Mechanics of gelatin-based hydrogels during finite strain tension, compression and shear

Easily injectable gelatin-nonanal hydrogel for endoscopic resectioning of gastrointestinal polyps

The use of submucosal injection is crucial for satisfactory submucosal elevation in the early resection of flat polyps originating from the gastrointestinal tract (GIT). Injectable hydrogels derived from natural polypeptides are attractive candidates due to their excellent biocompatibility and easy gelation properties. However, most of the reported hydrogels are not the class of catheter delivery materials due to quick gelation, high inherent viscosity, and injection clogging. This study presents a novel injectable shear-thinning hydrogel platform of small molecules (nonanal) modified gelatin polymer, which offers a promising submucosal injection for effective removal of polyps from GIT. Physicochemical characterizations of hydrogel demonstrate the suitable features as an effective submucosal injection, including shear thinning property, self-assembly, methylene blue dye encapsulation, flow behavior, stability, syringeability (18 G, 21 G, and 24 G needles) and fibrous morphology. Ex vivo investigations of developed submucosal formulation on goat intestines demonstrate the enhanced visibility of cushions and the ability to produce stable, long-lasting cushions of about 8.07 mm up to ∼60 min of submucosal injection. The rapid blood clotting behavior of hydrogel was observed in about 120 s without compromising hemocompatibility with the hemolysis of about 3.77 % only. In vitro biocompatibility of the hydrogel was also verified using the HepG2 and nHDF cells. In vivo study depicts desirable biocompatibility, a non-toxic organ profile, and optimal cushion height in mice models. Studies established the foundation of novel submucosal fluid to improve the therapeutic outcomes of early resection for gastrointestinal polyps.

Formation of hen egg white lysozyme derived amyloid-based hydrogels using different gelation agents: A potential tool for drug delivery

Amyloids are highly stable protein fibrillar aggregates that get deposited in various parts of our body and cause detrimental diseases. But in nature, the presence of functional amyloids is also noted in bacteria that help them by forming hyphae, biofilm, protein reservoirs, signalling messengers, etc. Keeping this perspective in mind, the idea behind this research was to develop functional amyloids in the form of hydrogel and analyse its potential in the biomedical sector as a drug-delivery tool. The synthesis and characterisation of three types of amyloid-based hydrogels have been reported in this work. Hen Egg-White Lysozyme (HEWL) protein was chosen as the principal ingredient as it is extensively used as a standard protein for studying amyloidogenesis and has inherent antibacterial properties. Comparative studies of different hydrogel properties exhibited variations in the hydrogels based on compositional differences in them. Finally, a drug release assay was done on the synthesized hydrogels to explore their potential as drug delivery tools.

Flow-induced oscillations of vocal-fold replicas with tuned extensibility and material properties

Human vocal folds are highly deformable non-linear oscillators. During phonation, they stretch up to 50% under the complex action of laryngeal muscles. Exploring the fluid/structure/acoustic interactions on a human-scale replica to study the role of the laryngeal muscles remains a challenge. For that purpose, we designed a novel in vitro testbed to control vocal-folds pre-phonatory deformation. The testbed was used to study the vibration and the sound production of vocal-fold replicas made of (i) silicone elastomers commonly used in voice research and (ii) a gelatin-based hydrogel we recently optimized to approximate the mechanics of vocal folds during finite strains under tension, compression and shear loadings. The geometrical and mechanical parameters measured during the experiments emphasized the effect of the vocal-fold material and pre-stretch on the vibration patterns and sounds. In particular, increasing the material stiffness increases glottal flow resistance, subglottal pressure required to sustain oscillations and vibratory fundamental frequency. In addition, although the hydrogel vocal folds only oscillate at low frequencies (close to 60 Hz), the subglottal pressure they require for that purpose is realistic (within the range 0.5-2 kPa), as well as their glottal opening and contact during a vibration cycle. The results also evidence the effect of adhesion forces on vibration and sound production.

Versatile fiber-reinforced hydrogels to mimic the microstructure and mechanics of human vocal-fold upper layers

Human vocal folds are remarkable soft laryngeal structures that enable phonation due to their unique vibro-mechanical performances. These properties are tied to their specific fibrous architecture, especially in the upper layers, which comprise a gel-like composite called lamina propria. The lamina propria can withstand large and reversible deformations under various multiaxial loadings. Despite their importance, the relationships between the microstructure of vocal folds and their resulting macroscopic properties remain poorly understood. There is a need for versatile models that encompass their structural complexity while mimicking their mechanical features. In this study, we present a candidate model inspired by histological measurements of the upper layers of human vocal folds. Bi-photonic observations were used to quantify the distribution, orientation, width, and volume fraction of collagen and elastin fibers between histological layers. Using established biomaterials, polymer fiber-reinforced hydrogels were developed to replicate the fibrillar network and ground substance of native vocal fold tissue. To achieve this, jet-sprayed poly(ε-caprolactone) fibrillar mats were successfully impregnated with poly(L-lysine) dendrimers/polyethylene glycol hydrogels. The resulting composites exhibited versatile structural, physical and mechanical properties that could be customized through variations in the chemical formulation of their hydrogel matrix, the microstructural architecture of their fibrous networks (i.e., fiber diameter, orientation and volume fraction) and their assembly process. By mimicking the collagen network of the lamina propria with polymer fibers and the elastin/ground substance with the hydrogel composition, we successfully replicated the non-linear, anisotropic, and viscoelastic mechanical behavior of the vocal-fold upper layers, accounting for inter/intra-individual variations. The development of this mimetic model offers promising avenues for a better understanding of the complex mechanisms involved in voice production. STATEMENT OF SIGNIFICANCE: Human vocal folds are outstanding vibrating soft living tissues allowing phonation. Simple physical models that take into account the histological structure of the vocal fold and recapitulate its mechanical features are scarce. As a result, the relations between tissue components, organisation and vibro-mechanical performances still remain an open question. We describe here the development and the characterization of fiber-reinforced hydrogels inspired from the vocal-fold microstructure. These systems are able to reproduce the mechanics of vocal-fold tissues upon realistic cyclic and large strains under various multi-axial loadings, thus providing a mimetic model to further understand the impact of the fibrous network microstructure in phonation.