Polyvinyl alcohol (PVA) hydrogels are widely used for flexible sensors by adding various conductive substances due to their excellent mechanical properties and self-healing properties. However, most of the conductive substances added to PVA hydrogel sensors are currently complicated to prepare, costly, and environmentally unfriendly. Herein, to overcome this challenge, we successfully prepared intrinsic conductive cellulose nanofiber (G-CNF) by simply applying sulfuric acid and a low-energy water bath with heat treatment, and obtained a powerful multifunctional self-healing PGC hydrogel biosensor using dynamic chemical cross-linking of PVA and borax with glycerol and G-CNF. The obtained PGC hydrogels have excellent mechanical properties (strain: 950%), good adhesion ability, robust self-healing properties, and room-temperature reversibility, due to the presence of conductive networks and hydrogen bonds within PGC hydrogel. Especially, PGC hydrogels with the graphene structured G-CNF have a fast response to various signals and good stability with gauge factor (GF) values up to 1.83, as well as a sensitive response to temperature (temperature coefficient of resistance (TCR) up to 1.9), which can be designed as a variety of biosensors, such as human motion monitoring, information encryption/transmission, and real-time temperature monitoring biosensors. Thus, PGC hydrogels as multifunctional self-healing hydrogel biosensors pave the way for the development of flexible biosensors in wearable devices, human–computer interaction, and artificial-related applications.

Advanced energy and sensor devices with novel applications (e.g., mobile equipment, electric vehicles, and medical-healthcare systems) are one of the important foundations of modern intelligent life. However, there are still some scientific issues that seriously hinder the further development of devices, including unsustainability, high material cost, complex fabrication process, safety issues, and unsatisfactory performance. Nanocellulose has aroused tremendous attention in recent decades, because of its abundant resources, renewability, degradability, low-cost, and unique physical/chemical properties. These merits make nanocellulose as matrix materials to fabricate advanced functional composites for use in energy-related fields extremely competitive. Here, we comprehensively discuss the recent progress of nanocellulose for emerging energy storage/harvesting and sensor applications. The preparation methodologies of nanocellulose combined with conductive materials are firstly highlighted, including carbon materials, conductive polymers, metal/metal oxide nanoparticles, metal-organic frameworks (MOFs), and covalent organic frameworks (COFs). We then focus on the nanocellulose-based advanced materials for the application in the areas of supercapacitors, lithium-ion batteries, solar cells, triboelectric nanogenerators, moisture-enabled electric generators, and sensors. Lastly, the future research directions of nanocellulose-based functional materials in energy-related devices are presented.

If a person comes into contact with pathogens on public facilities, there is a threat of contact (skin/wound) infections. More urgently, there are also reports about COVID-19 coronavirus contact infection, which once again reminds that contact infection is a very easily overlooked disease exposure route. Herein, we propose an innovative implantation strategy to fabricate a multi-walled carbon nanotube/polyvinyl alcohol (MWCNT/PVA, MCP) interpenetrating interface to achieve flexibility, anti-damage, and non-contact sensing electronic skin (E-skin). Interestingly, the MCP E-skin had a fascinating non-contact sensing function, which can respond to the finger approaching 0−20 mm through the spatial weak field. This non-contact sensing can be applied urgently to human–machine interactions in public facilities to block pathogen. The scratches of the fruit knife did not damage the MCP E-skin, and can resist chemical corrosion after hydrophobic treatment. In addition, the MCP E-skin was developed to real-time monitor the respiratory and cough for exercise detection and disease diagnosis. Notably, the MCP E-skin has great potential for emergency applications in times of infectious disease pandemics.

Flexible wearable electronics were developed for applications such as electronic skins, human–machine interactions, healthcare monitoring, and anti-infection therapy. But conventional materials showed impermeability, single sensing ability, and no designated therapy, which hindered their applications. Thus it was still a great challenge to develop electronic devices with multifunctional sensing properties and self-driven anti-infection therapy. Herein, flexible and breathable on-skin electronic devices for multifunctional fabric based sensing and self-driven designated anti-infection therapy were prepared successfully with cellulose nanocrystals/iron(Ⅲ) ion/polyvinyl alcohol (CNC/Fe³⁺/PVA) composite. The resultant composite films possessed robust mechanical performances, outstanding conductivity, and distinguished breathability (3.03 kg/(m²·d)), which benefited from the multiple interactions of weak hydrogen bonds and Fe³⁺ chelation and synergistic effects among CNC, polyaniline (PANI), and PVA. Surprisingly, the film could be assembled as a multifunctional sensor to actively monitor real-time physical and infection related signals such as temperature, moisture, pH, NH₃, and human movements even at sweat states. More importantly, this multifunctional device could act as a self-driven therapist to eliminate bacterial by the release of Fe³⁺, which was driven by the damage of metal coordination Fe–O bonds due to the high temperature caused by infection at wound sites. Thus, the composite films had potential versatile applications in electronic skins, smart wound dressings, human–machine interactions, and self-driven anti-infection therapy.