Negative-pressure soft pneumatic actuators enabled by asymmetrically distributed bending units

Soft pneumatic actuators are highly flexible and can adapt to complex environments, attracting significant attention for their ability to operate in settings where rigid actuators cannot. Most existing soft pneumatic actuators are powered by positive pressure, which has the disadvantage of volume increase during operation and risk of exploding under large pressures. In this study, we designed a new type of soft actuator by inducing asymmetric bending deformation throughout a holey structure under negative pressure. Using finite element analysis and a theoretical model, we studied the effects of various geometric parameters on the structure's bending behavior. We found that the displacement of the circle's center from the central axis is a parameter with the most significant impact on the bending behavior of the structure. By designing circular holes with offset from the central axis, the structure can bend toward the offset direction during subsequent bending deformation. Based on this deformation mechanism, we designed a soft gripper that bends upon actuation and effectively picks up objects. We further designed a bi-directional gripper that bends towards both sides and a circular gripper that contracts towards the center upon evacuation to hold objects. These soft grippers’ grasping capabilities are validated by experimental tests. Finally, by arranging the holes in a wavy pattern within the structure, we created a crawling robot that moves forward through cyclic negative pressure actuation. These findings highlight the potential of leveraging bending behaviors in asymmetrically distributed holey structures for the development of negative-pressure driven soft actuators and robots.