1
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Rane A, Tate S, Sumey JL, Zhong Q, Zong H, Purow B, Caliari SR, Swami NS. Open-Top Patterned Hydrogel-Laden 3D Glioma Cell Cultures for Creation of Dynamic Chemotactic Gradients to Direct Cell Migration. ACS Biomater Sci Eng 2024; 10:3470-3477. [PMID: 38652035 PMCID: PMC11094679 DOI: 10.1021/acsbiomaterials.4c00041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2024] [Revised: 03/27/2024] [Accepted: 04/04/2024] [Indexed: 04/25/2024]
Abstract
The laminar flow profiles in microfluidic systems coupled to rapid diffusion at flow streamlines have been widely utilized to create well-controlled chemical gradients in cell cultures for spatially directing cell migration. However, within hydrogel-based closed microfluidic systems of limited depth (≤0.1 mm), the biomechanical cues for the cell culture are dominated by cell interactions with channel surfaces rather than with the hydrogel microenvironment. Also, leaching of poly(dimethylsiloxane) (PDMS) constituents in closed systems and the adsorption of small molecules to PDMS alter chemotactic profiles. To address these limitations, we present the patterning and integration of a PDMS-free open fluidic system, wherein the cell-laden hydrogel directly adjoins longitudinal channels that are designed to create chemotactic gradients across the 3D culture width, while maintaining uniformity across its ∼1 mm depth to enhance cell-biomaterial interactions. This hydrogel-based open fluidic system is assessed for its ability to direct migration of U87 glioma cells using a hybrid hydrogel that includes hyaluronic acid (HA) to mimic the brain tumor microenvironment and gelatin methacrylate (GelMA) to offer the adhesion motifs for promoting cell migration. Chemotactic gradients to induce cell migration across the hydrogel width are assessed using the chemokine CXCL12, and its inhibition by AMD3100 is validated. This open-top hydrogel-based fluidic system to deliver chemoattractant cues over square-centimeter-scale areas and millimeter-scale depths can potentially serve as a robust screening platform to assess emerging glioma models and chemotherapeutic agents to eradicate them.
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Affiliation(s)
- Aditya Rane
- Chemistry, University of Virginia, Charlottesville, Virginia 22904, United States
| | - Steven Tate
- Electrical
and Computer Engineering, University of
Virginia, Charlottesville, Virginia 22904, United States
| | - Jenna L. Sumey
- Chemical
Engineering, University of Virginia, Charlottesville, Virginia 22904, United States
| | - Qing Zhong
- Neurology,
School of Medicine, University of Virginia, Charlottesville, Virginia 22903, United States
| | - Hui Zong
- Microbiology,
Immunology & Cancer Biology, School of Medicine, University of Virginia, Charlottesville, Virginia 22903, United States
| | - Benjamin Purow
- Neurology,
School of Medicine, University of Virginia, Charlottesville, Virginia 22903, United States
| | - Steven R. Caliari
- Chemical
Engineering, University of Virginia, Charlottesville, Virginia 22904, United States
- Biomedical
Engineering, University of Virginia, Charlottesville, Virginia 22904, United States
| | - Nathan S. Swami
- Chemistry, University of Virginia, Charlottesville, Virginia 22904, United States
- Electrical
and Computer Engineering, University of
Virginia, Charlottesville, Virginia 22904, United States
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2
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Taylor DP, Mathur P, Renaud P, Kaigala GV. Microscale hydrodynamic confinements: shaping liquids across length scales as a toolbox in life sciences. LAB ON A CHIP 2022; 22:1415-1437. [PMID: 35348555 DOI: 10.1039/d1lc01101d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Hydrodynamic phenomena can be leveraged to confine a range of biological and chemical species without needing physical walls. In this review, we list methods for the generation and manipulation of microfluidic hydrodynamic confinements in free-flowing liquids and near surfaces, and elucidate the associated underlying theory and discuss their utility in the emerging area of open space microfluidics applied to life-sciences. Microscale hydrodynamic confinements are already starting to transform approaches in fundamental and applied life-sciences research from precise separation and sorting of individual cells, allowing localized bio-printing to multiplexing for clinical diagnosis. Through the choice of specific flow regimes and geometrical boundary conditions, hydrodynamic confinements can confine species across different length scales from small molecules to large cells, and thus be applied to a wide range of functionalities. We here provide practical examples and implementations for the formation of these confinements in different boundary conditions - within closed channels, in between parallel plates and in an open liquid volume. Further, to enable non-microfluidics researchers to apply hydrodynamic flow confinements in their work, we provide simplified instructions pertaining to their design and modelling, as well as to the formation of hydrodynamic flow confinements in the form of step-by-step tutorials and analytical toolbox software. This review is written with the idea to lower the barrier towards the use of hydrodynamic flow confinements in life sciences research.
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Affiliation(s)
- David P Taylor
- IBM Research - Europe, Säumerstrasse 4, 8803 Rüschlikon, Switzerland.
- Microsystems Laboratory 4, École Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
| | - Prerit Mathur
- IBM Research - Europe, Säumerstrasse 4, 8803 Rüschlikon, Switzerland.
- Dept. of Chemistry and Applied Biosciences, Eidgenössische Technische Hochschule (ETH), Vladimir-Prelog-Weg 1-5/10, 8093 Zurich, Switzerland
| | - Philippe Renaud
- Microsystems Laboratory 4, École Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
| | - Govind V Kaigala
- IBM Research - Europe, Säumerstrasse 4, 8803 Rüschlikon, Switzerland.
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3
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Goyette PA, Boulais É, Normandeau F, Laberge G, Juncker D, Gervais T. Microfluidic multipoles theory and applications. Nat Commun 2019; 10:1781. [PMID: 30992450 PMCID: PMC6467910 DOI: 10.1038/s41467-019-09740-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2018] [Accepted: 03/14/2019] [Indexed: 11/09/2022] Open
Abstract
Microfluidic multipoles (MFMs) have been realized experimentally and hold promise for "open-space" biological and chemical surface processing. Whereas convective flow can readily be predicted using hydraulic-electrical analogies, the design of advanced microfluidic multipole is constrained by the lack of simple, accurate models to predict mass transport within them. In this work, we introduce the complete solutions to mass transport in multipolar microfluidics based on the iterative conformal mapping of 2D advection-diffusion around a simple edge into dipoles and multipolar geometries, revealing a rich landscape of transport modes. The models are validated experimentally with a library of 3D printed devices and found in excellent agreement. Following a theory-guided design approach, we further ideate and fabricate two classes of spatiotemporally reconfigurable multipolar devices that are used for processing surfaces with time-varying reagent streams, and to realize a multistep automated immunoassay. Overall, the results set the foundations for exploring, developing, and applying open-space microfluidic multipoles.
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Affiliation(s)
| | - Étienne Boulais
- Department of Engineering Physics, École Polytechnique de Montréal, Montréal, QC, H3T 1J4, Canada
| | - Frédéric Normandeau
- Biomedical Engineering Department and Genome Quebec Innovation Centre, McGill University, Montreal, QC, H3A 0G1, Canada
| | - Gabriel Laberge
- Department of Engineering Physics, École Polytechnique de Montréal, Montréal, QC, H3T 1J4, Canada
| | - David Juncker
- Biomedical Engineering Department and Genome Quebec Innovation Centre, McGill University, Montreal, QC, H3A 0G1, Canada
| | - Thomas Gervais
- Institut de Génie Biomédical, École Polytechnique de Montréal, Montréal, QC, H3T 1J4, Canada. .,Department of Engineering Physics, École Polytechnique de Montréal, Montréal, QC, H3T 1J4, Canada. .,Institut du Cancer de Montréal, Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Montréal, QC, H2X 0C1, Canada.
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4
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Abstract
In this work, we fabricate microfluidic probes (MFPs) in a single step by stereolithographic 3D printing and benchmark their performance with standard MFPs fabricated via glass or silicon micromachining. Two research teams join forces to introduce two independent designs and fabrication protocols, using different equipment. Both strategies adopted are inexpensive and simple (they only require a stereolithography printer) and are highly customizable. Flow characterization is performed by reproducing previously published microfluidic dipolar and microfluidic quadrupolar reagent delivery profiles which are compared to the expected results from numerical simulations and scaling laws. Results show that, for most MFP applications, printer resolution artifacts have negligible impact on probe operation, reagent pattern formation, and cell staining results. Thus, any research group with a moderate resolution (≤100 µm) stereolithography printer will be able to fabricate the MFPs and use them for processing cells, or generating microfluidic concentration gradients. MFP fabrication involved glass and/or silicon micromachining, or polymer micromolding, in every previously published article on the topic. We therefore believe that 3D printed MFPs is poised to democratize this technology. We contribute to initiate this trend by making our CAD files available for the readers to test our "print & probe" approach using their own stereolithographic 3D printers.
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5
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Tissue lithography: Microscale dewaxing to enable retrospective studies on formalin-fixed paraffin-embedded (FFPE) tissue sections. PLoS One 2017; 12:e0176691. [PMID: 28493979 PMCID: PMC5426611 DOI: 10.1371/journal.pone.0176691] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2017] [Accepted: 04/16/2017] [Indexed: 01/01/2023] Open
Abstract
We present a new concept, termed tissue lithography (TL), and its implementation which enables retrospective studies on formalin-fixed paraffin-embedded tissue sections. Tissue lithography uses a microfluidic probe to remove microscale areas of the paraffin layer on formalin-fixed paraffin-embedded biopsy samples. Current practices in sample utilization for research and diagnostics require complete deparaffinization of the sample prior to molecular testing. This imposes strong limitations in terms of the number of tests as well as the time when they can be performed on a single sample. Microscale dewaxing lifts these constraints by permitting deprotection of a fraction of a tissue for testing while keeping the remaining of the sample intact for future analysis. After testing, the sample can be sent back to storage instead of being discarded, as is done in standard workflows. We achieve this microscale dewaxing by hydrodynamically confining nanoliter volumes of xylene on top of the sample with a probe head. We demonstrate micrometer-scale, chromogenic and fluorescence-based immunohistochemistry against multiple biomarkers (p53, CD45, HER2 and β-actin) on tonsil and breast tissue sections and microarrays. We achieve stain patterns as small as 100 μm × 50 μm as well as multiplexed immunostaining within a single tissue microarray core with a 20-fold time reduction for local dewaxing as compared to standard protocols. We also demonstrate a 10-fold reduction in the rehydration time, leading to lower processing times between different stains. We further show the potential of TL for retrospective studies by sequentially dewaxing and staining four individual cores within the same tissue microarray over four consecutive days. By combining tissue lithography with the concept of micro-immunohistochemistry, we implement each step of the IHC protocol—dewaxing, rehydration and staining—with the same microfluidic probe head. Tissue lithography brings a new level of versatility and flexibility in sample processing and budgeting in biobanks, which may alleviate current sample limitations for retrospective studies in biomarker discovery and drug screening.
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6
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Saha-Shah A, Green CM, Abraham DH, Baker LA. Segmented flow sampling with push-pull theta pipettes. Analyst 2017; 141:1958-65. [PMID: 26907673 DOI: 10.1039/c6an00028b] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
We report development of a mobile and easy-to-fabricate theta pipette microfluidic device for segmented flow sampling. The theta pipettes were also used as electrospray emitters for analysis of sub-nanoliter segments, which resulted in delivery of analyte to the vacuum inlet of the mass spectrometer without multiple transfer steps. Theta pipette probes enable sample collection with high spatial resolution due to micron or smaller sized probe inlets and can be used to manipulate aqueous segments in the range of 200 pL to tens of nanoliters. Optimized conditions can enable sampling with high spatial and temporal resolution, suitable for chemical monitoring in biological samples and studies of sample heterogeneity. Intercellular heterogeneity among Allium cepa cells was studied by collecting cytoplasm from multiple cells using a single probe. Extracted cytoplasm was analyzed in a fast and high throughput manner by direct electrospray mass spectrometry of segmented sample from the probe tip.
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Affiliation(s)
- Anumita Saha-Shah
- Department of Chemistry, Indiana University, 800 E. Kirkwood Avenue, Bloomington, IN 47405, USA.
| | - Curtis M Green
- Department of Chemistry, Indiana University, 800 E. Kirkwood Avenue, Bloomington, IN 47405, USA.
| | - David H Abraham
- Department of Chemistry, Indiana University, 800 E. Kirkwood Avenue, Bloomington, IN 47405, USA.
| | - Lane A Baker
- Department of Chemistry, Indiana University, 800 E. Kirkwood Avenue, Bloomington, IN 47405, USA.
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7
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Horayama M, Shinha K, Kabayama K, Fujii T, Kimura H. Spatial Chemical Stimulation Control in Microenvironment by Microfluidic Probe Integrated Device for Cell-Based Assay. PLoS One 2016; 11:e0168158. [PMID: 27930750 PMCID: PMC5145238 DOI: 10.1371/journal.pone.0168158] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Accepted: 11/24/2016] [Indexed: 12/15/2022] Open
Abstract
Cell—cell interactions play an important role in the development and function of multicellular organisms. To investigate these interactions in detail, it is necessary to evaluate the behavior of a cell population when the minimum number of cells in the population is stimulated by some chemical factors. We propose a microfluidic device integrated with microfluidic probe (MFP) functionality; this device is capable of imparting a chemical stimulus to cells within a microenvironment, for cell-based assays. The device contains MFP channels at the walls of the cell culture microchannels, and it can control a localized chemical stimulation area at the scale of a single cell to a few cells using MFP fluid control in a microspace. The results of a finite element method-based simulation indicated that it is possible to control the chemical stimulation area at the scale of a single cell to a few cells by optimizing the MFP channel apex width and the flow ratio. In addition, localized cell staining was demonstrated successfully using a spatial chemical stimulus. We confirmed the device functionality as a novel cell-based assay tool. We succeeded in performing localized cell collection using this method, which suggested that the single cell analysis of a cell monolayer that is subjected to a specific chemical stimulus is possible. The method proposed in this paper can contribute significantly to the fields of cell biology and drug development.
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Affiliation(s)
- Masayuki Horayama
- Department of Mechanical Engineering, Tokai University, Hiratsuka, Kanagawa, Japan
| | - Kenta Shinha
- Department of Mechanical Engineering, Tokai University, Hiratsuka, Kanagawa, Japan
| | - Kazuya Kabayama
- Department of Chemistry, Osaka University, Toyonaka, Osaka, Japan
- Micro/Nano Technology Center, Tokai University, Hiratsuka, Kanagawa, Japan
| | - Teruo Fujii
- Institute of Industrial Science, The University of Tokyo, Meguro, Tokyo, Japan
| | - Hiroshi Kimura
- Department of Mechanical Engineering, Tokai University, Hiratsuka, Kanagawa, Japan
- Micro/Nano Technology Center, Tokai University, Hiratsuka, Kanagawa, Japan
- * E-mail:
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8
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Kashyap A, Cors JF, Lovchik RD, Kaigala GV. Rapid Subtractive Patterning of Live Cell Layers with a Microfluidic Probe. J Vis Exp 2016. [PMID: 27685165 DOI: 10.3791/54447] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
The microfluidic probe (MFP) facilitates performing local chemistry on biological substrates by confining nanoliter volumes of liquids. Using one particular implementation of the MFP, the hierarchical hydrodynamic flow confinement (hHFC), multiple liquids are simultaneously brought in contact with a substrate. Local chemical action and liquid shaping using the hHFC, is exploited to create cell patterns by locally lysing and removing cells. By utilizing the scanning ability of the MFP, user-defined patterns of cell monolayers are created. This protocol enables rapid, real-time and spatially controlled cell patterning, which can allow selective cell-cell and cell-matrix interaction studies.
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9
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Kashyap A, Autebert J, Delamarche E, Kaigala GV. Selective local lysis and sampling of live cells for nucleic acid analysis using a microfluidic probe. Sci Rep 2016; 6:29579. [PMID: 27411740 PMCID: PMC4944176 DOI: 10.1038/srep29579] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Accepted: 06/23/2016] [Indexed: 01/18/2023] Open
Abstract
Heterogeneity is inherent to biology, thus it is imperative to realize methods capable of obtaining spatially-resolved genomic and transcriptomic profiles of heterogeneous biological samples. Here, we present a new method for local lysis of live adherent cells for nucleic acid analyses. This method addresses bottlenecks in current approaches, such as dilution of analytes, one-sample-one-test, and incompatibility to adherent cells. We make use of a scanning probe technology - a microfluidic probe - and implement hierarchical hydrodynamic flow confinement (hHFC) to localize multiple biochemicals on a biological substrate in a non-contact, non-destructive manner. hHFC enables rapid recovery of nucleic acids by coupling cell lysis and lysate collection. We locally lysed ~300 cells with chemical systems adapted for DNA or RNA and obtained lysates of ~70 cells/μL for DNA analysis and ~15 cells/μL for mRNA analysis. The lysates were introduced into PCR-based workflows for genomic and transcriptomic analysis. This strategy further enabled selective local lysis of subpopulations in a co-culture of MCF7 and MDA-MB-231 cells, validated by characteristic E-cadherin gene expression in individually extracted cell types. The developed strategy can be applied to study cell-cell, cell-matrix interactions locally, with implications in understanding growth, progression and drug response of a tumor.
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Affiliation(s)
- Aditya Kashyap
- IBM Research - Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland
| | - Julien Autebert
- IBM Research - Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland
| | | | - Govind V Kaigala
- IBM Research - Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland
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10
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Autebert J, Cors JF, Taylor DP, Kaigala GV. Convection-Enhanced Biopatterning with Recirculation of Hydrodynamically Confined Nanoliter Volumes of Reagents. Anal Chem 2016; 88:3235-42. [PMID: 26837532 PMCID: PMC4794703 DOI: 10.1021/acs.analchem.5b04649] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
![]()
We
present a new methodology for efficient and high-quality patterning
of biological reagents for surface-based biological assays. The method
relies on hydrodynamically confined nanoliter volumes of reagents
to interact with the substrate at the micrometer-length scale. We
study the interplay between diffusion, advection, and surface chemistry
and present the design of a noncontact scanning microfluidic device
to efficiently present reagents on surfaces. By leveraging convective
flows, recirculation, and mixing of a processing liquid, this device
overcomes limitations of existing biopatterning approaches, such as
passive diffusion of analytes, uncontrolled wetting, and drying artifacts.
We demonstrate the deposition of analytes, showing a 2- to 5-fold
increase in deposition rate together with a 10-fold reduction in analyte
consumption while ensuring less than 6% variation in pattern homogeneity
on a standard biological substrate. In addition, we demonstrate the
recirculation of a processing liquid using a microfluidic probe (MFP)
in the context of a surface assay for (i) probing 12 independent areas
with a single microliter of processing liquid and (ii) processing
a 2 mm2 surface to create 170 antibody spots of 50 ×
100 μm2 area using 1.6 μL of liquid. We observe
high pattern quality, conservative usage of reagents, micrometer precision
of localization and convection-enhanced fast deposition. Such a device
and method may facilitate quantitative biological assays and spur
the development of the next generation of protein microarrays.
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Affiliation(s)
- Julien Autebert
- IBM Research-Zurich , Säumerstrasse 4, 8803 Rüschlikon, Switzerland
| | - Julien F Cors
- IBM Research-Zurich , Säumerstrasse 4, 8803 Rüschlikon, Switzerland
| | - David P Taylor
- IBM Research-Zurich , Säumerstrasse 4, 8803 Rüschlikon, Switzerland
| | - Govind V Kaigala
- IBM Research-Zurich , Säumerstrasse 4, 8803 Rüschlikon, Switzerland
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11
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Cors JF, Stucki A, Kaigala GV. Hydrodynamic thermal confinement: creating thermo-chemical microenvironments on surfaces. Chem Commun (Camb) 2016; 52:13035-13038. [DOI: 10.1039/c6cc08018a] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
We present a new, general concept termed Hydrodynamic Thermal Confinement (HTC), and its implementation for the creation of microscale dynamic thermo-chemical microenvironments on biological surfaces. We demonstrate selective DNA denaturation of single spots on a microarray using a 15% formamide solution at 60 °C.
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Affiliation(s)
- J. F. Cors
- IBM Research – Zurich
- 8803 Rüschlikon
- Switzerland
| | - A. Stucki
- IBM Research – Zurich
- 8803 Rüschlikon
- Switzerland
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12
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Hokkanen A, Stuns I, Schmid P, Kokkonen A, Gao F, Steinecker A, Budczies J, Heimala P, Hakalahti L. Microfluidic sampling system for tissue analytics. BIOMICROFLUIDICS 2015; 9:054109. [PMID: 26421088 PMCID: PMC4575324 DOI: 10.1063/1.4931045] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2015] [Accepted: 09/03/2015] [Indexed: 06/01/2023]
Abstract
We have developed a microfluidics based sampling system for tissue analytics. The proof-of-concept of the sampling system was demonstrated by extracting lipid samples from tissue biopsies. The sample collection system consists of a disposable silicon based multiport microneedle integrated with polymer microfluidics. The polymethyl methacrylate polymer microfluidic chip has a 10 μl sample reservoir and actuation membranes for liquid pumping. A special automated robotic system was developed to control the positioning of the needle and the sampling procedure on preselected spots on the tissue. Real breast cancer tissue samples were used to test the feasibility of the sampling system. We successfully measured indicative cancer biomarkers from the tissue surface. Phosphatidylcholine and phosphoethanolamine were extracted from the tissue membrane with methyl tert-butyl ether solvent and detected by mass spectrometry. In the future, this tool could be used in characterization of preoperative biopsies and tumour tissues removed during surgery.
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Affiliation(s)
- A Hokkanen
- VTT Technical Research Centre of Finland , Tietotie 3, 02044 VTT, Espoo, Finland
| | - I Stuns
- VTT Technical Research Centre of Finland , Tietotie 3, 02044 VTT, Espoo, Finland
| | - P Schmid
- CSEM Swiss Center for Electronics and Microtechnology , Untere Gründlistrasse 1, CH-6055 Alpnach, Switzerland
| | - A Kokkonen
- VTT Technical Research Centre of Finland , Kaitoväylä 1, 02044 VTT, Oulu, Finland
| | - F Gao
- VTT Technical Research Centre of Finland , Tietotie 3, 02044 VTT, Espoo, Finland
| | - A Steinecker
- CSEM Swiss Center for Electronics and Microtechnology , Untere Gründlistrasse 1, CH-6055 Alpnach, Switzerland
| | - J Budczies
- Charité-Universitätsmedizin Berlin , Institute of Pathology, Charitéplatz 1, D-10117 Berlin, Germany
| | - P Heimala
- VTT Technical Research Centre of Finland , Tietotie 3, 02044 VTT, Espoo, Finland
| | - L Hakalahti
- VTT Technical Research Centre of Finland , Kaitoväylä 1, 02044 VTT, Oulu, Finland
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