## 2 Cellulose Nanomaterials
### Bacterial Nanocellulose (BNC)  
Nanocellulose produced by bacteria is called microbial cellulose or bacterial nanocellulose (BNC), and its purity is higher than other kinds of nanocellulose [38; 39]. This type of nanostructured cellulose is produced by a bottom-up method consisting of assembling low-molecular-weight sugars by means of microorganisms; the single fibers that are achieved have a thickness of a few nanometers. Usually, two culture methods are used to produce BNC: static and stirred techniques; through the function of the chosen technique, it is possible to modify different characteristics, such as the surface morphology and physical and mechanical properties of the BNC and, therefore, to use it for several applications [26]. The main properties of BNC are its high crystallinity (80-90%), high purity, high flexibility, high water content (approximately 99% in the hydrogel structures inside the network of nanocellulose), and high mechanical and thermal resistance.  
Moreover, due to its biocompatibility, bio-functionality, and nonotoxicity, bacterial nanocellulose is a very promising material in the fields of medical implants and biotechnology, as well as for the applications of engineering tissues reconstruction or regenerative medicine. However, the principal challenge to be faced is the scale-up of industrial BNC production, which, today, is difficult to achieve due to the low productivity, highly expensive culture media, and high fermentation costs [3].  
One way to overcome these problems can be the use of industrial wastes as extraction sources, which have a low cost and are readily available, and can also be processed with clean technology approaches, thus promoting not only a reduction in disposal costs of waste for the industries that supply the raw materials, but also the protection of the environment [40].  
In conclusion, Table 2 shows the comparison between the different types of nanocellulose.  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline \multicolumn{2}{c}{**Cellulose Nanocrystals (CNCs)**} & **Cellulose Nanofibirls (CNFs)** & **Bacterial Nanocellulose (BNC)** \\ \hline \multirow{4}{*}{**Synonyms**} & Crystallites, whiskers, nanowchiskers, cellulose nanocrystals, rod-like cellululose microcrystals & Microfibrirls, cellulose, nanofibers & Biocellulose, bacterial cellulose, microbial cellulose \\ \hline \multirow{4}{*}{**Common source**} & Wood, cotton, hemp, flax, rice straw, wheat straw, ramie, avicel, mcc, tunicin, algae, bacterial cellulose, pea hull fibers, branch-bark of mulberry, black spruce and caucalyptus, tunicera, valonia, kraft pineapple leaf fibers, grass, swede root, chardonnay grape skins, coconut fibers, softwood wood flour, kenaf fibers, rice fibers, corrncob. & Pea hull, kenaf, hardwood and softwood pulp, cotton linter, cotton, cassava bagasse, sugarcane bagasse, cotton, algae (valonia), tunicate cellulose, bacterial cellulose, sugar beet pulp, wheat straw, date palm tree & Low molecular weight sugar, alcohols, several bacteria species such as gluconacetobacter, agrobacteriumium, pseudomonas, rhizobium, and sarcin. \\ \cline{1-1}  & Chemical or enzymatic treatment prior to delamination or wood pulp by mechanical pressure, acid hydrolysis & Acid hydrolysis, integration of mechanical shearing process via high pressure homogenization and enzymatic hydrolysis, TEMPO-mediated oxidation & Bacterial synthesis and cultivation in aqueous culture media present by glucose, oxygen and phosphate. \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparison between the different types of nanocellulose [29].