​Designing adaptive and active materials that dynamically reconfigure in response to changes in the surrounding environment is a multidisciplinary challenge. The development of new active composite materials will spark collective material properties and functionalities that are distinct from those of their constituent components. The concept parallels complex adaptive systems, where interactions among components and the environment drive emergent behaviors. Practically, these adaptive and active material systems can be used to realize autonomous actuation and passive adaptability, especially in scenarios where active spatiotemporal controls are lacking due to high cost, limited sensing abilities, unpredictable, or unsupervised environments.

My works focus on using the material-encoded negative feedback loops to realize 1) self-regulated autonomous motion with static stimuli and 2) passive adaptation to dynamic stimuli. For autonomous motions, many aspects can be used to convert static environmental stimuli to cyclical internal stimuli caused by deformation. In return, this cyclical stimulus dynamically changes the deformation. Thus, forming an environment–deformation–stimuli change–deformation adapts–negative feedback loop. With material and structure-encoded negative feedback loops, adaptivity to a dynamic equilibrium will emerge. We can use such properties to build passive components in robotics to complement active components to lower the control and sensing complexities of the whole system and develop analogous safety features for times like when electronic processors and sensors are down and when vision is hindered.

Magnetic putty as a reconfigurable, recyclable, and accessible soft robotic material
Li, M., Pal, A., Byun, J., Gardi, G., Sitti, M., Advanced Materials, 2304825 (2023). Link
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Abstract: In this study, magnetic putty is introduced as a magnetically hard and soft material with large remanence and low coercivity. It is shown that the magnetization of magnetic putty can be easily reoriented with maximum magnitude using an external field that is only one-tenth of its coercivity. Additionally, magnetic putty is a malleable, autonomous self-healing material that can be recycled and repurposed. The authors anticipate magnetic putty could provide a versatile and accessible tool for various magnetic robotics applications for fast prototyping and explorations for research and educational purposes.

Light-activated shape morphing and light-tracking materials using biopolymer-based programmable photonic nanostructures
Wang, Y.*, Li, M.*, et al., Omenetto, F. G., Nature Communications 12, 1–9 (2021). (*equal contribution) Link

Abstract: Here, we combine programmable structural colors with elastomeric material composites to generate optomechanical actuators that display controllable and tunable actuation as well as complex deformation in response to simple light illumination. Complex three-dimensional configurations, programmable motion patterns, and phototropic movement where the material moves in response to the motion of a light source are presented. A “photonic sunflower” demonstrator device consisting of a light-tracking solar cell is also illustrated to demonstrate the utility of the material composite. The strategy presented here provides new opportunities for the future development of intelligent optomechanical systems that move with light on demand.

Flexible magnetic composites for light-controlled actuation and interfaces
Li, M.*, Wang, Y.*, Chen, A., Naidu, A., Napier, B. S., Li, W., Rodriguez, C. L., Crooker, S. A., Omenetto, F. G., PNAS 115, 8119–8124 (2018) (*equal contribution) Link

​Abstract: We present here flexible material composites that, when illuminated, are capable of macroscale motion, through the interplay of optically absorptive elements and low Curie temperature magnetic materials. These composites can be formed into films, sponges, monoliths, and hydrogels, and can be actuated with light at desired locations. Light-actuated elastomeric composites for gripping and releasing, heliotactic motion, light-driven propulsion, self-sustained oscillation, and rotation are demonstrated as examples of the versatility of this approach.

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