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Microfluidic active pressure and flow stabiliser

ABSTRACT: In microfluidics, a well-known challenge is to obtain reproducible results, often constrained by unstable pressures or flow rates. Today, there are existing stabilisers made for low-pressure microfluidics or high-pressure macrofluidics, often consisting of passive membranes, which cannot stabilise long-term fluctuations. In this work, a novel stabilisation method that is able to handle high pressures in microfluidics is presented. It is based on upstream flow capacitance and thermal control of the fluid’s viscosity through a PID controlled restrictor-chip. The stabiliser consists of a high-pressure-resistant microfluidic glass chip with integrated thin films, used for resistive heating. Thereby, the stabiliser has no moving parts. The quality of the stabilisation was evaluated with an ISCO pump, an HPLC pump, and a Harvard pump. The stability was greatly improved for all three pumps, with the ISCO reaching the highest relative precision of 0.035% and the best accuracy of 8.0 ppm. Poor accuracy of a pump was compensated for in the control algorithm, as it otherwise reduced the capacity to stabilise longer times. As the dead volume of the stabiliser was only 16 nL, it can be integrated into micro-total-analysis- or other lab-on-a-chip-systems. By this work, a new approach to improve the control of microfluidic systems has been achieved.

SUBMITTER: Sodergren S

PROVIDER: S-EPMC8602347 | biostudies-literature |

REPOSITORIES: biostudies-literature

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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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Microfluidic active pressure and flow stabiliser

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