Constrained motion of self-propelling eccentric disks linked by a spring.

It has been supposed that the interplay of elasticity and activity plays a key role in triggering the non-equilibrium behaviors in biological systems. However, the experimental model system is missing to investigate the spatiotemporally dynamical phenomena. Here, a model system of an active chain, where active eccentric-disks are linked by a spring, is designed to study the interplay of activity, elasticity, and friction. Individual active chain exhibits longitudinal and transverse motions; however, it starts to self-rotate when pinning one end and self-beat when clamping one end. In addition, our eccentric-disk model can qualitatively reproduce such behaviors and explain the unusual self-rotation of the first disk around its geometric center. Furthermore, the structure and dynamics of long chains were studied via simulations without steric interactions. It was found that a hairpin conformation emerges in free motion, while in the constrained motions, the rotational and beating frequencies scale with the flexure number (the ratio of self-propelling force to bending rigidity), χ, as ∼(χ)4/3. Scaling analysis suggests that it results from the balance between activity and energy dissipation. Our findings show that topological constraints play a vital role in non-equilibrium synergy behaviors.

Cellulose ionic conductor with tunable Seebeck coefficient for low-grade heat harvesting.

Natural polymer-based thermoelectric materials are significant for sustainable development because they can be used to directly harvest heat into electricity while avoiding the utilization of petroleum-based resources. Herein, cellulose ionic conductors were fabricated by using cellulose as the hydrogel matrix and cellulose solvents as the electrolytes. p-type and n-type thermoelectric generators (TEG) based on cellulose ionic conductor were obtained, with Seebeck coefficient of 2.61 and -1.33 mV/K, due to the different interactions between quaternary ammonium cations and cellulose. The cellulose TEG-based supercapacitor showed a high specific capacitance and the ability of charging with thermal energy and powering electronic devices with a maximum power density of 0.42 mW/m2. Moreover, a flexible module-type TE harvester with 10 pairs of p-n legs was assembled for body heat harvesting, delivering a thermovoltage of 0.42 V for a temperature gradient of 13 K, enabling waste/biological heat conversion, temperature monitoring and temperature control.

Kick effect of enzymes causes filament compression.

We investigate the influence of enzymes on the structure and dynamics of a filament by dissipative particle dynamics simulations. Enzyme exerts a kick force on the filament monomer. We pay particular attention to two factors: the magnitude of kick force and enzyme concentration. Large kick force as well as high enzyme concentration prefers a remarkable compression of the filament reminiscent of the effective depletion interaction owing to an effective increase in enzyme size and the reduction of solvent quality. Additionally, the kick effect gives rise to an increase of enzyme density from the center-of-mass of the filament to its periphery. Moreover, the increase of enzyme concentration and kick force also causes a decrease in relaxation time. Our finding is helpful to understand the role of catalytic force in chemo-mechano-biological function and the filament behavior under chemical reaction via kick-induced change of solvent quality.

Structure and dynamics of an active polymer adsorbed on the surface of a cylinder.

The structure and dynamics of an active polymer on a smooth cylindrical surface are studied by Brownian dynamics simulations. The effect of an active force on the polymer adsorption behavior and the combined effect of chain mobility, length N, rigidity κ, and cylinder radius, R, on the phase diagrams are systemically investigated. We find that complete adsorption is replaced by the irregular alternative adsorption/desorption process at a large driving force. Three typical (spiral, helix-like, and rod-like) conformations of the active polymer are observed, dependent on N, κ, and R. Dynamically, the polymer shows rotational motion in the spiral state, snake-like motion in the intermediate state, and straight translational motion without turning back in the rod-like state. In the spiral state, we find that the rotation velocity ω and the chain length follow a power-law relation ω ∼ N-0.42, consistent with the torque-balance theory of general Archimedean spirals. And the polymer shows super-diffusive behavior along the cylinder for a long time in the helix-like and rod-like states. Our results highlight that the mobility, rigidity, and curvature of surface can be used to regulate the polymer behavior.

Flexible, anti-freezing self-charging power system composed of cellulose based supercapacitor and triboelectric nanogenerator.

A self-charging power system composed of cellulose organohydrogel based supercapacitor and triboelectric nanogenerator is constructed in the present work. Cellulose organohydrogels with flexibility, optical transparency, conductivity and excellent low temperature tolerance are fabricated via a dissolution and regeneration process. The optical transmittance, elongation at break, and conductivity of the cellulose organohydrogel reach 93%, 242%, and 1.92 S/m, as well as excellent anti-freezing property down to -54.3 °C, potential as flexible conductive device in harsh conditions. When demonstrated as energy storage device, the cellulose organohydrogel based supercapacitor demonstrates excellent supercapacitor performances, durability against deformation and resistance to low temperature. When demonstrated as energy harvesting device, the cellulose organohydrogel based triboelectric nanogenerator displays stability, and resistance to both low temperature and a large number of operation cycles. As the cellulose based triboelectric nanogenerator is integrated with cellulose based supercapacitor, a flexible and anti-freezing self-charging power system is built, capable of driving miniaturized electronics, demonstrating great potential as wearable power system in harsh conditions.

Transparent, conductive cellulose hydrogel for flexible sensor and triboelectric nanogenerator at subzero temperature.

Herein, flexible, transparent and conductive cellulose hydrogels were directly fabricated by regenerating the chemically cross-linked cellulose in NaCl aqueous solution, without further treatment. NaCl played a dominant role on the mechanical, optical, conductive and anti-freezing properties of cellulose hydrogel, also endowed the hydrogel with safety. After optimization, the transparency, tensile strength, elongation at break and conductivity of the cellulose hydrogel reached 94 % at 550 nm, 5.2 MPa, 235 %, and 4.03 S/m, respectively, as well as low temperature tolerance down to -33.5 ℃. Furthermore, sensors based on cellulose hydrogel demonstrated fast response and stable sensitivity to tensile strain, compressive pressure, and temperature, at both room and subzero temperature, without obvious hysteresis. The cellulose hydrogel based triboelectric nanogenerator demonstrated stability and durability as energy harvester in harsh conditions. In addition, the established approach can be used to prepare flexible, transparent and conductive cellulose hydrogel with various salts, indicating universality, simplicity and sustainability for the fabrication of cellulose based flexible conductive devices.

Electrodeposition of reduced graphene oxide with chitosan based on the coordination deposition method.

The electrodeposition of graphene has drawn considerable attention due to its appealing applications for sensors, supercapacitors and lithium-ion batteries. However, there are still some limitations in the current electrodeposition methods for graphene. Here, we present a novel electrodeposition method for the direct deposition of reduced graphene oxide (rGO) with chitosan. In this method, a 2-hydroxypropyltrimethylammonium chloride-based chitosan-modified rGO material was prepared. This material disperses homogenously in the chitosan solution, forming a deposition solution with good dispersion stability. Subsequently, the modified rGO material was deposited on an electrode through codeposition with chitosan, based on the coordination deposition method. After electrodeposition, the homogeneous, deposited rGO/chitosan films can be generated on copper or silver electrodes or substrates. The electrodeposition method allows for the convenient and controlled creation of rGO/chitosan nanocomposite coatings and films of different shapes and thickness. It also introduces a new method of creating films, as they can be peeled completely from the electrodes. Moreover, this method allows for a rGO/chitosan film to be deposited directly onto an electrode, which can then be used for electrochemical detection.

Layer-by-layer assembled biopolymer microcapsule with separate layer cavities generated by gas-liquid microfluidic approach.

In this work, a layer-by-layer (LbL) assembled biopolymer microcapsule with separate layer cavities is generated by a novel and convenient gas-liquid microfluidic approach. This approach exhibits combined advantages of microfluidic approach and LbL assembly method, and it can straightforwardly build LbL-assembled capsules in mild aqueous environments at room temperature. In particular, using this approach we can build the polyelectrolyte multilayer capsule with favorable cavities in each layer, and without the need for organic solvent, emulsifying agent, or sacrificial template. Various components (e.g., drugs, proteins, fluorescent dyes, and nanoparticles) can be respectively encapsulated in the separate layer cavities of the LbL-assembled capsules. Moreover, the encapsulated capsules present the ability as colorimetric sensors, and they also exhibit the interesting release behavior. Therefore, the LbL-assembled biopolymer capsule is a promising candidate for biomedical applications in targeted delivery, controlled release, and bio-detection.

Agar/gelatin bilayer gel matrix fabricated by simple thermo-responsive sol-gel transition method.

We present a simple and environmentally-friendly method to generate an agar/gelatin bilayer gel matrix for further biomedical applications. In this method, the thermally responsive sol-gel transitions of agar and gelatin combined with the different transition temperatures are exquisitely employed to fabricate the agar/gelatin bilayer gel matrix and achieve separate loading for various materials (e.g., drugs, fluorescent materials, and nanoparticles). Importantly, the resulting bilayer gel matrix provides two different biopolymer environments (a polysaccharide environment vs a protein environment) with a well-defined border, which allows the loaded materials in different layers to retain their original properties (e.g., magnetism and fluorescence) and reduce mutual interference. In addition, the loaded materials in the bilayer gel matrix exhibit an interesting release behavior under the control of thermal stimuli. Consequently, the resulting agar/gelatin bilayer gel matrix is a promising candidate for biomedical applications in drug delivery, controlled release, fluorescence labeling, and bio-imaging.