Biofabrication of a Hyaluronan/Bacterial Cellulose Composite Nanofibril by Secretion from Engineered Gluconacetobacter.

Naturally occurring polysaccharides, such as cellulose, hemicellulose, and chitin, have roles in plant skeletons and/or related properties in living organisms. Their hierarchically regulated production systems show potential for designing nanocomposite fabrication using engineered microorganisms. This study has demonstrated that genetically engineered Gluconacetobacter hansenii (G. hansenii) individual cells can fabricate naturally composited nanofibrils by simultaneous production of hyaluronan (HA) and bacterial cellulose (BC). The cells were manipulated to contain hyaluronan synthase and UDP-glucose dehydrogenase genes, which are essential for HA biosynthesis. Fluorescence microscopic observations indicated the production of composited nanofibrils and suggested that HA secretion was associated with the cellulose secretory pathway in G. hansenii. The gel-like nanocomposite materials produced by the engineered G. hansenii exhibited superior properties compared with conventional in situ nanocomposites. This genetic engineering approach facilitates the use of G. hansenii for designing integrated cellulose-based nanomaterials.

Facile surface modification of amphiphilic cellulose nanofibrils prepared by aqueous counter collision.

The present study concerns the chemical modification of the surfaces of cellulose nanofibrils (CNFs) prepared by aqueous counter collision (ACC). Wood-derived CNFs prepared by ACC were acetylated with acetic anhydride in an aqueous dispersion. The moderately acetylated nanofibrils were more readily dispersible in water than unmodified CNFs, although the original nanofibrous morphology comprising crystalline cellulose I remained almost unchanged. This indicates that the surfaces of the crystalline CNFs had been selectively acetylated, which possibly inhibited self-aggregation between the nanofibrils, thereby facilitating dispersion in the aqueous medium. Despite the absence of additives, the acetylated CNFs were readily adsorbed onto hydrophobic surfaces, and retained their compatibility with water, which improved their ability to stabilize emulsions and coat plastic resin particles in water. The results indicate that the amphiphilic properties of CNFs prepared by ACC can be controlled by this facile surface acetylation method, which potentially increases their usefulness in various fields.

Characterization of an Amphiphilic Janus-Type Surface in the Cellulose Nanofibril Prepared by Aqueous Counter Collision.

Cellulose nanofibrils, which attract extensive attention as a bio-based, sustainable, high-performance nanofibril, are believed to be predominantly hydrophilic. This study aimed to prove the presence of an amphiphilic "Janus-type fiber surface" in water with hydrophobic and hydrophilic faces in a cellulose nanofibril (ACC-CNF) that was prepared by the aqueous counter collision method. We clarified the surface characteristics of the ACC-CNF by confocal laser scanning microscopy with a carbohydrate-binding module and congo red probes for the hydrophobic planes on the cellulose fiber surfaces and calcofluor white as hydrophilic plane probes. The results indicated the presence of both characteristic planes on a single ACC-CNF surface, which verifies an amphiphilic Janus-type structure. Both hydrophobic probes adsorbed onto ACC-CNFs for the quantitative evaluation of the degree of ACC-CNF surface hydrophobicity by Langmuir's adsorption theory based on the optimal maximum adsorption amounts for various starting raw material types.