Microfluidic device mixing process

Owing to the increasing interest in digital or droplet-based microfluidics, the microfluidic generation of microdroplets, the associated active and passive mixing process, and the manipulation of microsized droplets in microfluidic devices will also be covered. 

As seen in this brief chapter, the direct-printing process, based on laser printing of layouts on polyester films or wax paper, has the potential to become a powerful technology for the rapid prototyping of microfluidic devices at very low cost, and even a source of low-cost production of disposable devices. This is supported by the fact that the required instrumentation is commonly found at offices and chemistry laboratories. Besides the typical injection and separation channels for electrophoresis, this technology has shown that mixing, preconcentration, clean-up, reactor devices. 

The lysis of cells on-chip (either after a cell-sorting step or fl-om mixed sample sources) will, undoubtedly, be an important step in the development of sample processing microfluidic devices for total sample handling of crude biofluids. There are many examples in the literature that describe the lysis of cells in microfluidic systems and that can be easily divided into two categories (1) those that utilize a chemical-based lysis and (2) those that employ a physical breakdown of the cell. Chemical cell lysis has been demonstrated using a variety of buffers and reagents and... 

Quake and coworkers [16] developed a PDMS microfluidic device (shown in Fig. 4c) for nucleic acid purification from a small number of bacterial or mammalian cells. This multilayer device contained fluidic channels and a system of membrane-actuated pneumatic valves and pumps, which enabled precise control of buffers, lysis agents, and cell solution and also allowed for parallel processing. Bacterial cells, dilution buffer, and lysis buffer are first introduced into the chip and then transferred into the rotary mixer. Once mixed, the lysate is flushed over a DNA affinity column and drained. The DNA... 

As aheady indicated, flow is laminar in microfluidic devices which results in great difficulty in attaining adequate mixing for chemical reaction processes. Scales for the general time (t vP ID) and length (z Uw lD) to achieve mixing in low Peclet number devices are known considering a channel of width w [1]. 

---