Fig. 4. Super-compliant picospring for initiating gripping action on cellular objects.

a, Schematic illustration of the microgripper’s working process. b, Opening and closing images of the microgripper. T^e, elastic torques from the deformed arc picosprings initiating the closing of the microgripper bucket. c, Time-sequential images showing the grip, transport and release of a microbead. Red arrows point at the targeted microbead. Black arrows indicate the rotating magnetic field and yellow circular arrows indicate the rotation directions of the magnetic field vector. The microgripper performs a rolling motion to approach the object under a rotating magnetic field of 16 mT. After the microgripper arrives at the target (for example, a 5 μm microbead), the magnetic field is decreased to 2 mT to decrease the magnetic torques. The elastic torques of picosprings draw the gripper bucket shut with the microbead cargo inside (0–2 s). After picking up the microbead, the microgripper transports it in a rolling motion mode under a rotating magnetic field of 2 mT (3–112 s). In the end, the microgripper releases the object by simply opening its fingers again (113–115 s) as the 16 mT magnetic field is reapplied. d–f, Object-adapted gripping control strategies in three stages (approach, arrival and grip): gentle gripping of a sensitive cancer cell (d); firm enclosing of a sperm head (e); firm clamping of a waste-mimicking microclot (f). g, Orientation manipulation of a three-cell cluster along all three axes in space. From top to bottom: pitch, yaw and roll. The brown circle arrows indicate the rotation directions of the cell cluster orientations. Scale bar, 40 μm.