Many technological revolutions have in the past been inspired by mimicry following which rapid application and diffusion of the new technology has caused abrupt societal changes. Smart structures are no exception if enhanced to self-reconfigure in response to an external stimulus. Such a development would completely realign multiple technological disciplines as they would give humans access and unprecedented control over the actuation of functional devices across length and time scales. Such an enticing future of stimuli responsive devices has caught the eye of many researchers, particularly, self-folding grippers that have potential medicine and micro/nanomanipulation applications. The self-folding microgrippers are an emerging class of smart structures whose functionalities rely on spatially patterned hinges to transform into 3D configurations in response to an external stimulus. Incorporation of hinges in the devices is problematic as it necessitates the processing of multiple layers which eventually increases the fabrication costs and actuation complexities.
Recently, University of Illinois researchers: Dr. Arif Abdullah, Professor Xuiling Li and Professor Paul Braun together with Professor K. Jimmy Hsia from the Carnegie Mellon University and Professor John Rogers from the Northwestern University demonstrated the generation of gripper-like configurations in an on-demand manner from simple planar bilayers that do not require hinges for their actuation. Their goal was to understand the bifurcation of hinge-less bilayers and develop design principles for generating tetherless gripper-like configurations in response to external stimulus. Their work has been published in the research journal, Advanced Materials.
The research team considered star-shaped bilayers for purposes of their study. In order to establish a mechanistic understanding of the stimulus-responsive morphing behavior of the star polygons, they employed Finite Element Modelling (FEM). The FEM predictions were then validated by performing swelling experiments of millimeter scale crosslinked poly(dimethylsiloxane) (PDMS) samples in organic solvents. The authors were able to demonstrate the capabilities of the presented architectures to capture, retain, sort, transport, and deliver cargos of different sizes in an as-required manner. Moreover, the team reported varying degrees of selective actuation of the bi-layered stars in response to a uniformly applied stimulus.
The authors also demonstrated the possibilities of the developed architectures to respond to multiple stimulus at the same time (changing solvent concentrations and external magnetic fields). As the computational models were based on the theory of elasticity which is independent of length scales and material properties, the reported design principles would be applicable to other classes of stimuli-responsive material systems such as metals (heat, magnetic fields), polymeric materials (light, biochemical enzymes), and hydrogels (pH, salt concentrations, water diffusion). Because of this versatility, the results of this work could be used to develop diverse classes of gripping and soft robotic devices for tissue biopsy, drug delivery, pick and place functionalities.
Arif M. Abdullah, Xiuling Li, Paul V. Braun, John A. Rogers, and K. Jimmy Hsia. Self-Folded Gripper-Like Architectures from Stimuli-Responsive Bilayers. Advanced Materials 2018, 1801669Go To Advanced Material