# Biocompatible Dispersants for Carbon Nanomaterials
## 6 Biocompatible Dispersants
### Cellulose
may apply to other CNMs [38]. The attraction between CNMs and NCC can also be varied by changing polymorph composition. Nanocelluloses can be functionalised to add another dimension of capabilities to this class of dispersant, as demonstrated by [PERSON] et al. earlier this year [43]. The study focussed on functionalising NCC and cellulose nanofibrils (CNFs)--with sulphate, carboxylate, and amino-silane moieties--to produce nanocellulose/multi-walled carbon nanotube (MWCNT) dispersions for electrochemical applications (Table 2 (4)). The functionalisation of the nanocellulose material tailored the final product's physiochemical properties by changing its crystal structure, density, and electrochemical behaviour [43]. Before this study, [PERSON] et al. experimented with carboxymethylated CNFs to produce high-quality SWCNT dispersions [44]. The cellulose material was obtained by treating softwood pulp with monochloroacetic acid, followed by sonication, shear mixing,  
Figure 3: TEM micrograph of SWCNT/NCC hybrids. (**A**) Type I NCC; (**B**) Type II NCC. Arrows show SWCNTs, and dotted circles show cellulose nanocrystals. Insets: Parallel and antiparallel NCC fibers [38]. Figure adapted with permission from [38] Copyright © 2019 American Chemical Society. and centrifugation steps to purify the dispersant. SWCNTs were added to the resulting solution and sonicated to produce the dispersion. This solution was then used to produce aerogels, conductive films, and anisotropic microscale fibres. The authors chose this strategy to lower the cost and increase the conductivity and strength of the final material and facilitate colloidal self-assembly of the composite material. However, it is important to note that only low concentrations of SWCNTs were dispersed, and no stability data was present [44] (Table 2 (5)). NCC also increases the electrical and thermal conductivity of CNM dispersions, as demonstrated by [PERSON] et al. in 2020 [5]. The study focused on using NCC to create stable, aqueous dispersions of MWCNTs and graphene for use as a heat transfer fluid--this was achieved by adding CNMs to solutions of varying concentrations of NCC and ultrasonication for 1 h. It was found that this strategy was able to form stable aqueous dispersions of both CNMs, whilst enhancing the thermal and electrical conductivity of the nanomaterials. Although the intended use of this dispersion was engineering-based, using a biocompatible dispersant in an aqueous solution meant that it was non-toxic and could be used for biomedical applications, such as drug delivery or cellular imaging. The details of this dispersion can be seen in Table 2 (6). In conclusion, cellulose-based dispersants are cheap, biocompatible, environmentally friendly and available in large quantities [21], making them ideal for industrial and biomedical applications. They are effective at dispersing a range of CNMs [39; 41]. However, no work has been done on using them to disperse 0D CNMs, such as carbon nano-onions (CNOs), fullerenes, and carbon quantum dots (CQDs). The benefits of these dispersants could very well translate to these materials. Functionalisation of cellulose dispersants allows for customisation of the material to suit a range of applications by modifying the dispersants physiochemical characteristics. This modifiability is particularly relevant when the dispersant will be used to produce a solid--aerogel, film, or coating--as factors such as porosity can be controlled [43]. However, it is important to note that the effects of covalent modification on celluloses structure, biocompatibility, and dispersing abilities are not well studied.