With the new ink, they can now “easily print a large number of reactive elements onto large surfaces,” Omenetto says. The team made the ink by breaking down raw silk fibers into constituent proteins, which the researchers suspended in water. Next they mixed in various reactive molecules and analyzed how the resulting products changed color when exposed to alterations in their environment. “In the case of a T-shirt, the wearer ‘paints’ the shirt [through] exercise—with colors correlating to the acidity distribution of their sweat,” Omenetto says. The new ink technology has “the potential to transform consumer wearables from recreational novelty devices into body-worn, clinical-grade physiological measurement tools that yield physician-actionable information,” he says.