Rigorous buoyancy driven bubble mixing for centrifugal microfluidics

Abstract

We present batch-mode mixing for centrifugal microfluidics operated at fixed rotational frequency. Gas is generated by the disk integrated decomposition of hydrogen peroxide (H2O2) to liquid water (H2O) and gaseous oxygen (O2) and inserted into a mixing chamber. There, bubbles are formed that ascent through the liquid in the artificial gravity field and lead to drag flow. Additionaly, strong buoyancy causes deformation and rupture of the gas bubbles and induces strong mixing flows in the liquids. Buoyancy driven bubble mixing is quantitatively compared to shake mode mixing, mixing by reciprocation and vortex mixing. To determine mixing efficiencies in a meaningful way, the different mixers are employed for mixing of a lysis reagent and human whole blood. Subsequently, DNA is extracted from the lysate and the amount of DNA recovered is taken as a measure for mixing efficiency. Relative to standard vortex mixing, DNA extraction based on buoyancy driven bubble mixing resulted in yields of 92 ± 8% (100 s mixing time) and 100 ± 8% (600 s) at 130g centrifugal acceleration. Shake mode mixing yields 96 ± 11% and is thus equal to buoyancy driven bubble mixing. An advantage of buoyancy driven bubble mixing is that it can be operated at fixed rotational frequency, however. The additional costs of implementing buoyancy driven bubble mixing are low since both the activation liquid and the catalyst are very low cost and no external means are required in the processing device. Furthermore, buoyancy driven bubble mixing can easily be integrated in a monolithic manner and is compatible to scalable manufacturing technologies such as injection moulding or thermoforming. We consider buoyancy driven bubble mixing an excellent alternative to shake mode mixing, in particular if the processing device is not capable of providing fast changes of rotational frequency or if the low average rotational frequency is challenging for the other integrated fluidic operations.

Siphon-Induced Droplet Break-Off for Enhanced Mixing on a Centrifugal Platform

“…Can require specific chemical reagents stored on disc. [73,76,77] Wall deformation Mixing is enhanced by deforming chamber walls to induce liquid movement.…”

“…While it is hard to make a general statement, active mixers tend to significantly accelerate mixing; however, they are typically more complicated to fabricate and integrate, and more complex to control.Passive mixers use the hydrodynamic energy, e.g., provided by a pressure difference created by a pump, gravity or centrifugal force, to restructure the liquid flows in such ways that fast mixing is promoted. Examples for passive mixing principles are bas/relief structures incorporated in the channel walls to induce advection in a liquid flow [63] and multi-lamination of flow [64], e.g., through split-and-recombine strategies [65,66].Mixing principles using the specific effects on centrifugal lab-on-a-disc platforms [67] include Coriolis-force induced split-and-recombine [68], advection [69], reciprocating flow induced by centrifugo-pneumatic pumping [52,70], mixing enhanced by the Euler force through periodically changing angular acceleration [71,72] and/or magnetic beads [51], mixing by use of chemically generated bubbles [73], and mixing enhanced by deformation of soft chamber walls [74,75]. Mixing can also be enhanced through external pumping such as provision of external air sources [76,77].…”

“…Mixing principles using the specific effects on centrifugal lab-on-a-disc platforms [67] include Coriolis-force induced split-and-recombine [68], advection [69], reciprocating flow induced by centrifugo-pneumatic pumping [52,70], mixing enhanced by the Euler force through periodically changing angular acceleration [71,72] and/or magnetic beads [51], mixing by use of chemically generated bubbles [73], and mixing enhanced by deformation of soft chamber walls [74,75]. Mixing can also be enhanced through external pumping such as provision of external air sources [76,77].…”

Automated analytical microsystem for the spectrophotometric monitoring of titratable acidity in white, rosé and red wines

“…The chamber was designed in order to minimize the most common problems related to the presence and the circulation of gas bubbles while monitoring absorbance, such as an increase in the noise and the appearance of transitory signals or baseline drifts [36]. The smooth contours of the cell prevented both the formation and accumulation of bubbles, which are usually favored by abrupt changes in the geometry of the fluidic features [37]. Besides, an increment in the flow rate at the exit of the chamber was used for favoring bubble evacuation in case any was produced.…”

A Review of Biomedical Centrifugal Microfluidic Platforms

“…Burger et al also presented a bubble mixing LOAD platform ( Figure 2 C). Here, air (oxygen) was generated by the decomposition of hydrogen peroxide and mixing was improved by the rupture of the bubbles which caused a strong buoyancy in centrifugal field [ 30 ].…”