# Acoustic tractor beams let researchers remotely program material stiffness - Date: 2026-03-22 - Category: Robotics There is a problem at the center of soft robotics that nobody has fully solved: how do you make something that is simultaneously safe enough to be near a human and rigid enough to do useful work? The usual answers — pneumatic bladders, vacuum-jammed granular packets, heated shape-memory alloys — ... ---