Bacterial Nanocellulose as a Renewable Material for Biomedical Applications
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Nanocellulose as a Renewable Material for Biomedical Applications Paul Gatenholm and Dieter Klemm
Abstract Nanocellulose, such as that produced by the bacteria Gluconacetobacter xylinus (bacterial cellulose, BC), is an emerging biomaterial with great potential as a biological implant, wound and burn dressing material, and scaffolds for tissue regeneration. BC has remarkable mechanical properties despite the fact that it contains up to 99% water. The water-holding ability is the most probable reason why BC implants do not elicit any foreign body reaction. Moreover, the nanostructure and morphological similarities with collagen make BC attractive for cell immobilization and cell support. The architecture of BC materials can be engineered over length scales ranging from nano to macro by controlling the biofabrication process. This article describes current and future applications of BC in the biomedical field.
Specific Structure and Properties of Bacterial Nanocellulose Bacterial cellulose (BC) combines, in an exciting manner, significant structural elements and properties of the well-known plant cellulose1–7 with the unique features of nanoscale materials. As a cellulosic polymer, BC is molecularly structured by the repeated connections of D-glucose (dextrose) building blocks, as can be seen from the molecular formula in Figure 1. The highly hydroxyl group-functionalized, linear stiff-chain homopolymer—polymeric dextrose—is characterized by distinct hydrophilicity, broad chemical modifying capacity, and important biocompatibility.8–13 Hydroxyl groups of cellulose form hydrogen bonding within and between the polymer chains, which results in the formation of crystalline morphologies at various length scales. This supramolecular structure determines the materials properties and the insolubility of cellulose in common solvents and allows it to fulfil its role as an important
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natural reinforcing agent. Moreover, it gives cellulose its thermal stability of 250–300°C, respectable for a biopolymer. BC is formed by Gluconacetobacter bacterial strains such as G. xylinus (e.g., DSMZ 14666) in aqueous culture media during a time period of days up to two weeks. These bacteria are found everywhere fermentation of sugars and plant carbohydrates take place, as on damaged fruits and flowers, and in unpasteurized or nonsterilized juice, beer, and wine. Pure strains can be bought from international collections of micro-organisms.
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The structure and properties of the biofabricated nanomaterial BC14–18 are dominated by the nanoscale cellulose fiber network architecture. Fibril diameters are around 30 nanometers, which is a hundred times thinner than the cellulose fibers in common plants. The main effect of the nanosize of the fibrils is an increase in surface area of the BC network, which is reflected in strong interactions with the surrounding environment. Therefore, BC binds large amounts of water—up to 99%—during biosynthesis in the aqueous culture media.19 Typical nanocellulose networks produced by r
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