Microfluidics for Biologists Fundamentals and Applications

(National Geographic (Little) Kids) #1

with four inlets and one outlet. Four events of cell capturing in different droplets,
cell lysis, reverse transcription reaction and gene amplification integrated into one
single chip made possible the event of cell capturing at the rate of 4000–12,000
cells per hour for their analysis. The device generates monodisperse droplets that
can be varied in the range of 1–5 nL at a rate of 10–100 drops per second,
simultaneously mixing aliquots from the inlets. Flow rates were 100μLh^1 for
cell suspension, 100μLh^1 for mixing of reagents, 10–20μLh^1 for mixing of
barcodes, and 90μLh^1 for carrier oil to produce 4 nL drops. The carrier oil used
was HFE-7500 fluorinated fluid with EA-surfactant. Jung et al. performed flow-
based sorting of human mesenchymal cells by using optimally designed MF chips
based on the principle of hydrodynamic filtration (HMD) [ 12 ]. Human bone
marrow-derived mesenchymal stem cells (hMSCs) were sorted into three subpop-
ulations by focusing the cells (with a proper ratio) between primary and side flows
and analyzing the surface marker expressions of cells from each outlet. The
specially designed MF chip consisted of a rectangular main channel of length
16 mm with 55 branches and three outlets to achieve the trimodal separation, as
shown in Fig.8.1A. The heights and the widths of primary as well as branch
channels, total lengths of main and branch channels, and inter-distances between
each branch channel were set by applying equations of steady state laminar flow for
the Newtonian fluid. The fluid circulation was done using syringe pumps at a flow
rate of 30μL min^1. Particles of certain size can escape from the main channel at a
specific branch where its ratio of the flow fraction is optimized for the right particle
size. Thus based on this hydrodynamic filtration method the cells are sorted into
three subpopulations: small (< 25 μm), medium (25–40μm), and large (> 40 μm)
cells. This process leads to the possibility of sorting stem cells rapidly without
damage. Kang et al. developed an efficient on-chip cell culture MF device capable
of repeated, temporal delivery of molecules into a population of cells tool [ 13 ]. The
design of the on-chip localized electroporation device (LEPD) consists of
microchannels, a cell culture chamber, built-in electrodes, and a porous substrate
containing micro- or nanochannels (Fig.8.1B). The width and height of the
microchannel are 200μm and ~20μm, respectively whereas the cell culture
chamber is 3 mm in diameter. The working electrode was built-in on a fabricated
glass cover slide while the second electrode (Ag/AgCl wire) was submerged into
the media in the cell culture chamber. On-chip cell culture was maintained by the
continuous flow of culture media through the circulation microchannels located
beneath the perforated substrate. For intercellular delivery by electroporation, a
solution containing biomolecules to be delivered into the cells was loaded into the
circulation microchannels. To elicit the formation of nanopores on the cell mem-
brane voltage was applied between the two microelectrodes due to which molecules
are transported into the cell by diffusion. Thus, utilizing this LEPD configuration,
localized electroporation was achieved that provides exceptional capabilities such
as the transfection of various molecules into primary cells, maintenance of consis-
tent pH levels by continuous media circulation, and application of a focused electric
field to a small portion of the cell membrane to minimize stress. Also, the device is
simple to use and cost effective. Further, an impedance sensors integrated


194 S. Solanki and C.M. Pandey


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