Autonomous Microfluidic Capillary System

Abstract

The transport of minute amounts of liquids using microfluidic systems has opened avenues for higher throughput and parallelization of miniaturized bio/chemical processes combined with a great economy of reagents. In this report, we present a microfluidic capillary system (CS) that autonomously transports aliquots of different liquids in sequence: liquids pipetted into the service port of the CS flow unidirectionally through the various sections of the CS, which comprises a 15-pL reaction chamber, into the capillary pump. A CS can thus be operated by simply delivering the different samples to its service port. The liquid transport concept presented here is advantageous because the pumping and valving functions are integrated into the device by means of capillary phenomena, and it therefore does not require any external power supply or control device. Thus, arrays of CSs can easily be formed by cloning a functional CS. Alternatively, the flow of liquids in CSs can also be interactively tuned if desired by (i) forcing the evaporating of liquid out of the capillary pumps and (ii) by contacting a secondary, removable capillary pump to the embedded ones. We illustrate the possibilities of CSs by conducting a surface immunoassay for a cardiac marker, within 25 min, on an area of 100 x 100 microm2, using 16 sequential filling steps.

3D visualization of convection patterns in lab-on-chip with open microfluidic outlet

“…Systems composed of a multitude of micro-channels with open outlets can be used for parallel assays and enable high throughput microfluidics (Juncker et al 2002;Park et al 2006;Zimmermann et al 2007;Namasivayam et al 2003). On the other hand, the use of open outlets is the cause of side effects mostly related to evaporation and contamination.…”

Capillary pumps with constant flow rate

“…For increasing positions s, Rh(s) increases. Consequently, a constant flow design requires a capillary suction P(s) that increases with s. CP designs with a constant porosity, and hence constant capillary pressure (Eddowes, 1988;Juncker, 2002;Gervais, 2011;Mirzaei, 2010) The maximum channel width occurs at s = 0, where w(0) = wmax is a design parameter. A decreasing w(s), in combination with a hydrophylic material surface with equilibrium contact angle < !…”

“…Note that in this example, the design features a CP consisting of parallel channels with nearly constant rectangular cross--section. This is possible because the flow resistance of the CP << R0, which was the a priori design requirement of previous CP designs (Eddowes, 1988;Juncker, 2002;Gervais, 2011;Mirzaei, 2010). Capillary pumps are often designed as micropillar arrays, which, due to their large amount of fluidic interconnections, are inherently robust against channel blockage by debris and against manufacturing imperfections.…”

“…Previous CP design approaches for providing a constant flow are based on providing a constant capillary pressure throughout the CP while not significantly increasing the overall flow resistance as the CP is being filled (Eddowes, 1988). Such designs have been realised in the form of parallel microchannels arranged in an arborescent pattern (Juncker, 2002) or arrays of posts (Gervais, 2011), or meshes (Mirzaei, 2010). Based on a microfluidic design by Melin et al (Melin, 2004), Safavieh et al reported a CP design with varying capillary flow based on a meandering channel design containing geometric capillary valves between the meander arms.…”

Liquid recirculation in microfluidic channels by the interplay of capillary and centrifugal forces

“…The interfacial pressure P C of the liquid front advancing into a rectangular channel is given by [3,7]:…”