Aggregation Behavior in Semidilute Rigid and Semirigid Polysaccharide Solutions

Reversible Microwheel Translation Induced by Polymer Depletion

For in vivo applications, microbots (μbots) must move, which is a need that has led to designs, such as helical swimmers, that translate through the bulk fluid. We have previously demonstrated that, upon application of a rotating magnetic field, colloidal particles in aqueous systems can be reversibly assembled from superparamagnetic particles into μbots that translate along surfaces using wet friction. Here, we show that high-molecular-weight polymers of a size that approaches the length scale of the gap between the μbot and surface can be excluded, impacting μbot transport. Using xanthan gum as a convenient high-molecular-weight model, we determine that polymer depletion imparts only a weak effect on colloid-surface interactions but has a significant influence on local viscosity, which is an effect great enough to induce a reversal in the μbot translation direction.

Hyaluronan Brush-like Copolymers Promote CD44 Declustering in Breast Cancer Cells

We report on the synthesis of hyaluronan (HA) brush-like copolymers and their application as antagonists of tumorigenic CD44-HA interactions. HA (4.8 kDa, ca. 24 saccharides) was grafted on 2-hydrohyethyl methacrylate (HEMA) by end-on oxime ligation. The obtained copolymers were compared with low and high molecular weight HA in terms of hydrolysis kinetics in the presence of hyaluronidase (isothermal titration calorimetry) and interactions with CD44 (surface plasmon resonance). The results evidenced that the high molecular weight HA and HA-g-HEMA have a much higher affinity to CD44 than low molecular weight HA. Additionally, slower enzymatic degradation was observed for the copolymer, making it an excellent candidate for active targeting of tumorigenic CD44-HA interactions. We, therefore, investigated the effect of the copolymer on cancer cell lines with different expression of CD44 and observed an efficient declustering of CD44 that is usually associated with reduction of metastasis and drug resistance.

Dual stimuli-sensitive carrageenan-based formulation for additive manufacturing

The design and development of controlled release systems of molecules of interest (nutrients, flavors, and drugs) have attracted significant attention over several years. Herein, we report a formulation of dual temperature and electro responsive κ- and ι-carrageenan based hydrogel for efficient food material and drug delivery. The microstructure and the thermal behavior of the hydrogel were characterized. The in-vitro drug release from the hydrogel was also studied. Using this carrageenan-based formulation and folic acid as the drug model, a high drug loading, and a sustained release because of either electric field or temperature were observed. In principle, the proposed formulation does not rely on 3D printing to perform its function; however, it adds to the feedstocks for 3D printing in the food and pharmaceutical industries. For the future, this could allow potentially more complex smart structures to be created from this material, further tuning release behavior.

Porous particles and novel carrier particles with enhanced penetration for efficient pulmonary delivery of antitubercular drugs

This study aimed to design dry powder inhaler formulations using a hydrophilic polymeric polysaccharide, phytoglycogen (PyG), as a multi-functional additive that increases the phagocytic activity of macrophage-like cells and enhances pulmonary delivery of drugs. The safety and usefulness of PyG were determined using in vitro cell-based studies. Dry powder inhaler formulations of an antitubercular drug, rifampicin, were fabricated by spray drying with PyG. The cytotoxicity, effects on phagocytosis, particle size, and morphology were evaluated. The aerosolization properties of the powder formulations were evaluated using an Andersen cascade impactor (ACI). Scanning electron microscope images of the particles on each ACI stage were captured to observe the deposition behavior. PyG showed no toxicity in A549, Calu-3, or RAW264.7 cell lines. At concentrations of 0.5 and 1 g/L, PyG facilitated the cellular uptake of latex beads and the expression of pro-inflammatory cytokine genes in RAW264.7 cells. Formulations with outstanding inhalation potential were produced. The fine particle fraction (aerodynamic size 2-7 µm) of the porous particle batch reached nearly 60%, whereas in the formulation containing wrinkled carrier particles, the extra-fine particle fraction (aerodynamic particle size < 2 μm) was 25.0% ± 1.7%. The deposition of porous and wrinkled particles on individual ACI stages was distinct. The inclusion of PyG dramatically improved the inhalation performance of porous and wrinkled powder formulations. These easily inhaled immunostimulatory carrier particles may advance the state of research by enhancing the therapeutic effect and alveolar delivery of antitubercular drugs.

Chain flexibility and dynamics of alginate solutions in different solvents

Mechanical rheometry, specifically rotational rheometry, squeeze flow, and capillary rheometry, and two microrheology methods, namely multiple-particle tracking (MPT) and diffusing wave spectroscopy (DWS) have been used to get new insight into structural and dynamical properties of alginate dissolved in solvents widely used for bioprinting, namely deionized water, phosphate-buffered saline (PBS), and Dulbecco Modified Eagle Medium (DMEM) cell media. Results demonstrate that alginate rheological properties depend on the solvent quality at concentrations higher than 1 wt.%. In this high concentration regime, in aqueous salt-free and PBS solutions, experimental scaling exponents for the concentration dependence of the specific viscosity ηsp and the plateau modulus G0 agree well with theoretical predictions for neutral polymers in good solvent whereas for the terminal relaxation time TR, the exponent is slightly higher than theoretically predicted, presumably due to the formation of aggregates. For alginate dissolved in DMEM, all exponents for ηsp, G0, and TR agree with predictions for polymers in theta solvents, which might be related to the formation of polyelectrolyte complex as a result of interactions between alginate and amino acids. Chain persistence length lp values, as determined directly from high frequency rheometry for the first time, are independent of alginate concentration and temperature. Lower absolute lp values were found for DMEM solutions compared with the other solvents. Moreover, scaling exponents for ηsp, G0, and TR do not change with temperature, within 20 and 60 °C. These findings suggest no change in the conformation of alginate chains with temperature.

Asymmetric polymer mixtures in good solvents: A light scattering study

Dilute solutions of asymmetric polystyrene/poly(methyl methacrylate) (PS/PMMA) mixtures in toluene and tetrahydrofuran (THF) are investigated by static and dynamic light scattering (SLS and DLS). Both solvents are good solvents for each of the two polymers. In toluene, the PMMA refractive index increment is close to zero and SLS provides a direct measurement of the PS static scattering functions. DLS correlatively leads to a single relaxation mode connected with these PS chains. Contrarily, two modes well separated in time are observed for identical PS/PMMA mixtures in THF. Scattering from the PMMA chains is no longer negligible and partial static scattering functions can only be obtained through SLS-DLS combination. For identical polymer concentration and PS/PMMA mixture composition, PS scattering functions are then found to be different in both solvents. The difference increases with concentration and is only partly due to distinct thermodynamic parameters according to the solvent. PMMA scattering functions lead to similar conclusions. The Random Phase Approximation (RPA) describes all scattering functions. However, the SLS-DLS combination affords a reasonable approximation for extracting the partial static scattering functions only for the lowest concentrations, i.e. provided the cross polymer correlation term remains negligible.

Concentration regimes of biopolymers xanthan, tara, and clairana, comparing dynamic light scattering and distribution of relaxation time

The aim of this work was to evaluate the utilization of analysis of the distribution of relaxation time (DRT) using a dynamic light back-scattering technique as alternative method for the determination of the concentration regimes in aqueous solutions of biopolymers (xanthan, clairana and tara gums) by an analysis of the overlap (c*) and aggregation (c**) concentrations. The diffusion coefficients were obtained over a range of concentrations for each biopolymer using two methods. The first method analysed the behaviour of the diffusion coefficient as a function of the concentration of the gum solution. This method is based on the analysis of the diffusion coefficient versus the concentration curve. Using the slope of the curves, it was possible to determine the c* and c** for xanthan and tara gum. However, it was not possible to determine the concentration regimes for clairana using this method. The second method was based on an analysis of the DRTs, which showed different numbers of relaxation modes. It was observed that the concentrations at which the number of modes changed corresponded to the c* and c**. Thus, the DRT technique provided an alternative method for the determination of the critical concentrations of biopolymers.

Hierarchical supramolecular structuring and dynamical properties of water soluble polyethylene glycol-perylene self-assemblies

The structural and dynamical properties of dilute aqueous solutions of poly(ethylene glycol)-perylene diimides (PEG(n)-PDI) have been investigated by means of static and dynamic light scattering, TEM microscopy, and small-angle X-ray scattering experiments. The amphiphilic PEG(n)-PDI molecules first self-assemble into stable and compact primary stacks of a few units of planar PDI through hydrophobic and π-π interactions. These primary stacks subsequently arrange in large and globular aggregates of typically 100-250 nm via weak PEG chain interpenetration. Surprisingly, the scattered electric field autocorrelation function g((1))(q,t) measured by dynamic light scattering evolves over very long periods of times (several months) and up to a bimodal distribution. The fast relaxation mechanism is associated to the diffusion of free primary stacks, whereas the slower relaxation still indicates the presence of large self-assemblies. Kinetic experiments show that the large supramolecular aggregates slowly release the free primary stacks whose proportion increases with time. This dissociation depends on several parameters such as PEG side chain length, total concentration, and shaking.

Micron range morphology of physical chitosan hydrogels

Physical chitosan hydrogels are potential biomaterials for several biomedical applications, such as wound healing, tissue repair, and drug delivery. Controlling the microstructural organization of chitosan gels is one of the keys for monitoring the physical, mechanical, and biological properties. As a result, the main objective of the present work was to explore the microstructural organization of chitosan hydrogels in relation with the processing conditions of gelation. For this purpose, different gelation routes were studied, that is, chitosan solution neutralization of an aqueous or hydroalcoholic solution and neutralization of an alco-gel. Overall, the resulting morphology after processing was determined by the medium viscosity during neutralization and the nature and concentration of the base. The effect of these processing parameters on the morphology was evaluated mainly through small angle light scattering (SALS) measurements including in situ measurements during chitosan neutralization. As a result, we reported different bulk microstructures consisting in 200-400 nm aggregates (primary particles) agglomerated into micrometer range clusters or arranged into more organized structures, that is, forming microchannels (4-6 μm). We thus established a qualitative and quantitative relation between supramolecular morphology and gelation conditions of chitosan hydrogels.

Cartilage aggrecan can undergo self-adhesion

Here it is reported that aggrecan, the highly negatively charged macromolecule in the cartilage extracellular matrix, undergoes Ca(2+)-mediated self-adhesion after static compression even in the presence of strong electrostatic repulsion in physiological-like solution conditions. Aggrecan was chemically end-attached onto gold-coated planar silicon substrates and gold-coated microspherical atomic force microscope probe tips (end radius R approximately 2.5 mum) at a density ( approximately 40 mg/mL) that simulates physiological conditions in the tissue ( approximately 20-80 mg/mL). Colloidal force spectroscopy was employed to measure the adhesion between opposing aggrecan monolayers in NaCl (0.001-1.0 M) and NaCl + CaCl(2) ([Cl(-)] = 0.15 M, [Ca(2+)] = 0 - 75 mM) aqueous electrolyte solutions. Aggrecan self-adhesion was found to increase with increasing surface equilibration time upon compression (0-30 s). Hydrogen bonding and physical entanglements between the chondroitin sulfate-glycosaminoglycan side chains are proposed as important factors contributing to aggrecan self-adhesion. Self-adhesion was found to significantly increase with decreasing bath ionic strength (and hence, electrostatic double-layer repulsion), as well as increasing Ca(2+) concentration due to the additional ion-bridging effects. It is hypothesized that aggrecan self-adhesion, and the macromolecular energy dissipation that results from this self-adhesion, could be important factors contributing to the self-assembled architecture and integrity of the cartilage extracellular matrix in vivo.

Self-Diffusion and Collective Diffusion of Charged Colloids Studied by Dynamic Light Scattering

A microemulsion of decane droplets stabilized by a nonionic surfactant film is progressively charged by substitution of a nonionic surfactant molecule by a cationic surfactant. We check that the microemulsion droplets remain identical within the explored range of volume fraction (0.02-0.18) and of the number of charges per droplet (0-40). We probe the dynamics of these microemulsions by dynamic light scattering. Despite the similar structures of the uncharged and charged microemulsions, the dynamics are very different. In the neutral microemulsion, the fluctuations of polarization relax, as is well-known, via the collective diffusion of the droplets. In the charged microemulsions, two modes of relaxation are observed. The fast one is ascribed classically to the collective diffusion of the charged droplets coupled to the diffusion of the counterions. The slow one has, to our knowledge, not been observed previously neither in similar microemulsions nor in charged spherical colloids. We show that the slow mode is also diffusive and suggest that its possible origin is the relaxation of local charge fluctuations via the local exchange of droplets bearing different numbers of charges. The diffusion coefficient associated with this mode is then the self-diffusion coefficient of the droplets.

A coarse-grained molecular model for glycosaminoglycans: application to chondroitin, chondroitin sulfate, and hyaluronic acid

A coarse-grained molecular model is presented for the study of the equilibrium conformation and titration behavior of chondroitin (CH), chondroitin sulfate (CS), and hyaluronic acid (HA)-glycosaminoglycans (GAGs) that play a central role in determining the structure and biomechanical properties of the extracellular matrix of articular cartilage. Systematic coarse-graining from an all-atom description of the disaccharide building blocks retains the polyelectrolytes' specific chemical properties while enabling the simulation of high molecular weight chains that are inaccessible to all-atom representations. Results are presented for the characteristic ratio, the ionic strength-dependent persistence length, the pH-dependent expansion factor for the end-to-end distance, and the titration behavior of the GAGs. Although 4-sulfation of the N-acetyl-D-galactosamine residue is found to increase significantly the intrinsic stiffness of CH with respect to 6-sulfation, only small differences in the titration behavior of the two sulfated forms of CH are found. Persistence length expressions are presented for each type of GAG using a macroscopic (wormlike chain-based) and a microscopic (bond vector correlation-based) definition. Model predictions agree quantitatively with experimental conformation and titration measurements, which support use of the model in the investigation of equilibrium solution properties of GAGs.

Structural and rheological properties of hydrophobically modified polysaccharide associative networks

The phase behavior of hydrophobically modified chitosans (HMCs) in aqueous solution has been investigated using scattering and rheology experiments. We observed four regions on the phase diagram of the associative polymer: (i) a supernatant phase (unimers phase) at low polymer concentration; (ii) a dilute solution of intermolecularly bridged flowerlike micelles at intermediate concentration; (iii) an associative gel phase at high polymer content; and (iv) a phase separation. In the present paper, we discuss the structural and dynamical properties of the HMC associative networks (c > c*) at a fixed hydrophobic degree of substitution of 2% and fixed alkyl side chains (stickers) length C8 (domains iii and iv of the phase diagram). As the polymer concentration is increasing, a connecting network is formed from the percolation of bridges between micellar aggregates. In this regime, small-angle neutron scattering and light scattering measurements show that -50-nm flower aggregates are acting like junction points in the network. The effect of the concentration, the stress, and the shear on the structure of the network is discussed. In particular, we observe bridge-to-loop transitions and then the formation of microgels or a low-connected network under shear. Therefore, our results are compared to recent theoretical models and to the results reported for telechelic systems.