Rapid Microfluidic Mixing

Abstract

A preformed T-microchannel imprinted in polycarbonate was postmodified with a pulsed UV excimer laser (KrF, 248 nm) to create a series of slanted wells at the junction. The presence of the wells leads to a high degree of lateral transport within the channel and rapid mixing of two confluent streams undergoing electroosmotic flow. Several mixer designs were fabricated and investigated. All designs were relatively successful at low flow rates (0.06 cm/s, > or = 75% mixing), but had varying degrees of success at high flow rates (0.81 cm/s, 45-80% mixing). For example, one design operating at high flow rates was able to split an incoming fluorescent stream into two streams of varying concentrations depending on the number of slanted wells present. The final mixer design was able to overcome stream splitting at high flow rates, and it was shown that the two incoming streams were 80% mixed within 443 microm of the T-junction for a flow rate of 0.81 cm/s. Without the presence of the mixer and at the same high flow rate, a channel length of 2.3 cm would be required to achieve the same extent of mixing when relying upon molecular diffusion entirely, while 6.9 cm would be required for 99% mixing.

Multivortex micromixing

“…Passive designs are often desirable in applications involving sensitive species (e.g., biological samples) because they do not impose strong mechanical, electrical, or thermal agitation. Examples of passive micromixing approaches that have been widely investigated include the following: (i) ''split-and-recombine'' strategies where the streams to be mixed are divided or split into multiple channels and redirected along trajectories that allow them to be subsequently reassembled as alternating lamellae yielding exponential reductions in interspecies diffusion length and time scales (4,(10)(11)(12); and (ii) ''chaotic'' strategies where transverse flows are passively generated that continuously expand interfacial area between species through stretching, folding, and breakup processes (13)(14)(15)(16)(17)(18)(19)(20). The microchannel structures associated with these mixing elements range from relatively simple topological features on one or more channel walls (ridges, grooves, or other protrusions that can, for example, be constructed by means of multiple soft lithography, alignment, and bonding steps) to intricate 3D flow networks requiring timescales on the order of days to fabricate.…”

Assessment of mixing in passive microchannels with fractal surface patterning

“…If the ridge apex is allowed to span the entire width of the channel, for a sizable number of ridges the apex is too close to the sidewalls of the channel to induce comparable counter rotating flows. In this extreme case, the design resembles the less efficient slanted groove micromixer one [37,38]. To optimize the design and fully map the mixing index, the spacing between the ridges is changed from 50 μm to 250 μm in 25 μm steps, while the apex range is adjusted from the full width of the channel (=200 μm) to the extreme in which all the ridge tips are aligned along the longitudinal symmetry axis of the channel.…”

A polymeric master replication technology for mass fabrication of poly(dimethylsiloxane) microfluidic devices

“…The primary advantage of polymer substrates lies in the ability for mass production at low costs based on replication (casting, embossing, imprinting, or injection molding) techniques for the possible disposable use [7]. Several important polymers including poly(dimethylsiloxane) (PDMS) [8][9][10][11], polymethylmethacrylate (PMMA) [12][13][14][15], polycarbonate [16,17], and polystyrene [18,19] are now increasingly used to fabricate microfluidic systems. In particular, PDMS is a soft polymer that is being actively developed for miniaturized bioassays due to its desirable features including easy replica molding, good optical transparency (down to 230 nm), no toxicity to proteins and cells, as well as easy irreversibly or reversibly sealing to itself and other materials [9,[20][21][22][23].…”