Particle Surface Chemistry Research Articles

Role of particle size, shape, and stiffness in design of intravascular drug delivery systems: insights from computations, experiments, and nature.

Packaging of drug molecules within microparticles and nanoparticles has become an important strategy in intravascular drug delivery, where the particles are designed to protect the drugs from plasma effects, increase drug residence time in circulation, and often facilitate drug delivery specifically at disease sites. To this end, over the past few decades, interdisciplinary research has focused on developing biocompatible materials for particle fabrication, technologies for particle manufacture, drug formulation within the particles for efficient loading, and controlled release and refinement of particle surface chemistries to render selectivity toward disease site for site-selective action. Majority of the particle systems developed for such purposes are spherical nano and microparticles and they have had low-to-moderate success in clinical translation. To refine the design of delivery systems for enhanced performance, in recent years, researchers have started focusing on the physicomechanical aspects of carrier particles, especially their shape, size, and stiffness, as new design parameters. Recent computational modeling studies, as well as, experimental studies using microfluidic devices are indicating that these design parameters greatly influence the particles' behavior in hemodynamic circulation, as well as cell-particle interactions for targeted payload delivery. Certain cellular components of circulation are also providing interesting natural cues for refining the design of drug carrier systems. Based on such findings, new benefits and challenges are being realized for the next generation of drug carriers. The current article will provide a comprehensive review of these findings and discuss the emerging design paradigm of incorporating physicomechanical components in fabrication of particulate drug delivery systems.

An Overview on Degree of Dispersion: Conformational Molecular Structure-Interaction Force Relationship of Adsorbed Additive

An overview on molecular structure of adsorbed additive orientates at particle interface in order to understand the ability of dispersants to affect dispersion behaviour is presented. With a wide range of molecular structures, adsorbed additive molecule generates different conformational molecular structure (CMS) combined with interaction of a range of forces occurring with the adsorbed additive molecules and between the adsorbed additive molecules; hence change the surface chemistry of particles in the dispersion.

The effect of milling additives on powder properties and sintered body microstructure of NiO

The evolution of powder particle size, crystal structure, and surface chemistry was evaluated for micron scale NiO powders subjected to impact milling with commonly employed milling additives: methanol, Vertrel XF, and amorphous carbon. The effect of the different comminution protocols on sintered body microstructure was evaluated for high temperature sintering in inert atmosphere (N2). X-ray photoelectron spectroscopy showed that NiO powder surface chemistry is surprisingly sensitive to milling additive choice. In particular, the proportion of powder surface defect sites varied with additive, and methanol left an alcohol or alkoxy residue even after drying. Upon sintering to intermediate temperatures (1100 °C), scanning electron microscopy (SEM) showed that slurry milled NiO powders exhibit hindered sintering behaviors. This effect was amplified for NiO milled with methanol, in which sub-500 nm grain sizes dominated even after sintering to 1100 °C. Upon heating to high temperatures (1500 °C), simultaneous differential scanning calorimetry/thermogravimetric analysis (DSC/TGA) showed that the powders containing carbon residues undergo carbothermal reduction, resulting in a melting transition between 1425 and 1454 °C. Taken together, the results demonstrated that when processing metal oxide powders for advanced ceramics, the choice of milling additive is crucial as it exerts significant control over sintered body microstructure.

Shear‐Induced Reinforcement Effect in Polymer/Fumed Silica Nanocomposites

A solid‐like particle network structure induced by steady shear flow is observed in polymer nanocomposites for the first time. This unique structural evolution is evidenced by the stress overshoot during start‐up of steady shear. After the steady shear ordering event, the enhanced rubbery response is measured using small amplitude oscillatory shear. The particle surface chemistry dominates the formation of the percolation structure: the shear‐induced reinforcement effect is observed at lower particle loadings for hydrophobic filler than for hydrophilic filler. These results indicate that reinforcement in nanocomposites can be controlled by filler surface functionality and shearing effects, enabling improved mechanical properties with low filler loadings.

Fabrication and application of porous silicon multilayered microparticles in sustained drug delivery

In the present study, the ability of porous silicon (PSi) based distributed Bragg reflector (DBR) microparticles for sustained and observable delivery of the antiviral agent acyclovir (ACV) is demonstrated. DBR was fabricated by electrochemical etching of single crystal silicon wafers and ultrasonic fractured to prepare microparticles. The hydrogen-terminated native surface of DBR microparticles was modified by thermal oxidation and thermal hydrosilylation. Particles were loaded with ACV and drug release experiments were conducted in phosphate buffered saline. Drug loading and surface chemistry of particles were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. Drug release profiles from PSi DBR particles show sustained release behavior from all three studied surface chemistries. Drug release from particles was also monitored from change in color of particles.

Detailed characterization of welding fumes in personal exposure samples

The objective of the project was to develop a method allowing for detailed characterization of welding particles including particle number concentration, size distribution, surface chemistry and chemical composition of individual particles, as well as metal concentration of various welding fumes in personal exposure samples using regular sampling equipment. A sample strategy was developed to evaluate the variation of the collection methods on mass concentration. Samples were collected with various samplers and filters at two different locations using our collection system. The first location was using a robotic welding system while the second was manual welding. Collected samples were analysed for mass concentration using gravimetryand metal concentration using ICP/OES. More advanced analysis was performed on selected filters using X-Ray Photoelectron Spectroscopy to determine surface composition of the particles, and X-Ray Diffraction to determine chemical composition of the fumes. Results showed that the robotic system had a lot of variation in space when the collection system was located close to the weld. Collection efficiency was found to be quite variable depending upon the type of filter. As well, metal concentrations in blank filters were dependent upon the type of filter with MCE presenting with the highest blank values. Results obtained with the XRD and XPS systems showed that it was possible to analyse a small of powdered welding fume sample but results on filters were not conclusive.

Hysteresis in the Soil Water Retention of a Sand–Clay Mixture with Contact Angles Lower than Ninety Degrees

Soil water retention curves (SWRCs) are usually obtained on the assumption small water menisci spread in the surface of particles yielding contact angles near zero degrees. While this is true at high water contents, where pores are filled by water or a film of water covers the particles, it is less likely for drier states, where the adhesion of water menisci to the surface of the particles is controlled by the nature of the particle surface (chemistry and surface roughness) and the presence of organic matter. Here, we investigate hysteretic effects in the relation between water content and soil particle wettability versus suction for model samples following drying and wetting paths. A comparison is done for a model material (mixture of sand and clay) with and without water repellent substances, being the samples with water repellent substances in a subcritical water repellent state (contact angles <90°). Wettability was manipulated by treatment with organic acids that mimic the chemistry of natural water repellent substances. Suction was measured directly with a high suction tensiometer and wettability via contact angles by the sessile drop method. The results revealed lower water retention and greater contact angles for the subcritical water repellent samples, following both drying and wetting paths. Hysteresis was present in the relation between the contact angles and suction for the subcritical water repellent samples.

CO2 Electrocatalytic Reduction at Gold and Copper Electrodes: Role of Particle Size and Surface Chemistry

Electrochemical CO2 reduction holds the potential to produce energy-dense liquid fuels using renewable energy sources. Previous works have shown that Cu provides some of the highest yields for valuable products such as methane or ethylene, yet the mechanisms for selectivity are not well understood. Of course, nature performs similar reactions using enzymes including nanocluster metal alloys and ligands with extraordinary selectivity. Here we discuss the effects of various ligands at Cu, Au and Au-Cu alloy electrocatalysts. From the literature, results of CO2 electroreduction on bulk Cu, Au and Au-Cu alloys are known (1-3) as are the size effects of Cu and Au nanoparticles (4, 5), but the effect of chemical surface modification is still unknown, as is the size effect of gold/copper alloy nanoparticles. In this work we demonstrate the effect of chemical surface modification and the size effect of Au-Cu alloy nanoparticles with the aim of combining the two effects to improve CO conversion and hydrogenation. The effect of surface chemistry is studied using planar electrodes modified by organic compounds. Copper and gold foils are exposed to strongly adsorbed ligands such as alkylthiols and glutathione (GSH) and subsequently used as electrocatalysts. As shown in Figure 1, where copper foil was modified with GSH, the adsorbed ligands strongly affect the product yields and selectivity. At the optimal CO yield potential, the yield of CO on the GSH-modified copper was 2.4 times that of blank bulk copper. Although the yield of CH4 has been decreased by a factor of 0.5 in exchange, the overall yield of gas product has been increased by a factor of 2 on the surface engineered electrode. The size effect of Au-Cu nanoparticles is investigated using nanoparticles synthesized via the Brust-Schiffrin method immobilized in various binder inks as electrocatalysts for CO2reduction. Ultimately, we consider the potential to break scaling relationships associated with conventional metal electrodes through the use of size control, alloys and ligands.

CO2 Electrocatalytic Reduction at Gold and Copper Electrodes: Role of Particle Size and Surface Chemistry

This work details the investigation into the effects of surface chemistry modifying agents on the electrochemical reduction of CO2 with the intent of controlling product selectivity and yield. Results for the reaction on gold and copper electrodes, both on the nano and macro scales are discussed.

Modulation of the coffee-ring effect in particle/surfactant mixtures: the importance of particle-interface interactions.

We study the effect of surfactants on the deposits formed after the evaporation of colloidal suspension drops, at initial concentrations lower than the critical micellar concentrations, for various particle/surfactant mixtures. We show that the surfactant-mediated interactions between particles and the liquid-gas (LG) and liquid-solid (LS) interfaces, rather than the flow patterns, primarily define the morphology of the dry deposit in a robust and reproducible manner. For like-charged particle/surfactant mixtures, most of the particles form a ring-shaped deposit (according to the so-called "Coffee-Ring Effect"), but some particles can also be deposited inside the ring in a way that is modulated by electrostatic interactions between the particles and the LS interface. For oppositely charged systems, surfactant adsorption to the particle surface strongly affects particle-LG interface interactions, which in turn control the deposition pattern. For low surfactant concentrations, coffee-rings are systematically observed. For intermediate concentrations, the charge of surfactant-decorated particles becomes nearly neutral, and their hydrophobicity is enhanced, which promotes particle trapping at the LG interface. A particle skin is formed and its deposition upon drying leads to homogeneous disk-like patterns. For high surfactant concentrations, particle charge is reversed, and coffee-rings are observed again. Notably, this ring-disk-ring evolution of the deposition behavior as a function of surfactant concentration is observed in a variety of mixtures, regardless of particle absolute charge and surface chemistry as well as of surfactant charge and hydrophobicity. Its apparent universal character makes it a promising strategy for a robust control of particle deposition from evaporating drops.

Proton Dynamics on Goethite Nanoparticles and Coupling to Electron Transport.

The surface chemistry of metal oxide particles is governed by the charge that develops at the interface with aqueous solution. Mineral transformation, biogeochemical reactions, remediation, and sorption dynamics are profoundly affected in response. Here we report implementation of replica-exchange constant-pH molecular dynamics simulations that use classical molecular dynamics for exploring configurational space and Metropolis Monte Carlo walking through protonation space with a simulated annealing escape route from metastable configurations. By examining the archetypal metal oxide, goethite (α-FeOOH), we find that electrostatic potential gradients spontaneously arise between intersecting low-index crystal faces and across explicitly treated oxide nanoparticles at a magnitude exceeding the Johnson-Nyquist voltage fluctuation. Fluctuations in adsorbed proton density continuously repolarize the surface potential bias between edge-sharing crystal faces, at a rate slower than the reported electron-polaron hopping rate in goethite interiors. This suggests that these spontaneous surface potential fluctuations will control the net movement of charge carriers in the lattice.

Pulmonary toxicity of instilled silver nanoparticles: influence of size, coating and rat strain.

Particle size and surface chemistry are potential determinants of silver nanoparticle (AgNP) respiratory toxicity that may also depend on the lung inflammatory state. We compared the effects of intratracheally-administered AgNPs (20nm and 110nm; polyvinylpyrrolidone (PVP) and citrate-capped; 0.1 mg/Kg) in Brown-Norway (BN) and Sprague-Dawley (SD) rats. In BN rats, there was both a neutrophilic and eosinophilic response, while in SD rats, there was a neutrophilic response at day 1, greatest for the 20nm citrate-capped AgNPs. Eosinophilic cationic protein was increased in bronchoalveolar lavage (BAL) in BN and SD rats on day 1. BAL protein and malondialdehyde levels were increased in BN rats at 1 and 7 days, and BAL KC, CCL11 and IL-13 levels at day 1, with increased expression of CCL11 in lung tissue. Pulmonary resistance increased and compliance decreased at day 1, with persistence at day 7. The 20nm, but not the 110 nm, AgNPs increased bronchial hyperresponsiveness on day 1, which continued at day 7 for the citrate-capped AgNPs only. The 20nm versus the 110 nm size were more proinflammatory in terms of neutrophil influx, but there was little difference between the citrate-capped versus the PVP-capped AgNPs. AgNPs can induce pulmonary eosinophilic and neutrophilic inflammation with bronchial hyperresponsiveness, features characteristic of asthma.

Impact of small changes in particle surface chemistry for unentangled polymer nanocomposites.

We report microstructural and rheological consequences of altering silica particle surface chemistry when the particles are suspended in unentangled polyethylene glycol with a molecular weight of 400. The particle surfaces are altered by reacting them with isobutyltrimethyoxysilane. Levels of silanization are chosen so that the particles remain dispersed in the polymer at all volume fractions studied. Our studies indicate that at the levels studied, silanization does not alter the hydrodynamic thickness of the absorbed polymer layer thickness. Rheological properties are not sensitive to levels of silanization up to particle volume fractions where the average particle separation h ∼ 6Rg (4.8 nm). At these volume fractions, composite microstructure undergoes changes associated with jamming of soft particles (decorrelations in the first peak of the particle structure factor and the onset of a non-diffusive mechanism that dominates particle density fluctuations at short times.) In the region of volume fractions where h/Rg < 6, the zero-shear rate viscosity of the composites is extremely sensitive to level of silanization with a decrease in the zero-shear rate viscosity by four orders of magnitude observed for the highest levels of silanization studied in comparison to the bare particles.

Diffusing Colloidal Probes of Cell Surfaces

To engineer nanoparticles for novel biosensing, diagnostic imaging, and drug delivery applications, the interactions of nanoparticles with the surface of cells must be characterized to better understand their influence on specific and non-specific cell surface adhesion, internalization pathways, and toxicity. In order to develop models to aid in optimization and design in these systems, direct measurements of colloidal interactions with cell surfaces are required that are both quantitative and sensitive to determine the impact of particle composition and surface chemistry. In this talk, we report the use of diffusing colloidal probes to directly measure cell surface interactions with kT-scale sensitivity with newly developed imaging and analysis techniques. Dark field video microscopy allows for label-free imaging of colloidal particles and live cells. With combined real-time particle tracking and cell boundary determination, particle trajectories can be monitored in relation to their distance from the cell surface which allows for direct measurement of equilibrium and non-equilibrium colloid-cell interactions. Using this technique, polymer, protein, and carbohydrate functionalized colloidal silica were used to measure specific and non-specific macromolecular interactions with the surface of epithelial breast cancer cells. Ultimately, our results demonstrate how diffusing colloidal probe microscopy can be used to characterize biomolecular and biophysical properties of cell surfaces.

Impact of particle surface chemistry on the structure and rheological properties of graphene-based particle/polydimethylsiloxane composites

The inter-particle interaction of graphene-based particles has a key effect on the structure and rheological properties of graphene-based particle/polydimethylsiloxane composites.

Self-propulsion of a catalytically active particle near a planar wall: from reflection to sliding and hovering.

Micron-sized particles moving through a solution in response to self-generated chemical gradients serve as model systems for studying active matter. Their far-reaching potential applications will require the particles to sense and respond to their local environment in a robust manner. The self-generated hydrodynamic and chemical fields, which induce particle motion, probe and are modified by that very environment, including confining boundaries. Focusing on a catalytically active Janus particle as a paradigmatic example, we predict that near a hard planar wall such a particle exhibits several scenarios of motion: reflection from the wall, motion at a steady-state orientation and height above the wall, or motionless, steady "hovering." Concerning the steady states, the height and the orientation are determined both by the proportion of catalyst coverage and the interactions of the solutes with the different "faces" of the particle. Accordingly, we propose that a desired behavior can be selected by tuning these parameters via a judicious design of the particle surface chemistry.

The influence of ethylenediamine tetra acetic acid (EDTA) on the transformation and solubility of metallic palladium and palladium(II) oxide in the environment.

The environmental occurrence of elevated concentrations of platinum (Pt), palladium (Pd) and rhodium (Rh) from automotive catalytic converters has been well-documented. Limited information exists regarding their chemical behavior post-emission, however, especially in the presence of commonly occurring complexing agents. The purpose of this study is to examine the influence of ethylenediamine tetra acetic acid (EDTA) on the possible environmental transformation and solubility of Pd by conducting batch experiments using metallic palladium (Pd black) and palladium(ii) oxide (PdO). Changes in the particle surface chemistry of treated samples were analyzed using X-ray Photoelectron Spectroscopy (XPS) and Transition Electron Microscopy/Energy Dispersive X-ray Spectrometry (TEM/EDX) techniques. Metallic palladium was partially transformed into PdOx (x < 1), while PdO remained largely unaffected. The pH of EDTA solutions was observed to modulate Pd solubility, with Pd black demonstrating a higher solubility compared to PdO. Solubility was also found to increase with a corresponding increase in the strength of EDTA solution concentrations, as well as with the length of extraction time. The overall solubility of Pd remained relatively low for most samples (<1 wt%). A dissolution rate of 2.01 ± 0.17 nmol m(-2) h(-1) was calculated for Pd black in 0.1 M EDTA (pH 7). In contrast to previously held assumptions about the environmental immobility of Pd, small amounts of this element emitted in metallic form are likely to be soluble in the presence of complexing agents such as EDTA.

The isotopic signature and distribution of particulate iron in the North Atlantic Ocean

Iron (Fe) is a key micronutrient for life in the oceans. Particles play an important role in the marine biogeochemical cycling of Fe as a reservoir of marine Fe that may be directly accessible to phytoplankton, and as sources and sinks for seawater dissolved Fe. Here, we report the stable isotopic composition of Fe (δ56Fe) in suspended (0.8–51μm) particles from the US GEOTRACES GA03 North Atlantic zonal transect, in order to facilitate a better understanding of the marine biogeochemical cycling of Fe. Data are presented both for a total digestion of the particles, and for ‘ligand-leachable’ phases of Fe using a newly-developed pH 8 oxalate–EDTA leach. For total particle digests, the mean δ56Fe across the whole GA03 section was 0.08±0.09‰ (1 S.D.) which is equivalent to the isotope composition of known lithogenic Fe sources to the ocean. In contrast, ligand-leachable Fe was generally lighter than continental material with a mean δ56Fe of −0.30±0.17‰ (1 S.D.). Our data also provide valuable insight into Fe biogeochemical cycling in several key regions. In the deep ocean, but above the depths where near-sediment nephloid layers are present, ligand-leachable Fe is isotopically lighter in the deep Western Basin compared to the deep Central and Eastern Basins suggesting differences in particle surface chemistry between resuspended seafloor sediments, which may predominate in the west, and Saharan dust that predominates in the center and in the east. Within a nephloid layer above reduced continental margin sediments in the Eastern Basin, below the Mauritanian upwelling region, we report the lowest particulate δ56Fe values for both total and ligand-leachable Fe, suggesting a transfer of isotopically light dissolved porewater Fe2+ to the particulate phase. In contrast, δ56Fe values within a nephloid layer near Bermuda are similar to values higher in the water column. Within a hydrothermal plume sampled at the TAG hydrothermal field on the mid-Atlantic Ridge, decreasing Fe concentration and δ56Fe with distance from the vent indicate the water-column precipitation of Fe oxyhydroxides within the plume. Comparison between total and ligand-leachable particulate Fe concentrations throughout the transect also provides useful biogeochemical information. In the chlorophyll maximum, a high proportion of Fe in the labile phase demonstrates a relative lack of lithogenic material, while the high proportion of labile Fe observed between 2000 and 4000m depth to the west of the mid-Atlantic Ridge suggests that hydrothermal oxyhydroxide particles can be transported thousands of kilometers away from vent sites. Throughout the North Atlantic, measurements of total and ligand-leachable Fe concentration and δ56Fe are therefore useful tools for studying the biogeochemical cycling of particulate Fe.

Shape-mediated biological effects of mesoporous silica nanoparticles.

For biomedical applications, mesoporous silica nanoparticles (MSNs)-based theranostic agents have shown to be a promising alternative. Rational design of particulate systems should consider, beside the physicochemical properties of particle size and surface chemistry, shape features as aspect ratio (AR) and morphology. Recent advances of fabrication technologies for manufacturing different shaped MSNs and evaluation means of its in vitro and in vivo biological performance provide new aspects and wisdom in nanomedicine development. In this review, we discussed the recent progress in the preparation of different shaped MSNs and the evaluation of shape-mediated biological effects. Firstly, we provide an overview of preparation strategies for fabricating MSNs with different aspect ratios and different morphologies, including hollow/rattle MSNs, multishell MSNs, and mesoporous silica nanocomposites. We then highlight the aspect ratio- and morphology-mediated biological effects of MSNs respectively. For AR-mediated biological effects of MSNs, we put our focus in the particle ARs effect on cellular uptake, biocompatibility, and drug delivery. For morphology-mediated biological effects of MSNs, we emphasize on how particle shapes could affect tumor therapy. Finally, for application considerations, we conclude with our personal perspectives on the directions in which future studies in this field might be placed.

The toolbox of designing nanoparticles for tumors.

Nanoparticles (NPs) show great promise in the treatment of a wide range of diseases, which provides advantages and offers a new prospect for tumor detection, prevention and treatment. In order to eradicate the cancer cell, the NPs need to flow to different regions of tumors via blood vessels, and then penetrate through the interstitial space to reach the target cells. However, the environment and physiological characteristics in tumor tissues are different from that in normal ones, mainly in the irregular blood vessels, the lack of lymphatic network, low pH, hypoxia, immune function and so on. Meanwhile, the differences also exist among different tumor tissues. To achieve the optimal therapeutic effect, the NPs should be carefully designed by considering the therapeutic application, the target site and the route of administration. This review shows a variety of barriers in the tumor tissues, and provides a toolbox of designing the NPs for tumor treatment. In particular, the particle size, shape and surface chemistry, and the NPs in preclinical and clinical stage use have been discussed.