Printable Alginate Hydrogels with Embedded Network of Halloysite Nanotubes: Effect of Polymer Cross-Linking on Rheological Properties and Microstructure

Bioinspired Bioinks for the Fabrication of Chemomechanically Relevant Standalone Disease Models of Hepatic Steatosis

Hepatotoxicity-related issues are poorly predicted during preclinical experimentation, as its relevance is limited by the inadequacy to screen all the non-physiological subclasses of the population. These pitfalls can be solved by implementing complex in vitro models of hepatic physiology and pathologies in the preclinical phase. To produce these platforms, extrusion-based bioprinting is focused on, since it allows to manufacture tridimensional cell-laden constructs with controlled geometries, in a high-throughput manner. Different bioinks, whose formulation is tailored to mimic the chemomechanical environment of hepatic steatosis, the most prevalent hepatic disorder worldwide, are proposed. Internally crosslinked alginate hydrogels are chosen as structural components of the inks. Their viscoelastic properties (G' = 512-730 Pa and G″ = 94-276 Pa, depending on frequency) are tuned to mimic those of steatotic liver tissue. Porcine hepatic ECM is introduced as a relevant biochemical cue. Sodium oleate is added to recall the accumulation of lipids in the tissue. Downstream analyses on 14-layered bioprinted structures cultured for 10 days reveal the establishment of steatotic-like features (intracellular lipid vesicles, viability decrease up to ≈50%) without needing external conditionings. The presented bioinks are thus suitable to fabricate complex models of hepatic steatosis to be implemented in a high-throughput experimental frame.

[Bioprinting technologies in ophthalmology]

Bioprinting allows additive fabrication of bioengineered constructs with defined two- or three-dimensional organization using live cells, biopolymers and other materials. This article reviews main bioprinting technologies and their capabilities in clinical and experimental ophthalmology. Analysis of literature sources helped reveal and describe the main types of bioprinting technologies: inkjet, laser-assisted, and extrusion. Extrusion bioprinting is the most widely used method, providing the ability to use various types of bioinks and a wide range of cell concentrations. The following materials can be used as the base for bioinks: alginate, collagen, gelatin, hyaluronic acid, chitosan, fibrin, as well as their different combinations. These materials can be modified for best bioprinting properties by adding various functional groups. The major directions of application of bioprinting technologies in ophthalmology are tissue engineering for regenerative medicine and fabrication of model systems for fundamental and preclinical studies. Experiments in creating a bioprinted cornea are being conducted in the field of regenerative medicine. Furthermore, there are studies on fabricating retinal tissue equivalents, although tissue engineering of this structure is a task of great complexity. Model systems, which can be fabricated by bioprinting, are represented by tissue equivalents of ocular structures and the appendages of the eye, as well as by microphysiological organ-on-a-chip systems. Another promising application of bioprinting is fabrication of biocompatible implantable electrode arrays for visual neuroprostheses.

Keratin/alginate hybrid hydrogels filled with halloysite clay nanotubes for protective treatment of human hair

Keratin/alginate hydrogels filled with halloysite nanotubes (HNTs) have been tested for the protective coating of human hair. Preliminary studies have been conducted on the aqueous colloidal systems and the corresponding hydrogels obtained by using Ca²⁺ ions as crosslinkers. Firstly, we have investigated the colloidal properties of keratin/alginate/HNTs dispersions to explore the specific interactions occurring between the biomacromolecules and the nanotubes. Then, the rheological properties of the hydrogels have been studied highlighting that the keratin/alginate interactions and the subsequent addition of HNTs facilitate the biopolymer crosslinking. Finally, human hair samples have been treated with the hydrogel systems by the dipping procedure. The protection efficiency of the hydrogels has been evaluated by studying the tensile properties of hair fibers exposed to UV irradiation. In conclusion, keratin/alginate hydrogel filled with halloysite represents a promising formulation for hair protective treatments due to the peculiar structural and rheological characteristics.

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.

Anionic exopolysaccharide from Cryptococcus laurentii 70766 as an alternative for alginate for biomedical hydrogels

Alginates are widely used polysaccharides for biomaterials engineering, which functional properties depend on guluronic and mannuronic acid as the building blocks. In this study, enzymatically crosslinked hydrogels based on sodium alginate (Na-Alg) and the exopolysaccharide (EPS) derived from Cryptococcus laurentii 70766 with glucuronic acid residues were synthesized and characterized as a new potential source of polysaccharide for biomaterials engineering. The EPS was extracted (1.05 ± 0.57 g/L) through ethanol precipitation. Then the EPS and Na-Alg were functionalized with tyramine hydrochloride to produce enzymatically crosslinked hydrogels in the presence of horseradish peroxidase (HRP) and H₂O₂. Major characteristics of the hydrogels such as gelling time, swelling ratio, rheology, cell viability, and biodegradability were studied. The swelling ratio and degradation profile of both hydrogels showed negative values, indicating an increased crosslinking degree and a lower water uptake percentage. The EPS hydrogel showed similar gelation kinetics compared to the Alg hydrogel. The EPS and its hydrogel were found cytocompatible. The results indicate the potential of EPS from C. laurentii 70766 for biomedical engineering due to its biocompatibility and degradability. Further studies are needed to confirm this EPS as an alternative for Alg in tissue engineering applications, particularly in the development of wound dressing products.

Modulation of Molecular Structure and Mechanical Properties of κ-Carrageenan-Gelatin Hydrogel with Multi-Walled Carbon Nanotubes

Hydrogels, three-dimensional hydrophilic water-insoluble polymer networks having mechanical properties inherent for solids, have attracted continuous research attention over a long time period. Here, we studied the structure and properties of hydrogel based on gelatin, κ-carrageenan and CNTs using the combination of SAXS, PXRD, AFM microscopy, SEM and rheology methods. We have shown that the integration of polysaccharide and protein in the composite hydrogel leads to suppression of their individual structural features and homogenization of two macromolecular components into a single structural formation. According to obtained SAXS results, we observed the supramolecular complex, which includes both polysaccharide and protein components associated with each other. It was determined that hydrogel structure formed in the initial solution state (dispersion) retains hydrogel supramolecular structure under its cooling up to gel state. The sizes of dense cores of these polyelectrolyte complexes (PEC) slightly decrease in the gel state in comparison with PEC water dispersion. The introduction of CNTs to hydrogel does not principally change the type of supramolecular structure and common structural tendencies observed for dispersion and gel states of the system. It was shown that carbon nanotubes embedded in hydrogel act as the supplementary template for formation of the three-dimensional net, giving additional mechanical strengthening to the studied system.

Printable Hydrogels Based on Alginate and Halloysite Nanotubes

The design of hydrogels for the controlled release of active species is an attractive challenge. In this work, we prepared hybrid hydrogels composed of halloysite nanotubes as the inorganic component, and alginate as the organic counterpart. The reported procedure allowed us to provide the resulting materials with a peculiar wire-like shape. Both optical and scanning electron microscopy were used to characterize the morphological properties of the hydrogel wires, whose diameters were ca. 0.19 and 0.47 mm, respectively. The possibility to be exploited as drug delivery systems was carried out by loading the nanoclay with salicylic acid and by studying the release profiles. Thermogravimetric experiments showed that the amount of encapsulated drug was 4.35 wt%, and the salicylic acid was thermally stabilized after the loading into the nanotubes, as observed by the shift of the degradation peak in the differential thermograms from 193 to 267 °C. The kinetics investigation was conducted using UV–Vis spectrophotometry, and it exhibited the profound effects of both the morphology and dimensions on the release of the drugs. In particular, the release of 50% of the payload occurred in 6 and 10 h for the filiform hydrogels, and it was slower compared to the bare drug-loaded halloysite, which occurred in 2 h. Finally, an induction period of 2 h was observed in the release profile from the thicker sample.