Shape programmable multi-stable polymer actuators

Recent advances in soft actuators have enabled systems that are safer to interact with, better at handling fragile objects, able to produce complex shapes with fewer components. However, being inherently soft differs these actuators from their rigid counterparts and requires the development of particular approaches to achieve complex and advanced functionalities. This thesis contributes to the soft actuator field through their integration with shape memory polymers (SMPs) to add attributes such as reconfiguration, latchability, and load-bearing. In this study, SMPs are combined with 1) pneumatic, 2) dielectric elastomer, and 3) electromagnetic soft actuators.

I developed a matrix of densely-packed individually addressable latchable microfluidic valves driven with a single pneumatic source combined with SMPs and stretchable heaters. Microfluidic platforms with 4x4 and 4x2 valve matrices in a 15mm x 15mm area are demonstrated. The valves are individually addressable and latchable allow extended cycles (>3000) and long-term latching (>15h). This method enables to increase the number of actuators independently of the pressure controller. It is an effective technique to address the large array of pneumatic actuators and is a promising approach to develop microfluidic large-scale integration systems.

I created reconfigurable and multi-stable soft surfaces by integrating dielectric elastomer actuators (DEAs) with SMP fibers and an array of stretchable heaters. Multiple distinct configurations are dynamically programmed by spatially tuning the rigidity of SMP fibers, locally reducing their stiffness by two orders of magnitude by Joule heating. In this system, the orientation and the location of the soft and hard regions define the deformed shapes when the DEA is actuated. Multimorphing ability is demonstrated by gripping objects with different shapes. Cooling down the SMP fibers locks these shapes into place and allows keeping the device in the actuated state at zero power. I developed an analytical model combining beam theory and shape memory effect to determine the design parameters for large deformations (>300° tip deflection angle) and high blocking forces (>27mN).

Finally, I developed shape programmable electromagnetic soft beams with multiple degrees of freedom by embedding liquid metal coils in silicone structure with SMP hinges. Each hinge is individually addressable by Joule heating and can twist or bend depending on the direction of the magnetic field. All types of deformations can be locked by cooling down the SMP layers. When cold, the beam has a robust mechanical structure and allows high blocking forces. Complex shape profiles are achieved through hierarchical deform-and-latch operations, a useful feature for applications that require sophisticated transformations.