Chaotic mixing using source–sink microfluidic flows in a PDMS chip

Abstract

We present an active fixed-volume mixer based on the creation of multiple source-sink microfluidic flows in a polydimethylsiloxane (PDMS) chip without the need of external or internal pumps. To do so, four different pressure-controlled actuation chambers are arranged on top of the 5 ll volume of the mixing chamber. After the mixing volume is sealed/fixed by microfluidic valves made using 'microplumbing technology', a virtual source-sink pair is created by pressurizing one of the membranes and, at the same time, releasing the pressure of a neighboring one. The pressurized air deforms the thin membrane between the mixing and control chambers and creates microfluidic flows from the squeezed region (source) to the released region (sink) where the PDMS membrane is turned into the initial state. Several schemes of operation of virtual source-sink pairs are studied. In the optimized protocol, mixing is realized in just a sub-second time interval, thanks to the implementation of chaotic advection.

Active Continuous-Flow Micromixer Using an External Braille Pin Actuator Array

“…The performance is quantified using a mixing index (MI) defined as the standard deviation of the pixel intensity values of an instantaneous image at time t from a certain reference image. In this study, the reference is defined as the image where the fluid is homogenized or completely mixed [11]. The expression for MI is given in Equation (1).…”

“…MI values of 1 and 0 indicate perfect laminar distribution and completely mixed state, respectively. Many of the literature consider 0.1 MI as a threshold value to define well mixed states [11,18]. Therefore, mixing time, which is the time it takes for the two fluids to be well mixed in the main channel, is defined as the time when the MI reaches 0.1.…”

“…The key to effective mixing lies in the generation of strong stretching and folding [5]. Chaotic advection is induced in passive mixers through channel geometries [6][7][8][9], whereas in active mixers, stretching and folding is introduced with the aid of external perturbation sources [10][11][12]. Active micromixers generally provide enhanced control over the process for a broader range of flow conditions [11,12].…”

“…Chaotic advection is induced in passive mixers through channel geometries [6][7][8][9], whereas in active mixers, stretching and folding is introduced with the aid of external perturbation sources [10][11][12]. Active micromixers generally provide enhanced control over the process for a broader range of flow conditions [11,12]. Several active mixers based on chaotic advection have been reported where efficient mixing was observed in sub-seconds [4,5,11].…”

“…Active micromixers generally provide enhanced control over the process for a broader range of flow conditions [11,12]. Several active mixers based on chaotic advection have been reported where efficient mixing was observed in sub-seconds [4,5,11]. Most of the previously reported active mixers have been fixed-volume mixers.…”