Jun You

Crab Chitin-Based 2D Soft Nanomaterials for Fully Biobased Electric Devices

2D nanomaterials have various size/morphology-dependent properties applicable in electronics, optics, sensing, and actuating. However, intensively studied inorganic 2D nanomaterials are frequently hindered to apply in some particular and industrial fields, owing to harsh synthesis, high-cost, cytotoxicity, and nondegradability. Endeavor has been made to search for biobased 2D nanomaterials with biocompatibility, sustainability, and biodegradability. A method of hydrophobization-induced interfacial-assembly is reported to produce an unprecedented type of nanosheets from marine chitin. During this process, two layers of chitin aggregations assemble into nanosheets with high aspect ratio. With super stability and amphiphilicity, these nanosheets have super ability in creating highly stable Pickering emulsions with internal phase up to 83.4% and droplet size up to 140 μm, in analogue to graphene oxide. Combining emulsifying and carbonization can further convert these 2D precursors to carbon nanosheets with thickness as low as ≈3.8 nm. Having biologic origin, conductivity, and dispersibility in various solvents, resultant carbon nanosheets start a new scenario of exploiting marine resources for fully biobased electric devices with sustainability and biodegradability, e.g., supercapacitor, flexible circuits, and electronic sensors. Hybrid films of chitin and carbon nanosheets also offer low-cost and environment-friendly alternative of conductive components desirable in green electronics, wearable electronics, biodegradable circuits, and biologic devices.

Biomimetic Hybridization of Kevlar into Silk Fibroin: Nanofibrous Strategy for Improved Mechanic Properties of Flexible Composites and Filtration Membranes

Silk, one of the strongest natural biopolymers, was hybridized with Kevlar, one of the strongest synthetic polymers, through a biomimetic nanofibrous strategy. Regenerated silk materials have outstanding properties in transparency, biocompatibility, biodegradability and sustainability, and promising applications as diverse as in pharmaceutics, electronics, photonic devices and membranes. To compete with super mechanic properties of their natural counterpart, regenerated silk materials have been hybridized with inorganic fillers such as graphene and carbon nanotubes, but frequently lose essential mechanic flexibility. Inspired by the nanofibrous strategy of natural biomaterials (e.g., silk fibers, hemp and byssal threads of mussels) for fantastic mechanic properties, Kevlar was integrated in regenerated silk materials by combining nanometric fibrillation with proper hydrothermal treatments. The resultant hybrid films showed an ultimate stress and Youngs modulus two times as high as those of pure regenerated SF films. This is not only because of the reinforcing effect of Kevlar nanofibrils, but also because of the increasing content of silk β-sheets. When introducing Kevlar nanofibrils into the membranes of silk nanofibrils assembled by regenerated silk fibroin, the improved mechanic properties further enabled potential applications as pressure-driven nanofiltration membranes and flexible substrates of electronic devices.

Guiding growth orientation of two-dimensional Au nanocrystals with marine chitin nanofibrils for ultrasensitive and ultrafast sensing hybrids

We demonstrate that marine chitin nanofibrils are able to modulate the growth direction of two-dimensional Au nanocrystals from nanoribbons, nanokites to nanosheets. The mechanism investigation reveals that deacetylation and exfoliation of chitin nanofibrils are essential to template directional growth of Au nanocrystals. The tight adhesion of chitin nanofibrils on the Au surface enables the design of functional hybrids as ultrafast and ultrasensitive responsive devices for humidity and pressure. Interestingly, the humidity responsive device shows an abrupt increase in resistance of up to 3 orders of magnitude with a tiny variation of relative humidity from 62% RH to 63% RH, and was capable of precisely sensing speech. As a conductive filler, only 0.09 vol% gold nanoribbons are able to append to tissue paper with a sheet resistance of up to 220 Ω sq-1, which can be used as a frequently-used pressure-sensing device. These sensing hybrids are highly promising in smart clothing and electronic skins.

Bioinspired catecholic activation of marine chitin for immobilization of Ag nanoparticles as recyclable pollutant nanocatalysts

Being one type of the most abundant marine polysaccharides in nature, chitin has inert chemical properties and thus prolonged been hindered for high-value utilization. A mussel-inspired catecholic chemistry was found to be able to confer nature-derived mesoporous chitin aerogels with high and tunable surface activities. When further combining with their high porosity, high specific surface area, mechanical toughness and unique nanofibrous architecture, these catechol-activated chitin aerogels could be used as a unique supporting matrix to immobilize Ag nanoparticles. Besides the mild synthesis conditions and the merits inherited from pristine chitin, the resultant chitin-Ag hybrid aerogels further exhibited high catalytic activity, excellent recyclability, super solvent endurance and fast regeneration ability. Their high mechanic properties and porous structures also enabled a convenient membrane process to remove organic dyes from water.

Activation of Actuating Hydrogels with WS2 Nanosheets for Biomimetic Cellular Structures and Steerable Prompt Deformation

Macroscopic soft actuation is intrinsic to living organisms in nature, including slow deformation (e.g., contraction, bending, twisting, and curling) of plants motivated by microscopic swelling and shrinking of cells, and rapid motion of animals (e.g., deformation of jellyfish) motivated by cooperative nanoscale movement of motor proteins. These actuation behaviors, with an exceptional combination of tunable speed and programmable deformation direction, inspire us to design artificial soft actuators for broad applications in artificial muscles, nanofabrication, chemical valves, microlenses, soft robotics, etc. However, so far artificial soft actuators have been typically produced on the basis of poly(N-isopropylacrylamide) (PNiPAM), whose deformation is motived by volumetric shrinkage and swelling in analogue to plant cells, and exhibits sluggish actuation kinetics. In this study, alginate-exfoliated WS2 nanosheets were incorporated into ice-template-polymerized PNiPAM hydrogels with the cellular microstructures which mimic plant cells, yet the prompt steerable actuation of animals. Because of the nanosheet-reinforced pore walls formed in situ in freezing polymerization and reasonable hierarchical water channels, this cellular hybrid hydrogel achieves super deformation speed (on the order of magnitude of 10° s), controllable deformation direction, and high near-infrared light responsiveness, offering an unprecedented platform of artificial muscles for various soft robotics and devices (e.g., rotator, microvalve, aquatic swimmer, and water-lifting filter).

Biomimetic engineering of spider silk fibres with graphene for electric devices with humidity and motion sensitivity

A fibrous and electronic spidroin sensor with humidity and human motion sensitivity was engineered by forming graphene sheaths with morphological ripples or overlapped cracks around spidroin fibres. Sensitivity-enhancement design inspired by plant tendrils and the slit organs of spider legs further enabled its application in wearable devices with multi-stimuli responsiveness, high sensitivity, flexibility, biocompatibility and sustainability.

Shapeable Fibrous Aerogels of Metal–Organic-Frameworks Templated with Nanocellulose for Rapid and Large-Capacity Adsorption

Conventional metal-organic framework (MOF) powders have periodic micro/mesoporous crystalline architectures tuned by their three-dimensional coordination of metal nodes and organic linkers. To add practical macroscopic shapeability and extrinsic hierarchical porosity, fibrous MOF aerogels were produced by synthesizing MOF crystals on the template of TEMPO-cellulose nanofibrils. Cellulose nanofibrils not only offered extrinsic porosities and mechanical flexibility for the resultant MOF aerogels, but also shifted the balance of nucleation and growth for synthesizing smaller MOF crystals, and further decreased their aggregation possibilities. Thanks to their excellent shapeability, hierarchical porosity up to 99%, and low density below 0.1 g/cm3, these MOF aerogels could make the most of their pores and accessible surface areas for higher adsorption capacity and rapid adsorption kinetics of different molecules, in sharp contrast to conventional MOF powders. Thus, this scalable and low-cost production pathway is able to convert MOF powders into a shapeable and flexible form and thereby extend their applications in more broad fields, for example, adapting a conventional filtration setup.

Supramolecular proteinaceous biofilms as trapping sponges for biologic water treatment and durable catalysis

Inspired by the bacterial biofilms and chorions of living organisms which are made by proteinaceous assemblies and functional for multi-applications, various artificial protein fibrils-based nanoporous films are developed, and show their potential applications in multiple fields. Here, a simple and environmental friendly method was identified to produce bovine serum albumin (BSA) nanofibrils based biofilms, through a combination of protein fibrillation and reverse dialysis. BSA nanofibrils formed biofilms through intermolecular interactions, the resultant biofilms showed tunable thickness by altering the initial protein amount, good stability in organic and salty solvents, transparency and fluorescence properties, hold high capacity of trapping different substances (e.g. nanomaterials, organic dyes, heavy-metal ions and enzymes), and further enabled applications in biologic water treatment and enzyme stabilization. Taken o-phenylenediamine as substrate, the trapped horseradish peroxidase showed a catalytic activity 9-38 folds higher than free ones in organic phase, together with enhanced stability. These protein nanofibrils-based films offered an attractive biologic platform to hybridize diverse materials for on-demand functions and applications.