Wearable tensile strain sensors have aroused substantial attention on account of their exciting applications in rebuilding tactile inputs of human and intelligent robots. Conventional such devices, however, face the dilemma of both sensitive response to pressure and bending stimulations, and poor breathability for wearing comfort. In this paper, a breathable, pressure and bending insensitive strain sensor is reported, which presents fascinating properties including high sensitivity and remarkable linearity (gauge factor of 49.5 in strain 0-100%, R 2 = 99.5%), wide sensing range (up to 200%), as well as superior permeability to moisture, air, and water vapor. On the other hand, it exhibits negligible response to wide-range pressure (0-100 kPa) and bending (0-75%) inputs. This work provides a new route for achieving wearing comfortable, high-performance, and anti-jamming strain sensors.

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E-textile consisting of natural fabrics has become a promising material to construct wearable sensors due to its comfortability and breathability on the human body. However, the reported fabric-based e-textile materials, such as graphene-treated cotton, silk, and flax, generally suffer from the electrical and mechanical instability in long-term wearing. In particular, fabrics on the human body have to endure heat variation, moisture evaporation from metabolic activities, and even the immersion with body sweat. To face the above challenges, here we report a wool-knitted fabric sensor treated with graphene oxide (GO) dyeing followed by l-ascorbic acid (l-AA) reduction (rGO). This rGO-based strain sensor is highly stretchable, washable, and durable with rapid sensing response. It exhibits excellent linearity with more than 20% elongation and, most importantly, withstand moisture from 30 to 90% (or even immersed with water) and still maintains good electrical and mechanical properties. We further demonstrate that, by integrating this proposed material with the near-field communication (NFC) system, a batteryless, wireless wearable body movement sensor can be constructed. This material can find wide use in smart garment applications.

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We propose a design strategy to fabricate a flexible bend sensor (BS) with ultrasensitivity towards airflow using all PVDF nanofiber web based sensing element and electrode to monitor human respiration. The unique electrospinning (rotational speed of collector of 2000 rpm and tip-to-collector distance of 4 cm) with silver nanoparticles interfacing was introduced to prepare an Ag-doped oriented PVDF nanofiber web with high β-phase content as sensing element (AgOriPVDF, β-phase crystallinity ~ 44.5 %). After that, a portion of the prepared AgOriPVDF was processed into flexible and electrically conductive electrode through electroless silver plating technique (SP-AgOriPVDF). Interestingly, the encapsulated AgOriPVDF BS with SP-AgOriPVDF electrode exhibited superior piezoelectric bending response (open-circuit peak-to-peak output voltage, Vp-p ≈ 4.6 V) to injected airflow, which is more than 200 times higher than that of the unpackaged randomly aligned PVDF nanofiber web BS with conductive tape electrode (Vp-p ≈ 0.02 V). In addition, the factors influencing the 2 bend sensitivity of BS such as β-phase content, nanofiber orientation, flexibility of electrode and so forth were thoroughly analyzed and then discussed. We also demonstrated that the AgOriPVDF BS has sufficient capability to detect and identify various respiratory signal, presenting a great potential for wearable applications, e.g. smart respiratory protective equipment.

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