An ultra-stretchable and force-sensitive hydrogel with surface self-wrinkling microstructure is demonstrated by in situ synthesizing polyacrylamide (PAAm) and polyaniline (PANI) in closely packed swollen chitosan microspheres, exhibiting ultra-stretchability (>600%), high sensitivity (0.35 kPa ) for subtle pressures (<1 kPa), and can detect force in a broad range (10 Pa-10 MPa) with excellent electrical stability and rapid response speed, potentially finding applications for E-skin.

Smart hydrogel actuators with excellent biocompatibility and biodegradation are extremely desired for biomedical applications. Herein, we have constructed bio-hydrogel actuators inspired by the bilayer structures of plant organs from chitosan and cellulose/carboxymethylcellulose (CMC) solution in an alkali/urea aqueous system containing epichlorohydrin (ECH) as a crosslinker, and demonstrated tight adhesion between two layers through strong electrostatic attraction and chemical crosslinking. The bilayer hydrogels with excellent mechanical properties could carry out rapid, reversible, and repeated self-rolling deformation actuated by pH-triggered swelling/deswelling, and transformed into rings, tubules, and flower-, helix-, bamboo-, and wave-like shapes by effectively designing the geometric shape and size. The significant difference in the swelling behavior between the positively charged chitosan and the negatively charged cellulose/CMC layers generated enough force to actuate the performance of the hydrogels as soft grippers, smart encapsulators, and bioinspired lenses, showing potential applications in a wide range of fields including biomedicine, biomimetic machines, etc.

Mechanically strong cellulose fibers spun with environmentally friendly technology have been under tremendous consideration in the textile industry. Here, by inducing the nanofibrous structure formation, a novel cellulose fiber with high strength has been designed and spun successfully on a lab-scale spinning machine. The cellulose–NaOH–urea solution containing 0.5 wt % LiOH was regenerated in 15 wt % phytic acid/5 wt % Na2SO4 aqueous solution at 5 °C, in which the alkali–urea complex as shell on the cellulose chain was destroyed, so the naked stiff macromolecules aggregated sufficiently in a parallel manner to form nanofibers with apparent average diameter of 25 nm. The cellulose fibers consisting of the nanofibers exhibited high degree of orientation with Herman’s parameter of 0.9 and excellent mechanical properties with tensile strength of 3.5 cN/dtex in the dry state and 2.5 cN/dtex in the wet state, as well as low fibrillation. This work provided a novel approach to produce high-quality cellulose multifilament with nanofibrous structure, showing a great potential in the material processing.

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