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.

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.

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.

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.