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Gels are attractive for applications in drug delivery, tissue engineering, and 3D printing. Here, physical colloidal gels were prepared by freeze–thaw (FT) cycling of cellulose nanocrystal (CNC) suspensions. The aggregation of CNCs was driven by the physical confinement of CNCs between growing ice crystal domains. FT cycling was employed to form larger aggregates of CNCs without changing the surface chemistry or ionic strength of the suspensions. Gelation of CNC suspensions by FT cycling was demonstrated in water and other polar solvents. The mechanical and structural properties of the gels were investigated using rheometry, electron microscopy, X-ray diffraction, and dynamic light scattering. We found that the rheology could be tuned by varying the freezing time, the number of FT cycles, and concentration of CNCs in suspension.

A cellulose nanocrystal (CNC) based adsorbent was synthesized by modifying pristine CNC with various amounts of a positively-charged surfactant (CTAB) and was used to study the adsorption behavior of Congo red (CR) in aqueous medium. The interaction of CTAB with CNCs, and potential alterations on the chemical and physical structure of CNCs are studied, and the synthesized adsorbent, modified cellulose nanocrystal (MCNC) was characterized using Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, elemental and zeta potential analysis. The amount of surfactant used for modification was optimized to maximize the adsorption capacity of the adsorbent. Furthermore, it was found that the amount of surfactant affects the CR-MCNC interactions and determines the mechanism of adsorption. The kinetics followed a pseudo-second order and intra-particle diffusion model implying that the rate-controlling step of the adsorption process was first dominated by film-diffusion, and consequently by intra-particle diffusion. Thermodynamic studies on the system suggested that the adsorption process is spontaneous and exothermic. Characterization of the adsorbent, before and after adsorption, coupled with the kinetic and isotherm studies indicated that electrostatic attraction, hydrogen bonding, and hydrophobic attraction are the main mechanisms/interactions of adsorption. The adsorbent is highly stable in water and retains its original adsorption capacity after successive dialysis cycles.

Cellulose nanocrystals (CNCs) derived from biomass spontaneously organize into a helical arrangement, termed a chiral nematic structure. This structure mimics the organization of chitin found in the exoskeletons of arthropods, where it contributes to their remarkable mechanical strength. Here, we demonstrate a photonic sensory mechanism based on the reversible unwinding of chiral nematic CNCs embedded in an elastomer, leading the materials to display stimuli-responsive stretchable optics. Vivid interference colors appear as the film is stretched and disappear when the elastomer returns to its original shape. This reversible optical effect is caused by a mechanically-induced transition of the CNCs between a chiral nematic and pseudo-nematic arrangement., Cellulose nanocrystals (CNCs) spontaneously organize into a helical arrangement but flexible CNC elastomer composite materials with this structure were so far not realized. Here the authors demonstrate the fabrication of a CNC based elastomer composite and its application as a photonic strain sensor.

The simple structural modification of replacing a terminal carboxylic acid with a primary amide group was found to lower the minimum gelation concentration (MGC), by at least an order of magnitude, for a series of N-lauroyl-l-amino acid phase-selective organogelators in decane. The amide-functionalized analogue N-lauroyl-l-alanine-CONH2 was demonstrated to gel a broad range of solvents from diesel to THF at MGCs of 2.5% w/v or less, as well as to produce gels with a higher thermal stability (ca. 30 °C) and enhanced mechanical properties (5 times increase in complex modulus), compared to the carboxylic acid analogue, N-lauroyl-l-alanine-COOH. These improved properties may be due to the additional hydrogen bonding in the primary amide analogue as revealed by SCXRD. Most significantly for this study, the introduction of the primary amide functionality enabled N-lauroyl-l-alanine-CONH2 to form a self-assembled fibrillar network in water. The aqueous network could then actively uptake and rapidly gel decane, diesel, and diluted bitumen ("dilbit") with MGCs of 2.5% w/v or less. This aqueous delivery method is advantageous for oil-remediation applications as no harmful carrier solvents are required and the gel can be easily separated from the water, allowing the oil to be recovered and the gelator recycled.

A carbon-dioxide-switchable (CO2-switchable) hydrogel was prepared by adding imidazole to a suspension of cellulose nanocrystals (CNCs). Sparging of CO2 through the imidazole-containing CNC suspension led to gelation of the CNCs, which was reversible by subsequent sparging with nitrogen (N2) to form a low-viscosity CNC suspension. The gelation process and the properties of the hydrogels have been investigated by rheology, ζ potential, pH, and conductivity measurements, and the gels were found to have interesting and reversible tunable mechanical properties. The present work describes a straightforward way to obtain switchable CNC hydrogels without the need to functionalize CNCs or add strong acids or bases. These CO2-responsive CNC hydrogels have potential for application in stimuli-responsive adsorbents, filters, and flocculants.

Cellulose nanocrystals (CNCs) spontaneously assemble into gels when mixed with a polyionic organic or inorganic salt. Here, we have used this ion-induced gelation strategy to create functional CNC gels with a rigid tetracationic macrocycle, cyclobis(paraquat-p-phenylene) (CBPQT4+ ). Addition of [CBPQT]Cl4 to CNCs causes gelation and embeds an active host inside the material. The fabricated CNC gels can reversibly absorb guest molecules from solution then undergo molecular recognition processes that create colorful host-guest complexes. These materials have been implemented in gel chromatography (for guest exchange and separation), and as elements to encode 2- and 3-dimensional patterns. We anticipate that this concept might be extended to design a set of responsive and selective gel-like materials functioning as, for instance, water-pollutant scavengers, substrates for chiral separations, or molecular flasks.

The functionalization of cellulose nanocrystal (CNC) aerogels was achieved through a two-step synthetic procedure. CNC aerogels were prepared under hydrothermal conditions, followed by solvent exchange and critical point drying. The CNC aerogels were functionalized with a methacrylate group and then underwent thiol-ene click chemistry to impart a range of functionalities onto the surface of the CNC aerogel. The use of the functionalized aerogels as oil absorbents was then investigated, with the most hydrophobic CNC aerogel, 1 H,1 H,2 H,2 H-perfluorodecanethiol-functionalized CNC aerogel, exhibiting the highest absorption of xylenes at 2.9 mL g-1.

Pressure-responsive chiral photonic aerogels are fabricated by combining liquid crystal self-assembly and ice-templating processes. The aerogels have a hierarchical structure in which the primary 2D chiral nematic structured walls of cellulose nanocrystals form ribbons that support a secondary 3D cellular network. Owing to the flexibility of the aerogels in solvent, the 3D structure of the aerogel can easily be transformed to a 2D structure by pressure-induced rearrangement. The aerogels vary from white in color, which arises from light scattering, to a reflective photonic crystal displaying bright iridescent colors that depend on the immersed solvent. A solvent-sensitive ink that shows quick color response to different solvents is designed using the pressure-responsive photonic aerogel. This material demonstrates a new response mechanism for the design of smart and mechanoresponsive photonic materials.

In Alzheimer’s disease, the microtubule-associated protein tau forms intracellular neurofibrillary tangles (NFTs). A critical step in the formation of NFTs is the conversion of soluble tau into insoluble filaments. Accordingly, a current therapeutic strategy in clinical trials is aimed at preventing tau aggregation. Here, we assessed altenusin, a bioactive polyphenolic compound, for its potential to inhibit tau aggregation. Altenusin inhibits aggregation of tau protein into paired helical filaments in vitro. This was associated with stabilization of tau dimers and other oligomers into globular structures as revealed by atomic force microscopy. Moreover, altenusin reduced tau phosphorylation in cells expressing pathogenic tau, and prevented neuritic tau pathology induced by incubation of primary neurons with tau fibrils. However, treatment of tau transgenic mice did not improve neuropathology and functional deficits. Taken together, altenusin prevents tau fibrillization in vitro and induced tau pathology in neurons., This work has been funded by the National Health & Medical Research Council (NH&MRC 1037746, 1020562, 1083209) and the Australian Research Council (ARC 130102027) to L.M.I. A.C. was supported by Postdoctoral Fellowship CONICYT (74140034). L.M.I. is an NH&MRC Senior Research Fellow.

We report the facile preparation of gels from the hydrothermal treatment of suspensions of cellulose nanocrystals (CNCs). The properties of the hydrogels have been investigated by rheology, electron microscopy, and spectroscopy with respect to variation in the temperature, time, and CNC concentration used in preparation. Desulfation of the CNCs at high temperature appears to be responsible for the gelation of the CNCs, giving highly porous networks. The viscosity and storage modulus of the gels was shown to increase when samples were prepared at higher treatment temperature. Considering the wide natural abundance and biocompatibility of CNCs, this simple, green approach to CNC-based hydrogels is attractive for producing materials that can be used in drug delivery, insulation, and as tissue scaffolds.

This chapter describes various emerging and potential biomedical applications of molecular gels, focusing on three main areas: drug delivery, tissue engineering and three-dimensional (3D) cell culture. Before discussing these in details, the generic benefits of using molecular gels for medical applications are discussed with focus on their ability to mimic the extracellular matrix (ECM). The first main area to be covered is then the use of molecular gels in drug delivery which again can be divided into three main categories; passive release of drugs from molecular gels, enzyme-trigged release and therapeutic molecular gels where the gelator molecule itself is the active drug. In all these cases the emphasis is on examples that have been tested or demonstrated in cell cultures (in vitro) or live animals (in vivo). The second main area concerns the use of molecular gels in tissue engineering highlighting successful examples of the how molecular gels can promote and direct the activity of stem cells to repair damaged tissues. The final main area discussed in this chapter is the development of 3D cell culture based on molecular gels. This emerging field illustrates well the advantages that molecular gels have in terms of chemical purity, synthetic ease and diversity, combined with their ECM mimicking ability, in comparison with polymeric or biologically sourced competing 3D cell culture models. The chapter concludes with some examples of emerging trends in the area and a discussion on what the future outlook is for the use of molecular gels in biomedicine.