Self-propelled, infinitely programmable synthetic cilia

Credit: Harvard University

Scientists have spent years attempting to develop artificial cilia for miniature robotic systems capable of complex actions such as bending, twisting, and reversing. Building these microstructures smaller than a human hair often requires multi-step production techniques and a variety of triggers to induce complicated movements, hence restricting their widespread uses.

Now, Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) researchers have created a single-material, single-stimuli microstructure that can outmaneuver biological cilia. These programmable, micron-scale structures could be used for a variety of purposes, such as soft robotics, biocompatible medical devices, and even dynamic information encryption.

Nature has published the research.

Joanna Aizenberg, the Amy Smith Berylson Professor of Materials Science and Professor of Chemistry & Chemical Biology at SEAS and senior author of the paper, stated, “Innovations in adaptive self-regulated materials that are capable of a diverse set of programmed motions represent a very active field that is being tackled by interdisciplinary teams of scientists and engineers.” “Advances in this discipline may have a substantial impact on how we build materials and gadgets for applications like as robotics, medicine, and information technology.”

In contrast to previous research, which relied primarily on complex multi-component materials to achieve programmable movement of reconfigurable structural elements, Aizenberg and her team designed a microstructure pillar made of a photoresponsive liquid crystal elastomer. Due to the alignment of the liquid crystal elastomer’s essential building pieces, when light strikes the microstructure, these building blocks realign and the structure changes shape.

As this transformation occurs, two things occur. First, the area where the light strikes becomes transparent, allowing the light to penetrate deeper into the material and cause further deformations. Second, when the material deforms and the shape shifts, a new part of the pillar is exposed to light, causing that area to likewise undergo shape change.

This feedback loop propels the microstructure into a cycle of motion resembling a stroke.

“This internal and external feedback loop provides us with a material that regulates itself. After being turned on, the light does its own work “Graduate student in the Department of Chemistry and Chemical Biology at Harvard and co-author of the paper, Shucong Li, stated the following.

When the light is turned off, the substance returns to its former shape.

These simple structures are infinitely reconfigurable and modifiable due to the material’s shape-dependent twists and movements. Using a model and experiments, the researchers exhibited the motions of round, square, L- and T-shaped, and palm-tree-shaped structures and outlined the other ways the material can be modified.

Michael M. Lerch, a postdoctoral fellow in the Aizenberg Lab and co-first author of the paper, explained, “We demonstrated that we can program the choreography of this dynamic dance by adjusting a variety of parameters, including illumination angle, light intensity, molecular alignment, microstructure geometry, temperature, and irradiation intervals and duration.”

In order to add an additional degree of complexity and utility, the research team demonstrated how these pillars interact with one another as part of an array.

“When these pillars are joined together, they interact in extremely complicated ways, as each deforming pillar throws a shadow on its neighbor, which changes throughout the deformation process,” Li explained. Programming how these shadow-mediated self-exposures alter and interact dynamically with one another could be beneficial for applications such as dynamic data encryption.

“The wide design space for individual and collective motions has the potential to revolutionize soft robotics, micro-walkers, sensors, and robust information encryption systems,” remarked Aizenberg.

Further information: Shucong Li et al, Self-regulated non-reciprocal motions in single-material microstructures, Nature (2022). DOI: 10.1038/s41586-022-04561-z

Journal information: Nature

Source: Harvard University