Injectable Hydrogels Based on Inter-Polyelectrolyte Interactions between Hyaluronic Acid, Gelatin, and Cationic Cellulose Nanocrystals

The present work dealt with the development of physically cross-linked injectable hydrogels with potential applications in tissue engineering. The hydrogels were composed of a ternary mixture of a polyanion and a polyampholyte, hyaluronic acid (HA) and gelatin, respectively, bridged by cationic cellulose nanocrystals (cCNCs). A 3D network is formed by employing attractive electrostatic interactions and hydrogen bonding between these components under physiological conditions. The hydrogels demonstrated low viscosity at high stresses, enabling easy injection, structural stability at low stresses (<15 Pa), and nearly complete structure recovery within several minutes. Increasing the cCNC content (>3%) reduced hydrogel swelling and decelerated the degradation in phosphate-buffered saline as compared to that in pure HA and HA-gelatin samples. Biological evaluation of the hydrogel elutions showed excellent cell viability. The proliferation of fibroblasts exposed to elutions of hydrogels with 5% cCNCs reached ∼200% compared to that in the positive control after 11 days. Considering these results, the prepared hydrogels hold great potential in biomedical applications, such as injectable dermal fillers, 3D bioprintable inks, or 3D scaffolds to support and promote soft tissue regeneration.

Electrostatically crosslinked cellulose nanocrystal and polyelectrolyte complex sponges with pH responsiveness

This work focuses on the development of a responsive sponge made of an anionic cellulose nanocrystal (CNC) skeleton that is electrostatically crosslinked by a pH-responsive poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) polyelectrolyte complex (PEC). The results prove the formation of a global percolated network comprised of disordered CNC rods crosslinked by PEC clusters. The bulk density of the freeze-dried CNC-PEC sponges increases from 35 to 93 mg/cm³ with PEC concentration, while the compression modulus of dry specimens increases from 7 up to 62 kPa. At the lowest PEC concentration of 1 wt%, at pH 2.0, the compression modulus decreases to 0.9 kPa, whereas at pH 5.5, it increases to 42 kPa. The intensive complexation between sponge constituents is also reflected in a reduced ability to bind charged dyes at neutral pH values. Decreasing the pH results in an increased adsorption efficiency for anionic dyes, while raising the pH improves the cationic dye adsorption.

Modulating the Structural Orientation of Nanocellulose Composites through Mechano-Stimuli

It is of great interest to dynamically manipulate the optical property by controlling nanostructures under external stimuli. In this work, chiral photonic cellulose nanocrystal (CNC) and elastic polyurethane (PU) composite films demonstrate reversible optical tunability arising from structural transition between the chiral nematic and layered pseudonematic order. The composite films exhibit impressive water resistance and mechanical adaptability. Reversible modulation of the optical property of the composite CNC/PU film is enabled during mechanical stretching and water absorption. Film stretching is accompanied by CNC transition from a chiral nematic to layered pseudonematic structure. After fixation, shape recovery takes place when exposed to water, and the CNC structure reverts to the initial chiral nematic order. These reversibly switchable shape and optical properties further advance the study and design of smart optical and mechanical sensors.

Structure and Rheology of Polyelectrolyte Complexes in the Presence of a Hydrogen-Bonded Co-Solvent

Intermolecular interactions as well as macromolecular conformation affect the rheological and microstructural properties of polyelectrolyte complexes (PECs) solutions. The properties of semi-dilute solutions of weakly charged PECs can be controlled by the degree of ionization and solvent composition. In this work, we examined the effect of ethanol as a co-solvent on PECs composed of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) at low pH. The aqueous PECs solution was turbid, indicating formation of large aggregates, whereas PECs solution in water/ethanol (60:40 w/w) was transparent, implying no aggregation, and demonstrated higher relative viscosity than the aqueous solution, implying pronounced network formation. Imaging PECs solution by transmission electron microscopy (TEM) demonstrated aggregation, whereas the solution prepared with the mixed solvent revealed almost no phase contrast. Small-angle X-ray scattering (SAXS) of PECs in the aqueous solution indicated the presence of aggregates, while PECs in mixed solvent demonstrated a swelled macromolecular conformation with diminished aggregation. PECs with no ionic interactions in the mixed solvent assumes a homogenous network structure, which enables PECs solution processing by electrospinning.

Controlled Assembly of Nanocellulose-Stabilized Emulsions with Periodic Liquid Crystal-in-Liquid Crystal Organization

Colloidal particles combined with a polymer can be used to stabilize an oil-water interface forming stable emulsions. Here, we described a novel liquid crystal (LC)-in-LC emulsion composed of a nematic oil phase and a cholesteric or nematic aqueous cellulose nanocrystal (CNC) continuous phase. The guest oil droplets were stabilized and suspended in liquid-crystalline CNCs, inducing distortions and topological defects inside the host LC phase. These emulsions exhibited anisotropic interactions between the two LCs that depended on the diameter-to-pitch ratio of suspended guest droplets and the host CNC cholesteric phase. When the ratio was high, oil droplets were embedded into a cholesteric shell with a concentric packing of CNC layers and took on a radial orientation of the helical axis. Otherwise, discrete surface-trapped LC droplet assemblies with long-range ordering were obtained, mimicking the fingerprint configuration of the cholesteric phase. Thus, the LC-in-LC emulsions presented here define a new class of ordered soft matter in which both nematic and cholesteric LC ordering can be well-manipulated.

Structure Evolution and Drying Dynamics in Sliding Cholesteric Cellulose Nanocrystals

The study of colloidal liquid crystals (LCs) reveals fundamental insights into the nature of ordered materials, giving rise to emergent properties with fascinating applications in soft matter nanotechnology. Here we investigate the shape instabilities, layer undulations, dynamic assembly, and collective behaviors in evaporating a cellulose nanocrystal-based cholesteric LC drop. During the drying process, the drop edges are pinned to the substrate with spontaneous convective flow occurring along the drop, which leads to nonequilibrium sliding of the individual cholesteric fragment with active ordering as well as hydrodynamic fluctuations and flow transitions in the bulk cholesteric phase.

Structural Transition in Liquid Crystal Bubbles Generated from Fluidic Nanocellulose Colloids

The structural transition in micrometer-sized liquid crystal bubbles (LCBs) derived from rod-like cellulose nanocrystals (CNCs) was studied. The CNC-based LCBs were suspended in nematic or chiral nematic liquid-crystalline CNCs, which generated topological defects and distinct birefringent textures around them. The ordering and structure of the LCBs shifted from a nematic to chiral nematic arrangement as water evaporation progressed. These packed LCBs exhibited a specific photonic cross-communication property that is due to a combination of Bragg reflection and bubble curvature and size.

Colloidally stable novel copolymeric system for gene delivery in complete growth media

Novel cationic pentablock copolymers based on poly(2-diethylaminoethylmethacrylate) (PDEAEM) and Pluronic F127 were evaluated as non-viral gene delivery vectors from a physiochemical point of view for stability and transfection efficiency in complete growth media. A novel strategy was introduced to sterically stabilize the polyplexes of such Pluronic-based cationic polymers against aggregation with serum proteins. As cationic pentablock copolymers condense plasmid DNA into nanoplexes of 100-150 nm diameter, unmodified Pluronic added to the formulation self-assemble with the pentablock copolymers on the surface of polyplexes and shield the cationic PDEAEM chains of pentablock copolymers sterically with its long poly(ethyleneoxide) chains. These coated polyplexes formed colloidally stable dispersions of 150-250 nm diameter in serum-supplemented buffers. Cryo-TEM micrographs also showed that coating polyplexes with unmodified Pluronic reduced aggregation in serum proteins. Pentablock copolymers preserved the integrity of plasmid DNA condensed inside the polyplexes and provided efficient resistance to its degradation by nucleases. Though the total amount of DNA retained by ExGen 500 polyplexes after nuclease digestion was more than that retained by pentablock copolymers, the amount of plasmid retained in supercoiled form was not significantly different. Polyplexes coated with unmodified Pluronic provided efficient transfection in SKOV3 cells in complete growth media, comparable to that provided by ExGen 500 in terms of number of cells transfected, and one order less in terms of total transgene protein expressed. These sterically shielded polyplexes also exhibited much lower cytotoxicities than uncoated polyplexes of pentablock copolymers, and significantly lower than the cytotoxicity of ExGen 500 at relevant concentrations. This colloidally stable, versatile, multi-component gene delivery system also forms thermo-reversible injectable hydrogels like Pluronics at physiological temperatures that can be used for sustained delivery of polyplexes, and is promising for systemic applications.