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The oral delivery of macromolecular therapeutics to the intestinal tract requires novel, robust, and controlled formulations. Here, we report on fabrication by molding of composite hydrogel cylinders made of cellulose nanocrystals (CNCs) and chitosan (Cht) and their performance as delivery vehicles. CNCs provide excellent mechanical and chemical stress resistance, whereas Cht allows scaffold degradation by enzyme digestion. The release of a representative medium size protein (bovine serum albumin) dispersed in the hydrogel is slow and shows a sigmoidal profile; meanwhile, the hydrogel scaffold degrades according to a preferred route, that is the cylinder is eroded along the vertical axis. The cup-like, scarcely interconnected porous network, with a gradient of hardness along the cylinder axis, and the compact skin-like layer covering the lateral wall which stayed in contact with the mold during gelification, explain the preferred erosion direction and the long-term protein release. The possible effect of the molding process on hydrogel structure suggests that molding could be a simple and cheap way to favor surface compaction and directional scaffold degradation.

With the purpose of designing active patches for photodynamic therapy of melanoma, transparent and soft hydrogel membranes (HMs) have been fabricated by cation-induced gelation of rod-like cellulose nanocrystals (CNCs) bearing negatively charged carboxylic groups. Na+ , Ca2+ , Mg2+ have been used as cross-linkers of cellulose nanocrystal (CNC). The biosafety of this material and of its precursors has been evaluated in vitro in cell cultures. Morphological changes, cell organelles integrity, and cell survival with the tetrazolium salt reduction (MTT) assay were utilized as tests of cytotoxicity. Preliminary investigation was performed by addition of the hydrogel components to the cell culture medium and by incubations of the CNC-HM in direct and indirect contact with a confluent monolayer of A375 melanoma cells. Direct contact assays suffered from interference of physical stress. Careful evaluation of cytotoxicity was obtained considering the overall picture provided by microscopy and biochemical tests performed with the CNC-HM in indirect contact with two melanoma cell lines (A375, M14) and human fibroblasts. CNCs have been demonstrated to be a safe precursor material and CNC-HMs have a good biocompatibility provided that the excess of cations, in particular of Ca2+ is removed. These results indicate that CNC and can be safely used to fabricate biomedical devices such as transparent hydrogel patches, although attention must be paid to the fabrication procedure.

The influence of the physical, rheological, and process parameters on the cellulose nanocrystal (CNC) drops before and after external gelation in a CaCl2 solution was investigated. The dominant role of the CNC’s colloidal suspension properties, such as the viscous force, inertial, and surface tension forces in the fluid dynamics was quantitatively evaluated in the formation of drops and jellified beads. The similarity and difference between the behavior of carbohydrate polymers and rod-like crystallites such as CNC were enlightened. Pump-driven and centrifugally-driven external gelation approaches were followed to obtain CNC hydrogel beads with tunable size and regular shape. A superior morphological control—that is, a more regular shape and smaller dimension of the beads—were obtained by centrifugal force-driven gelation. These results suggest that even by using a simple set-up and a low-speed centrifuge device, the extrusion of a colloidal solution through a small nozzle under a centrifugal field is an efficient approach for the production of CNC hydrogel beads with good reproducibility, control over the bead morphology and size monodispersion.

Bilayer membranes for food packaging applications were prepared by depositing on polylactic acid (PLA) substrates pure cellulose nanofibers' (CNF) coatings and nanocomposite coatings made of CNF with dispersed TiO2 nanoparticles. The gas barrier properties of the bilayer membranes were studied by gas phase permeation technique using CO2, N2, D2, He and ambient air as test gases. Few micrometer thick pure and nanocomposite CNF coatings act as effective gas permeation barriers impeding the CO2, N2 and O2 transport and reducing the He and D2 transport rates by 3 orders of magnitude when compared with the PLA substrate. Gas transport through the coatings obeys the solution-diffusion mechanism: D2 permeation process shows activation energy values of 44 ± 6 kJ/mol and 40 ± 6 kJ/mol in the pure and nanocomposite CNF coating, respectively. The addition of the TiO2 nanoparticles reduces the penetrant diffusivity by increasing the tortuosity of the penetrant migration path but does not affect the gas barrier performances. UV–Vis spectroscopy analyses show that the optical transparency of the PLA support is slightly decreased by the CNF coating: at 600 nm the optical transmittance decreases, in fact, from 95% to 91%. TiO2 nanoparticles strongly absorb UV radiation and slightly reduce the PLA transparency in the optical range due to light scattering effects.

We have studied the kinetics of gas transport through films made of self-assembled cellulose nanofibrils (CNF) by a time-resolved mass spectroscopy technique. Few micrometers thick films deposited on polylactic acid (PLA) substrates act as impermeable barriers for CO2, O2, and N2 and reduce the 2H2 (deuterium) and He permeation flux by a factor of ∼103 with respect to the uncoated substrate. Penetrant transport is controlled by the solution-diffusion mechanism and the coating acts as a diffusive barrier. 2H2 and He diffusivity values are in the 10–10 and 10–9 cm2 s–1 range, respectively, and their migration occurs by thermally activated process with 39 ± 1 and 33 ± 2 kJ mol–1 activation energy. Positron annihilation lifetime spectroscopy analysis indicates that the diffusive path between the packed nanofibrils consists of elongated cavities with cross-sectional size ∼ 0.31 nm. Results evidence that the selective transport of the small size penetrants is due to sieving effects and that small penetrant tran...

In this study we investigated the fabrication of small hydrogel objects by the coordination-driven assembly of supramolecular rod-like crystallites of nanocellulose, using ionotropic gelation as a methodological approach and Ca2+ as a gelling agent. We proved that the gelation process is diffusion-mediated and fitting the equations modelling this process to the profile of the Ca2+ front, a Ca2+ diffusion coefficient in the incipient hydrogel of (4.5 ± 1.1) × 10−6 cm2 s−1 was calculated. At the steady-state a spatially homogeneous distribution of Ca2+-crosslinked sites in the hydrogel network was observed. External ionotropic gelation produced beads, wires or disks, while core–shell capsules were obtained by inverse ionotropic gelation. We demonstrated that equilibrium and dynamics of the distribution of Ca2+ offer the opportunity to design precisely the size and shape of these small hydrogel objects. In particular, the core size and the shell thickness of the capsules can be tailored under kinetic controlled conditions. The proposed approach, with supramolecular structures of the natural source as assembling components and the water-in-water fabrication process, is fast, simple, and requires only sustainable chemistry and is easily implementable in automatic microfluidic platforms.

Sol-gel transition of carboxylated cellulose nanocrystals has been investigated using rheology, SAXS, NMR and optical spectroscopies to unveil the distinctive roles of ultrasound treatments and addition of various cations. Besides cellulose fiber fragmentation, sonication treatment induces fast gelling of the solution. The gelation is independent of the addition of cations, while the final rheological properties are highly influenced by the type, concentration and sequence of the operations since the cations must be added prior to sonication to produce stiff gels. The gel elastic modulus was found to increase proportionally to the ionic charge rather than the cationic size. In cases where ions were added after sonication, SAXS analysis of the Na+ hydrogel and Ca2+ hydrogel indicated the presence of structurally ordered domains in which water is confined, and 1H-NMR investigation showed the dynamics of water exchange within the hydrogels. Conversely, separated phases containing essentially free water were characteristic of the hydrogels obtained by sonication after Ca2+ addition, confirming that this ion induces irreversible fiber aggregation. The rheological properties of the hydrogels depend on the duration of the ultrasound treatments, enabling the design of programmed materials with tailored energy dissipation response.

Flexible optoelectronics has emerged as an outstanding platform to pave the road toward vanguard technology advancements. As compared to conventional rigid substrates, a flexible technology enables mechanical deformation while maintaining stable performance. The advantages include not only the development to novel applications, but also the implementation of a wearable technology directly in contact with a curved surface. Here the monolithic integration of a perovskite‐based optical waveguide amplifier together with a photodetector on a nanocellulose substrate is shown to demonstrate the feasibility of a stretchable signal manipulation and receptor system fabricated on a biodegradable material. An integrated optical amplifier–photodetector is developed in which the photocurrent is exploited that is generated in the organic–inorganic lead halide perovskite under an applied bias. Such photocurrent does not minimally perturb the amplifier operation and is used to monitor the light signal propagating along the waveguide, opening a broad range of applications for example to regulate the operation temperature.

The design of materials capable of mechanical responses to physical and chemical stimuli represents one of the most exciting and challenging areas of scientific research because of the huge number of their potential applications. This article is focused on the molecular events occurring in thin films of carboxylated nanocellulose fibers, which are capable of converting water gradients into mechanical movements at the macroscopic scale. The analysis of the mechano-actuation, and of the conditions to obtain it, shows that the film movement is fast and reproducible, the gradient intensity is transduced into rate of displacement, and the response is observed at vapor pressures as low as 1.2 mm Hg. The actuation mechanism is associated to an efficient and reversible water sorption process by the hydrophilic nanocellulose fibers at the film interface. Conversely, water desorption is slow and follows a kinetic behavior supporting the presence of two binding sites for water molecules. The adsorbed water induces swelling of the surface nanocellulose layers and local structural rearrangement, however transitions between ordered and random coil conformations are not observed. The understanding of the actuation mechanisms of nanocellulose offers exciting opportunities to design macroscopic structures responding to chemical gradients by the assembly of simple molecular components.