Reversible Switching of Hydrogel-Actuated Nanostructures into Complex Micropatterns
By Sung Hoon Kang
Title: Reversible Switching of Hydrogel-Actuated Nanostructures into Complex Micropatterns
Reference: Alexander Sidorenko,Tom Krupenkin, Ashley Taylor, Peter Fratzl, Joanna Aizenberg, Science 315, 487-490 (2007).
Soft matter keywords
hydrogel, humidity, artificial muscle
Abstract from the original paper
Responsive behavior, which is intrinsic to natural systems, is becoming a key requirement for advanced artificial materials and devices, presenting a substantial scientific and engineering challenge. We designed dynamic actuation systems by integrating high–aspect-ratio silicon nanocolumns, either free-standing or substrate-attached, with a hydrogel layer. The nanocolumns were put in motion by the “muscle” of the hydrogel, which swells or contracts depending on the humidity level. This actuation resulted in a fast reversible reorientation of the nanocolumns from tilted to perpendicular to the surface. By further controlling the stress field in the hydrogel, the formation of a variety of elaborate reversibly actuated micropatterns was demonstrated. The mechanics of the actuation process have been assessed. Dynamic control over the movement and orientation of surface nanofeatures at the micron and submicron scales may have exciting applications in actuators, microfluidics, or responsive materials.
Soft matter example
In this paper, the authors used combination of soft and hard elements for reversible actuation of rigid nano- and microstructures whose motion was controlled by the polymer layer. They combined a hydrogel with an array of isolatedd high aspect ratio rigid structures (AIRS) into hydrogel-AIRS assemblies (HAIRS) as shown in Fig 1. In this system, the ARIS gives structural rigidity whereas the soft hydrogel gives reponsive behavior to external stimuli.
The details of the fabrication procedure are described in the text and the supplemental information. The geometry of the AIRS used in this paper is consisted of square arrays of nanoposts with diameters d = 100 to 300 nm, heights h = 5 to 8 um, aspect ratios h/d = 15 to 80, and periodicities p = 2 to 4 mm.
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