Moving-part-free microfluidic systems for lab-on-a-chip

Abstract

Microfluidic systems are part of an emerging technology which deals with minute amount of liquids (biological samples and reagents) on a small scale. They are fast, compact and can be made into a highly integrated system to deliver sample purification, separation, reaction, immobilization, labelling, detection, etc, and thus are promising for applications such as lab-on-a-chip and handheld healthcare devices. Miniaturized micropumps typically consist of a moving-part component, such as a membrane structure, to deliver liquids, and they are unreliable, complicated in structure and difficult to be integrated with other control electronics circuits. The trend of new-generation micropumps is moving-part-free micropumps operated by advanced techniques, such as electrokinetic force, surface tension/energy, acoustic waves, etc. This paper reviews the development and advances of the relevant technologies, and introduces the electrowetting-on-dielectrics and acoustic wave-based microfluidics. The programmable electrowetting micropump has been realized to dispense and manipulate droplets in 2D with up to 1000 addressable electrodes and electronics built underneath. The acoustic wave-based microfluidics can be used not only for pumping, mixing and droplet generation but also for biosensors, suitable for single-mechanism-based lab-on-chips application.

Slippery Liquid-Infused Porous Surfaces and Droplet Transportation by Surface Acoustic Waves

“…So far, various techniques have been employed to drive microscale fluids, including pressure gradients, capillary forces, electrical and magnetic fields, and SAWs [13,19,25]. SAW microfluidic actuation has significant advantages over other technologies, such as simple device structures, easy processing and low fabrication cost, tuneable frequency response, and the ability to manipulate liquids on a flat surface with precision [26].…”

“…The energy and momentum of the longitudinal wave dissipated into the droplet provide a pressure or a body force on the droplet in the direction of propagation of the SAW. This provides the basis for droplet movement, pumping and mixing, streaming, manipulation and jetting/nebulisation [13,15,26,27,29].…”

The hummingbird tongue is a fluid trap, not a capillary tube

“…This oscillating transformation is driven by fluid and atmospheric forces acting directly on morphological elements of the tongue tips. This description of a (highly efficient) dynamic liquid collecting mechanism has implications for the development of capillary-driven self-assembly of flexible structures (34,35), and may be useful in microfluidic (36,37) and microelectromechanical (34,38) systems with a broad range of applications [e.g., micropliers (39)]. …”

Fabrication, Operation and Flow Visualization in Surface-acoustic-wave-driven Acoustic-counterflow Microfluidics

“…Among the proposed integrated micropumps 23 ,those based on surface acoustic waves (SAWs) are particularly attractive due to their associated capabilities in fluid mixing, atomization and particle concentration and separation 4 . In this paper we have demonstrated how to fabricate and operate a lab-on-chip device in which fluid is steered in a closed PDMS microchannel by integrated on-chip SAW actuators as first described by Cecchini et al 8 .…”