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Influence of buoyancy-driven flow on mass transfer in a two-stream microfluidic channel: Introduction of cryoprotective agents into cell suspensions.

ABSTRACT: A variety of methods have been used to introduce chemicals into a stream or to mix two or more streams of different compositions using microfluidic devices. In the following paper, the introduction of cryoprotective agents (CPAs) used during cryopreservation of cells in order to protect them from freezing injuries and increase viability post thaw is described. Dimethylsulphoxide (DMSO) is the most commonly used CPA. We aim to optimize the operating conditions of a two-stream microfluidic device to introduce a 10% vol/vol solution of DMSO into a cell suspension. Transport behavior of DMSO between two streams in the device has been experimentally characterized for a spectrum of flow conditions (0.7 < Re < 10), varying initial donor stream concentrations, (1% vol/vol < C o < 15% vol/vol) and different flow rate fractions (0.23 < f q < 0.77). The outlet cell stream concentration is analyzed for two different flow configurations: one with the cell stream flowing on top of the DMSO-rich donor stream, and the other with the cell stream flowing beneath the heavy DMSO-laden stream. We establish a transition from a diffusive mode of mass transfer to gravity-influenced convective currents for Atwood numbers (A t ) in the range of (1.7 × 10(-3) < A t < 3.1 × 10(-3)) for the latter configuration. Flow visualization with cells further our understanding of the effect of A t on the nature of mass transport. Cell motion studies performed with Jurkat cells confirm a high cell recovery from the device while underscoring the need to collect both the streams at the outlet of the device and suggesting flow conditions that will help us achieve the target DMSO outlet concentration for clinical scale flow rates of the cell suspension.

SUBMITTER: Bala Chandran R

PROVIDER: S-EPMC3522666 | biostudies-other | 2012

REPOSITORIES: biostudies-other

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Project description:Urban streams are susceptible to stormwater and sewage inputs that can impact their ecological health and water quality. Microbial communities in streams play important functional roles, and their composition and metabolic potential can help assess ecological state and water quality. Although these environments are highly heterogenous, little is known about the influence of isolated perturbations, such as those resulting from rain events on urban stream microbiota. Here, we examined the microbial community composition and diversity in an urban stream during dry and wet weather conditions with both 16S rRNA gene sequencing across multiple years and shotgun metagenomics to more deeply analyze a single storm flow event. Metagenomics was used to assess population-level dynamics as well as shifts in the microbial community taxonomic profile and functional potential before and after a substantial rainfall. The results demonstrated general trends present in the stream under storm flow versus base flow conditions and also highlighted the influence of increased effluent flow following rain in shifting the stream microbial community from abundant freshwater taxa to those more associated with urban/anthropogenic settings. Shifts in the taxonomic composition were also linked to changes in functional gene content, particularly for transmembrane transport and organic substance biosynthesis. We also observed an increase in relative abundance of genes encoding degradation of organic pollutants and antibiotic resistance after rain. Overall, this study highlighted some differences in the microbial community of an urban stream under storm flow conditions and showed the impact of a storm flow event on the microbiome from an environmental and public health perspective.IMPORTANCE Urban streams in various parts of the world are facing increased anthropogenic pressure on their water quality, and storm flow events represent one such source of complex physical, chemical, and biological perturbations. Microorganisms are important components of these streams from both ecological and public health perspectives. Analysis of the effect of perturbations on the stream microbial community can help improve current knowledge on the impact such chronic disturbances can have on these water resources. This study examines microbial community dynamics during rain-induced storm flow conditions in an urban stream of the Chicago Area Waterway System. Additionally, using shotgun metagenomics we identified significant shifts in the microbial community composition and functional gene content following a high-rainfall event, with potential environment and public health implications. Previous work in this area has focused on specific genes/organisms or has not assessed immediate storm flow impact.

Project description:Pancreatic islets of Langerhans release glucagon to maintain blood glucose levels, and release of this peptide is dysregulated in diabetes mellitus. Although the importance of proper secretion of this peptide has been shown, no measurement of its release at the single islet level has been reported. In previous work, a non-competitive assay for glucagon was developed with a 6 pM limit of detection, low enough to measure from a single islet. To incorporate this method in an online assay, a microfluidic system with several distinct features was developed. To maintain appropriate flow rates in the presence of the high concentration of salt that was required for the assay, a piezo-actuated pressure transducer with in-line flow sensors was used to drive sample flow through 80 × 50 μm (width × depth) channels, while electroosmotic flow was used to gate the sample away from 15 × 5 μm separation channel. Flow rates tested with this system were 50 - 200 nL min-1 with relative standard deviations (RSDs) ranging from 1 - 4 %. Use of the pressure-driven flow was found to increase the amount of clogs in the system, so a method to incorporate in-line filters into the channels was developed. A total of 4 low resistance, in-line microfabricated filters were evaluated, with all designs prolonging the operation time of the microfluidic device to more than 4 hours without clogs observed. Use of this system enabled highly reproducible injections (3-6% RSD). During initial incorporation of the noncompetitive assay for glucagon, it was determined that Joule heating was problematic and temperature measurements revealed the separation channel increased to more than 50°C during operation. A 3D-printed manifold was used to hold a Peltier cooler in place on the microfluidic device which produced a 2.6-fold improvement in the amount of the noncovalent glucagon complex that was detected compared to without cooling. These features are expected to be useful for not only long-term monitoring of the glucagon release from islets of Langerhans, but has the potential to be applied to a number of other microfluidic separation-based assays as well.

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Influence of buoyancy-driven flow on mass transfer in a two-stream microfluidic channel: Introduction of cryoprotective agents into cell suspensions.

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