2.5 Applications of Cellulose Nanocrystals (CNCs)
2.5.1 Enzyme Immobilisation
Cellulose Nanocrystals (CNCs) have been used as an agent for enzyme immobilisation due to its large surface area and non-porous structure (Lam et al., 2012). An enzyme activity of 594 U/g can be achieved when immobilisation is performed at room temperature and the conjugate is stable for 3 months at 5°C. The immobilised peroxidase demonstrates improved removal of chlorinated phenolic compounds compared to its soluble counterpart, probably due to protective effects of the immobilisation towards enzyme deactivation, as well as product precipitation induced by the conjugate amino groups.
2.5.2 Photonic Applications
A unique combination of chemical, mechanical and optical characteristics of CNCs leads into availability for application in pigments, security coating (banknotes, ID cards and passports), sensors and mesoporous chiral nanotemplates. By varying the concentration and evaporation of cholesteric liquid crystalline, dry films with strong photonic response could be obtained.
Frka-Petesic et al., (2017) conducted an optical analysis of CNCs under different magnetic environment to observe the unusual angular dependance of optical response. Their result shows a strong reflection and homogenous cholesteric in the of CNCs dried under tilted magnetic fields to obtain unprecedented control over the self-assembly of CNCs into colourful films.
Through evaporation of CNCs suspension, a chiral nematic, iridescent, coloured film of CNCs can be formed. Chiral nematic CNC films could selectively reflect left–handed light and appear colourful when the helicoidal pitch (P) is on the order of magnitude of the wavelength of visible light. Since pitch is sensitive to a variety of conditions, it is relatively easy to modulate film colour (Abitbol et al., 2016). Since a few years ago, CNC- templating had been used to obtain diverse range of chiral materials (mesoporous silica, organosilica, nanocrystalline titania and CNC nanocomposites). Chiral nematic composites from CNCs and the material of interest are produced, after which, one component may be selectively removed. The selective removal of one component of the previous nanocomposite gives a chiral mesoporous material. The potential applications of these systems include responsive hydrogels, optical filters, antireflective coatings, chiral plasmonics, soft actuators, and flexible electronics (Abitbol et al., 2016).
2.5.3 Oil and Gas Industry
Cellulose nanocrystals (CNCs) are used as stabilisers, thickeners, shear thinning agents, proppants or reinforcing agents in cements, and spacer fluids in the oil and gas industry. The high thermal stability of CNCs and attractive rheological properties are the key aspects for their application in oil and gas fields and are being extensively studied currently (Klemm et al., 2018).
2.5.4 Biomedical Applications
Driven by exceptional biocompatibility and right mechanical properties that is similar to natural tissues, nano-cellulose based biomaterials can provide a cell-friendly environment to encourage cells attachment and proliferation as special tissue bioscaffolds. Cellulose has a long history of application in the pharmaceutical and biomedical industry particularly as pharmaceutical excipients to abbreviate drug-loaded matrices as appropriate tablets for oral administration.
Kovac et al. (2010) had conduct an experiment in regard of eco-toxicology of CNCs with aquatic organism. It was reported that CNCs of low toxicity cause less harm to environment (Kovacs et al., 2010; Lin & Dufresne, 2014). Recently, CNCs are conducted for its utility in fluorescence bioassay and bioimaging applications. For example, functional groups on the surface of CNCs can be conjugated with different biological moietis (fluorescin -5′-isothiocyanate) which enable its use as an indicator in nanomedicine (Dong ; Roman, 2007; Brinchi et al., 2013).
CNCs can be applied in bioscaffolds for cellular cultures. The reinforcement of CNCs and electrospun maleic anhydride-grafted poly (lactic acid) can act as support scaffolds to culture the human adult adipose derived mesenchymal stem cells (hASCs) and promote cell proliferation. From the images of confocal laser scanning microscope (CLSM), Human Dental follicle cells (hDFCs) cultured on electrospun CNC/cellulose for more than 3 days could be observed. CNCs also capable to dispersed in electrospun scaffolds, allowing cultures to proliferate rapidly, not only on the surface, but also deep inside the scaffolds (Lin ; Dufresne, 2014).
CNCs are also can be applied as drug delivery carriers. CNCs-based drug carriers can be in the forms of microspheres, hydrogel and membranes or films. The presence of CNCs in alginate-based microspheres showed more consistent swelling patterns, higher encapsulation efficiency, and promising sustained release profiles of the drug. CNCs are chemically grafted with cyclodextrin to form hydrogels via host-guest inclusion interactions. Hydrogels as drug delivery vehicles exhibit prolonged drug release profile with special release kinetic and mechanisms, attributed to good dispersion of nanoparticles and rigid networks containing CNCs.