Learn More
The creasing instability of elastomer films under compression is studied by a combination of experiment and numerical simulation. Experimentally, we attach a stress-free film on a much thicker and stiffer pre-stretched substrate. When the substrate is partially released, the film is uniaxially compressed, leading to formation of an array of creases beyond a(More)
In a soft elastic film compressed on a stiff substrate, creases nucleate at preexisting defects and grow across the surface of the film like channels. Both nucleation and growth are resisted by the surface energy, which we demonstrate by studying creases for elastomers immersed in several environments--air, water, and an aqueous surfactant solution.(More)
Colorimetric temperature sensors are prepared from photo-crosslinkable polymers by sequentially spin-coating and crosslinking alternating layers of poly(N-isopropylacrylamide) and poly(para-methyl styrene). Layer thicknesses and copolymer chemistries are chosen to provide robust colorimetric temperature sensors that cover nearly the full visible spectrum.
Self-actuating materials capable of transforming between three-dimensional shapes have applications in areas as diverse as biomedicine, robotics, and tunable micro-optics. We introduce a method of photopatterning polymer films that yields temperature-responsive gel sheets that can transform between a flat state and a prescribed three-dimensional shape. Our(More)
Thin poly(N-isopropylacrylamide) (PNIPAM) hydrogels were allowed to swell under two conditions: as freestanding layers and as substrate-attached layers. Through a combination of particle tracking and defocusing methods, the positions of beads embedded within the gels were monitored over time via fluorescence microscopy, providing a convenient method to(More)
Although broadly admired for its aesthetic qualities, the art of origami is now being recognized also as a framework for mechanical metamaterial design. Working with the Miura-ori tessellation, we find that each unit cell of this crease pattern is mechanically bistable, and by switching between states, the compressive modulus of the overall structure can be(More)
Abstruct-This paper describes the simulation of stairs on a tread-m i l l style locomotion interface using torso force feedback. The active mechanical tether of the Sarcos Treadport locomotion interface applies a specialized force profile to simulate the forces of stair walking. under the specialized force prolile were compared. It was found that the tether(More)
This paper presents a new design of a harness for torso force application in locomotion interfaces. This mechanical coupling between a user's body and the force feedback device is a key aspect for the effective exploitation of this class of devices. Issues of compliance, backlash, force distribution, and comfort have been considered in the new design.(More)
Efforts to understand and engineer cell behavior in mechanically soft environments frequently employ two-dimensional cell culture substrates consisting of thin hydrogel layers with low elastic modulus supported on rigid substrates to facilitate culturing, imaging, and analysis. Here we characterize how an elastic creasing instability of the gel surface may(More)
When a stiff film on a soft substrate is compressed, the surface of the film forms wrinkles, with tunable wavelengths and amplitudes that enable a variety of applications. As the compressive strain increases, the film undergoes post-wrinkling bifurcations, leading to period doubling and eventually to formation of localized folds or ridges. Here we study the(More)