and Mechanobiology)
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Open AccessArticle
Direct Patterning of a Carbon Nanotube Thin Layer on a Stretchable Substrate
Micromachines 2019, 10(8), 530; https://doi.org/10.3390/mi10080530 - 11 Aug 2019
Abstract
Solution-based direct patterning on an elastomer substrate with meniscus-dragging deposition (MDD) enables fabrication of very thin carbon nanotube (CNT) layers in the nanometer scale (80–330 nm). To fabricate the CNT pattern with CNT solution, contact angle, electrical variation, mechanical stress, and surface cracks [...] Read more.
Solution-based direct patterning on an elastomer substrate with meniscus-dragging deposition (MDD) enables fabrication of very thin carbon nanotube (CNT) layers in the nanometer scale (80–330 nm). To fabricate the CNT pattern with CNT solution, contact angle, electrical variation, mechanical stress, and surface cracks of elastomer substrate were analyzed to identify the optimal conditions of O2 treatment (treatment for 30 s with RF power of 50 W in O2 atmosphere of 50 sccm) and mixture ratio between Ecoflex and polydimethylsiloxane (PDMS) (Ecoflex:PDMS = 5:1). The type of mask for patterning of the CNT layer was determined through quantitative analysis for sharpness and uniformity of the fabricated CNT pattern. Through these optimization processes, the CNT pattern was produced on the elastomer substrate with selected mask (30 μm thick oriented polypropylene). The thickness of CNT pattern was also controlled to have hundreds nanometer and 500 μm wide rectangular and circular shapes were demonstrated. Furthermore, the change in the current and resistance of the CNT layer according to the applied strain on the elastomer substrate was analyzed. Our results demonstrated the potential of the MDD method for direct CNT patterning with high uniformity and the possibility to fabricate a stretchable sensor. Full article
(This article belongs to the Special Issue Microfluidics for Soft Matter and Mechanobiology)
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Open AccessArticle
Microfluidic Generation of Amino-Functionalized Hydrogel Microbeads Capable of On-Bead Bioassay
Micromachines 2019, 10(8), 527; https://doi.org/10.3390/mi10080527 - 09 Aug 2019
Abstract
Microfluidic generation of hydrogel microbeads is a highly efficient and reproducible approach to create various functional hydrogel beads. Here, we report a method to prepare crosslinked amino-functionalized polyethylene glycol (PEG) microbeads using a microfluidic channel. The microbeads generated from a microfluidic device were [...] Read more.
Microfluidic generation of hydrogel microbeads is a highly efficient and reproducible approach to create various functional hydrogel beads. Here, we report a method to prepare crosslinked amino-functionalized polyethylene glycol (PEG) microbeads using a microfluidic channel. The microbeads generated from a microfluidic device were evaluated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and confocal laser scanning microscopy, respectively. We found that the microbeads were monodisperse and the amino groups were localized on the shell region of the microbeads. A swelling test exhibited compatibility with various solvents. A cell binding assay was successfully performed with RGD peptide-coupled amino-functionalized hydrogel microbeads. This strategy will enable the large production of the various functional microbeads, which can be used for solid phase peptide synthesis and on-bead bioassays. Full article
(This article belongs to the Special Issue Microfluidics for Soft Matter and Mechanobiology)
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Open AccessArticle
Sheathless High-Throughput Circulating Tumor Cell Separation Using Viscoelastic non-Newtonian Fluid
Micromachines 2019, 10(7), 462; https://doi.org/10.3390/mi10070462 - 10 Jul 2019
Abstract
Circulating tumor cells (CTCs) have attracted increasing attention as important biomarkers for clinical and biological applications. Several microfluidic approaches have been demonstrated to separate CTCs using immunoaffinity or size difference from other blood cells. This study demonstrates a sheathless, high-throughput separation of CTCs [...] Read more.
Circulating tumor cells (CTCs) have attracted increasing attention as important biomarkers for clinical and biological applications. Several microfluidic approaches have been demonstrated to separate CTCs using immunoaffinity or size difference from other blood cells. This study demonstrates a sheathless, high-throughput separation of CTCs from white blood cells (WBCs) using a viscoelastic fluid. To determine the fluid viscoelasticity and the flow rate for CTC separation, and to validate the device performance, flow characteristics of 6, 13, and 27 μm particles in viscoelastic fluids with various concentrations were estimated at different flow rates. Using 0.2% hyaluronic acid (HA) solution, MCF-7 (Michigan Cancer Foundation-7) cells mimicking CTCs in this study were successfully separated from WBCs at 500 μL/min with a separation efficiency of 94.8%. Small amounts of MCF-7 cells (~5.2%) were found at the center outlet due to the size overlap with WBCs. Full article
(This article belongs to the Special Issue Microfluidics for Soft Matter and Mechanobiology)
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Review

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Open AccessReview
Recent Advances in Droplet-based Microfluidic Technologies for Biochemistry and Molecular Biology
Micromachines 2019, 10(6), 412; https://doi.org/10.3390/mi10060412 - 20 Jun 2019
Abstract
Recently, droplet-based microfluidic systems have been widely used in various biochemical and molecular biological assays. Since this platform technique allows manipulation of large amounts of data and also provides absolute accuracy in comparison to conventional bioanalytical approaches, over the last decade a range [...] Read more.
Recently, droplet-based microfluidic systems have been widely used in various biochemical and molecular biological assays. Since this platform technique allows manipulation of large amounts of data and also provides absolute accuracy in comparison to conventional bioanalytical approaches, over the last decade a range of basic biochemical and molecular biological operations have been transferred to drop-based microfluidic formats. In this review, we introduce recent advances and examples of droplet-based microfluidic techniques that have been applied in biochemistry and molecular biology research including genomics, proteomics and cellomics. Their advantages and weaknesses in various applications are also comprehensively discussed here. The purpose of this review is to provide a new point of view and current status in droplet-based microfluidics to biochemists and molecular biologists. We hope that this review will accelerate communications between researchers who are working in droplet-based microfluidics, biochemistry and molecular biology. Full article
(This article belongs to the Special Issue Microfluidics for Soft Matter and Mechanobiology)
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