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IONO-ELASTOMERS FOR WEARABLE ELECTRONICS 617

decreases upon stretching. When stress is released, the iono-elastomer materials described here, we envi-
as shown in Figure 6 (b), the bridging polymers that sion our product to be a do it yourself (DIY) reusable,
were extended now retract to their random coil con- flexible biometric motion strain sensor kit, which we
formation, which in turn pulls the micelles back to have named an “MSP Kit.” This would be the first
their original configuration. This explains the increase large strain amplitude, stretchable, resistive strain
in electric resistance upon unloading stress as a con- sensor patch that can be easily mounted on clothing
sequence of the increase in ion transport tortuosity or directly attached to the body to measure the local
when the randomly oriented FCC grain morphology displacement under workload and/or motion. The
is recovered. A detailed elucidation of the scientific MSP Kit enables customers (e.g., athletes, patients
basis of this novel mechano-electrical response for undergoing physical therapy, physical trainers, bio-
this self-assembled material is presented in a recent mechanicians, etc.) to accurately track motion and
publication in ACS Macro Letters (36). A baseline performance of specific joints and/or muscles on
study of the hierarchically self-assembled material their smart phones, tablets, or computers via Blue-
without crosslinking and its behavior under flow is tooth wireless communication, with applications in
published in Macromolecules (35). The provisional motion capturing, sports performance tracking, and
patent for this material invention has been filed with rehabilitation monitoring.
the University of Delaware (UD), U.S. Patent Serial As shown in Figure 7 (a), our envisioned MSP
No. 62/393,133 with priority date September 12, 2016 is a transparent sensor comprising a soft (dispos-
(37), and the international patent was filed on April able) iono-elastomer integrated into the Smart Plug
7, 2017 (38). and the electronics in the Smart Outlet. The Smart
Plug is constructed as a sandwiched structure. Our
Description of Motion Strain Sensor Invention iono-elastomer (in red) is sandwiched in between
Strain sensors respond to mechanical deforma- two waterproof and adhesive encapsulant films (in
tions, typically by the change in electrical characteris- yellow) on the top and bottom, which is connected
tics, such as resistance or capacitance. Due to simple to the electronics via a Plug (in green) attached to
device structures and easy read-out transduction one end. The waterproofing provides additional water
mechanisms, resistive strain sensors have attracted and sweat resistance, shielding the iono-elastomer
significant attention, and impressive progress has from the environment. The adhesive property enables
been achieved in their development. Building upon attaching directly to clothing, devices, or the skin.

Figure 3. Demonstration of high flexibility of the iono-elastomer via (a, d) stretching, (b, e) twisting then stretching, (c, f)
bending. (a), (b) and (c) are photos before course of action, while (d), (e) and (f) are photos post each corresponding course of
action. The figure was reproduced from and with permission of the American Chemical Society, copyright 2016 (36).