Meng Li1 Yu Wang1 Aiping Chen2 Bradley Napier1 Wenyi Li1 Scott Crooker3 Fiorenzo Omenetto1

1, Tufts University, Medford, Massachusetts, United States
2, Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
3, National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico, United States

Actuators are components that are used to move a mechanical system or perform shape morphing under certain stimulus. Among various stimuli, light has distinguishing advantages of non-contact control, and being capable of localized actuation with high resolution. Most optomechanical devices can perform simple movement such as bending, twisting, or expansion with simple light modulation. However, it is only with complicated light patterning or structured design that they can achieve complex movement like rotating, folding, walking or waving. There are many situations where complex modulations cannot be enacted, and the versatility is limited by the specific design.
In this work, we introduce an approach of wireless actuation based on optically-induced demagnetization which provides multiple opportunities for shape-morphing and deformation in response to light in easy-to-use formats. We fabricate light-responsive magnetic composites by incorporating CrO2 in multiple flexible, elastomeric, and mechanically robust, durable materials. Because of their polymorphic nature along with their flexibility and high failure strain, biopolymers (silk fibroin) and elastomers (PDMS) are used as magnetically inert host material matrices for ferromagnetic dopants. When illuminated, the composite are capable of macroscale motion, through the interplay of optically-absorptive elements and low-Curie temperature magnetic materials (CrO2). These composites can be formed into films, sponges, monoliths and hydrogels, and can be actuated with light at desired locations. With no need for specific pattern design and complicated light modulation, we have successfully demonstrated a gripper that is activated by stationary light and is able to grab and release objects. The gripper experiences cyclic tightening and loosening, which has the potential for continuous object gripping and relocation. The combination of magnetic force and localized laser illumination can achieve more complex actuation patterns, other than bending and twisting. A Curie rotary engine powered by light is demonstrated at a rotation speed of 2 rpm. The concepts presented here represent a comprehensive baseline of a composite platform that merges optomechanical and magnetic functions. We believe that this approach offers an interesting platform to achieve delicate and desired light-induced motion with easily accessible equipment and facile manufacturing processes, opening opportunities ofr manufacturing flexible, simple, and cheap actuators at multiple forms from the micro- to the macro-scale.