Advancement in self-powered portable and wearable electronics mostly depends on the realization of an efficient human activity-based energy harvester and electronic skin (e-skin)-mimicking tactile mechanosensing property of natural human skin. A human activity-based energy harvester can supply power to flexible, potable, electronics equipment associated with the human body, whereas a tactile e-skin mechanosensor can precisely detect static and dynamic pressure stimuli. Here, we report development of a NiO@ SiO 2 /PVDF nanocomposite, a facile piezoelectric material possessing superior flexibility that is light in weight and has low cost, which is an excellent choice for the next generation mechanical energy harvester and tactile e-skin sensors. The fabricated piezoelectric nanogenerator (PNG) comprising nanocomposites shows very promising output under application of the biomechanical force on it. PNG15 exhibits high output voltage (53 V), adequate current density (∼0.3 μA/cm 2 ), high power density (685 W/m 3 ), and superior conversion efficiency (13.86%). Gentle human finger imparting onto the PNG produces enough electric power to directly illuminate as many as 85 numbers of commercial LEDs and charge a 2.2 μF capacitor up to 22 V within 450 s. The nanogenerator is successfully exploited to generate electrical power by converting mechanical energy from different human activities. We also demonstrate the high mechanosensing capability of a thin, flexible e-skin sensor based on NiO@SiO 2 /PVDF nanocomposites. Because of the high sensitivity, the fabricated e-skin sensor can detect precisely the spatiotemporal distribution of pressure stimuli in static and dynamic conditions. The e-skin sensor is capable of sensing very low level pressure stimuli with a short response time. The promising role of e-skin in real time healthcare monitoring is assessed where a hand-data glove attached with self-powered e-skin sensors can distinguish movements of different fingers. The spatial distribution of pressure stimuli is also resolved by a sensing matrix containing e-skin sensors as pixels. Moreover the operation mechanical stability of the composites is very high which enables this composite to be used in e-skin sensor and energy harvester applications. Our work verifies the scope of NiO@SiO 2 /PVDF nanocomposites in nanogenerators and e-skin applications which are essential components in the field of wearable self-powered electronics, healthcare monitoring, and artificial intelligence attached to a human body.

The macroscopic mechanical properties of biological hydrogels are broadly studied and successfully mimicked in synthetic materials, but little is known about the molecular interactions that mediate these properties. Here, we use two-dimensional infrared spectroscopy to study the pH-induced gelation of hyaluronic acid, a ubiquitous biopolymer, which undergoes a transition from a viscous to an elastic state in a narrow pH range around 2.5. We find that the gelation originates from the enhanced formation of strong interchain connections, consisting of a double amide–COOH hydrogen bond and an N–D–COO– hydrogen bond on the adjacent sugars of the hyaluronan disaccharide unit. We confirm the enhanced interchain connectivity in the elastic state by atomic force microscopy imaging.

The influence of copper oxide nanoparticles on the polymorphism of PVDF is systematically investigated. Strong interfacial interactions between the negative nanoparticle surface and positive –CH2 dipoles of PVDF enhance the electroactive β-phase.

Smart, self-powered, and wearable e-skin that mimics the pressure sensing property of the human skin is indispensable to boost up cutting edge robotics, artificial intelligence, prosthesis, and health-care monitoring technologies. Here, fabrication of a facile and flexible hybrid piezoelectric e-skin (HPES) with multifunctions of tactile mechanosensing, energy harvesting, self-cleaning, ultraviolet (UV)-protecting, and microwave shielding properties is reported. The principal block of the HPES is an SnO2 nanosheets@SiO2 (silica-encapsulated tin oxide nanosheets)/poly­(vinylidene fluoride) (PVDF) nanocomposite (SS)-based PES acting as a single unit for simultaneous energy harvesting and tactile mechanosensing. Gentle human finger imparting onto the PES showed outstanding energy conversion efficiency (16.7%) with high power density (550 W·m–3) and current density (0.40 μA·cm–2). This device can generate high enough electrical power to directly drive portable electronics like a light-emitting diode (LED) panel (consisting of 85 commercial LEDs) and to charge up capacitors very rapidly. Thin PES mechanosensors demonstrated promising performance for quantitatively detecting static and dynamic pressure stimuli with a high sensitivity of 0.99 V·kPa–1 and a short response time of 1 ms. PES was also integrated to a health-data glove for precisely monitoring and discriminating fine motions of proximal interphalangeal, metacarpophalangeal, and distal interphalangeal joints of a human finger and bending motion of different human fingers. A (4 × 4) sensing matrix of PES was successfully employed to detect the spatial distribution of static pressure stimuli. The sensing matrix can precisely record the shape and size of an object placed onto it. PES was encapsulated with a nanocomposite film for providing self-cleaning and UV and microwave protection capability to the HPES. The hydrophobic SS film wrapping (water drop contact angle ∼85.6°) of the HPES enables the self-cleaning feature and makes HPES resistive against water and dirt. The HPES was integrated with in-house-made robotic hands, and the responses of the sensors due to grabbing of an object were evaluated. This work explores new prospects for UV- and microwave-protective, self-cleaning e-skin for energy harvesting and mechanosensation, which can eventually boost up the self-powered electronics, robotics, real-time health-care monitoring, and artificial intelligence technologies.

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