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Focusing of mammalian cells under an ultrahigh pH gradient created by unidirectional electropulsation in a confined microchamber†Electronic supplementary information (ESI) available: Figures S1-S5 and videos S1-S2. See DOI: 10.1039/c4sc00319eClick here for additional data file.Click here for additional data file.Click here for additional data file.

ABSTRACT: The transport and manipulation of cells in microfluidic structures are often critically required in cellular analysis. Cells typically make consistent movement in a dc electric field in a single direction, due to their electrophoretic mobility or electroosmotic flow or the combination of the two. Here we demonstrate that mammalian cells focus to the middle of a closed microfluidic chamber under the application of unidirectional direct current pulses. With experimental and computational data, we show that under the pulses electrochemical reactions take place in the confined microscale space and create an ultrahigh and nonlinear pH gradient (?2 orders of magnitude higher than the ones in protein isoelectric focusing) at the middle of the chamber. The varying local pH affects the cell surface charge and the electrophoretic mobility, leading to focusing in free solution. Our approach provides a new and simple method for focusing and concentrating mammalian cells at the microscale.

SUBMITTER: Loufakis DN

PROVIDER: S-EPMC4348711 | biostudies-literature | 2014 Aug

REPOSITORIES: biostudies-literature

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Focusing of mammalian cells under an ultrahigh pH gradient created by unidirectional electropulsation in a confined microchamber†Electronic supplementary information (ESI) available: Figures S1-S5 and videos S1-S2. See DOI: 10.1039/c4sc00319eClick here for additional data file.Click here for additional data file.Click here for additional data file.

Loufakis Despina Nelie DN Cao Zhenning Z Ma Sai S Mittelman David D Lu Chang C

Chemical science 20140620 8

The transport and manipulation of cells in microfluidic structures are often critically required in cellular analysis. Cells typically make consistent movement in a dc electric field in a single direction, due to their electrophoretic mobility or electroosmotic flow or the combination of the two. Here we demonstrate that mammalian cells focus to the middle of a closed microfluidic chamber under the application of unidirectional direct current pulses. With experimental and computational data, we ...[more]

PMID: 25750708

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Project description:Thiol-ene 'click' chemistries have been widely used in biomaterials applications, including drug delivery, tissue engineering, and controlled cell culture, owing to their rapid, cytocompatible, and often orthogonal reactivity. In particular, hydrogel-based biomaterials formed by photoinitiated thiol-ene reactions afford spatiotemporal control over the biochemical and biomechanical properties of the network for creating synthetic materials that mimic the extracellular matrix or enable controlled drug release. However, the use of charged peptides functionalized with cysteines, which can form disulfides prior to reaction, and vinyl monomers that require multistep syntheses and contain ester bonds, may lead to undesired inhomogeneity or degradation under cell culture conditions. Here, we designed a thiol-ene hydrogel formed by the reaction of allyloxycarbonyl-functionalized peptides and thiol-functionalized poly(ethylene glycol). Hydrogels were polymerized by free radical initiation under cytocompatible doses of long wavelength ultraviolet light in the presence of water-soluble photoinitiators (lithium acylphosphinate, LAP, and 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone, Irgacure 2959). Mechanical properties of these hydrogels were controlled by varying the monomer concentration to mimic a range of soft tissue environments, and hydrogel stability in cell culture medium was observed over weeks. Patterns of biochemical cues were created within the hydrogels post-formation and confirmed through the incorporation of fluorescently-labeled peptides and Ellman's assay to detect free thiols. Human mesenchymal stem cells remained viable after encapsulation and subsequent photopatterning, demonstrating the utility of the monomers and hydrogels for three-dimensional cell culture. This facile approach enables the formation and characterization of hydrogels with well-defined, spatially-specific properties and expands the suite of monomers available for three-dimensional cell culture and other biological applications.

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