A novel method for hydrogel nanostructuring

An Electroconductive, Thermosensitive, and Injectable Chitosan/Pluronic/Gold-Decorated Cellulose Nanofiber Hydrogel as an Efficient Carrier for Regeneration of Cardiac Tissue

Myocardial infarction is a major cause of death worldwide and remains a social and healthcare burden. Injectable hydrogels with the ability to locally deliver drugs or cells to the damaged area can revolutionize the treatment of heart diseases. Herein, we formulate a thermo-responsive and injectable hydrogel based on conjugated chitosan/poloxamers for cardiac repair. To tailor the mechanical properties and electrical signal transmission, gold nanoparticles (AuNPs) with an average diameter of 50 nm were physically bonded to oxidized bacterial nanocellulose fibers (OBC) and added to the thermosensitive hydrogel at the ratio of 1% w/v. The prepared hydrogels have a porous structure with open pore channels in the range of 50−200 µm. Shear rate sweep measurements demonstrate a reversible phase transition from sol to gel with increasing temperature and a gelation time of 5 min. The hydrogels show a shear-thinning behavior with a shear modulus ranging from 1 to 12 kPa dependent on gold concentration. Electrical conductivity studies reveal that the conductance of the polymer matrix is 6 × 10−2 S/m at 75 mM Au. In vitro cytocompatibility assays by H9C2 cells show high biocompatibility (cell viability of >90% after 72 h incubation) with good cell adhesion. In conclusion, the developed nanocomposite hydrogel has great potential for use as an injectable biomaterial for cardiac tissue regeneration.

Visualization of supramolecular structure of Pluronic F127 micellar hydrogels using cryo-TEM

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Visualization of individual Pluronic® F127 micelles in hydrogels.

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Supramolecular structure evolution of micellar hydrogels as a function of concentration.

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Plunge-freezing of high viscosity solutions.

Pluronic® F127 micellar hydrogels are of growing interest to the biomedical field due to their versatility as drug delivery systems. Pluronic® F127 is a symmetric and amphiphilic triblock copolymer which in aqueous medium self-assembles into micelles that pack togetherwith increasing temperature or concentration, leading to non-flowable hydrogels. The microstructure of these hydrogels is usually investigated by small-angle X-ray scattering, which is not a readily available technique. Conversely, cryo-TEM is a widespread technique used for investigating the morphology of aqueous systems. In the case of Pluronic® F127 micellar systems, the elevated viscosity poses a significant challenge for specimen preparation and, consequently, for cryo-TEM observation. Herein, we show a trustworthy, inexpensive and readily available methodology for preparing specimens of highly viscous micellar solutions and non-flowable hydrogels using an automated vitrification system. With this methodology we were able to visualize not only the morphology of individual Pluronic® F127 micelles -but also the supramolecular structure evolution as a function of concentration. This methodology opens up a wide range of opportunities for hydrogel characterization, although additional systematic studies might be required in order to optimize and replicate it for similar systems.

Fibrinogen-Based Hydrogel Modulus and Ligand Density Effects on Cell Morphogenesis in Two-Dimensional and Three-Dimensional Cell Cultures

There is a need to further explore the convergence of mechanobiology and dimensionality with systematic investigations of cellular response to matrix mechanics in 2D and 3D cultures. Here, a semisynthetic hydrogel capable of supporting both 2D and 3D cell culture is applied to investigate cell response to matrix modulus and ligand density. The culture materials are fabricated from adducts of polyethylene glycol (PEG) or PluronicF127 and fibrinogen fragments, formed into hydrogels by free-radical polymerization, and characterized by shear rheology. Control over the modulus of the materials is accomplished by changing the concentration of synthetic PEG-diacrylate crosslinker (0.5% w/v), and by altering the molecular length of the PEG (10 and 20 kDa). Control over ligand density is accomplished by changing fibrinogen concentrations from 3 to 12 mg mL^-1 . In 2D culture, cell motility parameters, including cell speed and persistence time are significantly increased with increasing modulus. In both 2D and 3D culture, cells express vinculin and there is evidence of focal adhesion formation in the high stiffness materials. The modulus- and ligand-dependent morphogenesis response from the cells in 2D culture is contradictory to the same measured response in 3D culture. In 2D culture, anchorage-dependent cells become more elongated and significantly increase their size with increasing ligand density and matrix modulus. In 3D culture, the same anchorage-dependent cells become less spindled and significantly reduce their size in response to increasing ligand density and matrix modulus. These differences arise from dimensionality constraints, most notably the encapsulation of cells in a non-porous hydrogel matrix. These insights underscore the importance of mechanical properties in regulating cell morphogenesis in a 3D culture milieu. The versatility of the hydrogel culture environment further highlights the significance of a modular approach when developing materials that aim to optimize the cell culture environment.

Temperature-Responsive Smart Nanocarriers for Delivery Of Therapeutic Agents: Applications and Recent Advances

Smart drug delivery systems (DDSs) have attracted the attention of many scientists, as carriers that can be stimulated by changes in environmental parameters such as temperature, pH, light, electromagnetic fields, mechanical forces, etc. These smart nanocarriers can release their cargo on demand when their target is reached and the stimulus is applied. Using the techniques of nanotechnology, these nanocarriers can be tailored to be target-specific, and exhibit delayed or controlled release of drugs. Temperature-responsive nanocarriers are one of most important groups of smart nanoparticles (NPs) that have been investigated during the past decades. Temperature can either act as an external stimulus when heat is applied from the outside, or can be internal when pathological lesions have a naturally elevated termperature. A low critical solution temperature (LCST) is a special feature of some polymeric materials, and most of the temperature-responsive nanocarriers have been designed based on this feature. In this review, we attempt to summarize recent efforts to prepare innovative temperature-responsive nanocarriers and discuss their novel applications.