Accumulation of magnetic iron oxide nanoparticles coated with variably sized polyethylene glycol in murine tumors

Iron oxide nanoparticles have found widespread applications in different areas including cell separation, drug delivery and as contrast agents. Due to water insolubility and stability issues, nanoparticles utilized for biological applications require coatings such as the commonly employed polyethylene glycol (PEG). Despite its frequent use, the influence of PEG coatings on the physicochemical and biological properties of iron nanoparticles has hitherto not been studied in detail. To address this, we studied the effect of 333-20,000 Da PEG coatings that resulted in larger hydrodynamic size, lower surface charge, longer circulation half-life, and lower uptake in macrophage cells when the particles were coated with high molecular weight (M(w)) PEG molecules. By use of magnetic resonance imaging, we show coating-dependent in vivo uptake in murine tumors with an optimal coating M(w) of 10,000 Da.     

Packaging materials with tailor made light transmission properties for food protection

Packaging material with optimal light barrier properties can prevent food quality deterioration. For dairy products, wavelength in the visible region between 400–450 nm and 600–650 nm should be blocked out due to the content of chlorophyll in dairy products. Six low density polyethylene blown films were formulated with the combination of four different pigments and additives: green, yellow, silver additive, and optical brightener, in addition to four reference samples. All films were transparent. Optical properties and light transmission were measured for each film, and microscopy analyses were used to investigate the surface topography. The sample containing high concentration of both green and yellow pigments had the lowest value in gloss and transmittance. This film blocked the light below 450 nm and transmitted 10% at 600–650 nm. Optical brightener had an effect only on visual appearance but not on light transmission properties. Samples containing silver additive were more intense green and gave a higher light transmission in blue region (380–500 nm) and lower in red region (600–700 nm) compared with samples without silver additive. These developed films can be applied in dairy products and other food products in the future. POLYM. ENG. SCI., 52:2015–2024, 2012. © 2012 Society of Plastics Engineers     

Conductivity enhancement in carbon nanocone adhesive by electric field induced formation of aligned assemblies

We show how an alternating electric field can be used to assemble carbon nanocones (CNCs) and align these assemblies into microscopic wires in a commercial two-component adhesive. The wires form continuous pathways that may electrically connect the alignment electrodes, which leads to directional conductivity (～10(-3) S/m) on a macroscopic scale. This procedure leads to conductivity enhancement of at least 2-3 orders of magnitude in the case where the CNC fraction (～0.2 vol %) is 1 order of magnitude below the percolation threshold (～2 vol %). The alignment and conductivity are maintained on curing that joins the alignment electrodes permanently together. If the aligned CNC wires are damaged before curing, they can be realigned by an extended alignment period. This concept has implications in areas such as electronic packaging technology.     

Polyethylenimine-carbon nanotube nanohybrids for siRNA-mediated gene silencing at cellular level

Carbon nanotubes (CNTs) covalently modified with low molecular weight polyethylenimine (PEI) are able to bind and deliver siRNA to cells with higher efficacy than a reference lipidic carrier. The performances of the nanohybrid are rationalized by the combination of the cell penetration and endosomal escape properties of CNTs and PEI, respectively.     

Emergent membrane-affecting properties of BSA-gold nanoparticle constructs

By adsorbing bovine serum albumin (BSA) on gold nanoparticles (Aunps) with diameters 30 nm and 80 nm, different degrees of protein unfolding were obtained. Adsorption and adlayer conformation were characterized by UV-vis spectroscopy, ζ-potential measurements, steady-state and time-resolved fluorescence. The unfolding was also studied using 1-anilino-8-naphthalene sulfonate (ANS) as an extrinsic probe, showing that BSA unfolds more on 80 nm Aunp than on 30 nm Aunp. Langmuir monolayer studies using two distinct methods of introducing the BSA and BSA-Aunp constructs accompanied with Brewster Angle Microscopy (BAM) and Digital Video Microscope (DVM) imaging demonstrated that BSA-Aunp constructs induce film miscibility with L-α-phosphatidylethanolamine not seen for BSA or Aunp alone. The changes induced by partial unfolding clearly give better film-penetration ability, as well as disruption of liquid crystalline domains in the film, thereby inducing film miscibility. Gold or protein only does not possess the nanoscale film-affecting properties of the protein-gold constructs, and as such the surface-active and miscibility-affecting characteristics of the BSA-Aunp represent emergent qualities.     

“SPURT FRACTURE” IN CAPILLARY FLOW

The critical conditions under which flow curves in capillary flow abruptly change their slope to zero (spurt) and the influence of solvent additive and solvent power on this phenomenon have been investigated. Based on a forced high elastic state concept an expression for the so-called spurt phenomenon, i.e. fracture-induced slip at the wall in a capillary of a capillary rheometer, is deduced. It is found that the spurt fracture stress, τ^s _cr, and the spurt fracture shear rate, γ^s _cr, can be represented by the master curve log (τ ^s _crr ((p/M_c)PE(M_c/p))^2/3 against log (a_T γ^s _cr), where a_T is the WLF shift factor, M_c the molecular weight between entanglements and p the density.

Estimation of slip rates at the wall and measurements on slightly crosslinked high density polyethylene supports the assumption that spurt results from melt fracture at the capillary wall.

Only addition of the non-solvent calcium stearate (with high density polyethylene) results in flow behavior which significantly deviates from that found for samples containing good solvents. Gel permeation chromato-graphy indicates that if chain scission resulting in lower molecular weight takes place, it will be limited to thin layers near the capillary wall.

melt fracture in the capillary cannot be reached. The flow behavior is influenced by addition of the non-solvent calcium stearate. The slopes of the flow curves is changed at relatively low shear rates but the high molecular weight polymer DMDS 5140 never the less shows spurt behavior at the same stress as for the pure sample.

This behavior may tentatively be interpreted as being caused by the formation of a boundary layer of non-solvent at low shear rate the thickness of which depends on the polymer and flow field. At stresses corresponding to the critical conditions, fracture in the polymer takes place. The interface between the non-solvent layer and the polymer matrix must according to Han61 be expected to be unstable     

Functionalization of electrospun fibers of poly(ε-caprolactone) with star shaped NCO-poly(ethylene glycol)-<Emphasis Type="Italic">stat</Emphasis>-poly(propylene glycol) for neuronal cell guidance

Microfibers produced with electrospinning have recently been used in tissue engineering. In the development of artificial implants for nerve regeneration they are of particular interest as guidance structures for cell migration and axonal growth. Using electrospinning we produced parallel-orientated biocompatible fibers in the submicron range consisting of poly(ε-caprolactone) (PCL) and star shaped NCO-poly(ethylene glycol)-stat-poly(propylene glycol) (sPEG). Addition of the bioactive peptide sequence glycine-arginine-glycine-aspartate-serine (GRGDS) or the extracellular matrix protein fibronectin to the electrospinning solution resulted in functionalized fibers. Surface characteristics and biological properties of functionalized and non-functionalised fibers were investigated. Polymer solutions and electrospinning process parameters were varied to obtain high quality orientated fibers. A polymer mixture containing high molecular weight PCL, PCL-diol, and sPEG permitted a chemical reaction between hydroxyl groups of the diol and isocyanante groups of the sPEG. Surface analysis demonstrated that sPEG at the fiber surface minimized protein adhesion. In vitro experiments using dorsal root ganglia explants showed that the cell repellent property of pure PCL/sPEG fibers was overcome by functionalization either with GRGDS peptide or fibronectin. In this way cell migration and axonal outgrowth along fibers were significantly increased. Thus, functionalized electrospun PCL/sPEG fibers, while preventing non-specific protein adsorption, are a suitable substrate for biological and medical applications.     

Pattern Noise in the Frequency ΔΣ Modulator

In this paper, we show that the first-order frequency delta–sigma modulator is equivalent to a traditional delta–sigma modulator with respect to pattern noise. We further propose two techniques for reducing the effect of pattern noise. The first technique is based on time-domain dithering which is implemented by adding white phase noise to the FM signal. The second technique is based on locating the narrow dynamic range that may be in this kind of modulators, in a pattern noise valley. This technique can utilize pattern noise to make the modulator provide significantly higher digital resolution than the white quantization noise model predicts. Finally, the theory is verified by measurements.