Polyethylene Glycol Layer Research Articles

Adsorption of Plasma Proteins onto PEGylated Lipid Bilayers: The Effect of PEG Size and Grafting Density.

Lipid bilayers grafted with polyethylene glycol (PEG) of different sizes (Mw = 750, 2000, and 5000) and grafting densities (1.6-25 mol % of PEGylated lipid in dipalmitoylphosphatidylcholine (DPPC) lipid molecules) were simulated with human serum albumin (HSA) using coarse-grained force fields. At low enough grafting density, the PEG has a conformation similar to that of an isolated chain in water, and its Flory radius RF is smaller than the distance between the grafting points (d), which is the so-called "mushroom" regime. In contrast, densely grafted PEG chains (RF > d) extend like brushes, with brush layer thickness given by the Alexander-de Gennes theory. A nearly spherical HSA added to this simulation migrates to the bilayer surface because of the charge interactions between anion residues of HSA and cationic cholines of DPPC, but this HSA-bilayer binding can be sterically suppressed by the PEG chains to an extent that depends on the PEG size and grafting density. In particular, regardless of the extent of the coverage of the PEG on the bilayer, the binding between HSAs and bilayers is suppressed by the PEG layer in a brush but not in a mushroom, indicating that the attractive force between proteins and bilayers can overcome the steric effect of the PEG layer in the mushroom state or in the transition region from mushroom to brush. This helps explain and clarify experiments that show much less adsorption of plasma proteins onto the particle or membrane surface when PEGs are in the brush rather than in the mushroom state.

Unexpected Temperature Behavior of Polyethylene Glycol Spacers in Copolymer Dendrimers in Chloroform.

We have studied copolymer dendrimer structure: carbosilane dendrimers with terminal phenylbenzoate mesogenic groups attached by poly(ethylene) glycol (PEG) spacers. In this system PEG spacers are additional tuning to usual copolymer structure: dendrimer with terminal mesogenic groups. The dendrimer macromolecules were investigated in a dilute chloroform solution by 1H NMR methods (spectra and relaxations). It was found that the PEG layer in G = 5 generations dendrimer is “frozen” at high temperatures (above 260 K), but it unexpectedly becomes “unfrozen” at temperatures below 250 K (i.e., melting when cooling). The transition between these two states occurs within a small temperature range (~10 K). Such a behavior is not observed for smaller dendrimer generations (G = 1 and 3). This effect is likely related to the low critical solution temperature (LCST) of PEG and is caused by dendrimer conformations, in which the PEG group concentration in the layer increases with growing G. We suppose that the unusual behavior of PEG fragments in dendrimers will be interesting for practical applications such as nanocontainers or nanoreactors.

Thermal Transport across Surfactant Layers on Gold Nanorods in Aqueous Solution.

Ultrafast transient absorption experiments and molecular dynamics simulations are utilized to investigate the thermal transport between aqueous solutions and cetyltrimethylammonium bromide (CTAB)- or polyethylene glycol (PEG)-functionalized gold nanorods (GNRs). The transient absorption measurement data are interpreted with a multiscale heat diffusion model, which incorporates the interfacial thermal conductances predicted by molecular dynamics. According to our observations, the effective thermal conductance of the GNR/PEG/water system is higher than that of the GNR/CTAB/water system with a surfactant layer of the same length. We attribute the enhancement of thermal transport to the larger thermal conductance at the GNR/PEG interface as compared with that at the GNR/CTAB interface, in addition to the water penetration into the hydrophilic PEG layer. Our results highlight the role of the GNR/polymer thermal interfaces in designing biological and composite-based heat transfer applications of GNRs, and the importance of multiscale analysis in interpreting transient absorption data in systems consisting of low interfacial thermal conductances.

Studies into the effect of temperature on the impact of model particles in co-melt granulation

In co-melt granulation, collisions occur between the particles to be agglomerated and the binder material. Depending on the stage of granulation, the binder material can be in the solid or liquid phase. The outcome of these collisions controls the dynamics of the granulation process and the fundamental physics of the impacts are of interest. This paper examines the impact of glass beads (model particles) and solid Poly Ethylene Glycol (PEG) flakes on a substrate of PEG as the temperature of the PEG layer is increased from below its melting point to above it. While the layer is in the solid state, the result of the impact can be quantified by the coefficient of restitution. When the layer is in the liquid state, the impact can be quantified by the immersion behaviour. The results obtained show that the coefficient of restitution between either glass beads and PEG flakes and the PEG layer is strongly affected by temperatures. As the PEG layer approaches its melting point, the coefficient of restitution falls to zero. Once the temperature of the PEG layer exceeds the melting point, the impact is characterised by a transient maximum indentation and then rebound to an equilibrium position. These too are strongly dependent on temperature.

Intense PEGylation of Enzyme Surfaces: Relevant Stabilizing Effects.

This chapter describes the physicochemical coating of the surface of immobilized enzymes with a dense layer of polyethylene glycol (PEG) to improve enzyme stability. One hypothesis is that a dense, viscous, polar PEG layer around the enzyme would enhance enzyme thermal stability, while still providing access to the active site. PEG groups were attached by using aldehyde-dextran polymers, the dextran polymers are in turn attached to the enzyme surface that have been enriched with excess primary amino groups. The enzymes themselves were initially attached onto porous solids such that they may be separated easily from the reaction mixtures for easy downstream processing and that they may be recycled to reduce the cost of the biocatalyst. The hierarchical modification of enzyme surface with three different sublayers, under chemical design, provided a rational control at several structural levels. Few methods for increasing the number of amino groups on the surface of the enzyme are described: (a) chemical amination of carboxyl residues and (b) coating of the enzyme surface with cationic polymers containing a high percentage of primary amines. Reliable protocols for the PEGylation of four different enzymes are described here. For example, lipases from Thermomyces lanuginosa, Candida antarctica B, and Rhizomucor miehei attached to octyl sepharose and chemically modified via PEGylation are stabilized from 7- to 50-fold when compared to the stability of the corresponding unmodified enzyme. A derivative of endoxylanase from Trichoderma reesei, immobilized by multipoint covalent attachment on glyoxyl agarose, is stabilized by 50-fold. Very likely, the PEG layer generated a dense, high viscosity medium surrounding the enzyme surface and this increase in viscosity around the enzyme microenvironment resists distortion of enzyme structure by heat or other denaturing agents.

Probing protein complexes inside living cells using a silicon nanowire-based pull-down assay.

Most proteins perform their functions as interacting complexes. Here we propose a novel method for capturing an intracellular protein and its interacting partner out of living cells by utilizing intracellular access of antibody modified vertical silicon nanowire arrays whose surface is covered with a polyethylene glycol layer to prevent strong cell adhesion. Such a feature facilitates the removal of cells by simple washing, enabling subsequent detection of a pulled-down protein and its interacting partner, and further assessment of a drug-induced change in the interacting complex. Our new SiNW-based tool is thus suitable for authentication of protein networks inside living cells.

Two surface gradients of polyethylene glycol for a reduction in protein adsorption.

Polyethylene glycol (PEG) coatings have been commonly used in reducing protein adsorption with the intent of improving a biomaterial's biocompatibility. To elucidate the role of PEG surface density in reducing protein adsorption, two types of grafted PEG surface density gradients were evaluated for the adsorption and desorption of albumin and fibrinogen, two blood proteins. PEG density gradients were characterized using contact angle measurements and X-ray photoelectron spectroscopy. Total internal reflection fluorescence was used to measure protein adsorption kinetics and adsorption profiles on the two types of PEG gradients. The PEG gradient generated by the flow method decreased adsorption of both proteins in proportion to the PEG surface density; however, their desorption by buffer solution from the grafted PEG layer was not complete. In contrast, desorption of two proteins from the grafted PEG layer generated by a UV oxidation method resulted in near-zero adsorbed amount. The difference between the two types of gradients might have originated from counter-diffusion of PEG and water molecules occurring during the flow method procedure.

Rapid and quantitative detection of C-reactive protein based on quantum dots and immunofiltration assay.

Convenient and rapid immunofiltration assays (IFAs) enable on-site “yes” or “no” determination of disease markers. However, traditional IFAs are commonly qualitative or semi-quantitative and are very limited for the efficient testing of samples in field diagnostics. Here, we overcome these limitations by developing a quantum dots (QDs)-based fluorescent IFA for the quantitative detection of C-reactive proteins (CRP). CRP, the well-known diagnostic marker for acute viral and bacterial infections, was used as a model analyte to demonstrate performance and sensitivity of our developed QDs-based IFA. QDs capped with both polyethylene glycol (PEG) and glutathione were used as fluorescent labels for our IFAs. The presence of the surface PEG layer, which reduced the non-specific protein interactions, in conjunction with the inherent optical properties of QDs, resulted in lower background signal, increased sensitivity, and ability to detect CRP down to 0.79 mg/L with only 5 µL serum sample. In addition, the developed assay is simple, fast and can quantitatively detect CRP with a detection limit up to 200 mg/L. Clinical test results of our QD-based IFA are well correlated with the traditional latex enhance immune-agglutination aggregation. The proposed QD-based fluorescent IFA is very promising, and potentially will be adopted for multiplexed immunoassay and in field point-of-care test.

Tumor-targeting, pH-sensitive nanoparticles for docetaxel delivery to drug-resistant cancer cells.

The attachment of polyethylene glycol (PEG) increases the circulation time of drug-containing nanoparticles; however, this also negatively affects cellular uptake. To overcome this problem, unique lipid polymer hybrid (LPH) nanoparticles were developed with a pH-responsive PEG layer that detached prior to cell uptake. Docetaxel (DTX) was incorporated into the lipid core of the nanoparticles, which was then shielded with the pH-responsive block co-polymer polyethylene glycol-b-polyaspartic acid (PEG-b-PAsp) using a modified emulsion method. The optimized LPH nanoparticles were ~200 nm and had a narrow size distribution. Drug release from DTX-loaded LPH (DTX-LPH) nanoparticles was pH-sensitive, which is beneficial for tumor targeting. More importantly, DTX-LPH nanoparticles were able to effectively induce apoptosis in cancer cells. The negative surface charge and PEG shell of vehicle remarkably enhanced the blood circulation and physiological activity of DTX-LPH nanoparticles compared with that of free DTX. The nanoparticles were also found to reduce the size of tumors in tumor-bearing xenograft mice. The in vivo anticancer effect of DTX-LPH nanoparticles was further confirmed by the elevated levels of caspase-3 and poly ADP ribose polymerase found in the tumors after treatment. Thus, the results suggest that this novel LPH system could be an effective new treatment for cancer.

Imaging of Polyethylene Glycol Layers on Nanoparticles

Journal Article Imaging of Polyethylene Glycol Layers on Nanoparticles Get access Sarah R Anderson, Sarah R Anderson Electron Microscopy Laboratory, and Search for other works by this author on: Oxford Academic Google Scholar Mackensie C Smith, Mackensie C Smith Nanotechnology Characterization Laboratory, Cancer Research Technology Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21702 Search for other works by this author on: Oxford Academic Google Scholar Jeffrey D Clogston, Jeffrey D Clogston Nanotechnology Characterization Laboratory, Cancer Research Technology Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21702 Search for other works by this author on: Oxford Academic Google Scholar Anil K Patri, Anil K Patri Nanotechnology Characterization Laboratory, Cancer Research Technology Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21702 Search for other works by this author on: Oxford Academic Google Scholar Scott E McNeil, Scott E McNeil Nanotechnology Characterization Laboratory, Cancer Research Technology Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD 21702 Search for other works by this author on: Oxford Academic Google Scholar Ulrich Baxa Ulrich Baxa Electron Microscopy Laboratory, and Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 21, Issue S3, 1 August 2015, Pages 231–232, https://doi.org/10.1017/S1431927615001956 Published: 23 September 2015

Localized delivery of non-viral gene-bearing nanoparticles into the rat brain following focused ultrasound-mediated BBB opening

By preventing more than 98% of currently used pharamaceutical agents from entering the brain, the blood-brain barrier critically reduces the ability of therapeutics to treat a variety of central nervous system (CNS) disorders including glioblastoma and neurodegenerative diseases. Focused ultrasound (FUS) mediated microbubble oscillation and subsequent blood brain barrier (BBB) permeabilization has been explored as a powerful non-invasive strategy for the delivery of circulating therapeutic agents into the CNS. FUS in conjunction with microbubbles has been shown to facilitate non-damaging, reversible and localized disruption of the BBB, leading to substantial increases in nanoparticle (NP) concentrations in ultrasound-treated tissue. Once beyond the BBB, the extracellular matrix acts as a steric and adhesive barrier and limits NP distribution. Coating sub-100 nm nanoparticles with a dense brush layer of polyethylene glycol (PEG) to limit the interactions with the ECM leads to a significant improvement of their diffusivity in brain tissue. The current study investigates the ability of FUS to deliver densely PEGylated brain penetrating cationic polymer-based gene vectors across the BBB to mediate robust and long-term transgene expression.

Ultrasound-microbubble targeted delivery of ICAM-1 in mouse model of peripheral arterial disease

Peripheral arterial disease (PAD) affects 12 million people in the United States. Unfortunately, current treatments are highly invasive and have limited efficacy. Ultrasound (US) in conjunction with microbubbles (MB) has recently been explored as a non-invasive strategy for the delivery of intravascularly circulating therapeutic agents. US mediated MB oscillation can lead to non-damaging, reversible and localized vascular permeabilization resulting in substantial increases of nanoparticle (NP) concentrations in US-treated tissue. Furthermore, by coating NPs with a brush layer of polyethylene glycol (PEG), NPs have long circulating half-lives and limited toxicity. This study investigates the ability of US to deliver ICAM-1-bearing PEG/polyethylenimine (PEG/PEI) NPs to the vascular endothelium in a mouse model of PAD. ICAM-1, an adhesion molecule, expressed post-occlusion by the endothelium of collateral arteries has previously been shown to aid in blood flow restoration. Overexpression of ICAM-1 in this model aims to re-establish pre-occlusion blood flow non-invasively.

Nanostructural, morphological and magnetic studies of PEG/Mn(1−x)Zn(x)Fe2O4 nanoparticles synthesized by co-precipitation

The coating of Polyethylene Glycol (PEG) on zinc substituted manganese ferrite nanoparticles has been reported in the present study. Single phase nanoferrites bearing the chemical formula Mn(1−x)Zn(x)Fe2O4 (0.0≤x≤1.0) were produced under low reaction temperature of 75°C and their morphological, structural and magnetic characterizations were performed. The prepared ferrites were characterized using X-ray diffraction (XRD), field emission scan electron microscopy images (FE-SEM), Fourier transform infrared spectroscopy (FT-IR) and vibrating sample magnetometer (VSM) techniques. XRD revealed the formation of spinel single-phase structure for the samples with Zn-content. The crystallite sizes estimated using Scherer formula were in the range 4.50–15.89nm. The characteristic bands of PEG as observed in its Fourier transform infrared spectrum technique were also present in PEG layer on Mn–Zn ferrite nanoparticles, hence confirming its presence. The presence of PEG on Mn(1−x)Zn(x)Fe2O4 nanoparticles, spherical formation of PEG coated Mn(1−x)Zn(x)Fe2O4 nanoparticles and reduced agglomeration in the Mn(1−x)Zn(x)Fe2O4 nanoparticles were revealed by FE-SEM. The measurements of magnetic properties at room temperature by VSM showed that all samples behaved superparamagnetic with magnetization (M) and coercivity in the range of 1.86–20.66emu/g and 12.922–30.253Oe, respectively. The M–H loop of all the samples is narrow with low value of coercivity and retentivity; indicating the superparamagnetic nature of these samples.

Seeing sonic hot spots

Materials Science![Figure][1] PTFE coatiing on an NaCl crystal degraded by ultrasonic heating PHOTO: S. YOU ET AL, NATURE COMMUNICATIONS 6 (2 APRIL 2015) © NATURE PUBLISHING GROUP Mechanical impact can detonate explosives, but how impact heats these materials to initiate reactions has been unclear. You et al. used mild ultrasound irradiation to study composite materials—small crystals of sucrose or table salt in rubber—while performing thermal imaging. Uncoated particles remained unheated, but particles that had a coating that could delaminate (a polyethylene glycol layer that liquefies or Teflon) heated very rapidly (up to ∼22,000 K per second). Delamination allows the particle to move and friction-heat against the matrix, an effect that authors also saw in samples of polymer-bonded explosive (PBX). Nat. Commun. 10.1038/ncomms7581 (2015). [1]: pending:yes

Identification of polyethylene glycol-resistant macrophages on stealth imaging in vitro using fluorescent organosilica nanoparticles.

An in vitro imaging system to evaluate the stealth function of nanoparticles against mouse macrophages was established using fluorescent organosilica nanoparticles. Surface-functionalized organosilica nanoparticles with polyethylene glycol (PEG) were prepared by a one-step process, resulting in a brush-type PEG layer. A simultaneous dual-particle administration approach enabled us to evaluate the stealth function of nanoparticles with respect to single cells using time-lapse fluorescent microscopic imaging and flow cytometry analyses. Single-cell imaging and analysis revealed various patterns and kinetics of bare and PEGylated nanoparticle uptake. The PEGylated nanoparticles revealed a stealth function against most macrophages (PEG-sensitive macrophages); however, a stealth function against certain macrophages (PEG-insensitive macrophages) was not observed. We identified and characterized the PEG-resistant macrophages that could take up PEGylated nanoparticles at the same level as bare nanoparticles.

Efficient Drug Delivery and Induction of Apoptosis in Colorectal Tumors Using a Death Receptor 5-Targeted Nanomedicine

Death Receptor 5 (DR5) is a pro-apoptotic cell-surface receptor that is a potential therapeutic target in cancer. Despite the potency of DR5-targeting agents in preclinical models, the translation of these effects into the clinic remains disappointing. Herein, we report an alternative approach to exploiting DR5 tumor expression using antibody-targeted, chemotherapy-loaded nanoparticles. We describe the development of an optimized polymer-based nanotherapeutic incorporating both a functionalized polyethylene glycol (PEG) layer and targeting antibodies to limit premature phagocytic clearance whilst enabling targeting of DR5-expressing tumor cells. Using the HCT116 colorectal cancer model, we show that following binding to DR5, the nanoparticles activate caspase 8, enhancing the anti-tumor activity of the camptothecin payload both in vitro and in vivo. Importantly, the combination of nanoparticle-induced DR5 clustering with camptothecin delivery overcomes resistance to DR5-induced apoptosis caused by loss of BAX or overexpression of anti-apoptotic FLIP. This novel approach may improve the clinical activity of DR5-targeted therapeutics while increasing tumor-specific delivery of systemically toxic chemotherapeutics.

Dispersion and bilayer interaction of single-walled carbon nanotubes modulated by covalent and noncovalent PEGylation

Single-walled carbon nanotubes (SWNTs) covalently functionalised with polyethylene glycol (PEG) or noncovalently coated with PEGylated lipids were simulated in water and in lipid bilayers at different PEG sizes and grafting densities using coarse-grained force fields. Starting with the random position of three SWNT–PEG complexes in water, larger PEGs at higher grafting densities more significantly inhibit the aggregation of SWNTs because of larger radii of gyration and hydrodynamic radii of the SWNT–PEG complex, which influence the thickness and the wrapping extent of PEG layer. In particular, PEG-functionalised SWNTs, where PEGs are evenly grafted along the SWNT, disperse, while PEG-coated SWNTs aggregate because SWNTs are less covered by randomly adsorbed PEGylated lipids. Simulations of SWNT–PEGs in lipid bilayers show that PEG (Mw = 550 and 2000)-functionalised SWNTs bind to the bilayer surface but do not insert into the bilayer, while PEG-coated SWNTs insert into the bilayer because PEGylated lipids detach from SWNTs and mix with bilayer lipids. These findings support recent experiments at the same PEG size and density, which suggested that PEG-coated SWNTs may form bundles and thus cannot be easily excreted through the renal route, while PEG-functionalised SWNTs may remain individual and thus show more renal excretion.

Water-Based Synthesis of Ultrasmall PEGylated Gold–Silica Core–Shell Nanoparticles with Long-Term Stability

Ultrasmall gold nanoparticles have attracted great interest in biomedical applications due to the intrinsic properties of gold nanoparticles and their potential renal clearance capability. We present a synthetic method for a type of sub-10 nm core–shell nanoparticle composed of an ultrasmall gold core, a thin silica shell, and a polyethylene glycol (PEG) outer layer. The thin silica shell is crucial in terms of maintaining colloidal stability of the nanoparticles. The PEG layer provides a neutral surface as well as steric stabilization. The core–shell nanoparticles show long-term stability for nearly a year in both water and PBS buffer solution even when stored at room temperature. The nanoparticle suspensions further exhibit high contrast in a microscale computed tomography scanner. This study suggests that these ultrasmall gold–silica core–shell nanoparticles can be used as a promising platform for future biomedical applications in imaging, diagnostics, and theranostics.

Nanoparticle penetration of human cervicovaginal mucus: the effect of polyvinyl alcohol.

Therapeutic nanoparticles must rapidly penetrate the mucus secretions lining the surfaces of the respiratory, gastrointestinal and cervicovaginal tracts to efficiently reach the underlying tissues. Whereas most polymeric nanoparticles are highly mucoadhesive, we previously discovered that a dense layer of low MW polyethylene glycol (PEG) conferred a sufficiently hydrophilic and uncharged surface to effectively minimize mucin-nanoparticle adhesive interactions, allowing well-coated particles to rapidly diffuse through human mucus. Here, we sought to investigate the influence of surface coating by polyvinyl alcohol (PVA), a relatively hydrophilic and uncharged polymer routinely used as a surfactant to formulate drug carriers, on the transport of nanoparticles in fresh human cervicovaginal mucus. We found that PVA-coated polystyrene (PS) particles were immobilized, with speeds at least 4000-fold lower in mucus than in water, regardless of the PVA molecular weight or incubation concentration tested. Nanoparticles composed of poly(lactide-co-glycolide) (PLGA) or diblock copolymers of PEG-PLGA were similarly immobilized when coated with PVA (slowed 29,000- and 2500-fold, respectively). PVA coatings could not be adequately removed upon washing, and the residual PVA prevented sufficient coating with Pluronic F127 capable of reducing particle mucoadhesion. In contrast to PVA-coated particles, the similar sized PEG-coated formulations were slowed only ~6- to 10-fold in mucus compared to in water. Our results suggest that incorporating PVA in the particle formulation process may lead to the formation of mucoadhesive particles for many nanoparticulate systems. Thus, alternative methods for particle formulation, based on novel surfactants or changes in the formulation process, should be identified and developed in order to produce mucus-penetrating particles for mucosal applications.

CXCR4-targeted and MMP-responsive iron oxide nanoparticles for enhanced magnetic resonance imaging.

MRI offers high spatial resolution with excellent tissue penetration but it has limited sensitivity and the commonly administered contrast agents lack specificity. In this study, two sets of iron oxide nanoparticles (IONPs) were synthesized that were designed to selectively undergo copper-free click conjugation upon sensing of matrix metalloproteinase (MMP) enzymes, thereby leading to a self-assembled superparamagnetic nanocluster network with T2 signal enhancement properties. For this purpose, IONPs with bioorthogonal azide and alkyne surfaces masked by polyethylene glycol (PEG) layers tethered to CXCR4-targeted peptide ligands were synthesized and characterized. The IONPs were tested in vitro and T2 signal enhancements of around 160 % were measured when the IONPs were incubated with cells expressing MMP2/9 and CXCR4. Simultaneous systemic administration of the bioorthogonal IONPs in tumor-bearing mice demonstrated the signal-enhancing ability of these ‘smart’ self-assembling nanomaterials.