Microfluidics for Biologists Fundamentals and Applications

angular orientations in respect of the flow direction. Various strategies have been
developed for micro-mixing which has been broadly classified as Active and
Passive mixing.

3.1 Micro-mixer Design and Characterization

A micro-mixer is a device which can passively (without using energy) or actively
(with external energy) is enabled to mix multiple fluids. This device is associated
heavily with key technological advancements in many fields like chemical engi-
neering, pharmaceuticals, bio-chemistry, analytical chemistry and high-throughput
synthesis and drug screening etc. The micro pathways or parts which are heavily
deployed in promoting active or passive mixing may vary from a long serpentine
channel to a piezoelectrically vibrating membrane.
The development of micro-mixers has progressed rapidly in the last decade.
Initially, the devices manufactured used to be housed within silicon or glass wafers
[ 31 ] and from then a number of micro-mixers with polymeric parts have been
fabricated and successfully developed [ 32 ]. As a result of their overall simple
design, passive micromixers have found a lot of applications as analytical chemistry
tools. While surveying the various the polymeric microfluidic systems, a simply
designed microfluidic system with efficient passive micromixing is a natural choice
for many applications in chemical and biochemical analyses [ 33 ]. Researchers have
proposed various designs of micro-mixers (Fig.2.9) and their use including simple

1

0.1

0.01

0.001

1 10 100

Epsilon (W/kg)

1000 104 105

Mixing time (s)

Mikroglas

T-mixer Triangular interdigital

Starlam IMM

Tangential IMTEK

± 30%

Caterpillar

IMM

tm = 0.15e –0.45

h = 10% h = 3%

Fig. 2.9 Comparison of various micromixers with respect to time and specific power dissipation
(Reproduced from Falk and Commenge [ 34 ] with permission from the Elsevier)

2 Microfluidics Overview 45