Biophotovoltaic living hydrogel of an ion-crosslinked carboxymethylated cellulose nanofiber/alginate.

Due to the low electrical power generation in liquid cultures of photosynthetic microalgae, a solid medium culture is demanded for the efficient design of biophotovoltaic (BPV) cells. In particular, the conductivity of the culture medium and the contact of microalgae with an electrode are crucial in harvesting electrons in BPV cells. Here, an ion-crosslinked carboxymethylated cellulose nanofiber (CM-CNF)/alginate is proposed as a living hydrogel for the green power generation of Chlorella vulgaris embedded in the hydrogel. The hydrogel crosslinked with Ca2+ and Fe3+ ions showed more efficient BPV properties than the hydrogel crosslinked with only Ca2+ due to the increase of conductivity. The efficient transport of electrons generated by C. vulgaris improves the power generation of BPV cells. Moreover, the fluid channels imprinted in the living hydrogel maintain the viability of C. vulgaris even under the ambient environment by preventing the solid medium from being dried out.

Mimicry of the plant leaf with a living hydrogel sheet of cellulose nanofibers.

Here, we composite an artificial leaf comprising a transparent hydrogel sheet, vein structures, and a photosynthetic system using cellulose nanofibers (CNFs) which can be produced from a biomass. A simple imprinting using a 3D printed stamp enabled the formation of fluidic channels in the hydrogel, embedding living cells without toxic chemistry or a drying process. Microalgae in the hydrogel grows and proliferates under ambient condition for a long period because of the continuous supply of nutrient from the channels, which is more effective for metabolic bioactivity than a flat sheet cultured in a bulk solution. This mimicry of the plant leaf provides a potential for a whole artificial plant. In addition, the simple fabrication of fluidic channels in the hydrogel can be applied to diverse living organisms, including bacteria, animal, and plant cells.

Protective coating of strawberries with cellulose nanofibers.

Since shelf life of perishable foods is short, a compelling challenge is to prolong the freshness of foods with a cost-effective strategy. A perishable fruit, the strawberry, is chosen as a model perishable food and an edible film coating is applied to it using carboxymethylated cellulose nanofibers (CM-CNFs) stabilized by cationic salts. A transparent and impermeable CM-CNF film is formed at the strawberry surface using a dip coating process. The formation of the film is dependent on the electrostatic interaction between anionic CM-CNF and salt cations. Physical properties of the film are characterized and the effectiveness of edible film coating on the freshness of perishable fruit is evaluated by the measurement of weight loss, CO2 release, firmness, total solid sugar and acidity. Cellulose nanofiber is a promising cost-effective material appropriate for use as an edible coating that contributes to the long-term storage and prolonged freshness of foods.

3D structure of lightweight, conductive cellulose nanofiber foam.

We investigate the three-dimensional (3D) structuring of cellulose nanofiber (CNF) foam-based ink using direct ink writing 3D printing and the transformation of CNF foam from an insulator to a conductor. The colloidal stability of a CNF foam is critical to producing a solid CNF foam which can be used as a template for the synthesis of conducting polymers. Liquid CNF foam ink is produced by simple stirring of CNF suspension with sodium dodecyl sulfate as an emulsifier. The shear thinning behavior of the liquid CNF foam ink enables printing through a needle. Flexible design of CNF foam structures is enabled by 3D printing using computer-aided design. Lightweight conductive CNF foams are prepared via in situ polymerization of polypyrrole on a solid CNF foam. The topological features of the resultant porous conductive CNF foams are observed, and their conductivity is investigated.