Probing hydrogen bond interactions in a shear thickening polysaccharide using nonlinear shear and extensional rheology

An Innovative Methodology to Characterize, at the Molecular Scale, Interactions in Polysaccharide Aqueous Solutions

Characterizing molecular interactions at the microscopic level remains difficult and, therefore, represents a key target to better understand macromolecule and biomacromolecule behaviors in solution, alone, or in mixtures with others. Therefore, accurate characterization in liquid media, especially in aqueous solutions, without causing any perturbation of the system in which they are studied, is quite difficult. To this purpose, the present paper describes an innovative methodology based on fluorescence spectrophotometry. Two molecular fluorescent probes, namely 8-anilino-1-naphtalenesulfonic acid (ANS) and 2-benzofuryl-3-hydroxy-4(1H)-quinolone (3HQ-Bf), were selected to characterize, respectively, the dipole-dipole interactions and hydrophobic micro-domains, for the first one, and hydrogen bonding, for the second. As a support to study molecular interactions, xanthan, galactomannan, and corresponding mixtures of these substances which are well known to exhibit a synergy of interactions in well-defined mixture conditions were chosen. Once the methodology was set up, the existence of the three types of interactions in these systems was demonstrated, thus allowing the elucidation of the mechanisms of interactions at the molecular scale.

Does harvesting age matter? Changes in structure and rheology of a shear-thickening polysaccharide from Cyathea medullaris as a function of age

A shear-thickening polysaccharide from the New Zealand Black tree fern (Cyathea medullaris, commonly known as mamaku) extracted from different age fronds (stage 1: young, stage 2: fully grown and stage 3: old) was characterised in terms of structure and rheological properties. Constituent sugar analysis and 1H and 13C NMR revealed a repeating backbone of -4)-β-D-GlcpA-(1 → 2)-α-D-Manp-(1→, for all mamaku polysaccharide (MP) samples from different age fronds without any alterations in molecular structure. However, the molecular weight (Mw) was reduced with increasing age, from ~4.1 × 106 to ~2.1 × 106 Da from stage 1 to stage 3, respectively. This decrease in Mw (and size) consequently reduced the shear viscosity (ηs-Stage 1 > ηs-Stage 2 > ηs-Stage 3). However, the extent of shear-thickening and uniaxial extensional viscosity of MP stage 2 was greater than MP stage 1, which was attributed to a greater intermolecular interaction occurring in the former. Shear-thickening behaviour was not observed in MP stage 3.

Microrheological characterisation of Cyanoflan in human blood plasma

Naturally occurring polysaccharidic biopolymers released by marine cyanobacteria are of great interest for numerous biomedical applications, such as wound healing and drug delivery. Such polymers generally exhibit high molecular weight and an entangled structure that impact the rheology of biological fluids. However, biocompatibility tests focus not so much on rheological properties as on immune response. In the present study, the rheological behaviour of native blood plasma as a function of the concentration of a cyanobacterium biopolymer is investigated via multiple particle tracking microrheology, which measures the Brownian motion of probes embedded in a sample, and cryogenic scanning electron microscope microstructural characterisation. We use Cyanoflan as the biopolymer of choice, and profit from our knowledge of its chemical structure and its exciting potential for biotechnological applications. A sol-gel transition is identified using time-concentration superposition and the power-law behaviour of the incipient network's viscoelastic response is observed in a variety of microrheological data. Our results point to rheology-based principles for blood compatibility tests by facilitating the assignment of quantitative values to specific properties, as opposed to more heuristic approaches.

Shear Thickening Behavior in Injectable Tetra-PEG Hydrogels Cross-Linked via Dynamic Thia-Michael Addition Bonds

Injectable poly(ethylene glycol) (PEG)-based hydrogels were reversibly cross-linked through thia-conjugate addition bonds and demonstrated to shear thicken at low shear rates. Cross-linking bond exchange kinetics and dilute polymer concentrations were leveraged to tune hydrogel plateau moduli (from 60 to 650 Pa) and relaxation times (from 2 to 8 s). Under continuous flow shear rheometry, these properties affected the onset of shear thickening and the degree of shear thickening achieved before a flow instability occurred. The changes in viscosity were reversible whether the shear rate increased or decreased, suggesting that chain stretching drives this behavior. Given the relevance of dynamic PEG hydrogels under shear to biomedical applications, their injectability was investigated. Injection forces were found to increase with higher polymer concentrations and slower bond exchange kinetics. Altogether, these results characterize the nonlinear rheology of dilute, dynamic covalent tetra-PEG hydrogels and offer insight into the mechanism driving their shear thickening behavior.

Rheological Issues on Oropharyngeal Dysphagia

There is an increasing proof of the relevance of rheology on the design of fluids for the diagnosis and management of dysphagia. In this sense, different authors have reported clinical evidence that support the conclusion that an increase in bolus viscosity reduces the risks of airway penetration during swallowing. However, this clinical evidence has not been associated yet to the definition of objective viscosity levels that may help to predict a safe swallowing process. In addition, more recent reports highlight the potential contribution of bolus extensional viscosity, as elongational flows also develops during the swallowing process. Based on this background, the aim of this review paper is to introduce the lecturer (experts in Dysphagia) into the relevance of Rheology for the diagnosis and management of oropharyngeal dysphagia (OD). In this sense, this paper starts with the definition of some basic concepts on Rheology, complemented by a more extended vision on the concepts of shear viscosity and elongational viscosity. This is followed by a short overview of shear and elongational rheometrical techniques relevant for the characterization of dysphagia-oriented fluids, and, finally, an in-depth analysis of the current knowledge concerning the role of shear and elongational viscosities in the diagnosis and management of OD (shear and elongational behaviors of different categories of dysphagia-oriented products and contrast fluids for dysphagia assessment, as well as the relevance of saliva influence on bolus rheological behavior during the swallowing process).

How a sticky fluid facilitates prey retention in a carnivorous pitcher plant (Nepenthes rafflesiana)

Nepenthes pitcher plants grow in nutrient-poor soils and produce large pitfall traps to obtain additional nutrients from animal prey. Previous research has shown that the digestive secretion in N. rafflesiana is a sticky viscoelastic fluid that retains insects much more effectively than water, even after significant dilution. Although the retention of prey is known to depend on the fluid's physical properties, the details of how the fluid interacts with insect cuticle and how its sticky nature affects struggling insects are unclear. In this study, we investigated the mechanisms behind the efficient prey retention in N. rafflesiana pitcher fluid. By measuring the attractive forces on insect body parts moved in and out of test fluids, we show that it costs insects more energy to free themselves from pitcher fluid than from water. Moreover, both the maximum force and the energy required for retraction increased after the first contact with the pitcher fluid. We found that insects sink more easily into pitcher fluid than water and, accordingly, the surface tension of N. rafflesiana pitcher fluid was lower than that of water (60.2 vs. 72.3 mN/m). By analysing the pitcher fluid's wetting behaviour, we demonstrate that it strongly resists dewetting from all surfaces tested, leaving behind residual films and filaments that can facilitate re-wetting. This inhibition of dewetting may be a further consequence of the fluid's viscoelastic nature and likely represents a key mechanism underlying prey retention in Nepenthes pitcher plants. STATEMENT OF SIGNIFICANCE: Carnivorous Nepenthes pitcher plants secrete sticky viscoelastic fluids that prevent insects from escaping after falling into the pitcher. What physical mechanisms are responsible for the fluid's retentive function? First, insects sink and drown more readily in N. rafflesiana pitcher fluid due to its reduced surface tension. Second, once within the fluid, our force measurements show that it costs more energy to separate insects from pitcher fluid than from water. Third, the fluid strongly resists dewetting, making it harder for insects to extract themselves and covering their cuticle with residues that facilitate re-wetting. Such striking inhibition of dewetting may represent a previously unrecognised mechanism of prey retention by Nepenthes. Pitcher fluid fulfils a well-defined biological function and may serve as a model for studying the mechanics of complex fluids.

Food polysaccharides and roles of rheology and tribology in rational design of thickened liquids for oropharyngeal dysphagia: A review

In today's market environment, an aging society is recognized as one of the megatrends in the world. The demographic change in the world population age structure has driven a huge demand in healthcare products as well as services that include the technological innovation for the health and wellness of the elderly. Dysphagia or swallowing difficulty is a common problem in the elderly as many changes in swallowing function come with aging. The presence of a strong relationship between swallowing ability, nutritional status, and health outcomes in the elderly leads to the importance of dysphagia management in the population group. Modification of solid food and/or liquid is a mainstay of compensatory intervention for dysphagia patients. In this regard, texture-modified foods are generally provided to reduce risks associated with choking, while thickened liquids are recommended for mitigating risks associated with aspiration. In this review, we discuss thickened liquids and other issues including the importance of their rheological and tribological properties for oropharyngeal dysphagia management in the elderly. The review focuses on both commercial thickeners that are either based on modified starch or xanthan gum and other potential polysaccharide alternatives, which have been documented in the literature in order to help researchers develop or improve the characteristic properties of thickened liquids required for safe swallowing. Furthermore, some research gaps and future perspectives, particularly from the nutrition aspect related to the interaction between thickeners and other food ingredients, are suggested as such interaction may considerably control the rate of nutrient absorption and release within our body.

3D bioprinting of bicellular liver lobule-mimetic structures via microextrusion of cellulose nanocrystal-incorporated shear-thinning bioink

3D bioprinting of living cellular constructs with heterogeneity in cell types and extra cellular matrices (ECMs) matching those of biological tissues remains challenging. Here, we demonstrate that, through bioink material design, microextrusion-based (ME) bioprinting techniques have the potential to address this challenge. A new bioink employing alginate (1%), cellulose nanocrystal (CNC) (3%), and gelatin methacryloyl (GelMA) (5%) (namely 135ACG hybrid ink) was formulated for the direct printing of cell-laden and acellular architectures. The 135ACG ink displayed excellent shear-thinning behavior and solid-like properties, leading to high printability without cell damage. After crosslinking, the ACG gel can also provide a stiff ECM ideal for stromal cell growth. By controlling the degree of substitution and polymer concentration, a GelMA (4%) bioink was designed to encapsulate hepatoma cells (hepG2), as GelMA gel possesses the desired low mechanical stiffness matching that of human liver tissue. Four different versions of to-scale liver lobule-mimetic constructs were fabricated via ME bioprinting, with precise positioning of two different cell types (NIH/3T3 and hepG2) embedded in matching ECMs (135ACG and GelMA, respectively). The four versions allowed us to exam effects of mechanical cues and intercellular interactions on cell behaviors. Fibroblasts thrived in stiff 135ACG matrix and aligned at the 135ACG/GelMA boundary due to durotaxis, while hepG2 formed spheroids exclusively in the soft GelMA matrix. Elevated albumin production was observed in the bicellular 3D co-culture of hepG2 and NIH/3T3, both with and without direct intercellular contact, indicating that improved hepatic cell function can be attributed to soluble chemical factors. Overall, our results showed that complex constructs with multiple cell types and varying ECMs can be bioprinted and potentially useful for both fundamental biomedical research and translational tissue engineering.

Adsorption of enhanced oil recovery polymer, schizophyllan, over carbonate minerals

Schizophyllan is a natural polysaccharide that has shown great potential as enhanced oil recovery (EOR) polymer for high-temperature, high-salinity reservoirs. Nevertheless, the adsorption behavior of schizophyllan over carbonate minerals remains ambiguous element towards its EOR applications. Here, we investigate the adsorption of schizophyllan on different carbonate minerals. The effect of mineral type, salinity, and background ions on adsorption is analyzed. Our results indicate the adsorption capacity is higher on calcite and dolomite compared to silica and kaolin and the adsorption capacity decreases with salinity. Moreover, the adsorption kinetics follows pseudo-second order mechanism regardless of the mineral type. Adsorption over calcite is diminished in presence of water structure making ions and enhanced in presence of structure breaking ion and in presence of urea. Gel permeation chromatography results reveal the preferential adsorption of longer chains. The adsorption over carbonate minerals proceed via complex formation between polymer molecule and mineral surface.

Structure of Dense Adsorption Layers of Escin at the Air-Water Interface Studied by Molecular Dynamics Simulations

Saponins are natural surfactants with high surface activity and unique surface properties. Escin is a triterpenoid saponin which has unusually high surface viscoelasticity [Golemanov et al. Soft Matter 2013, 9, 5738] and low permittivity to molecular gas diffusion of its adsorption layers. In our previous study [Tsibranska et al. Langmuir 2017, 33, 8330], we investigated the molecular origin of this unconventional behavior and found that escin molecules rapidly assemble in a compact and stable surface cluster. This behavior was explained with long-range attraction between the hydrophobic aglycones combined with intermediate dipole-dipole attraction and strong short-range hydrogen bonds between the sugar residues in the adsorbed escin molecules. In this study, we performed atomistic molecular simulations of escin molecules in dense adsorption layers with two different areas per molecule. The results show that the surfactant molecules in these systems are much less submerged in water and adopt a more upright position compared to the dilute layers studied previously. A significant number of trapped water molecules are located around the hydrophilic groups placed above the water equimolecular surface to solvate them in the dense layer. To maintain the preferred orientation of the escin molecules with respect to the interface, the most compact adsorption layer acquires a significant spontaneous curvature. The substantial elasticity of the neutral escin layers, as in our previous study, is explained with the presence of a specific interaction, which is intermediate between hydrogen bonding and dipole-dipole attraction (populated lengths in the range 0.16 to >0.35 nm), supplemented by substantial flexibility of the surfactant heads, optimal curvature of the interface, and significant normal displacement of the molecules to allow their tight surface packing. The simulations reveal long-range order within the layers, which signifies the role of the collective behavior of the saponin molecules in such dense adsorption layers.

Polysaccharides from New Zealand Native Plants: A Review of Their Structure, Properties, and Potential Applications

Water-soluble, non-starch polysaccharides from plants are used commercially in a wide range of food and non-food applications. The increasing range of applications for natural polysaccharides means that there is growing demand for plant-derived polysaccharides with different functionalities. The geographical isolation of New Zealand and its unique flora presents opportunities to discover new polysaccharides with novel properties for a range of applications. This review brings together data published since the year 2000 on the composition and structure of exudate gums, mucilages, and storage polysaccharides extracted from New Zealand endemic land plants. The structures and properties of these polysaccharides are compared with the structures of similar polysaccharides from other plants. The current commercial use of these polysaccharides is reviewed and their potential for further exploitation discussed.

Influence of gas injection on viscous and viscoelastic properties of Xanthan gum

Xanthan gum is widely used as a model fluid for sludge to mimic the rheological behaviour under various conditions including impact of gas injection in sludge. However, there is no study to show the influence of gas injection on rheological properties of xanthan gum specifically at the concentrations at which it is used as a model fluid for sludge with solids concentration above 2%. In this paper, the rheological properties of aqueous xanthan gum solutions at different concentrations were measured over a range of gas injection flow rates. The effect of gas injection on both the flow and viscoelastic behaviour of Xanthan gum (using two different methods - a creep test and a time sweep test) was evaluated. The viscosity curve of different solid concentrations of digested sludge and waste activated sludge were compared with different solid concentrations of Xanthan gum and the results showed that Xanthan gum can mimic the flow behaviour of sludge in flow regime. The results in linear viscoelastic regime showed that increasing gas flow rate increases storage modulus (G'), indicating an increase in the intermolecular associations within the material structure leading to an increase in material strength and solid behaviour. Similarly, in creep test an increase in the gas flow rate decreased strain%, signifying that the material has become more resistant to flow. Both observed behaviour is opposite to what occurs in sludge under similar conditions. The results of both the creep test and the time sweep test indicated that choosing Xanthan gum aqueous solution as a transparent model fluid for sludge in viscoelastic regime under similar conditions involving gas injection in a concentration range studied is not feasible. However Xanthan gum can be used as a model material for sludge in flow regime; because it shows a similar behaviour to sludge.

A review of diet standardization and bolus rheology in the management of dysphagia

PURPOSE OF REVIEW

Texture modification is a widespread practice as a strategy for the management of dysphagia and can be very effective in individual cases. However, it is often performed in a qualitative, subjective manner and practices vary internationally according to multiple sets of national guidelines. This article aims to identify best practice by reviewing the theory and practice of texture modification, focussing on recent advances.

RECENT FINDINGS

Instrumental assessment of texture modification in vivo is challenging, and studies including rheology and perception have indicated that fluid viscosity is only one of many factors affecting texture modification in practice. Systematic reviews have identified a historical lack of high-quality clinical evidence, but recent controlled studies are beginning to identify positive and negative aspects of thickened fluids. Research and practice to date have been limited by the lack of control and standardization of foods and drinks. However in 2015 a not-for-profit organization, the International Dysphagia Diet Standardisation Initiative, has published a framework for texture modification from thin liquids to solid foods based on all the existing documentation and guidance, and the - limited - available clinical evidence.

SUMMARY

Rheology exists in the lab; however, normal practice is often subjective or lacking control and standardization. In the near future, cohesion of practice and the availability of practical standardization tools may increase awareness and use of rheology.

The first of the viscoceuticals? A shear thickening gum induces gastric satiety in rats

We examined the effect of gavage of 4 ml of a viscous shear-thickening polysaccharide solution (15% w/w) extracted from the fronds of the mamaku tree fern (Cythea medullaris) in reducing appetite and delaying gastric emptying in twenty six Sprague Dawley rats.