Make it simple: long-term stable gradient generation in a microfluidic microdevice

Microfluidics-based gradient generators have been used for various biological applications, specifically chemotaxis in cell culture. However, the ability to generate and maintain long term gradients alongside the ability to quickly switch solutions is a challenge of the current microfabricated systems. In this study, a simple flow-driven microfluidic system was developed to achieve long-term stable concentration gradients. Computational modelling was performed to highlight the fluid dynamics as well as to verify the ability of maintaining stable gradients over 7days. Numerical simulation was analysed to evaluate the static pressure, velocity magnitude and wall shear stress distribution in the chamber. A microdevice fabricated with polydimethylsiloxane (PDMS), using a standard soft lithography technique is presented. It consists of eight parallel microchannels (5 mu mx30 mu mx1,800 mu m) linking source and sink chambers; a syringe pump drives fluid through the sink chamber, advection/diffusion from source to sink establishes a gradient. A gradient of a fluorescent dye was generated under the low flow control at 1-10 mu l/h of a simple syringe pump equipped with a pulsation damper that was comparable to a pulseless microfluidic pump. Concentration gradients were formed in 1h and stable from 2h out to 5days and consuming less than 1.0ml of solution. This study focuses on a novel solution to achieve a long-term microfluidic gradient generator using simple engineering techniques of biomedical microdevices.