The process of repairing wounds to individual cells isn’t well understood. What’s needed to improve that understanding is a method that can quickly damage many cells in a controlled way. To do this, Sindy K. Y. Tang of Stanford University and coworkers designed a microfluidic “guillotine” that slices single-cell organisms in half as they squeeze past a plastic blade (Proc. Natl. Acad. Sci. USA 2017, DOI: 10.1073/pnas.1705059114). The researchers have tested the knifelike device on individual cells of the protozoan Stentor coeruleus, which are typically 100 to 200 µm wide but can stretch up to 1 mm. At slow flow rates, the knife tip cuts each cell into two approximately equal pieces, which are shunted into separate channels. Many of these cell pieces survive and regenerate within 24 to 48 hours. At higher flow rates, the knife ruptures the cell into multiple pieces, spilling the cell’s contents. Fewer of these cells survive. In both flow regimes, bits of cell membranes stick to the knife and clog up the device. The researchers find that encapsulating each cell in a water droplet cleans away the debris and increases the throughput. They were able to cut the cells at a rate of 64 cells per minute, which is more than 200 times as fast as manually cutting with a handheld needle. Such rapid wounding makes it possible to study cohorts of cells at the same stage of the repair process.