Polymer brushes—polymer chains attached to a surface in such a way that they stand up like blades of grass from the ground—are promising for making patterned smart surfaces and microarrays for testing biological recognition and bioadhesion. The properties of polymer brush patterns depend on monomer composition, polymer height, and brush distribution across the surface. Until now, there has been no method that independently varies these parameters with micrometer resolution. By using a digital micromirror device, microfluidics, and an oxygen-free reaction chamber, chemists led by Adam B. Braunschweig at the City University of New York found they could change these three variables and create complex patterns from polymer brushes (Nat. Commun. 2020, DOI: 10.1038/s41467-020-14990-x). The setup works by introducing monomer solutions into the reaction chamber via microfluidics. A computer-controlled digital micromirror device then shines light on specific locations so that photoinduced surface-initiated atom-transfer radical polymerization occurs. Using this technique, the team can vary the composition, height, and distribution of the polymers in a brush with each pixel measuring less than 5 μm. “In the broadest terms, this is a tool for creating films and patterns for any research program where interactions at interfaces are being studied or need to be carefully controlled,” Braunschweig says.