An on-chip microfluidic pressure regulator that facilitates reproducible loading of cells and hydrogels into microphysiological system platforms - PubMed (original) (raw)

An on-chip microfluidic pressure regulator that facilitates reproducible loading of cells and hydrogels into microphysiological system platforms

Xiaolin Wang et al. Lab Chip. 2016.

Abstract

Coculturing multiple cell types together in 3-dimensional (3D) cultures better mimics the in vivo microphysiological environment, and has become widely adopted in recent years with the development of organ-on-chip systems. However, a bottleneck in set-up of these devices arises as a result of the delivery of the gel into the microfluidic chip being sensitive to pressure fluctuations, making gel confinement at a specific region challenging, especially when manual operation is performed. In this paper, we present a novel design of an on-chip regulator module with pressure-releasing safety microvalves that can facilitate stable gel delivery into designated microchannel regions while maintaining well-controlled, non-bursting gel interfaces. This pressure regulator design can be integrated into different microfluidic chip designs and is compatible with a wide variety of gel injection apparatuses operated automatically or manually at different flow rates. The sensitivity and working range of this pressure regulator can be adjusted by changing the width of its pressure releasing safety microvalve design. The effectiveness of the design is validated by its incorporation into a microfluidic platform we have developed for generating 3D vascularized micro-organs (VMOs). Reproducible gel loading is demonstrated for both an automatic syringe pump and a manually-operated micropipettor. This design allows for rapid and reproducible loading of hydrogels into microfluidic devices without the risk of bursting gel-air interfaces.

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Figures

Fig. 1

Pressure regulator module design. (A) Schematic of basic pressure regulator module structure. (B) Example of one pressure regulator design and its integration into a perfusion-based 3D culture device. (C) A simplified electronic circuit analogy model corresponding to the mechanism of gel loading into the device with pressure regulator module. (D) Simulation results for the gel loading process in both tissue chamber and pressure regulator module without bursting when the hydraulic pressure inside the gel loading channel is less than the burst pressure of their interconnected capillary burst valves. Color scheme: blue represents gel, red represents air and yellow represents gel/air interface.

Fig. 2

(A) Simplified model of gel loading along the microfluidic channel, consisting of two stages. (B) Schematic of gel movement along the loading channel when the contact angles of gel interface with all sidewalls exceed the critical advancing contact angle. (C) Schematic of the capillary burst valve design with gentle slope and different contact angle of gel interface with sidewalls at the vertices.

Fig. 3

(A) Performances of the pressure regulator at two stages by automated dye-mixed gel loading with syringe pump under different flow rates, and a well-controlled gel interface positioned at vertices of the perfusion microvalves. Dashed rectangle in gel interface column represents the slightly bulged gel interface at the high flow rate of 320μL/min. (B) Control experiment using the same gel loading channel without the pressure regulator module.

Fig. 4

(A) Experimental results on dye-mixed gel loading using 55μm and 85μm wide safety microvalves at different flow rates. (B) Comparison results for sensitivity and working range of the pressure regulator with different widths. The narrow safety microvalve has a large working range, while wide safety microvalves have high sensitivity.

Fig. 5

Gel confinement with a 100 μm wide perfusion microvalve. Both the pressure regulator module and the gel interface at the perfusion microvalve were sensitive to the applied flow rate. At higher flow rates, smaller gel volumes (e.g. 10μL) could effectively prevent gel bursting from the perfusion microvalve with a wide opening.

Fig. 6

(A) Experimental results on manual cell-seeded fibrinogen gel loading with micropipettor under different pipetting speed. B0: no safety microvalve bursting, B1: bursting of one safety microvalve, and B2: bursting of two safety microvalves. Dashed rectangle represents the gel bursting region inside the pressure regulator module. (B) Corresponding vessel network formation inside the microfluidic device after 7 days in culture.

Fig. 7

Heterotypic dye-mixed gel loading into a microfluidic device with a pressure regulator module at each end serving as a gel loading outlet. (A) Step 1: green dye-mixed gel loading into left chamber and bursting of two safety microvalves. (B) Step 2: red dye-mixed gel loading into right chamber and bursting of only one safety microvalve. (C) Step 3: blue dye-mixed gel loading into central connecting channel to connect the two (green and red) chambers. Diffusion between the chambers then occurred.

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An on-chip microfluidic pressure regulator that facilitates reproducible loading of cells and hydrogels into microphysiological system platforms - PubMed (original) (raw)