Nanocellulose, bacteria

Because of the extraordinary supramolecular structure and exceptional product characteristics as high-molecular and high-crystalline cellulosics with a water content up to 99%, nanocelluloses require increasing attention. This review assembles the current knowledge in research, development, and application in the field of nanocelluloses through examples. The topics combine selected results on nanocelluloses from bacteria and wood as well as their use as technical membranes and composites with the first longtime study of cellulosics in the animal body for the development of medical devices such as artificial blood vessels, and the application of bacterial nanocellulose as animal wound dressings and cosmetic tissues. 

As described before, one type of nanocellulose is formed directly as the result of biosynthesis of special bacteria. A very pure product with subsequently reported important properties is formed that necessitates challenging biosynthesis/biotechnological handling and the development of large-scale production. 

Membranes and composites from cellulose and cellulose esters are important domains in the development and application of these polymer materials. The most important segment by volume in the chemical processing of cellulose contains regenerated cellulose fibers, films, and membranes, hi the case of the cellulose esters mainly cellulose nitrate and cellulose acetate as well as novel high-performance materials created therefrom are widely used as laminates, composites, optical/photographic films and membranes, or other separation media, as reviewed in [1], The previously specified nanocelluloses from bacteria and wood tie in with these important potentials and open novel fields of application. 

Nanocellulose, such as that produced by the bacteria Gluconacetobacter xylinus (bacterial cellulose, BC), is an emerging biomaterial with great potential in several applications. The performance of bacterial cellulose stems from its high purity, ultra-fine network structure and high mechanical properties in the dry state [114]. These features allow its applications in scaffold for tissue regeneration, medical applications and nanocomposites. A few researchers have used bacterial cellulose mats to reinforce polymeric matrices and scaffolds with wound healing properties [115-121]. BC is pure cellulose made by bacterial fabrication via biochemical... 

BNC is biosynthesized by several species of bacteria, most importantly G. xylinus (Klemm et al., 2005, 2006, 2009). This biosynthesis process was first discovered by Brown (1886). Systematic and comprehensive research of recent years has given broad knowledge about the formation and structure of the BNC. The formation of BNC by fermentation opens up new vistas for the in situ shaping of nanocellulose. This bioshaping allows the production of flat pellicles, beads, fibers, and hollow bodies with high effectiveness by changing the conditions of the bacteria cultivation (Klemm et al., 2006, 2009). Stationary fermentation gives pellicles of BNC, while as a result of nonstationary conditions mainly the beads can be obtained. 

Bacterial nanocellulose has the same molecular formula as plant cellulose, but it is fundamentally different because of its nanofiber architecture, which results in unique properties. Bacteria-produced ribbons typically show rectangular cross-sections with thicknesses aroxmd 3-10 nm, 30-100 nm in width, and 1-9 xm in length [39,40,41]. Figure 2.4 shows electron... 

The nanocellulose from various sources, sueh as eotton, tunicate, algae, bacteria, ramie, and wood for preparation of high-performance composite materials, have been investigated extensively (Azizi, et. al., 2005). Both natnral and synthetic polymers were explored as the matrixes. Natnral polymers such as poly (P-lydrox-yoctanoate) (PHO) (Dubief, Samain, Dufresne, 1999), soy protein (Wang, Cao,... 

Acetohacter xylinum (or Glucomcetobacter xylinus) is the most effident producer of BC. BC is secreted as a ribbon-shaped fibril, less than 100 nm wide, which is composed of much finer 2-4 nm nanofibrils [99, lOOj. In comparison to the methods for obtaining nanocellulose through mechanical or chemo-mechanical processes, BC is produced by bacteria through cellulose biosynthesis and the building up of bundles of microfibrils [lOlj. 

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