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The authors demonstrate strong adhesion of cationic hydrogels to bovine tissues under a DC electric field. Such electroadhesion can be reversed by switching the polarity of the field. This approach could enable simpler surgeries, where sutures are not needed.

Multiple concentric layers are present in a variety of structures present in nature, including the onion. Here, the authors show an inside-out strategy to synthesize multilayered polymer capsules, with different layers having specific composition and thereby specific responses to stimuli such as pH and temperature.

Liposomes have been extensively studied and are used in the treatment of several diseases. Liposomes improve the therapeutic efficacy by enhancing drug absorption while avoiding or minimizing rapid degradation and side effects, prolonging the biological half-life and reducing toxicity. The unique feature of liposomes is that they are biocompatible and biodegradable lipids, and are inert and non-immunogenic. Liposomes can compartmentalize and solubilize both hydrophilic and hydrophobic materials. All these properties of liposomes and their flexibility for surface modification to add targeting moieties make liposomes more attractive candidates for use as drug delivery vehicles. There are many novel liposomal formulations that are in various stages of development, to enhance therapeutic effectiveness of new and established drugs that are in preclinical and clinical trials. Recent developments in multimodality imaging to better diagnose disease and monitor treatments embarked on using liposomes as diagnostic tool. Conjugating liposomes with different labeling probes enables precise localization of these liposomal formulations using various modalities such as PET, SPECT, and MRI. In this review, we will briefly review the clinical applications of liposomal formulation and their potential imaging properties.

The triblock copolymer Pluronic F127 (PF127) is frequently used in colloidal and pharmaceutical formulations. Concentrated aqueous solutions of PF127 (>15 wt %) are known to undergo thermogelling(i.e., a sol-to-gel transition upon heating), which is attributed to the formation of a volume-filling cubic array of micelles. Here, we report that thermogelling can occur at much lower PF127 concentrations (1.2 to 8 wt %) if nanoparticles of laponite (25-nm-diameter disks) are also present in the formulation. Thermogelling in laponite/PF127 mixtures requires each component to be present above a minimum level. The gels have moduli around 100 Pa, and they can be reversibly liquefied to sols upon cooling. Rheological techniques, small-angle neutron scattering (SANS), and transmission electron microscopy (TEM) are used to characterize the thermogels. We attribute the onset of thermogelling to depletion flocculation of the laponite particles into a network by spherical micelles of PF127. [ABSTRACT FROM AUTHOR]

Telechelic associating polymers (hydrophilic ethoxylated backbone, hydrophobic n-alkyl end-groups) form viscous solutions in water due to associations between the hydrophobes. The addition of α-, β-, or γ-cyclodextrin (CD) substantially reduces the solution viscosity because the CD molecules envelop and sequester the hydrophobes in their hydrophobic cavities. The present paper explores the variation in polymer−CD solution viscosity with temperature. We find that, in the case of α-CD alone, the solutions show “thermothickening”, i.e., the viscosity increasesfrom 25 to ca. 60 °C whereupon it reaches a peak value and then drops. In contrast, solutions with β- and γ-CD show monotonic drops in viscosity upon heating. At a fixed polymer content, the thermothickening is higher for higher α-CD concentrations. We have also studied how surfactants and lipids impact the thermothickening. Addition of single-tailed micelle-forming surfactants causes the viscosity to revert to the more typical decreasing trend with temperature. However, addition of double-tailed lipids to a polymer/α-CD solution accentuates the thermothickening behavior. The thermothickening is explained by the propensity of α-CDs to unbind from the hydrophobes and form inclusion complexes with the polymer backbone as the temperature is raised. [ABSTRACT FROM AUTHOR]

Gel formation by surfactant molecules is argued to be a process similar to micellization rather than crystallization; it is controlled by thermodynamics rather than kinetics. The properties of surfactant-based gels are compared with those of gels with crystalline fibrillar networks, and questions associated with the nature of these gels are raised. [ABSTRACT FROM AUTHOR]

Strain-stiffening, that is, an increase in material stiffness at large deformations, is a property of many biological materials. Currently, model systems for the study of this phenomenon are elastic networks (gels) of semiflexible filamentous biopolymers such as actin, keratin, or fibrin. Here, we demonstrate strain-stiffening in a class of viscoelasticsolutions, comprising reverse wormlike micelles. These structures are formed by the coassembly of the physiological surfactants, lecithin and bile salt, in an organic solvent, cyclohexane. In contrast to the biopolymer gels, the networks here are transient and are formed by the physical entanglement of relatively flexible worms. Our results suggest that neither a permanent network nor a high filament rigidity is required for strain-stiffening. We suggest a different origin, based on a temporary strain-induced increase in the volume fraction of entangled worms. Our system can also serve as a convenient synthetic model for future studies into this phenomenon. [ABSTRACT FROM AUTHOR]

For the first time, an interpenetrating phase polymer nanocomposite formed by the percolation of multiwalled carbon nanotubes (MWCNTs) in polystyrene (PS) has been quantitatively characterized through electrical conductivity measurements and melt rheology. Both sets of measurements, in conjunction with scanning electron microscopy (SEM) images, indicate the presence of a continuous phase of percolated MWCNTs appearing at particle concentrations exceeding 2 vol% MWCNTs in PS. To quantify the amount of this continuous phase present in the PS/MWCNT composite, electrical conductivity data at various MWCNT concentrations, b, are correlated with a proposed degree of percolation, \bar {C}(\beta) , developed using a conventional power-law formula with and without a percolation threshold. To quantify the properties of the interpenetrating phase polymer nanocomposite, the PS/MWCNT composite is treated as a combination of two phases: a continuous phase consisting of a pseudo-solid-like network of percolated MWCNTs, and a continuous PS phase reinforced by non-interacting MWCNTs. The proposed degree of percolation is used to quantify the distribution of MWCNTs among the phases, and is then used in a rule-of-mixtures formulation for the storage modulus, G''(\beta,\bar {C}(\beta), \omega) , and the loss modulus, G''''(\beta,\bar {C}(\beta),\omega) , to quantify the properties of the continuous phase consisting of percolated MWCNTs and the continuous PS phase reinforced by non-interacting MWCNTs from the experimental melt rheology data. The properties of the continuous phase of percolated MWCNTs are indicative of a scaffold-like microstructure exhibiting an elastic behavior with a complex modulus of 360 kPa at lower frequencies and viscoplastic behavior with a complex viscosity of 6 kPa s rad[?]1 at higher frequencies, most likely due to a stick-slip friction mechanism at the interface of the percolated MWCNTs. Additional evidence of this microstructure was obtained via scanning electron microscopy. This research has important implications in providing a new methodology based on the electrical and rheological properties of the polymer nanocomposite for quantifying the continuous phase formed by the percolation of new functionalized nanostructures being developed for: (a) controlling the percolation of the nanostructures through self-assembly, (b) enhancing their interaction with the continuous reinforced polymer phase, (c) enhancing the cohesion between nanostructures. [ABSTRACT FROM AUTHOR]