Microfluidic pumps for cell sorting

Microfluidic cell sorting has shown promising advantages over traditional bulky cell sorting equipment and has demonstrated wide-reaching applications in biological research and medical diagnostics. The most important characteristics of a microfluidic cell sorter are its throughput, ease of use, and integration of peripheral equipment onto the chip itself. In this review, we discuss the six most common methods for pumping fluid samples in microfluidic cell sorting devices, present their advantages and drawbacks, and discuss notable examples of their use. Syringe pumps are the most commonly used method for fluid actuation in microfluidic devices because they are easily accessible but they are typically too bulky for portable applications, and they may produce unfavorable flow characteristics. Peristaltic pumps, both on- and off-chip, can produce reversible flow but they suffer from pulsatile flow characteristics, which may not be preferable in many scenarios. Gravity-driven pumping, and similarly hydrostatic pumping, require no energy input but generally produce low throughputs. Centrifugal flow is used to sort cells on the basis of size or density but requires a large external rotor to produce centrifugal force. Electroosmotic pumping is appealing because of its compact size but the high voltages required for fluid flow may be incompatible with live cells. Emerging methods with potential for applications in cell sorting are also discussed. In the future, microfluidic cell sorting methods will trend toward highly integrated systems with high throughputs and low sample volume requirements.