Nanoparticle dispersion in disordered porous media with and without polymer additives.

In purely viscous Newtonian fluids, mechanical mixing of the fluid stream as it moves through an unstructured porous medium controls the long-time dispersion of molecular tracers. In applications ranging from environmental remediation to materials processing, however, particles are transported through porous media in polymer solutions and melts, for which the fluid properties depend on the shear rate and extent of deformation. How the flow characteristics of polymer solutions affect the spreading of finite-sized particles remains poorly understood - both on the microscopic scale as local velocity profiles, and on the macroscale as dispersion. Here, we show across a range of flow rates and disordered porous media configurations that the long-time transport coefficients of particles flowed in water, in a viscous Newtonian fluid, and in a non-Newtonian shear-thinning polymer solution collapse onto scaling curves, independent of the fluid rheology. Thus the addition of polymer does not impact nanoparticle dispersion through disordered porous media.

Nanoparticle diffusion in crowded and confined media.

We identify distinct mechanisms controlling slowing of nanoparticle diffusion through complex media featuring both rigid geometrical confinement and soft mobile crowders. Towards this end, we use confocal microscopy and single particle tracking to probe the diffusion of 400 nm nanoparticles suspended in Newtonian water, in a Newtonian glycerol/water mixture, or in a non-Newtonian polymer solution through a model porous medium, a packed bed of microscale glass beads. The mobility of nanoparticles, as quantified by the long-time diffusion coefficient extracted from the particle mean-squared displacement, slows as the average pore size of the packed bed media decreases for both Newtonian and non-Newtonian solutions. The distribution of particle displacements is non-Gaussian, consistent with the spatial heterogeneity of the geometrical confinement imposed by the packed bed. The slowing of nanoparticle mobility in all solutions follows the predictions of models that describe hydrodynamic interactions with the packed bed. In non-Newtonian solutions, depletion interactions due to the polymers near the glass beads result in temporary adsorption of particles onto the bead surface, as indicated by a stretched-exponential distribution of residence times. Our results therefore suggest that the confined diffusive dynamics of nanoparticles in polymer solutions is controlled by two competing mechanisms: hydrodynamic interactions between particles and spatial obstacles, which dictate the long-time slowing of diffusion, and depletion interactions between particles and confining walls due to the macromolecules, which control transient adsorption and hence alter the statistics of the short-time motion.

Electric field induced changes in protein conformation.

The effect of a low strength oscillating electric field on the conformation of Bovine Serum Albumin (BSA) and Lysozyme in solution has been measured. A purpose built cell has been used to measure the real time autofluorescence and Circular Dichroism of the protein solutions exposed to electric fields of differing strength and frequency. Exposure to the electric fields results in protein unfolding for both Lysozyme and BSA. The applied field strengths are extremely small compared to the protein inter-chain intra-molecular forces. We propose a model whereby the electrophoretic motion of the proteins leads to a frictional force that results in protein unfolding. For BSA and Lysozyme in the electric fields used in this study, the shear rates at the protein surface under electrophoretic motion are of order 10(3) and 10(4) s(-1) respectively. Prolonged electric field exposure results in significant frictional energy dissipation in the proteins. The energy dissipated in the proteins results in protein unfolding, which is a critical initial step for protein aggregation and potentially amyloid fibril formation.

The effect of concentration, temperature and stirring on hen egg white lysozyme amyloid formation.

Lysozyme is associated with hereditary systemic amyloidosis in humans. Hen egg white lysozyme (HEWL) has been extensively studied as an amyloid forming protein. In this study, we investigated HEWL amyloid formation over a range of temperatures at two stirring speeds and at low concentrations to avoid gel formation. The amyloid fibril formation was found to follow first order kinetics with the rate determining step being the unfolding of the lysozyme. Both the rate of formation and final amount of amyloid formed show maxima with temperature at approximately at 65 °C. CD measurements show that the lysozyme is unfolded by 55 °C. The decrease in amyloid formation at temperatures above 65 °C is attributed to competing amorphous aggregation. The majority of the non-fibrillar aggregates are small and uniform in size with a few larger amorphous aggregates observed in the AFM images.

Shear flow induced changes in apolipoprotein C-II conformation and amyloid fibril formation.

The misfolding and self-assembly of proteins into amyloid fibrils that occur in several debilitating diseases are affected by a variety of environmental factors, including mechanical factors associated with shear flow. We examined the effects of shear flow on amyloid fibril formation by human apolipoprotein C-II (apoC-II). Shear fields (150, 300, and 500 s(-1)) accelerated the rate of apoC-II fibril formation (1 mg/mL) approximately 5-10-fold. Fibrils produced at shear rates of 150 and 300 s(-1) were similar to the twisted ribbon fibrils formed in the absence of shear, while at 500 s(-1), tangled ropelike structures were observed. The mechanism of the shear-induced acceleration of amyloid fibril formation was investigated at low apoC-II concentrations (50 µg/mL) where fibril formation does not occur. Circular dichroism and tryptophan fluorescence indicated that shear induced an irreversible change in apoC-II secondary structure. Fluorescence resonance energy transfer experiments using the single tryptophan residue in apoC-II as the donor and covalently attached acceptors showed that shear flow increased the distance between the donor and acceptor molecules. Shear-induced higher-order oligomeric species were identified by sedimentation velocity experiments using fluorescence detection, while fibril seeding experiments showed that species formed during shear flow are on the fibril formation pathway. These studies suggest that physiological shear flow conditions and conditions experienced during protein manufacturing can exert significant effects on protein conformation, leading to protein misfolding, aggregation, and amyloid fibril formation.

Osteosarcoma treatment: state of the art.

Osteosarcoma (OS) is a class of cancer originating from bone, mainly afflicting children or young adults. It is the second highest cause of cancer-related death in these age groups, mainly due to development of often fatal metastasis, usually in the lungs. Survival for these patients is poor despite the aggressive use of surgery, chemotherapy, and/or radiotherapy. Thus, new effective drugs and other forms of therapy are needed. This article reviews the biology and the state of the art management of OS. New experimental drugs and potential therapies targeting molecular pathways of OS are also discussed.

Shear Induced Interactions Cause Polymer Compression.

Shear induced particle pressure occurs in concentrated suspensions of particles. Importantly, the significance of the shear induced particle pressure has not been recognized in polymer rheology. The shear induced particle pressure results in an inward pressure on the polymer chains resulting in a shear dependent compressive force. The analytical form of the force balance equations that incorporate the effect of shear induced particle pressure predict a reduced polymer blob size and reducing viscosity with increasing shear rate as has been observed experimentally. Power law behavior is found for the viscosity in accord with the general observations for concentrated polymer rheology.

Tyrosine autofluorescence as a measure of bovine insulin fibrillation.

The traditional approach to investigating the partial unfolding and fibrillation of insulin, and proteins at large, has involved use of the dyes 1-anilinonaphthalene-8-sulphonic acid (ANS) and Thioflavin T (ThT), respectively. We compare the kinetic profiles of ThT, ANS, light scattering, and intrinsic Tyr fluorescence during insulin fibrillation. The data reveal that the sequence of structural changes (dimers --> monomers --> partially unfolded monomers --> oligomeric aggregates --> fibrils) accompanying insulin fibrillation can be detected directly using intrinsic Tyr fluorescence. The results indicate that at least two distinguishable structural intermediates precede fibril development. There is no evidence of tyrosinate or dityrosine during insulin aggregation. Obtaining such critical information from the protein itself is complementary to existing aggregation probes and affords the advantage of directly examining structural changes that occur at the molecular level, providing concrete details of the early events preceding fibrillation.

Shear-induced deformation of bovine insulin in Couette flow.

We have applied a uniform, shear-driven flow field (Couette flow) to study the effect of shear on the structure and conformation of aqueous bovine insulin, in situ and in real time, using intrinsic Tyr fluorescence and circular dichroism (CD) spectroscopy. The morphology of post-shear insulin samples was analyzed using atomic force microscopy (AFM). Both fluorescence and CD data show a shear-dependent deformation of bovine insulin in Couette flow. The shear effect is more pronounced with increasing shear rate. AFM images show large aggregates for insulin samples sheared at 200 and 400 s(-1), whereas samples sheared at 600 s(-1) contained fibrillar forms. We hypothesize that helical segments unfold upon extensional strain in the deformation flow field, resulting in unstructured, aggregation-prone insulin molecules. The occurrence of rotational diffusion in the direction of flow facilitates the coalescence of deformed insulin molecules into oligomeric aggregates. The size of the insulin aggregates diminished with increasing shear rate. This shows that the deformation cycle in fast flow fields retards the formation of large aggregates and promotes the ordering of deformed insulin molecules into the more stable fibrillar forms.

Aggregation of water-soluble conjugated polymers in Couette shear flow.

Aqueous solutions of the conjugated polymer poly(2,5-disulfopropoxy-1,4-phenylene vinylene) (DPS-PPV) blended with poly(vinyl alcohol) (PVA) have been exposed to Couette shear flow and studied using fluorescence techniques. Significant aggregation of the DPS-PPV and PVA molecules occurred during shear exposure, resulting in an 80% decrease in solution fluorescence intensity and formation of visible polymer particles. The aggregation process caused a separation of the DPS-PPV molecules where the fluorescence of the aggregated particles had a red-shifted emission peak at a wavelength of 594 nm, and the remaining solution had a blue-shifted emission at 513 nm, as compared to an initial emission peak at 574 nm. The fluorescence excitation spectra of the aggregated particles became broadened while the excitation peak of the remaining solution narrowed. This has great implications for the processing of aqueous conjugated polymer systems in various polymer blends, because aggregation could cause significant problems for device manufacture.

The viscosity-radius relationship for concentrated polymer solutions.

A key assumption of polymer physics is that the random chain polymers extend in flow. Recent experimental evidence has shown that polymer chains compress in Couette flow in a manner counter to expectation. Here, scaling arguments and experimental evidence from the literature are used to determine the relationship between the viscosity, η, and chain radius of gyration, RG. The viscosity-radius of gyration relationship is found to be [Formula: see text] where m([Formula: see text]) is the power law exponent of the viscosity-temperature relationship that depends on the specific polymer-solvent system and the shear rate, [Formula: see text]. The viscosity is shown to be a power law function of the radius, and to decrease with decreasing radius under conditions where the chains are ideal random walks in concentrated solution. Furthermore, this relationship is consistent with both the widely observed viscosity-temperature and viscosity-shear rate behavior observed in polymer rheology. The assumption of extension is not consistent with these observations as it would require that the chains increase in size with increasing temperature. Shear thinning is thus a result of a decreasing radius with increasing shear rate as [Formula: see text] where n is the power law exponent. Furthermore, the thermal expansion coefficients determine the variation in the power law exponents that are measured for different polymer systems. Typical values of n enable the measured reduction in coils size behavior to be fitted. Furthermore, the notion that polymer chains extend to reduce the viscosity implies that an increasing chain size results in a reduced viscosity is addressed. This assumption would require that the viscosity increases with reducing coil radius which is simply unphysical.

Combined Fenton and starvation therapies using hemoglobin and glucose oxidase.

Separately, Fenton and starvation cancer therapies have been recently reported as impressive methods for tumor destruction. Here, we introduce natural hemoglobin and glucose oxidase (GOx) for efficient cancer treatment following combined Fenton and starvation therapies. GOx and hemoglobin were encapsulated in zeolitic imidazolate frameworks 8 (ZIF-8) to fabricate a pH-sensitive MOF activated by tumor acidity. In the slightly acidic environment of cancer cells, GOx is released and it consumes d-glucose and molecular oxygen, nutrients essential for the survival of cancer cells, and produces gluconic acid and hydrogen peroxide, respectively. The produced gluconic acid increases the acidity of the tumor microenvironment leading to complete MOF destruction and enhances hemoglobin and GOx release. The Fe ions from the heme groups of hemoglobin also release in the presence of both endogenous and produced H2O2 and generate hydroxyl radicals. The produced OH˙ radical can rapidly oxidize the surrounding biomacromolecules in the biological system and treat the cancer cells. In vitro experiments demonstrate that this novel nanoparticle is cytotoxic to cancer cells HeLa and MCF-7, at very low concentrations (<2 µg mL-1). In addition, the selectivity index values are 5.52 and 11.04 for HeLa and MCF-7 cells, respectively, which are much higher than those of commercial drugs and those of similar studies reported by other research groups. This work thus demonstrates a novel pH-sensitive system containing hemoglobin and GOx for effective and selective cancer treatment using both radical generation and nutrient starvation.

How does shear affect Abeta fibrillogenesis?

The fibrillogenesis of Abeta1-40 proceeds via three main stages: (i) formation of aggregates from monomers, (ii) linear association of these aggregates to form "beaded" protofibrils, and (iii) fusion and structural reorganization of protofibrils into mature fibrils. We have studied the effect of shear on the rate of each of these steps through a combination of fluorescence, atomic force microscopy, and circular dichroism experiments. We find that shear increases the rate of the first two stages (aggregation and protofibril formation) and inhibits the third. Our hypothesis is that in the first stage shear mechanically perturbs the peptide from its native state inducing aggregation via hydrophobic interactions; in the second stage, shear enhances the linear alignment of aggregates due to minimization of drag in the shear flow field; in the third stage, exposure to constant and uniform shear inhibits the formation of mature fibrils.

Effect of natural biopolymers on amyloid fibril formation and morphology.

Amyloid fibrils are associated with the pathogenesis of protein misfolding diseases such as Alzheimer's disease. These fibrils typically exhibit different morphologies when grown in vitro, and this has been known to affect their biological properties and cytotoxicity. The formation kinetics and resultant morphology of fibrils formed from the model proteins Bovine Insulin and Hen Egg White Lysozyme have been measured. We show that the presence of gum arabic and pectin during fibril formation cause the amyloid fibrils formed to associate into higher order fibrillar aggregates. It is postulated that the carbohydrates act as a template to promote inter-fibril association, resulting in larger, thicker fibrils. This observation provides some insight into the differences in growing amyloid fibrils in vitro in the absence or presence of other high molecular weight compounds. Furthermore, these findings suggest a method of tailoring fibril structure for applications in nanotechnology and bio-template applications.

Cancer Treatment through Nanoparticle-Facilitated Fenton Reaction.

Currently, cancer is the second largest cause of death worldwide and has reached critical levels. In spite of all the efforts, common treatments including chemotherapy, photodynamic therapy, and photothermal therapy suffer from various problems which limit their efficiency and performance. For this reason, different strategies are being explored which improve the efficiency of these traditional therapeutic methods or treat the tumor cells directly. One such strategy utilizing the Fenton reaction has been investigated by many groups for the possible treatment of cancer cells. This approach is based on the knowledge that high levels of hydrogen peroxide exist within cancer cells and can be used to catalyze the Fenton reaction, leading to cancer-killing reactive oxygen species. Analysis of the current literature has shown that, due to the diverse morphologies, different sizes, various chemical properties, and the tunable structure of nanoparticles, nanotechnology offers the most promising method to facilitate the Fenton reaction with cancer therapy. This review aims to highlight the use of the Fenton reaction using different nanoparticles to improve traditional cancer therapies and the emerging Fenton-based therapy, highlighting the obstacles, challenges, and promising developments in each of these areas.

Targeted Graphene Oxide Networks: Cytotoxicity and Synergy with Anticancer Agents.

An effective strategy to inhibit endocytosis in cancer cells is presented where modified net-type graphene oxide (GO) sheets, bound with multiple cell surface receptors, are introduced and synthesized as novel anticancer agents. The results suggest that the binding connects GO sheets with neighboring lipid rafts, neutralizes endocytosis, and causes metabolic deprivation. As a result, tumor cell survival and proliferation are reduced. Live cell confocal microscopy imaging reveals that GO-PEGFA (folate-PEGylated GO) (PEG, polyethylene glycol) is internalized by tumor cells, while GO-PEGRGD (tripeptide Arg-Gly-Asp PEGylated GO) associates with the external cell membrane (not internalized). In vitro exposure of tumor cells to GO-PEGFA or GO-PEGRGD reduces the cell viability by 35%, compared to 50% reduction using methotrexate (100 µM). The combination of modified GO sheets with methotrexate or doxorubicin shows a greater toxicity (80% reduction in cell viability) than the individual agents. The proposed setup demonstrates a significant synergy in limiting tumor cell growth.

Photophysical and Fluorescence Anisotropic Behavior of Polyfluorene ß-Conformation Films.

We demonstrate a systematic visualization of the unique photophysical and fluorescence anisotropic properties of polyfluorene coplanar conformation (ß-conformation) using time-resolved scanning confocal fluorescence imaging (FLIM) and fluorescence anisotropy imaging microscopy (FAIM) measurements. We observe inhomogeneous morphologies and fluorescence decay profiles at various micrometer-sized regions within all types of polyfluorene ß-conformational spin-coated films. Poly(9,9-dioctylfluorene-2,7-diyl) (PFO) and poly[4-(octyloxy)-9,9-diphenylfluoren-2,7-diyl]-co-[5-(octyloxy)-9,9-diphenylfluoren-2,7-diyl] (PODPF) ß-domains both have shorter lifetime than those of the glassy conformation for the longer effective conjugated length and rigid chain structures. Besides, ß-conformational regions have larger fluorescence anisotropy for the low molecular rotational motion and high chain orientation, while the low anisotropy in glassy conformational regions shows more rotational freedom of the chain and efficient energy migration from amorphous regions to ß-conformation as a whole. Finally, ultrastable ASE threshold in the PODPF ß-conformational films also confirms its potential application in organic lasers. In this regard, FLIM and FAIM measurements provide an effective platform to explore the fundamental photophysical process of conformational transitions in conjugated polymer.

Tris(2,2'-bipyridyl)ruthenium(II) chemiluminescence enhanced by silver nanoparticles.

Mixtures of silver(I) and citrate that are used to produce silver nanoparticles evoke intense chemiluminescence with tris(2,2'-bipyridyl)ruthenium(II) and cerium(IV), which can be exploited for the determination of citrate ions and other analytes over a wide concentration range.

Terraced self assembled nano-structures from laminarin.

The formation of self assembled nano-structures from the biopolymer laminarin dried onto mica is reported. The observed structures are composed of stacked terraced layers decreasing in size away from the mica surface. The layers display a high degree of dimensional regularity as observed using atomic force microscope imaging (AFM). The width of the layers is linearly dependent upon the number of layers in the structure and decreases with layer number away from the mica substrate. The thickness of the layers is uniform throughout the structure. A pore is contained in the central region of each structure with more than one layer. We postulate that these structures have potential use as templates in microelectronic devices and sensors where the central pore has the potential to immobilise functional materials.

MOF-Mediated Destruction of Cancer Using the Cell's Own Hydrogen Peroxide.

A novel reduced iron metal-organic framework nanoparticle with cytotoxicity specific to cancer cells is presented. This nanoparticle was prepared via a hydrothermal method, reduced using hydroquinone, and finally conjugated with folic acid (namely, rMOF-FA). The synthesized nanoparticle shows the controlled release of iron in an acidic ex-vivo environment. Iron present on the rMOF-FA and released into solution can react with high levels of hydrogen peroxide found specifically in cancer cells to increase the hydroxyl radical concentration. The hydroxyl radicals oxidize proteins, lipids, and/or DNA within the biological system to decrease cell viability. In vitro experiments demonstrate that this novel nanoparticle is cytotoxic to cancer cells (HeLa) through generation of OH• inside the cells. At low concentrations of rMOF-FA, the cancer cell viability decreases dramatically, with no obvious reduction of normal cell (NIH-3T3) viability. The calculated half-maximum inhibitory concentration value (IC50) was 43 µg/mL for HeLa cells, which was significantly higher than 105 µg/mL for NIH-3T3. This work thus demonstrates a new type of agent for controlled hydroxyl radical generation using the Fenton reaction to kill the tumor cells.