Relevance of Rheological Properties of Sodium Alginate in Solution to Calcium Alginate Gel Properties

Abstract. The purpose of this study is to determine whether sodium alginate solutions' rheological parameters are meaningful relative to sodium alginate's use in the formulation of calcium alginate gels. Calcium alginate gels were prepared from six different grades of sodium alginate (FMC Biopolymer), one of which was available in ten batches. Cylindrical gel samples were prepared from each of the gels and subjected to compression to fracture on an Instron Universal Testing Machine, equipped with a 1-kN load cell, at a cross-head speed of 120 mm/min. Among the grades with similar % G, (grades 1, 3, and 4), there is a significant correlation between deformation work (L E ) and apparent viscosity (η app ). However, the results for the partial correlation analysis for all six grades of sodium alginate show that L E is significantly correlated with % G, but not with the rheological properties of the sodium alginate solutions. Studies of the ten batches of one grade of sodium alginate show that η app of their solutions did not correlate with L E while tan δ was significantly, but minimally, correlated to L E . These results suggest that other factors-polydispersity and the randomness of guluronic acid sequencing-are likely to influence the mechanical properties of the resultant gels. In summary, the rheological properties of solutions for different grades of sodium alginate are not indicative of the resultant gel properties. Interbatch differences in the rheological behavior for one specific grade of sodium alginate were insufficient to predict the corresponding calcium alginate gel's mechanical properties

Extracellular matrix hydrogels from decellularized tissues: structure and function

Extracellular matrix (ECM) bioscaffolds prepared from decellularized tissues have been used to facilitate constructive and functional tissue remodeling in a variety of clinical applications. The discovery that these ECM materials could be solubilized and subsequently manipulated to form hydrogels expanded their potential in vitro and in vivo utility; i.e. as culture substrates comparable to collagen or Matrigel, and as injectable materials that fill irregularly-shaped defects. The mechanisms by which ECM hydrogels direct cell behavior and influence remodeling outcomes are only partially understood, but likely include structural and biological signals retained from the native source tissue. The present review describes the utility, formation, and physical and biological characterization of ECM hydrogels. Two examples of clinical application are presented to demonstrate in vivo utility of ECM hydrogels in different organ systems. Finally, new research directions and clinical translation of ECM hydrogels are discusse

Varying the Blending Protocol to Control the Morphology of Model Compatibilized Polymer Blends

in Wiley InterScience (www.interscience.wiley.com). The structure of an oil/water emulsion is known to depend on its preparation method. Here, we test whether the preparation protocol can be used to control the morphology of ''model'' blends of immiscible polymers compatibilized by a diblock copolymer. Two preparation protocols were tested. In the ''double blending'' protocol, a droplet-matrix blend was blended with additional drop-phase fluid. As in oil/water emulsions, this yielded a drop-within-drop ''double emulsion'' morphology. Coalescence suppression due to compatibilizer was found crucial to double emulsion stability. The rheology of the double emulsion was qualitatively similar to that of a simple droplet-matrix blend, but with an effectively higher drop volume fraction. In the ''multistep concentration'' protocol, the drop phase was added gradually (rather than all-at-once) to the matrix phase. While this protocol can realize a high-dispersed phase emulsion in oil/water systems, in this case, phase inversion occurred when the drop volume fraction exceeded 0.5. 2008 American Institute of Chemical Engineers AIChE J, 54: [791][792][793][794][795][796][797][798][799][800][801] 200

Renewable Elastomers Based on Blends of Maleated Polypropylene and Plasticized Starch

ABSTRACT: Most recent developments in polymers from renewable resources have focused on thermoplastics, whereas there has been no comparable development of plastics with elastomeric properties. Here we evaluate the possibility of developing renewable elastomers based on starch. Potato starch plasticized with glycerol (called plasticized starch, or PLS) was melt-blended with small quantities (5 wt % or 15 wt%) of maleated polypropylene (MAPP). The maleic anhydride groups of the polypropylene are expected to react with the hydroxy groups of starch under melt blending conditions. The resulting blends of MAPP and PLS were characterized by mechanical testing, SEM, DMA, and DSC. SEM, solubility and adhesion tests indicate that the blends are two-phase materials, in which the continuous phase PLS is physically crosslinked by polypropylene domains. The materials showed rubbery properties as judged by a low glass transition temperature ($À50 C independent of polypropylene content), and a wide rubbery plateau in DMA experiments that extended from room temperature to as high as 170 C. The tensile properties are also characteristic of elastomers. However, slow aging due to starch crystallization, and extraction of glycerol upon water exposure remain two challenges that must be overcome before the materials can be used as practical elastomers

Swelling-Induced Delamination Causes Folding of Surface-Tethered Polymer Gels

When a polymer film that is weakly attached to a rigid substrate is exposed to solvent, swelling-induced compressive stress nucleates buckle delamination of the film from the substrate. Surprisingly, the buckles do not have a sinusoidal profile, instead, the film near the delamination buckles slides toward the buckles causing growth of sharp folds of high aspect ratio. These folds do not result from a wrinkle-to-fold transition; instead, the film goes directly from a flat state to a folded state. The folds persist even after the solvent evaporates. We propose that patterned delamination and folding may be exploited to realize high-aspect ratio topological features on surfaces through control of a set of boundary constraints arising from the interrelation of film-surface adhesion, film thickness and degree of swellabilty

Swelling-Induced Delamination Causes Folding of Surface-Tethered Polymer Gels

When a polymer film that is weakly attached to a rigid substrate is exposed to solvent, swelling-induced compressive stress nucleates buckle delamination of the film from the substrate. Surprisingly, the buckles do not have a sinusoidal profile, instead, the film near the delamination buckles slides toward the buckles causing growth of sharp folds of high aspect ratio. These folds do not result from a wrinkle-to-fold transition; instead, the film goes directly from a flat state to a folded state. The folds persist even after the solvent evaporates. We propose that patterned delamination and folding may be exploited to realize high-aspect ratio topological features on surfaces through control of a set of boundary constraints arising from the interrelation of film-surface adhesion, film thickness and degree of swellabilty

Swelling-Induced Delamination Causes Folding of Surface-Tethered Polymer Gels

When a polymer film that is weakly attached to a rigid substrate is exposed to solvent, swelling-induced compressive stress nucleates buckle delamination of the film from the substrate. Surprisingly, the buckles do not have a sinusoidal profile, instead, the film near the delamination buckles slides toward the buckles causing growth of sharp folds of high aspect ratio. These folds do not result from a wrinkle-to-fold transition; instead, the film goes directly from a flat state to a folded state. The folds persist even after the solvent evaporates. We propose that patterned delamination and folding may be exploited to realize high-aspect ratio topological features on surfaces through control of a set of boundary constraints arising from the interrelation of film-surface adhesion, film thickness and degree of swellabilty

Salt Effects on the Phase Behavior and Cocrystallization Kinetics of POCB–Water Mixtures

Mixtures of water with polyoxacyclobutane (POCB) have a unique phase diagram which combines liquid–liquid equilibrium (LLE) at high temperatures and cocrystallization of a POCB-hydrate at low temperatures. Such cocrystal hydrate formation is extremely rare among polymers. We report on the effects of adding NaCl salt on the phase behavior of POCB–water mixtures and the kinetics of hydrate crystallization from such mixtures. Salt loadings of less than 0.1 wt % were found to greatly expand the LLE region. Salt loadings of ∼10 wt % were found to significantly decrease the melting temperature of the hydrate below its ∼37 °C value under salt-free conditions. The hydrate was found to be remarkably tolerant of salt and persists at room temperature even when equilibrated with salt-saturated water. Salt was found to slow down hydrate crystallization, and the degree of slowing was greater than that expected from the salt-induced decrease in undercooling due to melting point depression

Aggregation and Separation in Ternary Particle/Oil/Water Systems with Fully Wettable Particles

We report that a variety of ternary particle/liquid/liquid mixtures heavily aggregate or separate completely if (1) the particles are fully or almost fully wetted by one fluid, and (2) if the wetting fluid volume fraction is comparable to the particle volume fraction. Aggregation and separation do not happen if the particles are partially wetted by both fluids, in which case Pickering emulsions appear at all compositions. Rheological and geometric criteria for aggregation are proposed and compared with a state diagram of a ternary system composed of oil, water, and hydrophilic glass particles. Analogies are drawn to wet granulation and spherical agglomeration, two particle processing operations in which wetting phenomena are important