Evaluation of Radius of Gyration and Intrinsic Viscosity Molar Mass Dependence and Stiffness of Hyaluronan

Glycerol-driven adaptive evolution for the production of low-molecular-weight Welan gum: Characterization and activity evaluation

Through adaptive laboratory evolution (ALE) of Sphingomonas sp. ATCC 31555, fermentation for production of low-molecular-weight welan gum (LMW-WG) was performed using glycerol as sole carbon source. During ALE, GPC-MALS analysis revealed a gradual decrease in WG molecular weight with the increase of adaptation cycles, accompanied by changes in solution conformation. LMW-WG was purified and structurally analyzed using GPC-MALS, monosaccharide composition analysis, infrared spectroscopy, NMR analysis, atomic force microscopy, and scanning electron microscopy. Subsequently, LMW-WG obtains hydration, transparency, antioxidant activity, and rheological properties. Finally, an in vitro simulation colon reactor was used to evaluate potential prebiotic properties of LMW-WG as dietary fiber. Compared with WG produced using sucrose as substrate, LMW-WG exhibited a fourfold reduction in molecular weight while maintaining moderate viscosity. Structurally, L-Rha nearly completely replaced L-Man. Furthermore, LMW-WG demonstrated excellent hydration, antioxidant activity, and high transparency. It also exhibited resistance to saliva and gastrointestinal digestion, showcasing a favorable colonization effect on Bifidobacterium, making it a promising symbiotic agent.

Hyaluronic acid from bluefin tuna by-product: Structural analysis and pharmacological activities

The fishing and aquaculture industries generate a huge amount of waste during processing and preservation operations, especially those of tuna. Recovering these by-products is a major economic and environmental challenge for manufacturers seeking to produce new active biomolecules of interest. A new hyaluronic acid was extracted from bluefin tuna's vitreous humour to assess its antioxidant and pharmacological activities. The characterization by infrared spectroscopy (FT-IR), nuclear magnetic resonance ((1D1H) and 2D (1H COSY, 1H/13C HSQC)) and size exclusion chromatography (SEC/MALS/DRI/VD) revealed that the extracted polysaccharide was a hyaluronic acid with high uronic acid content (55.8 %) and a weight average molecular weight of 888 kDa. This polymer possesses significant anti-radical activity and ferrous chelating capacity. In addition, pharmacological evaluation of its anti-inflammatory and analgesic potential, using preclinical models, in comparison with reference drugs (Dexamethasone, diclofenac, and acetylsalicylate of lysine), revealed promising anti-inflammatory activity as well as interesting peripheral and central antinociceptive activity. Therefore, our new hyaluronic acid compound may therefore serve as a potential drug candidate for the treatment of pain sensation and inflammation of various pathological origins.

Dimension and Flexibility of Polystyrenesulfonate Chains in Methanol-Water

The influence of the relative permittivity of the solvent medium on the single-chain dimension and flexibility of sodium polystyrenesulfonate chains has been investigated in mixed solvent media of methanol and water using viscosity experiments. Particular attention has been paid to explore the effect of the added low-molar-mass electrolyte. The root-mean-square (rms) radii of gyration of the chains in the unperturbed state have been calculated by applying the Flory model, while the intrinsic persistence lengths by the Benoit-Doty equation on the basis of the Kratky-Porod worm-like chain model. Estimation of the expansion factors for the rms radius of gyration, and the electrostatic persistence length helps evaluate the rms radii of gyration and the total persistence length of polystyrenesulfonate chains in the presence of varying amount of the supporting electrolyte. The polyion chains are highly extended at low ionic strengths but exhibit coil-like behavior with small persistence lengths when an excess of the supporting electrolyte is added in all the methanol-water mixtures investigated. Specifically, in the investigated solvent media, the polystyrenesulfonate chains have been found to shrink by ∼63-65% in the θ-state from their expanded conformation in the presence of 0.0001 mol L-1 NaCl. The chain dimensions pass through a maximum as the medium becomes richer in methanol, which could be explained by the formation and breakup of internal rings involving the polyion chain and water and/or methanol molecules. The intrinsic persistence length of sodium polystyrenesulfonate in a methanol-water mixture containing 0.1 mole fraction of methanol is ca. 1.3 times that in a medium with 0.3 mole fraction of methanol, indicating that flexibility of the polyion depends appreciably on the relative permittivity of the medium.

Natural polysaccharides and their derivatives as potential medical materials and drug delivery systems for the treatment of peripheral nerve injuries

Peripheral nerve repair following injury is one of the most serious problems in neurosurgery. Clinical outcomes are often unsatisfactory and associated with a huge socioeconomic burden. Several studies have revealed the great potential of biodegradable polysaccharides for improving nerve regeneration. We review here the promising therapeutic strategies involving different types of polysaccharides and their bio-active composites for promoting nerve regeneration. Within this context, polysaccharide materials widely used for nerve repair in different forms are highlighted, including nerve guidance conduits, hydrogels, nanofibers and films. While nerve guidance conduits and hydrogels were used as main structural scaffolds, the other forms including nanofibers and films were generally used as additional supporting materials. We also discuss the issues of ease of therapeutic implementation, drug release properties and therapeutic outcomes, together with potential future directions of research.

A One-Bead-Per-Saccharide (1BPS) Model for Glycosaminoglycans

Glycosaminoglycans (GAGs) are polysaccharide compounds that play key roles in various biological processes. GAGs are important structural components of cartilage and the extracellular matrix of the brain. Due to the large size of these polysaccharides, coarse-grained approaches are indispensable for modeling these biopolymers. We develop a one-bead-per-saccharide model of chondroitin sulfates and hyaluronic acid based on an existing three-bead-per-saccharide coarse-grained model. Our coarse graining is carried out by using iterative Boltzmann inversion (IBI), including an additional coupling potential to incorporate the correlation between dihedral angles. The predictions of the model are verified against those of the existing three-bead-per-saccharin model and the experimental radius of gyration for hyaluronic acid.

Conformational entropy of hyaluronic acid contributes to taste enhancement

Natural taste/flavor enhancers are essential ingredients that could potentially address condiments overconsumption. For the first time, we report that hyaluronic acid (HA) could modulate taste perception, governed by the dynamic interactions among taste compounds, mucin, and HA. Various conformations of HA impact taste perception. The high molecular weight (Mw) of 1090 kDa HA inhibits the sense of taste due to its increased viscosity, which hinders the penetration of Na⁺ into the mucin layer. HA with low and medium Mw (100 kDa, 400 kDa) could enhance taste perception. Isothermal titration calorimetry analysis confirms the stronger binding between mucin and HA. The intensity of their interaction increases as the Mw of HA increases from 8 kDa to 400 kDa. Quartz crystal microbalance with dissipation characterization further indicates that the rigid conformation of 100 kDa HA facilitates the binding of Na⁺ with taste receptors, thereby enhancing taste perception. The flexible conformation of 400 kDa HA may conceal the taste receptor cells, reducing taste enhancement. Our work advances the understanding of conformational entropy of natural mucoadhesion and mucopenetration polymers, which lays the foundation for their potential use as taste enhancers.

Structural change study of pepsin in the presence of spermidine trihydrochloride: Insights from spectroscopic to molecular dynamics methods

Spermidine is an aliphatic polyamine that directs a set of biological processes. This work aimed to use UV-Vis spectroscopy, fluorescence spectroscopy, thermal stability, kinetic methods, docking, and molecular dynamic simulations to examine the influence of spermidine trihydrochloride (SP) on the structure and function of pepsin. The results of the fluorescence emission spectra indicated that spermidine could quench pepsin's intrinsic emission in a static quenching process, resulting in the formation of the pepsin-spermidine complex. The results discovered that spermidine had a strong affinity to the pepsin structure because of its high binding constant. The obtained results from spectroscopy and molecular dynamic approaches showed the binding interaction between spermidine and pepsin, induced micro-environmental modifications around tryptophan residues that caused a change in the tertiary and secondary structure of the enzyme. FTIR analysis showed hypochromic effects in the spectra of amide I and II and redistribution of the helical structure. Moreover, the molecular dynamic (MD) and docking studies confirmed the experimental data. Both experimental and molecular dynamics simulation results clarified that electrostatic bond interactions were dominant forces.

Insight into the assembly of lipid-hyaluronan complexes in osteoarthritic conditions

Interactions between molecules in the synovial fluid and the cartilage surface may play a vital role in the formation of adsorbed films that contribute to the low friction of cartilage boundary lubrication. Osteoarthritis (OA) is the most common degenerative joint disease. Previous studies have shown that in OA-diseased joints, hyaluronan (HA) not only breaks down resulting in a much lower molecular weight (MW), but also its concentration is reduced ten times. Here, we have investigated the structural changes of lipid-HA complexes as a function of HA concentration and MW to simulate the physiologically relevant conditions that exist in healthy and diseased joints. Small angle neutron scattering and dynamic light scattering were used to determine the structure of HA-lipid vesicles in bulk solution, while a combination of atomic force microscopy and quartz crystal microbalance was applied to study their assembly on a gold surface. We infer a significant influence of both MW and HA concentrations on the structure of HA-lipid complexes in bulk and assembled on a gold surface. Our results suggest that low MW HA cannot form an amorphous layer on the gold surface, which is expected to negatively impact the mechanical integrity and longevity of the boundary layer and could contribute to the increased wear of the cartilage that has been reported in joints diseased with OA.

Structure and dynamics of the hyaluronan oligosaccharides and their solvation shell in water: organic mixed solvents

Hyaluronan (HA) is a natural polysaccharide occurring ubiquitously in the connective tissues of vertebrates widely used in the cosmetic and pharmaceutic industries. In numerous applications HA oligosaccharides are being chemically modified using reactions incompatible with aqueous solutions, often carried out in water:organic mixed solvents. We carry out molecular-dynamics (MD) simulations of HA oligosaccharides in water:1,4-dioxane and water:tert-butanol mixtures of different compositions. HA molecule causes a separation of the solvent components in its surroundings, especially in tert-butanol containing solutions, constituting thus a solvation shell enriched by water. Furthermore, interactions with ions are stronger than in pure water and depend on the solvent composition. Consequently, the dynamics of the HA chain varies with the solvent composition and causes observable conformational changes of the HA oligosaccharide. Composition of mixed solvents thus enables us to modify the interaction of HA with other molecules as well as its reactivity.

Influence of Low-Molar-Mass Xyloglucans on the Rheological Behavior of Concentrated Cellulose Nanocrystal Suspensions

Hydrogels were prepared at high solid contents (70-100 g/L) with cellulose nanocrystals (CNC) and very short xyloglucans (XGs). At 70 g/L, CNCs form cholesteric liquid crystals regularly spaced by a distance of 30 nm. This structure was preserved after adsorption of XG with a molar mass (M_w) of 20,000 g/mol (XG20) but was lost at 40,000 g/mol (XG40). Rheological measurements discriminated domains where an increasing M_w from XG20 to XG40 gave rise to drastic changes in storage moduli (on 3 orders of magnitude). At 40,000 g/mol, transient systems were obtained and a re-entrant glass-gel-glass transition was observed with increasing XG concentrations. This was interpreted in terms of the length and stiffness of the chain in relation to the inter-CNC distance. Liquid-to-glass-to-gel transitions were attributed to an XG adsorption type according to train or trail conformations or interconnected structures. Such tunable properties may further have implications on the in vivo role of XG during cell wall extension.

Formulation of Magneto-Responsive Hydrogels from Dually Cross-Linked Polysaccharides: Synthesis, Tuning and Evaluation of Rheological Properties

Smart hydrogels based on natural polymers present an opportunity to fabricate responsive scaffolds that provide an immediate and reversible reaction to a given stimulus. Modulation of mechanical characteristics is especially interesting in myocyte cultivation, and can be achieved by magnetically controlled stiffening. Here, hyaluronan hydrogels with carbonyl iron particles as a magnetic filler are prepared in a low-toxicity process. Desired mechanical behaviour is achieved using a combination of two cross-linking routes—dynamic Schiff base linkages and ionic cross-linking. We found that gelation time is greatly affected by polymer chain conformation. This factor can surpass the influence of the number of reactive sites, shortening gelation from 5 h to 20 min. Ionic cross-linking efficiency increased with the number of carboxyl groups and led to the storage modulus reaching 103 Pa compared to 101 Pa–102 Pa for gels cross-linked with only Schiff bases. Furthermore, the ability of magnetic particles to induce significant stiffening of the hydrogel through the magnetorheological effect is confirmed, as a 103-times higher storage modulus is achieved in an external magnetic field of 842 kA·m−1. Finally, cytotoxicity testing confirms the ability to produce hydrogels that provide over 75% relative cell viability. Therefore, dual cross-linked hyaluronan-based magneto-responsive hydrogels present a potential material for on-demand mechanically tunable scaffolds usable in myocyte cultivation.

Hydrodynamic and conformational characterization of aqueous sodium alginate solutions with varying salinity

Insight into the role of electrostatic interactions on the hydrodynamics and conformation of aqueous sodium alginate was gained through viscometry. Alginate chains are found to shrink in salt-free solutions more rapidly with increasing polymer concentration compared to salt-solutions. For salt-free solutions, a reduced polymer concentration of less than 1 suffices to make the alginate coil volume half of that at infinite dilution which becomes invariant when the reduced concentration exceeds 8. In saline media having salt concentration greater than 0.1 mol·L^-1, the chains become more flexible, caused by the shielding of intra-chain repulsions. The chains effectively reached unperturbed state when the added salt concentration becomes ≥0.5 mol·L^-1. Alginate chains are shown to remain stiff up to about 8-10 monomers within the investigated temperature range. This study explores the possible modification of the individual chain behavior induced by the neighboring chains or by the variation of temperature.

Identification of the SARS-CoV-2 surface therapeutic targets and drugs using molecular modeling methods for inhibition the virus entry

Although COVID-19 emerged as a major concern to public health around the world, no licensed medication has been found as of yet to efficiently stop the virus spread and treat the infection. The SARS-CoV-2 entry into the host cell is driven by the direct interaction of the S1 domain with the ACE-2 receptor followed by conformational changes in the S2 domain, as a result of which fusion peptide is inserted into the target cell membrane, and the fusion process is mediated by the specific interactions between the heptad repeats 1 and 2 (HR1 and HR2) that form the six-helical bundle. Since blocking this interaction between HRs stops virus fusion and prevents its subsequent replication, the HRs inhibitors can be used as anti-COVID drugs. The initial drug selection is based on existing molecular databases to screen for molecules that may have a therapeutic effect on coronavirus. Based on these premises, we chose two approved drugs to investigate their interactions with the HRs (based on docking methods). To this end, molecular dynamics simulations and molecular docking were carried out to investigate the changes in the structure of the SARS-CoV-2 spike protein. Our results revealed, cefpiramide has the highest affinity to S protein, thereby revealing its potential to become an anti-COVID-19 clinical medicine. Therefore, this study offers new ways to re-use existing drugs to combat SARS-CoV-2 infection.

Assessment of the Substance Antioxidative Profile by Hyaluronan, Cu(II) and Ascorbate

In the minireview presented here, the authors discuss the evaluation of inhibitory effect of substances in the phases of initiation and propagation of high-molar-mass hyaluronan oxidative degradation. The experimental approach should be considered as original since on using a simple experimental assay it is possible to prove both the so-called “preventive” and “chain-breaking” antioxidant activity of investigated water-soluble endo- or exogenous substances.

The rate and evenness of the substitutions on hyaluronan grafted by dodecanoic acid influenced by the mixed-solvent composition

In this work, low molecular weight (17 kDa) hyaluronan was modified by dodecanoyl substituents. The activation of dodecanoic acid was mediated by benzoyl chloride towards the preparation of a mixed anhydride, which reacts in a second step with HA in water mixed with an organic solvent. The effect of the cosolvent was studied and showed an even distribution of substituents and higher reaction rate in water: 1,4-dioxane compared to water:tert-butanol where substituents occupy adjacent positions. The chemical characterization of the prepared derivatives was elucidated by NMR, FTIR spectroscopy, thermal analyses, and gas chromatography, while the distribution of substituents was evaluated by enzymatic degradation. Molecular-dynamics simulations reveal opposite solvent separations around HA and dodecanoyl chains, that is stronger in water:tert-butanol solution. The resulting incompatibility of solvation-shells of the two entities repels the reaction intermediates from the HA chain and drives them towards the already bound substituents, explaining the observed differences in the distribution evenness. Thus, the influence of the solvent on the reaction selectivity is observed by shielding reactive sites around HA. Therefore, a control of the distribution of the substituents was obtained by defining the concentration of HA and used cosolvent.

The Influences of Sulphation, Salt Type, and Salt Concentration on the Structural Heterogeneity of Glycosaminoglycans

The increasing recognition of the biochemical importance of glycosaminoglycans (GAGs) has in recent times made them the center of attention of recent research investigations. It became evident that subtle conformational factors play an important role in determining the relationship between the chemical composition of GAGs and their activity. Therefore, a thorough understanding of their structural flexibility is needed, which is addressed in this work by means of all-atom molecular dynamics (MD) simulations. Four major GAGs with different substitution patterns, namely hyaluronic acid as unsulphated GAG, heparan-6-sulphate, chondroitin-4-sulphate, and chondroitin-6-sulphate, were investigated to elucidate the influence of sulphation on the dynamical features of GAGs. Moreover, the effects of increasing NaCl and KCl concentrations were studied as well. Different structural parameters were determined from the MD simulations, in combination with a presentation of the free energy landscape of the GAG conformations, which allowed us to unravel the conformational fingerprints unique to each GAG. The largest effects on the GAG structures were found for sulphation at position 6, as well as binding of the metal ions in the absence of chloride ions to the carboxylate and sulphate groups, which both increase the GAG conformational flexibility.

Cancer cell migration in collagen-hyaluronan composite extracellular matrices

Hyaluronan (HA) is a key component in the tumor microenvironment (TME) that participates in cancer growth and invasiveness. While the molecular weight (MW) dependent properties of HA can cause tumor-promoting and -repressing effects, the elevated levels of HA in the TME impedes drug delivery. The degradation of HA using hyaluronidases (HYALs), resulting in fragments of HA, is a way to overcome this, but the consequences of changes in HA molecular weight and concentration is currently unknown. Therefore, it is critical to understand the MW-dependent biological effects of HA. Here we examine the influence of HA molecular weight on biophysical properties that regulate cell migration and extracellular matrix (ECM) remodeling. In our study, we used vLMW, LMW and HMW HA at different physiologically relevant concentrations, with a particular interest in correlating the mechanical and structural properties to different cell functions. The elastic modulus, collagen network pore size and collagen fiber diameter increased with increasing HA concentration. Although the collagen network pore size increased, these pores were filled with the bulky HA molecules. Consequently, cell migration decreased with increase in HA concentration due to multiple, long-lived and unproductive protrusions, suggesting the influence of steric factors. Surprisingly, even though elastic modulus increased with HA molecular weight and concentration, gel compaction assays showed an increased degree of ECM compaction among HMW HA gels at high concentrations (2 and 4 mg mL^-1 [0.2 and 0.4%]). These results were not seen in collagen gels that lacked HA, but had similar stiffness. HA appears to have the effect of decreasing migration and increasing collagen network contraction, but only at high HA molecular weight. Consequently, changes in HA molecular weight can have relatively large effects on cancer cell behavior. STATEMENT OF SIGNIFICANCE: Hyaluronan (HA) is a critical component of the tumor microenvironment (TME). Overproduction of HA in the TME results in poor prognosis and collapse of blood vessels, inhibiting drug delivery. Hyaluronidases have been used to enhance drug delivery. However, they lead to low molecular weight (MW) HA, altering the mechanical and structural properties of the TME and cancer cell behavior. Understanding how HA degradation affects cancer cell behavior is critical for uncovering detrimental effects of this therapy. Very little is known about how HA MW affects cancer cell behavior in tumor-mimicking collagen-HA composite networks. Here we examine how MW and HA content in collagen-HA networks alter structural and mechanical properties to regulate cell migration and matrix remodeling in 3D TME-mimicking environments.

Hyaluronic acid-coated gold nanorods enhancing BMP-2 peptide delivery for chondrogenesis

Bone morphogenic protein-2 (BMP-2) knuckle epitope peptide has been recently discovered and known to activate chondrogenesis. However, the applications of this soluble peptide remain very limited due to rapid diffusion resulting in poor cellular uptake into target cells. We herein designed nanoparticles made from hyaluronic acid functionalized gold nanorods (GNRs) to conjugate with thiolated BMP-2 knuckle epitope peptide via a two-step reaction. Hyaluronic acid was modified to have thiol functional groups to replace the cetyl trimethylammonium bromide ligands on the surface of GNRs. The thiolated peptides were subsequently reacted with hyaluronic acid on the surface on GNRs via a maleimide-hydrazide crosslinker. The conjugation was confirmed by the change of surface charge of GNRs and the plasmon shift. A colorimetric peptide assay suggested more than 69% of the thiolated peptides were conjugated with the hyaluronic acid coated gold nanorods. Moreover, in vitro cell viability showed that BMP-2 conjugated hyaluronic acid functionalized gold nanorods (B2HGR) were cytocompatible and did not cause cytotoxicity to fibroblast cells. The B2HGRs also significantly promote cellular uptake of the BMP-2 peptides in both human mesenchymal stem cells and porcine chondrocytes due to multivalent ligand binding to the BMP receptors on the cell surface resulting in receptor-mediated endocytosis. The enhanced cellular uptake was clearly observed under a confocal microscope resulting in the significant activation of type II collagen gene expression and glucosaminoglycan secretion in those cells. Furthermore, our delivery system is a proof-of-concept of using scaffolds in combination with nanodelivery platform to enhance cartilaginous repair. The peptide loading capacity and the release is not limited by the scaffolds. Therefore, our delivery platform has potential applications for cartilage regeneration in a preclinical and clinical setting in the future.

Martini Coarse-Grained Model of Hyaluronic Acid for the Structural Change of Its Gel in the Presence of Monovalent and Divalent Salts

Hyaluronic acid (HA) has a wide range of biomedical applications including the formation of hydrogels, microspheres, sponges, and films. The modeling of HA to understand its behavior and interaction with other biomolecules at the atomic level is of considerable interest. The atomistic representation of long HA polymers for the study of the macroscopic structural formation and its interactions with other polyelectrolytes is computationally demanding. To overcome this limitation, we developed a coarse grained (CG) model for HA adapting the Martini scheme. A very good agreement was observed between the CG model and all-atom simulations for both local (bonded interactions) and global properties (end-to-end distance, a radius of gyration, RMSD). Our CG model successfully demonstrated the formation of HA gel and its structural changes at high salt concentrations. We found that the main role of CaCl₂ is screening the electrostatic repulsion between chains. HA gel did not collapse even at high CaCl₂ concentrations, and the osmotic pressure decreased, which agrees well with the experimental results. This is a distinct property of HA from other proteins or polynucleic acids which ensures the validity of our CG model. Our HA CG model is compatible with other CG biomolecular models developed under the Martini scheme, which allows for large-scale simulations of various HA-based complex systems.

Effect of solvent and ions on the structure and dynamics of a hyaluronan molecule

Hyaluronic acid (hyaluronan, HA) is a negatively charged polysaccharide forming highly swollen random coils in aqueous solutions. Their size decreases along with growing salt concentration, but the mechanism of this phenomenon remains unclear. We carry out molecular-dynamics simulations of a 48-monosaccharide HA oligomer in varying salt concentration and temperature. They identify the interaction points of Na⁺ ions with the HA chain and reveal their influence on the HA solvation-shell structure. The salt-dependent variation of the molecular size does not consist in the distribution of the dihedral angles of the glycosidic connections but is driven by the random flips of individual dihedral angles, which cause the formation of temporary hairpin-like structures effectively shortening the chain. They are induced by the frequency of cation-chain interactions that grow with the salt concentration, but is reduced by the simultaneous decrease of ions' activities. This leads to an anomalous random-coil shrinkage at 0.6 M salt concentration.

Amphiphilic multicomponent molecular brushes

Multicomponent molecular brushes containing amphiphilic polymer moieties are promising objects of research of macromolecular chemistry. The development of stimulus-responsive systems sensitive to changes in environmental parameters, based on the molecular brushes, opens up new possibilities for their applications in medicine, biochemistry and microelectronics. The review presents the current understanding of the structures of main types of amphiphilic multicomponent brushes, depending on the chemical nature and type of coupling of the backbone and side chains. The approaches to the controlled synthesis of multicomponent molecular brushes of different architecture are analyzed. Self-assembly processes of multicomponent molecular brushes in selective solvents are considered.

The bibliography includes 259 references.

Phenomenological Changes in Lignin Following Polymerization and Its Effects on Flocculating Clay Particles

Cationic kraft lignin (CKL) macromolecules were produced via polymerizing kraft lignin (KL) with [2-(acryloyloxy)ethyl]trimethylammonium chloride (ATAC) or [2-(methacryloyloxy)ethyl]trimethylammonium methyl sulfate (METAM). Despite slightly different charge densities (2.3-2.5 mmol/g) of CKL, lignin-METAM (KL-METAM) had a significantly larger molecular weight and radius of gyration. A correlation was observed between the structure of CKLs and their impacts on the surface hydrophilicity of kaolin particles. In interacting with kaolin particles, KL-METAM generated larger and stronger flocs with looser structures than did KL-ATAC. Compared to ATAC, METAM had one additional methyl substituent on its structure, which provided fundamental evidence on how a small group (i.e., a methyl group) on the structure of a cationic monomer can have a substantial influence on its polymerization with lignin and subsequently on the efficiency of the induced macromolecule as a flocculant in a kaolin suspension system.

Influence of high hydrostatic pressure on solid supported DPPC bilayers with hyaluronan in the presence of Ca2+ ions

The molecular mechanisms responsible for outstanding lubrication of natural systems, like articular joints, have been the focus of scientific research for several decades. One essential aspect is the lubrication under pressure, where it is important to understand how the lubricating entities adapt under dynamic working conditions in order to fulfill their function. We made a structural investigation of a model system consisting of two of the molecules present at the cartilage interface, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and hyaluronan, at high hydrostatic pressure. Phospholipid layers are found at the cartilage surfaces and are able to considerably reduce friction. Their behavior under load and varied solution conditions is important as pressures of 180 bar are encountered during daily life activities. We focus on how divalent ions, like Ca2+, affect the interaction between DPPC and hyaluronan, as other investigations have indicated that calcium ions influence their interaction. It could be shown that already low amounts of Ca2+ strongly influence the interaction of hyaluronan with DPPC. Our results suggest that the calcium ions increase the amount of adsorbed hyaluronan indicating an increased electrostatic interaction. Most importantly, we observe a modification of the DPPC phase diagram as hyaluronan absorbs to the bilayer which results in an Lα-like structure at low temperatures and a decoupling of the leaflets forming an asymmetric bilayer structure.

Frictional characterization of injectable hyaluronic acids is more predictive of clinical outcomes than traditional rheological or viscoelastic characterization

Hyaluronic acid injections have been a mainstay of arthritis treatment for decades. However, much controversy remains about their clinical efficacy and their potential mechanism of action. This approach to arthritis therapy is often called viscosupplementation, a term which is rooted in the elevated viscosity of the injected solutions. This terminology also suggests a mechanical pathway of action and further implies that their efficacy is dependent on viscosity. Notably, previous studies of the relationship between viscous properties of hyaluronic acid solutions and their clinical efficacy have not been definitive. Recently we developed an experimental and analytical framework for studying cartilage lubrication that captures the Stribeck-like behavior of cartilage in an elastoviscous transition curve. Here we apply this framework to study the lubricating behavior of six hyaluronan products currently used for injectable arthritis therapy in the US. Despite the fact that the source and chemical modifications endow these products with a range of lubricating properties, we show that the lubricating effect of all of these materials can be described by this Stribeck-like elastoviscous transition. Fitting this data to the elastoviscous transition model enables the calculation of effective lubricating viscosities for each material, which differ substantially from the viscosities measured using standard rheometry. Further we show that while data from standard rheometry are poor predictors of clinical performance of these materials, measurements of friction coefficient and effective lubricating viscosity correlate well (R2 = 0.77; p < 0.005) with assessments of improved clinical function reported previously. This approach offers both a novel method that can be used to evaluate potential clinical efficacy of hyaluronic acid formulations and provide new insight on their mode of action.

Shearing-induced contact pattern formation in hydrogels sliding in polymer solution

The contact of a hydrogel during the rotational shearing on a glass surface in concentrated polymer solution was observed in situ. Dynamic contact patterns that rotate in-phase with the rotational shearing of the gel were observed for the first time. The contact patterns with a periodicity in the circumferential direction appeared and became fine with the shearing time. The patterns appeared more quickly at an elevated sliding velocity, polymer concentration, and normal pressure. Furthermore, the softness of the gel also substantially influenced the characteristics of the patterns. The pattern formation was discussed in terms of the non-linear rheology of the polymer solution at the rotational soft interface.

Equilibrium Modeling of the Mechanics and Structure of the Cancer Glycocalyx

The glycocalyx is a thick coat of proteins and carbohydrates on the outer surface of all eukaryotic cells. Overproduction of large, flexible or rod-like biopolymers, including hyaluronic acid and mucins, in the glycocalyx strongly correlates with the aggression of many cancer types. However, theoretical frameworks to predict the effects of these changes on cancer cell adhesion and other biophysical processes remain limited. Here, we propose a detailed modeling framework for the glycocalyx incorporating important physical effects of biopolymer flexibility, excluded volume, counterion mobility, and coupled membrane deformations. Because mucin and hyaluronic biopolymers are proposed to extend and rigidify depending on the extent of their decoration with side chains, we propose and consider two limiting cases for the structural elements of the glycocalyx: stiff beams and flexible chains. Simulations predict the mechanical response of the glycocalyx to compressive loads, which are imposed on cells residing in the highly confined spaces of the solid tumor or invaded tissues. Notably, the shape of the mechanical response transitions from hyperbolic to sigmoidal for more rod-like glycocalyx elements. These mechanical responses, along with the corresponding equilibrium protein organizations and membrane topographies, are summarized to aid in hypothesis generation and the evaluation of future experimental measurements. Overall, the modeling framework developed provides a theoretical basis for understanding the physical biology of the glycocalyx in human health.

Hyaluronan and Hyaluronan Fragments

The glycosaminoglycan hyaluronan (HA) is a key component of the microenvironment surrounding cells. In healthy tissues, HA molecules have extremely high molecular mass and consequently large hydrodynamic volumes. Tethered to the cell surface by clustered receptor proteins, HA molecules crowd each other, as well as other macromolecular species. This leads to severe nonideality in physical properties of the biomatrix, because steric exclusion leads to an increase in effective concentration of the macromolecules. The excluded volume depends on both polymer concentration and hydrodynamic volume/molecular mass. The biomechanical properties of the extracellular matrix, tissue hydration, receptor clustering, and receptor-ligand interactions are strongly affected by the presence of HA and by its molecular mass. In inflammation, reactive oxygen and nitrogen species fragment the HA chains. Depending on the rate of chain degradation relative to the rates of new synthesis and removal of damaged chains, short fragments of the HA molecules can be present at significant levels. Not only are the physical properties of the extracellular matrix affected, but the HA fragments decluster their primary receptors and act as endogenous danger signals. Bioanalytical methods to isolate and quantify HA fragments have been developed to determine profiles of HA content and size in healthy and diseased biological fluids and tissues. These methods have potential use in medical diagnostic tests. Therapeutic agents that modulate signaling by HA fragments show promise in wound healing and tissue repair without fibrosis.

Highly stretchable hydrogels from complex coacervation of natural polyelectrolytes

The controlled complex coacervation of oppositely charged hyaluronic acid (M_w ≈ 800-1000 kg mol^-1) and chitosan (M_w ≈ 160 kg mol^-1, degree of acetylation = 15%) led to hydrogels with controllable properties in terms of elasticity and strength. In this work, we performed desalting by dialysis of high ionic strength solutions of mixed polyelectrolytes and showed that the control of the pH during the polyelectrolyte assembly greatly impacts the mechanical properties of the hydrogel. First, for pHs from 5.5 to 7.5, a slight coacervation was observed due to low chitosan protonation and poor polyelectrolyte associations. Then, for pHs from 3.0 to 5.5, coacervation and syneresis led to free-standing and easy to handle hydrogels. Finally, for pHs from 2.0 to 3.0 (close to the pK_a of the hyaluronic acid), we observed the unusual stretchability of these hydrogels that could arise from the pre-folding of hyaluronic acid chains while physical crosslinking was achieved by hyaluronic acid/chitosan polyelectrolyte complexation.

Sheathless Microflow Cytometry Using Viscoelastic Fluids

Microflow cytometry is a powerful technique for characterization of particles suspended in a solution. In this work, we present a microflow cytometer based on viscoelastic focusing. 3D single-line focusing of microparticles was achieved in a straight capillary using viscoelastic focusing which alleviated the need for sheath flow or any other actuation mechanism. Optical detection was performed by fiber coupled light source and photodetectors. Using this system, we present the detection of microparticles suspended in three different viscoelastic solutions. The rheological properties of the solutions were measured and used to assess the focusing performance both analytically and numerically. The results were verified experimentally, and it has been shown that polyethlyene oxide (PEO) and hyaluronic acid (HA) based sheathless microflow cytometer demonstrates similar performance to state-of-the art flow cytometers. The sheathless microflow cytometer was shown to present 780 particles/s throughput and 5.8% CV for the forward scatter signal for HA-based focusing. The presented system is composed of a single capillary to accommodate the fluid and optical fibers to couple the light to the fluid of interest. Thanks to its simplicity, the system has the potential to widen the applicability of microflow cytometers.

Mechanics of Fluid-Filled Interstitial Gaps. II. Gap Characteristics in Xenopus Embryonic Ectoderm

The ectoderm of the Xenopus embryo is permeated by a network of channels that appear in histological sections as interstitial gaps. We characterized this interstitial space by measuring gap sizes, angles formed between adjacent cells, and curvatures of cell surfaces at gaps. From these parameters, and from surface-tension values measured previously, we estimated the values of critical mechanical variables that determine gap sizes and shapes in the ectoderm, using a general model of interstitial gap mechanics. We concluded that gaps of 1-4 μm side length can be formed by the insertion of extracellular matrix fluid at three-cell junctions such that cell adhesion is locally disrupted and a tension difference between cell-cell contacts and the free cell surface at gaps of 0.003 mJ/m² is generated. Furthermore, a cell hydrostatic pressure of 16.8 ± 1.7 Pa and an interstitial pressure of 3.9 ± 3.6 Pa, relative to the central blastocoel cavity of the embryo, was found to be consistent with the observed gap size and shape distribution. Reduction of cell adhesion by the knockdown of C-cadherin increased gap volume while leaving intracellular and interstitial pressures essentially unchanged. In both normal and adhesion-reduced ectoderm, cortical tension of the free cell surfaces at gaps does not return to the high values characteristic of the free surface of the whole tissue.

Molecular Dynamic Analysis of Hyaluronic Acid and Phospholipid Interaction in Tribological Surgical Adjuvant Design for Osteoarthritis

Tribological surgical adjuvants constitute a therapeutic discipline made possible by surgical advances in the treatment of damaged articular cartilage beyond palliative care. The purpose of this study is to analyze interactions between hyaluronic acid and phospholipid molecules, and the formation of geometric forms, that play a role in the facilitated lubrication of synovial joint organ systems. The analysis includes an evaluation of the pathologic state to detail conditions that may be encountered by adjuvants during surgical convalescence. The synovial fluid changes in pH, hyaluronic acid polydispersity, and phospholipid concentration associated with osteoarthritis are presented as features that influence the lubricating properties of adjuvant candidates. Molecular dynamic simulation studies are presented, and the Rouse model is deployed, to rationalize low molecular weight hyaluronic acid behavior in an osteoarthritic environment of increased pH and phospholipid concentration. The results indicate that the hyaluronic acid radius of gyration time evolution is both pH- and phospholipid concentration-dependent. Specifically, dipalmitoylphosphatidylcholine induces hydrophobic interactions in the system, causing low molecular weight hyaluronic acid to shrink and at high concentration be absorbed into phospholipid vesicles. Low molecular weight hyaluronic acid appears to be insufficient for use as a tribological surgical adjuvant because an increased pH and phospholipid concentration induces decreased crosslinking that prevents the formation of supramolecular lubricating forms. Dipalmitoylphosphatidylcholine remains an adjuvant candidate for certain clinical situations. The need to reconcile osteoarthritic phenotypes is a prerequisite that should serve as a framework for future adjuvant design and subsequent tribological testing.

What is special about 200 kDa hyaluronan that activates hyaluronan receptor signaling?

The polydispersity of hyaluronan (HA) presents challenges for analyzing its solution properties, such as the relationship between mass and particle size. The broad mass range of natural HA (≤50-fold) makes molecular characterization difficult and ambiguous compared to molecules with known molecular weights (e.g., proteins). Biophysical studies show that large >MDa HA behaves like a random coil, whereas very small (e.g., 10 kDa) HA behaves like a rod. However, the mass range for this conformational transition is not easily determined in natural polydisperse HA. Some HA receptors (e.g., CD44 and HARE) initiate signaling responses upon binding HA in the 100-300 kDa range, but not larger MDa HA. Size-dependent responses are studied using nonnatural HA: purified narrow-size range HA [Pandey MS, Baggenstoss BA, Washburn J, Harris EN, Weigel PH. 2013. The hyaluronan receptor for endocytosis (HARE) activates NF-κB-mediated gene expression in response to 40-400 kDa, but not smaller or sarger, hyaluronans. J Biol Chem. 288:14068-14079] and very narrow size range Select-HA made chemo-enzymatically [Jing W, DeAngelis PL. 2004. Synchronized chemoenzymatic synthesis of monodisperse hyaluronan polymers. J Biol Chem. 279:42345-42349]. Here, we used size exclusion chromatography and multiangle light scattering to determine the weight-average molar mass and diameter of ~60 very narrow size preparations from 29 to 1650 kDa. The ratio of HA mass to HA diameter showed a transition in the 150-250 kDa size range (~65 nm). The HA rod-to-coil transition occurs within the size range that specifically activates cell signaling by some receptors. Thus, size-specific signaling could be due to unique external receptor•HA conformation changes that enable transmembrane-mediated activation of cytoplasmic domains. Alternatively and more likely, transition-size HA may enable multiple receptors to bind the same HA, creating new internal signal-competent cytoplasmic domain complexes.

Reducing Friction in the Eye: A Comparative Study of Lubrication by Surface-Anchored Synthetic and Natural Ocular Mucin Analogues

Biomaterials used in the ocular environment should exhibit specific tribological behavior to avoid discomfort and stress-induced epithelial damage during blinking. In this study, two macromolecules that are commonly employed as ocular biomaterials, namely, poly(vinylpyrrolidone) (PVP) and hyaluronan (HA), are compared with two known model glycoproteins, namely bovine submaxillary mucin (BSM) and α₁-acid glycoprotein (AGP), with regard to their nonfouling efficiency, wettability, and tribological properties when freely present in the lubricant, enabling spontaneous adsorption, and when chemisorbed under low contact pressures. Chemisorbed coatings were prepared by means of photochemically triggered nitrene insertion reactions. BSM and AGP provided boundary lubrication when spontaneously adsorbed in a hydrophobic contact with a coefficient of friction (CoF) of ∼0.03-0.04. PVP and HA were found to be excellent boundary lubricants when chemisorbed (CoF ≤ 0.01). Notably, high-molecular-weight PVP generated thick adlayers, typically around 14 nm, and was able to reduce the CoF below 0.005 when slid against a BSM-coated poly(dimethylsiloxane) pin in a tearlike fluid.

Competitive Adsorption of Polyelectrolytes onto and into Pellicle-Coated Hydroxyapatite Investigated by QCM-D and Force Spectroscopy

A current effort in preventive dentistry is to inhibit surface attachment of bacteria using antibacterial polymer coatings on the tooth surface. For the antibacterial coatings, the physisorption of anionic and cationic polymers directly onto hydroxyapatite (HA) and saliva-treated HA surfaces was studied using quartz crystal microbalance, force spectroscopy, and atomic force microscopy. First, single species adsorption is shown to be stronger on HA surfaces than on silicon oxide surfaces for all polymers (i.e., Gantrez, sodium hyaluronate (NaHa), and poly(allylamine-co-allylguanidinium) (PAA-G75)). It is observed through pH dependence of Gantrez, NaHa, and PAA-G75 adsorption on HA surfaces that anionic polymers swell at high pH and collapse at low pH, whereas cationic polymers behave in the opposite fashion. Thicknesses of Gantrez, NaHa, and PAA-G75 are 52 nm (46 nm), 35 nm (11 nm), and 6 nm (54 nm) at pH 7 (3.5), respectively. Second, absorption of charged polymer is followed by absorption of the oppositely charged polymer. Upon exposure of the anionic polymer layers, Gantrez and NaHa, to the cationic polymer, PAA-G75, films collapse from 52 to 8 nm and 35 to 11 nm, respectively. This decrease in film thickness is attributed to the electrostatic cross-linking between anionic and cationic polymers. Third, for HA surfaces pretreated with artificial saliva (AS), the total thickness decreases from 25 to 16 nm upon exposure to PAA-G75. Force spectroscopy is used to further investigate the PAA-G75/AS coating. The results show that the interaction between a negatively charged colloidal bead and the AS surface is strongly repulsive, whereas PAA-G75/AS is attractive but varies across the surface. Additionally, AFM studies show that AS/HA is smooth with a RMS roughness of 1.7 nm, and PAA-G75-treated AS/HA is rough (RMS roughness of 5.4 nm) with patches of polymer distributed across the surface with an underlying coating. The high roughness of PAA-G75 treated AS/HA is attributed to the strong adsorption of the relatively small PAA-G75 onto the heterogeneously distributed negatively charged AS surface. In addition, uptake of PAA-G75 by pellicle layer (saliva-treated HA surface) is observed, and the adsorbed amount of PAA-G75 on/into pellicle layer is ∼2 times more than that on/into AS layer. These studies show that polymer adsorption onto HA and saliva-coated HA depends strongly on the polymer type and size and that there is an electrostatic interaction between polymer and saliva and/or oppositely charged polymers that stabilizes the coatings on HA. Lastly, assessing the viability of the adherent bacteria collected from the PAA-G75-coated surfaces showed a significant reduction (∼93%) in bacterial viability when compared to bacteria collected from untreated and Gantrez-coated HA. These results suggest the potential antimicrobial activity of PAA-G75.

Structural behaviour of sodium hyaluronate in concentrated oppositely charged surfactant solutions

This work discusses the polyelectrolyte sodium hyaluronate (HA) and its polyelectrolyte/surfactant complexes (PESCs) with tetradecyltrimethylammonium bromide (TTAB) in the semi-dilute regime of HA and at high concentrations of TTAB. The structure and flow properties in the surfactant excess region were studied by light scattering and small angle neutron scattering (SANS) as well as by rheology. The unique behaviour of HA to maintain its high viscosity was observed even at very high TTAB concentrations of 496 mM and this effect was systematically studied in the concentration range from 1 to 25 mM HA. From the data, it could be concluded that: (1) extended rod-like structures of the PESCs prevent molecular dissolution of HA by TTAB. (2) HA and TTAB micelles interact rather weakly as seen by a low fraction of bound micelles. (3) At very high TTAB concentrations a decompaction of PESCs (fractal dimension D_f going from 2.0 to 1.2) occurs with increasing HA concentration but (4) both the entanglement of HA and the structure of the micelles are not affected.

Branching Analysis of Multivalent Conjugates Using Size Exclusion Chromatography-Multiangle Light Scattering

Multivalent conjugates (MVCs) (conjugation of multiple proteins to a linear polymer chain) are powerful for improving the bioactivity and pharmacokinetics of a bioactive molecule. Since this effect is highly dependent upon the valency of the conjugated proteins, it is imperative to have a technique for analysis of the conjugation ratio. Studies of MVCs have used size exclusion chromatography-multiangle light scattering (SEC-MALS), which allows for the separate and individual analysis of the protein and biopolymer components based on their specific refractive index increment and UV extinction coefficient constants to determine the number of proteins bound per biopolymer molecule. In this work, we have applied traditional branching analysis to the SEC-MALS data, with the primary assumption that the polymer backbone can be used as the linear counterpart. We demonstrated good agreement between the branching values and the valency determined by traditional analysis, demonstrating that branching analysis can be used as an alternative technique to approximate the valency of MVCs. The branching analysis method also provides a more complete picture of the distribution of the measured values, provides important branching information about the molecules, and lowers the cost and complexity of the characterization. However, since MVC molecules are both conjugate molecules and branched molecules, the most powerful approach to their characterization would be to use both traditional multivalent conjugate analysis and branching analysis in conjunction.

Hyaluronic Acid Molecular Weight Determines Lung Clearance and Biodistribution after Instillation

Hyaluronic acid (HA) has emerged as a versatile polymer for drug delivery. Multiple commercial products utilize HA, it can be obtained in a variety of molecular weights, and it offers chemical handles for cross-linkers, drugs, or imaging agents. Previous studies have investigated multiple administration routes, but the absorption, biodistribution, and pharmacokinetics of HA after delivery to the lung is relatively unknown. Here, pharmacokinetic parameters were investigated by delivering different molecular weights of HA (between 7 and 741 kDa) to the lungs of mice. HA was labeled with either a near-infrared dye or with iodine-125 conjugated to HA using a tyrosine linker. In initial studies, dye-labeled HA was instilled into the lungs and fluorescent images of organs were collected at 1, 8, and 24 h post administration. Data suggested longer lung persistence of higher molecular weight HA, but signal diminished for all molecular weights at 8 h. To better quantitate pharmacokinetic parameters, different molecular weights of iodine-125 labeled HA were instilled and organ radioactivity was determined after 1, 2, 4, 6, and 8 h. The data showed that, after instillation, the lungs contained the highest levels of HA, as expected, followed by the gastrointestinal tract. Smaller molecular weights of HA showed more rapid systemic distribution, while 67 and 215 kDa HA showed longer persistence in the lungs. Lung exposure appeared to be optimum in this size range due to the rapid absorption of <67 kDa HA and the poor lung penetration and mucociliary clearance of viscous solutions of HA > 215 kDa. The versatility of HA molecular weight and conjugation chemistries may, therefore, provide new opportunities to extend pulmonary drug exposure and potentially facilitate access to lymph nodes draining the pulmonary bed.