Variable Stiffness Fiber with Self‐Healing Capability

Tonazzini, Alice; Mintchev, Stefano; Schubert, Bryan Edward; Mazzolai, Barbara; Shintake, Jun; Floreano, Dario

doi:10.1002/adma.201602580

Cited by 168 publications

(167 citation statements)

References 36 publications

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“…Compared to other classes of shape‐memory materials, shape‐memory polymers and composites are lightweight, inexpensive, can be made into parts using a variety of manufacturing technologies, and can have a broad range of properties . Thanks to these characteristics, they find applications in a variety of engineering areas including aerospace, wearable electronics, and biomedicine . The design of shape‐memory polymers is usually based on the combination of two distinct phases, a stable phase and a programmable phase.…”

mentioning

confidence: 99%

“…[3] Thanks to these characteristics, they find applications in a variety of engineering areas including aerospace, [4] wearable electronics, [5] and biomedicine. [6] The design of shapememory polymers is usually based on the combination of two distinct phases, a stable phase and a programmable phase. The programmable phase can undergo a reversible stiffening transition triggered by an external stimulus, while the stable phase remains unaffected.…”

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confidence: 99%

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Magnetically Addressable Shape‐Memory and Stiffening in a Composite Elastomer

et al. 2019

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With a specific stimulus, shape‐memory materials can assume a temporary shape and subsequently recover their original shape, a functionality that renders them relevant for applications in fields such as biomedicine, aerospace, and wearable electronics. Shape‐memory in polymers and composites is usually achieved by exploiting a thermal transition to program a temporary shape and subsequently recover the original shape. This may be problematic for heat‐sensitive environments, and when rapid and uniform heating is required. In this work, a soft magnetic shape‐memory composite is produced by encasing liquid droplets of magneto‐rheological fluid into a poly(dimethylsiloxane) matrix. Under the influence of a magnetic field, this material undergoes an exceptional stiffening transition, with an almost 30‐fold increase in shear modulus. Exploiting this transition, fast and fully reversible magnetic shape‐memory is demonstrated in three ways, by embossing, by simple shear, and by unconstrained 3D deformation. Using advanced synchrotron X‐ray tomography techniques, the internal structure of the material is revealed, which can be correlated with the composite stiffening and shape‐memory mechanism. This material concept, based on a simple emulsion process, can be extended to different fluids and elastomers, and can be manufactured with a wide range of methods.

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Magnetically Addressable Shape‐Memory and Stiffening in a Composite Elastomer

et al. 2019

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“…[17] Replacing conventional electromagnetic clutches with custom designs tailored for wearable applications has helped in reducing size and weight of these components for unpowered exoskeletons. [22][23][24][25][26][27] However, several limitations are still present, such as the achieved blocking forces, the elongation ratio, and the low response time in the case of variable stiffness technologies. [14,[18][19][20] Electrostatic clutches, developed by flexible materials such as a polyethylene terephthalate film, demonstrate to be a promising soft robotics technology for the application in an unpowered ankle foot orthosis.…”

Section: Introductionmentioning

confidence: 99%

A Wearable Sensory Textile‐Based Clutch with High Blocking Force

et al. 2019

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A sensory textile-based clutch (STBC) activated by vacuum is presented. The STBC is an assembly of two inextensible webbings equipped with 2.3 mm wide rigid bumps fabricated directly on them by a hot embossing technique, and two elastic bands, all air sealed by a silicone elastomer cover. While, in passive mode, the clutch provides low resistance to elongation, upon vacuum, the specular rigid bumps interlock and provide a high withstanding force. The embedded capacitive-based transducer allows encoding the clutch's elongation, with a position resolution reaching 1.15 mm, owing to a real-time processing algorithm. The STBC (140 mm Â 30 mm Â 8 mm) sustains up to 419 N force with an activation pressure of À0.5 atm. The small size of the rigid components and a priming strategy (keeping the pressure at À0.01 atm in disengaged mode) enable response times down to 14 ms for a 115 N blocking force. A preliminary demonstration of a fully worn device shows the potential of the STBC approach for enabling the control of the engagement and disengagement of blocking forces, as well as monitoring of typical parameters of human movement such as knee bending angles, for future developments of light and efficient unpowered exoskeletons.

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“…For example, Tonazzini et al reported the use of paraffin wax to tune the stiffness of fibers. As the paraffin solidified, the stiffness of fibers increased . Meerbeek et al reported the morphing of liquid metal alloys and bicontinuous elastic foams by varying the stiffness induced by temperature.…”

Section: Introductionmentioning

confidence: 99%

Softening and Shape Morphing of Stiff Tough Hydrogels by Localized Unlocking of the Trivalent Ionically Cross‐Linked Centers

Wang

Fan

et al. 2018

Macromol. Rapid Commun.

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The mechanical properties (e.g., stiffness, stretchability) of prefabricated hydrogels are of pivotal importance for diverse applications in tissue engineering, soft robotics, and medicine. This study reports a feasible method to fabricate ultrasoft and highly stretchable structures from stiff and tough hydrogels of low stretchability and the application of these switchable hydrogels in programmable shape-morphing systems. Stiff and tough hydrogel structures are first fabricated by the mechanical strengthening of Ca -alginate/polyacrylamide tough hydrogels by addition of Fe ions, which introduces Fe ionically cross-linked centers into the Ca divalent cross-linked hydrogel, forming an additional and much less flexible trivalent ionically cross-linked network. The resulting stiff and tough hydrogels are exposed to an L-ascorbic acid (vitamin C, VC) solution to rapidly reduce Fe to Fe . As a result, flexible divalent ionically cross-linked networks are formed, leading to swift softening of the stiff and tough hydrogels. Moreover, localized stiffness variation of the tough hydrogels can be realized by precise patterning of the VC solution. To validate this concept, sequential steps of VC patterning are carried out for local tuning of the stiffness of the hydrogels. With this strategy, localized softening, unfolding, and sequential folding of the tough hydrogels into complex 3D structures is demonstrated.

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Variable Stiffness Fiber with Self‐Healing Capability

Cited by 168 publications

References 36 publications

Magnetically Addressable Shape‐Memory and Stiffening in a Composite Elastomer

Magnetically Addressable Shape‐Memory and Stiffening in a Composite Elastomer

A Wearable Sensory Textile‐Based Clutch with High Blocking Force

Softening and Shape Morphing of Stiff Tough Hydrogels by Localized Unlocking of the Trivalent Ionically Cross‐Linked Centers

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