Wavelength-selective actuators show multi-directional Marangoni effect–based swimming and direct measurement of driving force.

Here we demonstrate a facile method for naked-eye detection of urea based on the structure color change of pH-sensitive photonic crystals.

The aim of microencapsulation is to achieve controllable and sustainable release at the desired site. Despite the many methods developed in recent years, there is still a need to advance the strategies for higher controllability and scalability. Taking inspiration from the heart, which pumps blood by continual contraction of muscles, we demonstrate a novel releasing method, in which the core release is controlled by the compression–relaxation cycles of microcapsules upon the application of a magnetic field. This idea is realized by embedding Fe₃O₄ particles into a polymer shell. When the magnetic field is applied, the Fe₃O₄ particles align along the field direction and stretch the shell, resulting in compression of the microcapsules and release of the core contents; the shape is restored after the field is removed. We demonstrated various release patterns by altering the strength of the magnetic field and the compression frequency. This release method provides repeated and pulsatile delivery, enhanced spreading distance and ejection speed, and is site specific and proactive, providing a new option for controlled release applications.