Bimorph Silk Microsheets with Programmable Actuating Behavior: Experimental Analysis and Computer Simulations

Abstract

Microscaled self-rolling construct sheets from silk protein material have been fabricated, containing a silk bimorph composed of silk ionomers as an active layer and cross-linked silk β-sheet as the passive layer. The programmable morphology was experimentally explored along with a computational simulation to understand the mechanism of shape reconfiguration. The neutron reflectivity shows that the active silk ionomers layer undergoes remarkable swelling (eight times increase in thickness) after deprotonation while the passive silk β-sheet retains constant volume under the same conditions and supports the bimorph construct. This selective swelling within the silk-on-silk bimorph microsheets generates strong interfacial stress between layers and out-of-plane forces, which trigger autonomous self-rolling into various 3D constructs such as cylindrical and helical tubules. The experimental observations and computational modeling confirmed the role of interfacial stresses and allow programming the morphology of the 3D constructs with particular design. We demonstrated that the biaxial stress distribution over the 2D planar films depends upon the lateral dimensions, thickness and the aspect ratio of the microsheets. The results allow the fine-tuning of autonomous shape transformations for the further design of complex micro-origami constructs and the silk based rolling/unrolling structures provide a promising platform for polymer-based biomimetic devices for implant applications.

Modeling and simulation of thermally actuated bilayer plates

“…To explore possible failure of controlled production of microtubes reported in [28,33,34] we consider a bilayer square ω = (−1, 1) 2 of side lengths 2.0 mm that is clamped and thermally insulated on the side ∂ D ω = {−1} × [−1, 1], namely y h satisfies (20) and ∂ n θ = 0 on ∂ D ω. On the remaining part ∂ R ω = ∂ω \ ∂ D ω the plate is free and heated via external heat transfer obeying Newton's law of cooling, i.e., the normal Figure 5.…”

Programmable Mechanically Active Hydrogel‐Based Materials

“…This is exemplified by the work of Ye et al, demonstrating that the thickness and aspect ratio of silk fibroin-based hydrogel nanosheets controls their internal stress production and ultimate deformation under a specific stimulus. [29] The size, shape, and composition of a MAM can also adjust its speed of actuation (Table 1, Figure 4g). In general, smaller structures are able to respond more rapidly than larger ones [30] due to the ability to more rapidly move water out of the hydrogel to induce deswelling.…”

Active Reconfigurable Tristable Square‐Twist Origami

“…Origami structure has been widely concerned by the scientific and engineering field because of its deployment ability, reconfigurability, loading ability, bending ability, and twistable capability, and it has also produced applications as shape‐morphing systems utilized in a broad range of applications including smart structures, sensors and actuators, autonomous robotics, tissue engineering, metamaterials, etc. Active origami structures with programmable patterns hold the ability to create complex 3D steric configurations, promising foldable or deployable structures and machines . With remarkable explorations on origami shape transformation as well as manipulation strategies, a variety of active reconfigurable devices, whose shape is required drastically altered under certain environmental stimuli, are extensively developed to realize variable functions …”