Self-assembled morphologies of polyelectrolyte-grafted nanoparticles directed by oppositely charged polymer matrices.

Self-assembled structure of polymer grafted nanoparticles is an interesting and growing subject in the field of hybrid electronics and high energy density materials. In light of this, the self-assembled morphologies of polyelectrolyte (PE) sparsely grafted nanoparticles tuned by oppositely charged matrix chains are studied using molecular dynamics simulations. Our focus is to elucidate the effect of matrix chain polymerization on modulating the stretching properties of tethered PE layers, on the self-assembled structuring of nanoparticles. Through varying the matrix chain length and stiffness as well as electrostatic interaction strength, rich phase behaviors of PE coated nanoparticles are predicted, including spherical micelle-like structures being preferred with short matrix chains and percolating network morphologies favored with long matrix chains, which is more pronounced with an enhanced matrix chain rigidness. To pinpoint the mechanisms of self-assembled structure formation, the thickness of grafted layers, the gyration radius of tethered chains, and pair correlation functions between nanoparticles are analyzed carefully. Additionally, electrostatic correlations, manifested as the bridging via matrix chains, are examined by identifying three states of matrix PE chains. Our simulation results may be useful for designing smart polymer nanocomposites based on PE coated nanoparticles.

Self-assembly of polyelectrolyte diblock copolymers within mixtures of monovalent and multivalent counterions.

In this study, the self-assembly behavior of polyelectrolyte (PE) diblock copolymers in solutions containing mixtures of monovalent and multivalent counterions was investigated using molecular dynamics simulation. The properties of the assembled micelles and counterion condensations at different charge fractions of multivalent ions have been discussed. The bridging effect of multivalent ions induces the electrostatic correlations of the PE chains, leading to the fusion of large micelles and the formation of bulky aggregates. Notably, lamellar and well-organized face-centered cubic (FCC) arrangements of the assembled micelles were observed in the mixture of monovalent and trivalent ions. At large fractions of multivalent ions, cylindrical and lamellar precipitates composed of the assembled micelles were formed owing to the inter-connecting coronas. The mixtures of monovalent and multivalent counterions allow the regulation of the electrostatic interactions and tuning of the properties in assembled micelles.

Self-assembly of polyelectrolyte diblock copolymers at monovalent and multivalent counterions.

In this work, the self-assembly behaviors of diblock copolymers consisting of one hydrophobic block and one ionizable polyelectrolyte (PE) block in the presence of monovalent and multivalent counterions are systematically discussed through molecular dynamics simulation. Copolymers are molded as bead-spring chains and the ions are explicitly considered. First, the self-assembled structures of symmetrical block copolymers at different charge fractions are analyzed in detail. Spherical hydrophobic cores are favored by all of the micelles. The effect of counterion valence is much more noticeable at high values of charge fraction. When the PE blocks are fully charged, the presence of multivalent counterions preferably provokes the formation of macroscopic structures. A precipitant spherical micelle is generated in the presence of divalent counterions. Special shapes of coronas are created in the presence of trivalent ions, and a remarkable one dimensional macroscopic cylindrical aggregation of micelles forms; the whole assembly is not typical core-shell micelles, but rather a cylinder with alternating spherical micelles arranged perpendicular to the cylinder axis. The self-assemblies with different lengths of fully charged PE blocks are also discussed. Surprisingly, in the presence of divalent counterions, two dimensional in-plane macroscopic aggregation of micelles is realized when the proportion of PE blocks is larger than 1/2; the self-assembled spherical micelles locate approximately in the same plane to form an inter-linked network. One dimensional aggregation of micelles in the presence of trivalent counterions is maintained with an increased proportion of the PE block. Owing to the dominant intra- and inter-condensation of divalent and trivalent counterions, respectively, two and one dimensional macroscopic aggregation of the micelles is achieved. Our findings indicate that varying the counterion valence is a powerful mechanism to tune the properties of self-assemblies, and the bridging effect introduced by multivalent counterions is the key parameter for the aggregation of the micelles.

Surface morphologies of spherical polyelectrolyte brushes induced by trivalent salt ions.

The surface morphologies of spherical polyelectrolyte brushes in salt solutions with opposite trivalent ions are studied using molecular dynamics (MD) simulations. The impact of salt concentration, grafting density, and charge fraction on brush morphologies is investigated systematically. A variety of surface patterns are predicted and the phase diagrams are presented. Both lateral and radial microphase separated structures in the brushes are observed upon varying the salt concentration. With low grafting density the spherical brush is separated into several patches, the number of which decreases with the addition of salt. At high grafting density, the polymer brush changes its morphology from an extended micelle to a 'carpet + brush' to the collapsed state upon increasing the salt concentration. Especially, the 'carpet + brush' structure consists of a core formed by partially collapsed brush chains and a corona formed by other stretched chains. The inter-chain 'bridging' interactions mediated by trivalent ions and the curvature effect play important roles in determining the chain conformations and brush structures.

TWEAK/Fn14 signaling: a promising target in intervertebral disc degeneration.

Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) is a potent chemoattractant cytokine with various biological functions, such as stimulation of angiogenesis, induction of proinflammatory cytokines, regulation of cellular proliferation and apoptosis. Therefore, it has also been implicated in several pathological processes, from cancer to inflammatory diseases. Remarkably, TWEAK and its receptors, fibroblast growth factor inducible 14 (Fn14), are also present in intervertebral disc (IVD) tissue, where they play a role in the pathogenesis of IVD degeneration. The interaction of TWEAK with Fn14 is involved in physiological and pathological activities of IVD degeneration patients, which includes apoptosis of endplate chondrocytes, extracellular matrix degradation, reduction in proteoglycan synthesis and so on. The blockade of this interaction results in suppressing over-production of proinflammatory factors and cell death in in vivo or in vitro experiments, suggesting that TWEAK/Fn14 signaling may be therapeutically relevant in IVD degeneration, and the targeting of TWEAK or Fn14 has been proposed as a potential therapeutic approach for autoimmune diseases such as Rheumatoid arthritis (RA). In this article, we discuss the biological features of TWEAK/Fn14 signaling and summarize recent advances in our understanding of the role of TWEAK/Fn14 signaling in the pathogenesis and treatment of IVD degeneration. We think that the blockade of TWEAK/Fn14 signaling may be a promising therapeutic strategy for IVD degeneration in the near future.

Tibial Tuberosity Avulsion Fracture and Open Proximal Tibial Fracture in an Adult: A Case Report and Literature Review.

A displaced tibial tuberosity avulsion fracture associated with an open extra-articular proximal tibial diaphyseal fracture is an uncommon fracture pattern. This case report describes the successful management of such a fracture pattern in a 45-year old male using an open reduction and lag screw fixation of the tuberosity with a minimally invasive reduction and plate fixation of the proximal tibial diaphyseal fracture. A literature search was done to determine the expected clinical outcome of this fracture pattern. This is the first reported adult case of an avulsion fractures of the tibial tuberosity associated with an open proximal tibial diaphyseal fracture successfully treated by an anatomical reduction and fixation of the avulsion fracture of the tibial tuberosity combined with minimally invasive percutaneous plate osteosynthesis of the proximal tibial diaphyseal fractures.