Valves for autonomous capillary systems

Abstract

Autonomous capillary systems (CSs) are microfluidic systems inside which liquids move owing to capillary forces. CSs can in principle bring the high-performances of microfluidic-based analytical devices to near patient and environmental testing applications. In this paper, we show how wettable capillary valves can enhance CSs with novel functionalities, such as delaying and stopping liquids in microchannels. The valves employ an abruptly changing geometry of the flow path to delay a moving liquid filling front in a wettable microchannel. We show how to combine delay valves with capillary pumps, prevent shortcuts of liquid along the corners of microfluidic channels, stop liquids filling microchannels from a few seconds to over 30 min, trigger valves using two liquid fronts merging, and time a liquid using parallel microfluidic paths converging to a trigger valve. All together, these concepts should add functionality to passive microfluidic systems without departing from their initial simplicity of use.

Reconfigurable microfluidic hanging drop network for multi-tissue interaction and analysis

“…Open conduits have previously been used to construct autonomous capillary systems 43,44 . The idea of inverting the substrates and including circular areas for drop formation within a network of fluidic channels has not been reported to date and offers completely new perspectives in association with multicellular spheroid cultures.…”

“…We implemented this option with on-demand reconfiguration of the connection between the hanging drops by using capillary valving 43 (Fig. 3a).…”

3D-Printed Autonomous Capillaric Circuits†

“…2,5,6,[11][12][13]26,27 Cleanroom-fabricated TVs have small features (~ 20 µm) and smooth, vertical channel walls (Fig. 1a & 1c).…”

“…Previously, the success rate of capillary stop valves and TVs was only reported over a 5-minute period. 16,26 Here we defined TV success as when a valve holds liquid for at least 30 minutes without leakage. This allowed autonomous microfluidic operations in a walk-away format where the user pre-loads samples and reagents onto the chip and subsequently starts the assay at a time of their choosing, without needing to fit their operations to a strict 5-minute window.…”

“…17,26,28 Fig. 2a shows the geometric parameters known to affect the performance of capillary TVs: the height of the TV, width of the TV, and the .…”