Method of fabricating a flow constriction within a channel of a microfluidic device

A method is provided for fabricating a constriction region in a channel of a microfluidic device. The method includes the steps of introducing a pre-polymer mixture including a monomer, cross-linking agent and photoinitiator into the channel. The pre-polymer mixture is polymerized at a localized area of the channel so as to shrink and solidify the liquid mixture. The solidified and shrunken liquid mixture provides the constriction region in the channel.