The ability to tune the interfacial and functional properties of cellulose nanomaterials has been identified as a critical step for the full utilization of nanocellulose in the development of new materials. Here, we use triazine chemistry in a modular approach to install various functionalities and chemistries onto cellulose fibers and cellulose nanocrystals (CNCs). The surface modification is demonstrated in aqueous and organic media. Octadecyl, monoallyl-PEG, benzyl, and propargyl triazinyl derivatives were grafted onto cellulose/ CNCs via aromatic nucleophilic substitution in the presence of base as hydrochloric acid scavenger. The covalent nature and degree of substitution of grafted aliphatic, polymeric, alkyne chains, and aromatic rings were characterized through Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, elemental analysis, and thermogravimetric analysis. In addition, AFM and DLS analysis showed minimal change in the geometry and individualized character of CNCs after surface modification. X-ray diffraction analysis confirmed that the modification happened only at the CNC surface, while the bulk crystalline core remained unmodified. Modified cellulose/CNCs showed hydrophilic or hydrophobic properties depending on the grafted functionality, which resulted in stable colloidal suspensions of CNCs in polar and nonpolar organic solvents. Furthermore, the reactive nature of propargyl-modified cellulose was demonstrated by the successful grafting of an azido-fluorescein dye via copper-catalyzed Huisgen 1,3-dipolar cycloaddition. The triazinyl chemistry thus presents a versatile route for tuning the interfacial properties of nanocellulose, with the possibility of postmodification for applications that require the conjugation of molecules onto cellulose through bio-orthogonal chemistries.

Poly(dimethylsiloxane) (PDMS) has become the material of choice for fabricating microfluidic channels for lab-on-a-chip applications. Key challenges that limit the use of PDMS in microfluidic applications are its hydrophobic nature, and the difficulty in obtaining stable surface modifications. Although a number of approaches exist to render PDMS hydrophilic, they suffer from reversion to hydrophobicity and, frequently, surface cracking or roughening. In this study, we describe a one-step in-mould method for the chemical modification of PDMS surfaces, and its use to assess the ability of different surfactants to render PDMS surfaces hydrophilic. Thin films of ionic and non-ionic surfactants were patterned into an array format, transferred onto silicone pre-polymer, and subsequently immobilized onto the PDMS surface during vulcanization. The hydrophilicity of the resulting surfaces was assessed by contact angle measurements. The wettability was observed to be dependent on the chemical structure of the surfactants, their concentration and interactions with PDMS. The morphology of modified PDMS surfaces and their change after wetting and drying cycles were visualized using atomic force microscopy. Our results show that while all surfactants tested can render PDMS surfaces hydrophilic through the in-mould modification, only those modified with PEG-PDMS-PEG copolymer surfactants were stable over wetting/dying cycles and heat treatments. Finally, the in-mould functionalization approach was used to fabricate self-driven microfluidic devices that exhibited steady flow rates, which could be tuned by the device geometry. It is anticipated that the in-mould method can be applied to a range of surface modifications for applications in analytical separations, biosensing, cell isolation and small molecule discovery.

Cellulose, the primary component of the plant cell wall, has fueled the wood, textile, pulp and paper industries for centuries, and has recently been used for the production of renewable nanomaterials. The tight crystalline packing of glucan chains within cellulose fibrils is responsible for its superior mechanical properties but renders this material recalcitrant to biochemical and chemical breakdown and limits its use as a green resource. The presence of nanoscale dislocations within cellulose fibrils has been postulated for decades and is thought to be responsible for the production and size of cellulose nanocrystals (CNCs) following acid hydrolysis. However, dislocations have never been directly visualized and their prevalence and size have remained elusive. In this study, we have used super-resolution (SR) fluorescence microscopy to directly visualize and measure alternating crystalline and disordered regions within individual fluorescently labelled bacterial cellulose fibrils. The measured size of the crystalline regions ranges from 40 – 400 nm and shows striking overlap with the length distribution of bacterial CNCs produced through sulfuric acid hydrolysis, supporting the fringed micellar model for the supramolecular structure of cellulose fibrils. The disordered regions were found to be 20 – 120 nm in length and show heterogeneous accessibility, which directs fibril cleavage during the initial stages of cellulose acid hydrolysis. Two-colour SR imaging of cellulose fibrils and bound exoglucanases (Cel7A), in combination with degree of crystallinity measurements suggest that these dislocations are nanoscale in size, and do not result in amorphous cellulose pockets large enough to accommodate enhanced enzyme binding. Through characterization of disordered regions in cellulose fibrils, we have gained insight into the role of cellulose nanostructure in its breakdown by chemical and enzymatic means.

In nature, cells exist in three-dimensional (3D) microenvironments with topography, stiffness, surface chemistry, and biological factors that strongly dictate their phenotype and behavior. The cellular microenvironment is an organized structure or scaffold that, together with the cells that live within it, make up living tissue. To mimic these systems and understand how the different properties of a scaffold, such as adhesion, proliferation, or function, influence cell behavior, we need to be able to fabricate cellular microenvironments with tunable properties. In this work, the nanotopography and functionality of scaffolds for cell culture were modified by coating 3D printed materials (DS3000 and poly­(ethylene glycol)­diacrylate, PEG-DA) with cellulose nanocrystals (CNCs). This general approach was demonstrated on a variety of structures designed to incorporate macro- and microscale features fabricated using photopolymerization and 3D printing techniques. Atomic force microscopy was used to characterize the CNC coatings and showed the ability to tune their density and in turn the surface nanoroughness from isolated nanoparticles to dense surface coverage. The ability to tune the density of CNCs on 3D printed structures could be leveraged to control the attachment and morphology of prostate cancer cells. It was also possible to introduce functionalization onto the surface of these scaffolds, either by directly coating them with CNCs grafted with the functionality of interest or with a more general approach of functionalizing the CNCs after coating using biotin–streptavidin coupling. The ability to carefully tune the nanostructure and functionalization of different 3D-printable materials is a step forward to creating in vitro scaffolds that mimic the nanoscale features of natural microenvironments, which are key to understanding their impact on cells and developing artificial tissues.

The visualization of naturally derived cellulose nanofibrils (CNFs) and nanocrystals (CNCs) within nanocomposite materials is key to the development of packaging materials, tissue culture scaffolds, and emulsifying agents, among many other applications. In this work, we develop a versatile and efficient two-step approach based on triazine and azide–alkyne click-chemistry to fluorescently label nanocelluloses with a variety of commercially available dyes. We show that this method can be used to label bacterial cellulose fibrils, plant-derived CNFs, carboxymethylated CNFs, and CNCs with Cy5 and fluorescein derivatives to high degrees of labeling using minimal amounts of dye while preserving their native morphology and crystalline structure. The ability to tune the labeling density with this method allowed us to prepare optimized samples that were used to visualize nanostructural features of cellulose through super-resolution microscopy. The efficiency, cost-effectiveness, and versatility of this method make it ideal for labeling nanocelluloses and imaging them through advanced microscopy techniques for a broad range of applications.