Abstract
In the steadily emerging field of applications for the natural biopolymer bacterial nanocellulose (BNC), the development of environmentally-friendly and cost-saving techniques to form xerogels by partial or complete dewatering is of great interest for convenient storage, handling and a reduced risk of microbial contamination. Air-dried BNC itself is not able to rehydrate after complete drying due to a structural collapse. In the present paper, it was supplemented with different hydrophilic, water-binding additives and characterized regarding morphology, re-swelling behavior, mechanical stability and potential as drug delivery system. A fast rehydration could be obtained by the addition of magnesium chloride > glucose > sucrose > sorbitol, with a maximum re-swelling percentage up to about 88% (magnesium chloride) of the initial wet weight. In contrast, poly(ethylene glycol) (8 kDa), lactose and trehalose reached only 12–30% whereas mannitol and sodium chloride only had a negligible effect. A high re-swelling value was found to be correlated with the preservation of the three-dimensional BNC network structure and mechanical characteristics such as compression and tensile strength. Confirming the relevance of these findings, the use of the hydrophilic model drug azorubine demonstrated the applicability of the shape-memorized bacterial nanocellulose as drug delivery system with controllable release profiles.
Highlights
In the steadily emerging field of applications for the natural biopolymer bacterial nanocellulose (BNC), the development of environmentally-friendly and cost-saving techniques to form xerogels by partial or complete dewatering is of great interest for convenient storage, handling and a reduced risk of microbial contamination
Bacterial nanocellulose was produced by Komagataeibacter xylinus at the air–liquid interface as stable hydrogel eeces
For the production of air-dried BNC with an enhanced swelling rate, a post synthesis modi cation was applied comprising a 24 h incubation of native, wet BNC in an additive solution and a subsequent thorough air-drying to constant mass at room temperature
Summary
For applications in tissue engineering, moist wound treatment, or as blood-vessel substitute, the high-water-content hydrogel is preferred. From the viewpoint of material storage and packaging, convenient handling and a reduced risk of microbial contamination, a partial or complete dewatering to form xerogels is desired. The ability of BNC to absorb or provide uid can be adjusted by full or partial dewatering. Several techniques for the dewatering of BNC were described in the literature: (i) freeze-drying by sublimation of frozen water for the production of aerogels, (ii) critical point drying by treatment with supercritical carbon dioxide a er replacement of water with suitable liquid solvents, (iii) stepwise solvent exchange for water displacement, (iv) water removal under pressure using water-absorbing materials and/or additional heating to prepare thin foils and membranes, and (v) air-drying by evaporation of water at elevated temperatures or vacuum
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