3.5 Micro-valve
Micro-valves are designed to control the switching action of flows in
microchannels. This helps in controlling the flow rates so that proper manipulation
of the biological entities being carried by biological fluids can occur and hence the
overall efficiency of the microfluidic system to handle and deliver increases. Micro-
valves can also be characterized as active and passive microvales. Atwe et al. has
developed a novel pH-sensitive hydrogel based micro-valve for intelligent valving
system for metered flow [ 46 ]. Figure2.14ashows the design of micro-valve using
hydrogel developed through precursors chitosan and polyvinyl alcohol (PVA).
The hydrogel solution has been shown to be prepared through Chitosan and
polyvinyl alcohol (PVA) in acetic acid (CH 3 COOH) and crystallized using glutar-
aldehyde, crosslinking agent in thin wafers form and this has been found to be very
sensitive to pH changes. The pore structure of hydrogel had been investigated
Fig. 2.14 (a) Design of the micro-valve; (b) Valve performance through PIV measurements as a
function of diametral distance from wall of the channel; (c) architecture of a solenoidal
microvalve; (d) valve performance plot of flow rate versus time corresponding to a compressed
air pressure of 5 psi. (Reproduced from Atwe et al. [ 46 ] and Singh et al. [ 47 ] with permission from
the Springer)
2 Microfluidics Overview 51