Oral drug delivery with polymeric nanoparticles: the gastrointestinal mucus barriers.

A review of nonlinear oscillatory shear tests: Analysis and application of large amplitude oscillatory shear (LAOS)

Dielectric Relaxation and Solvation Dynamics of Water in Complex Chemical and Biological Systems

First-generation nanoparticles (NPs) have been clinically translated as pharmaceutical drug delivery carriers for their ability to improve on drug tolerability, circulation half-life, and efficacy. Toward the development of the next-generation NPs, researchers have designed novel multifunctional platforms for sustained release, molecular targeting, and environmental responsiveness. This review focuses on environmentally responsive mechanisms used in NP designs, and highlights the use of pH-responsive NPs in drug delivery. Different organs, tissues, and subcellular compartments, as well as their pathophysiological states, can be characterized by their pH levels and gradients. When exposed to these pH stimuli, pH-responsive NPs respond with physicochemical changes to their material structure and surface characteristics. These include swelling, dissociating or surface charge switching, in a manner that favors drug release at the target site over surrounding tissues. The novel developments described here may ...

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pH-Responsive nanoparticles for drug delivery.

Over the past century, hydrogels have emerged as effective materials for an immense variety of applications. The unique network structure of hydrogels enables very high levels of hydrophilicity and biocompatibility, while at the same time exhibiting the soft physical properties associated with living tissue, making them ideal biomaterials. Stimulus-responsive hydrogels have been especially impactful, allowing for unprecedented levels of control over material properties in response to external cues. This enhanced control has enabled groundbreaking advances in healthcare, allowing for more effective treatment of a vast array of diseases and improved approaches for tissue engineering and wound healing. In this extensive review, we identify and discuss the multitude of response modalities that have been developed, including temperature, pH, chemical, light, electro, and shear-sensitive hydrogels. We discuss the theoretical analysis of hydrogel properties and the mechanisms used to create these responses, highlighting both the pioneering and most recent work in all of these fields. Finally, we review the many current and proposed applications of these hydrogels in medicine and industry.

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Stimulus-responsive hydrogels: Theory, modern advances, and applications

This paper describes the rheological behavior of a HEUR (hydrophobic ethoxylated urethane) associative polymer with C16H33 end groups at 2.0 wt % concentration in aqueous solution. Under normal steady shear, this solution exhibits Newtonian behavior at low shear rates and, as the shear rate is increased, passes through a shear-thickening region before exhibiting a sharp decrease in viscosity. Here we report superposition-of-oscillation experiments on steady-shear flows to examine the state of the network structure under different shear conditions. The technique involves applying a steady shear deformation to the fluid, and once the steady state is achieved, a small amplitude oscillation is imposed on the sample to measure the linear viscoelastic properties. We observe that within the shear-thickening region, the plateau modulus is larger than in the Newtonian region, suggesting that shear-thickening is the result of a shear-induced increase in the density of mechanically active chains, which may be due to...

A structural model of hydrophobically modified urethane-ethoxylate (HEUR) associative polymers in shear flows

The viscoelastic properties over a range of steady shear conditions of an alkali-swellable associative polymer have been determined using the technique of superposition of oscillations upon steady shear flow, thus enabling the structure of the polymer to be investigated. The associative polymer studied consists of a backbone of methacrylic acid and ethyl acrylate to which is attached macromolecules containing C20 hydrophobes via an ethylene oxide−isocyanate linkage. A 1 wt % solution with its pH adjusted to 9.5 was used. At high pHs, the polymer solubilizes to form a network of both intra- and intermolecular associating hydrophobic junctions. The solution shows a non-power-law shear-thinning behavior:  the viscosity flow curve, when plotted against shear stress, shows two distinct regions where network rupture is prominent, at stress of 2 Pa and between 40 and 50 Pa. By superimposing small amplitude oscillations on to shear flow at constant stresses, the network structure of the polymer is unperturbed and...

Superposition of Oscillations on Steady Shear Flow as a Technique for Investigating the Structure of Associative Polymers

The rheological properties of 1 wt % aqueous solutions (at pH between 8.7 and 9.5) of model associative (HASE) polymers are presented. These polymers are the polymerization product of methacrylic acid, ethyl acrylate, and macromonomers which contain hydrophobes with the alkyl chain ranging in length from C12 to C20. At high pH, the polymers form a network of temporarily associating hydrophobic junctions, resulting in an enhancement of the shear viscosity which increases with the hydrophobe chain length. Strain amplitude sweep results show that the strength of the hydrophobic association increases with the length of the hydrophobe. This is also reflected in the increase in the ratio of the elastic to viscous components of the linear viscoelastic properties. When sheared beyond its equilibrium state, the associative polymers display a terminal (second-order) viscoelastic behavior at higher frequencies as the network is increasingly being disrupted by higher applied stresses. The general behavior of the poly...

Rheological properties of model alkali-soluble associative (HASE) polymers : Effect of varying hydrophobe chain length

Rheological and photophysical data are presented for a hydrophobically modified alkali-soluble copolymer, of a constitution similar to materials currently employed as rheology modifiers in water-borne coatings. The copolymer comprises a polyelectrolyte backbone bearing ethoxylate side chains capped with complex alkylaryl groups of a high molar volume. In aqueous alkaline media, the hydrophobes associate dynamically, the topology of the network so formed being dependent on the polymer concentration. Photophysical studies, employing pyrene as a hydrophobic fluorescent probe, indicate the presence of hydrophobic associations. At concentrations below the coil overlap concentration, c*, these associations are predominantly intramolecular. At higher polymer concentrations, intermolecular interactions become more probable. This change in network topology is in qualitative agreement with previous theoretical considerations of associative polymer systems and is reflected in an unusually high concentration dependen...

Solution rheology of a hydrophobically modified alkali-soluble associative polymer

Polymers are disclosed which comprise: (A) about 1-99.9 weight percent of one or more alpha, beta-monoethylenically unsaturated carboxylic acids, typically methacrylic acids; (B) about 0-98.9 weight percent of one or more monoethylenically unsaturated monomers, typically ethyl acrylate; (C) about 0.1-99 weight percent of one or more monoethylenically unsaturated macromonomers, and (D) about 0-20 weight percent or greater of one or more polyethylenically unsaturated monomers. These polymers can be solubilized in water with the aid of an alkali, like ammonium hydroxide. When the polymers are added to latex paints and neutralized, the viscosity of the paint is increased, brush drag is increased, and the paint rheology is otherwise improved.

Richard Duane Jenkins

Papers

A structural model of hydrophobically modified urethane-ethoxylate (HEUR) associative polymers in shear flows

Superposition of Oscillations on Steady Shear Flow as a Technique for Investigating the Structure of Associative Polymers

Rheological properties of model alkali-soluble associative (HASE) polymers : Effect of varying hydrophobe chain length

Solution rheology of a hydrophobically modified alkali-soluble associative polymer

Polymers containing macromonomers