films or sheets is < 10gpa at most. the sheet's high young's modulus has been attributed to the unique super-molecular structure in which fibrils of biological origin are preserved and bound tightly by hydrogen bonds. this young's modulus does not vary with temperature nor the cultivation process used. the very high young's modulus of this material must be ascribed to its super-molecular structure. this property arises from adjacently aligned glucan chains participating in inter- and intrachain hydrogen bonding. bacterial cellulose subfibrils are crystallized into microfibrils which group to form bundles, that then form 'ribbons'. these fibers are two orders of magnitude thinner than cellulose fibers produced by pulping wood. today, it is known that the pellicle comprises a random assembly of fibrils (< 130 nm wide), which are composed of a bundle of much finer microfibrils (2 to 4 nm diameter). it is also known that the pellicle gives a film or sheet when dried if the shrinkage across the plane is restricted. the ultrafine ribbons of microbial cellulose form a dense reticulated structure, stabilized by extensive hydrogen bonding. bacterial cellulose is also distinguished from its plant counterpart by a high crystallinity index (above 60%). two common crystalline forms of cellulose, designated as i and ii, are distinguishable by x-ray, nuclear magnetic resonance (nmr), raman spectroscopy, and infrared analysis. bacterial cellulose belongs crystallographically to cellulose i, common with natural cellulose of vegetable origin, in which two cellulose units are arranged parallel in a unit cell. the term cellulose i is used for this parallel arrangement, whereas crystalline fibrils bearing antiparallel polyglucan chains arise forming the thermodynamically stable cellulose ii. the molecular arrangement in the sheet, confirmed by x-ray diffraction, was such that the molecular chain axis lay randomly perpendicular to the thickness such that the (1 1 0) plane was oriented parallel to the surface. although cellulose forms a distinct crystalline structure, cellulose fibers in nature are not purely crystalline. in addition to the crystalline and amorphous regions, cellulose fibers contain various types of irregularities, such as kinks or twists of the microfibrils, or voids such as surface micropores, large pits, and capillaries. thus, the total surface area of a cellulose fiber is much greater than the surface area of an ideally smooth fiber of the same dimension. the net effect of structural heterogeneity within the fiber is that the fibers are at least partially hydrated by water when immersed in aqueous media, and some micropores and capillaries are sufficiently spacious to permit penetration. scanning electron microscopy of a fractured edge has revealed a pile of very thin layers. it is suggested that these fibrils in layers are bound through interfibrillar hydrogen bonds, just as in pulp-papers, but the density of the interfibrillar hydrogen bonds must be much higher as the fibrils are finer, hence the contact area is larger. applications bacterial cellulose has a wide variety of current and potential future applications. due to its many unique properties, it has been used in the food industry, the medical field, commercial and industrial products, and other technical areas. bacterial cellulose is a versatile structural material, allowing it to be shaped in a variety of ways to accommodate different uses. a number of patents have been issued for processes involving this material. . bacterial cellulose pellicles were proposed as a temporary skin substitute in case of human burns and other dermal injuries . food the oldest known use of bacterial cellulose is as the raw material of nata de piña, a traditional sweet candy dessert of the philippines. several natural colored pigments (oxycarotenoids, anthocyanins and related antioxidants and free radical scavengers) were incorporated in to bacterial cellulose cubes in order to render the dessert more attractive . bacterial cellulose has also been used as a thickener to maintain the viscosity in food and as a stabilizing agent. due to its texture and fiber content, it has been added to many food products as a dietary fiber. a specific example is cellulon ®, which is a bulking agent used as a food ingredient to act as a thickener, texturizer, and/or calorie reducer. microbial cellulose has also been used as an additive in diet beverages in japan since 1992, specifically kombucha, a fermented tea drink. commercial products bacterial cellulose also has wide applications in commercial industries. in papermaking, it is used as an ultra-strength paper and as a reticulated fine fibre network with coating, binding, thickening and suspending characteristics. due to its high sonic velocity and low dynamic loss, bacterial cellulose has been used as an acoustic or filter membrane in hi-fidelity loudspeakers and headphones as marketed by the sony corporation. bacterial cellulose is also used as an additive in the cosmetic industry. furthermore, it is being tested in the textile industry, with the possibility of manufacturing cellulose based clothing. medical in more modern applications, microbial cellulose has become relevant in the medical sector. it has been tested and successfully used as a wound dressing, especially in burn cases. studies have shown that burns treated with microbial cellulose coverings healed faster than traditional treatments and had less scarring. the microbial cellulose topical applications are effective due to the cellulose's water holding ability and water vapor permeability. the high water holding ability provides a moist atmosphere at the injury site, which is critical in healing, while the wicking ability allows seepage from the wound to be removed from the site. also, the microbial cellulose molds very well to the surface of the skin, providing a conformal covering even in usually difficult places to dress wounds, such as areas on the face. this technique has been so successful that commercial microbial cellulose products, such as biofill ®, have been developed. another microbial cellulose commercial treatment product is xcell produced by the xylos corporation, which is mainly used to treat wounds from venous ulcers. studies have also been performed where traditional gauze dressings are treated with a microbial cellulose biopolymer to enhance the properties of the gauze. in addition to increasing the drying time and water holding abilities, liquid medicines were able to be absorbed by the microbial cellulose coated gauze, allowing them to work at the injury site. microbial cellulose has also been used for internal treatments, such as bone grafts and other tissue engineering and regeneration. a key ability of microbial cellulose for medical applications is that it can easily be molded into various shapes while still retaining all of its useful properties. by molding microbial cellulose into long, hollow tubes, they can be used as replacement structures for several different areas, such as the cardiovascular system, the digestive tract, urinary tract, or the trachea. a recent application of microbial cellulose has been as synthetic blood vessels and stents. the cellulose can also be modeled into mesh membranes that can be used for internal replacement structures, such as the brain's outer membrane, the dura mater. in addition to replacement, these structures have also been used as grafts to interact with existing internal biological material. microbial cellulose has also been used in guided tissue regeneration. bioprocess ® and gengiflex ® are some of the common trademarked products of microbial cellulose that now have wide applications in surgery and dental implants. one example involves the recovery of periodontal tissues by separating oral epithelial cells and gingival connective tissues from the treated root surface. current research/future applications an area of active research on microbial cellulose is in the area of electronic paper. currently, plant cellulose is used to produce the bulk of traditional paper, but due to its low purity it must be mixed with other substances such as lignin. however, due to microbial cellulose's higher purity and microfibril structure, it may prove to be an excellent candidate for an electronic paper substrate. microbial cellulose can be fashioned into sheets approximately 100 micrometers thick, about the thickness of normal paper, by a wet synthesis process. the microbial cellulose produces a sturdy substrate with a microfibril structure that allows the paper to be implanted with dopants. through the application of solutions to the microbial cellulose paper, conductive dopants and electrochromic dyes can be placed into the microfibril structure. the bistable dyes change from clear to dark upon the application of the appropriate voltages, which when placed in a pixel structure, would allow images to be formed. this technology is still in the research stage and has not yet been scaled to commercial production levels. further research has been done to apply bacterial cellulose as a substrate in electronic devices with the potential to be used as e-book tablets, e-newspapers, dynamic wall papers, rewritable maps and learning tools. another possible example of bacterial cellulose use in the electronics industry includes the manufacture of organic light-emitting diodes (oleds). challenges/limitations due to the inefficient production process, the current price of bacterial cellulose remains too high to make it commercially attractive and viable on a large scale. traditional production methods cannot produce microbial cellulose in commercial quantities, so further advancements with reactor based production must be achieved to be able to market many microbial cellulose products.