Wicking pumps for microfluidics

This review describes mechanisms for pulling fluids through microfluidic devices using hydrophilic structures at the downstream end of the device. These pumps enable microfluidic devices to get out of the lab and become point-of-care devices that can be used without external pumps. We briefly summarize prior related reviews on capillary, pumpless, and passively driven microfluidics then provide insights into the fundamental physics of wicking pumps. No prior reviews have focused on wicking pumps for microfluidics. Recent progress is divided into four categories: porous material pumps, hydrogel pumps, and 2.5D- and 3D-microfabricated pumps. We conclude with a discussion of challenges and opportunities in the field, which include achieving constant flow rate, priming issues, and integration of pumps with devices.