Researchers describe the material as a cephalopod-inspired “smart synthetic skin” made from hydrogel and fabricated using a technique the team calls halftone-encoded 4D printing. Most synthetic materials—even advanced ones—are designed to do just one thing well. A coating might change color, a polymer might bend when heated, or a gel might respond to moisture. The term “4D printing” refers to structures that change after printing. Unlike conventional 3D printing, where a shape is fixed once fabrication ends, 4D-printed materials are engineered to transform in response to external stimuli, such as heat, solvents, or mechanical stress. ... The novel system is...