Fluid steering in a microfluidic chip by means of thermally responsive phospholipids

The viscosity of aqueous phospholipid preparations comprised of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC) increases with temperature. This macroscopic change occurs over a narrow temperature range beginning at 24 °C and reaching a maximum at a temperature as high as 29 °C, which makes this lipid preparation functional as a thermally responsive material for fluid steering in a microfluidic device. Based on systematic evaluation of similar preparations, we demonstrate the utility of this material to direct fluid flow in a double-T microfluidic chip using a simple lab-built temperature control system. Flow of fluorescein labeled lipid preparation through the microfluidic channels is monitored with an inverted epi-fluorescence microscope and captured as digital video. The fact that phospholipids are also used in analytical separations alludes to the potential of this material to simultaneously direct fluid and provide chemical selectivity in lab-on-a-chip devices. This is the first example of directed fluid flow in a microfluidic device with biologically compatible DMPC–DHPC preparations.