Active nematic fluids borrow their ingredients from biology. Using long, rigid microtubules and kinesin motor proteins capable of cross-linking between and “walking” along tubules, researchers create these complex flow patterns. Here, a team took the system a step further by seeding the flow with a hydrogel that turns into a polymer when exposed to light. Then, by shining light patterns on the flow, the scientists can create rigid or flexible structures inside the active fluid. In this case, they show off some of the neat flow patterns they can create. (Video and image credit: G. Pau et al.)