High Aspect Ratio Nanoparticles Research Articles

Silicon nanowire aqueous dispersions for processing into macroscopic network materials.

Nanowires and other high aspect ratio nanoparticles are building blocks to form network materials in formats such as films, sheets, fibres and electrodes that thus bridge the nano and macro scales. The assembly of nanowire network materials is enabled by a new floating catalyst chemical vapour deposition synthesis method that produces crystalline silicon nanowires (SiNW) on a scale of grams per day. Here, we produce SiNW dispersions in water by sonication through steric and electrostatic stabilisation of the negatively charged particles in basic pH or with cationic surfactants. Negative charge arises from the 1.3 nm-thin native oxide layer. Some permanent aggregates are found as a consequence of cross-links between the thin oxide at the surface of adjacent SiNWs. Removing them by centrifugation yields SiNW dispersions of 52 μg mL-1. Processing into macroscopic materials is demonstrated as transparent films and as freestanding sheets. In the sheets, the SiNWs are predominately aligned parallel to the sheet thickness, as a paper-like SiNW solid with tensile strength above 10 MPa, modulus above 1 GPa and toughness of 0.5 J g-1.

Hybrid peptides as platform for synchronized combination therapy

Combination therapy, where two or more therapeutic agents are combined to target different cellular pathways, is an effective tool in cancer treatment but often difficult to execute. Here we present the collagen peptide-based platform that allows for synchronous and colocalized cellular delivery of three different agents. The peptide is a hybrid between collagen and cell penetrating peptide (CPP) that assembles into a heterotrimer helix and forms fully organic, high aspect ratio nanoparticles. The validity of the approach was tested with three chemically different agents (Paclitaxel, Doxorubicin, and 5-Fluorouracil; a combination used in clinical treatment of (ER)-positive and (PR)-positive breast cancer) conjugated to N-terminus of the peptide. The design of this peptide-based drug delivery system provides several advantages: it avoids drug loading problems; removes the need for orthogonal synthesis; and allows for colocalized delivery of up to three drugs (which leads to the same biodistribution for each drug). In addition, hybrid collagen/CPP peptides are known to enhance cellular uptake and improve solubility of drugs. The synergistic effect, in terms of enhanced efficacy, of the Paclitaxel-Doxorubicin-5-Fluorouracil combination was also calculated. We envision self-assembling peptides as a platform for drug codelivery that can be expanded into a library of personalized combinations that may also include other functionalities like targeting or imaging.

Lactate and glucose responsive boronic acid-substituted amphiphilic block copolymer nanoparticles of high aspect ratio

The establishment of conditions for formation of higher order morphologies (e.g. rods and worms) is important, as such nanoparticles are more efficient than spheres in drug delivery. Glucose-binding of core–shell nanoparticles comprising of boronic acid (BA) moieties occurs under basic conditions at above the pKa of the BA (pH 8.7). The resulting increased solubility of the core-forming BA-containing block is utilised in the delivery of therapeutics to diabetics. In contrast, the binding of the key anaerobic metabolite lactate to the BA moiety of amphiphilic block copolymers is unreported, despite occurring at lower physiological neutral pH 7.4. Herein, for the first time, high aspect ratio nanoparticles are observed for (unprotected) BA-substituted amphiphilic block copolymers in water, achieved by incorporating a non-stimuli responsive hydrophobic (tert-butylacrylamide) block. Amphiphilic diblock (Mn = 24,100 and 27,700 gmol−1) and triblock copolymers (Mn = 21,500 and 25,200 gmol−1) with relatively narrow molecular weight distributions (ᴆ = 1.31–1.48) were prepared by reversible addition-fragmentation chain transfer (RAFT) solution polymerizations. Aggregates formed upon dialysis with lactate at pH 7.4 were generally similar to those formed upon self-assembly with glucose at pH 8.7. Spherical nanoparticles for poly(N,N-dimethylacrylamide, DMA)28-b-(3-(acrylamidophenyl)boronic acid, 3-BAPhA)84-TTC (trithiocarbonate) decreased in size from Dh = 259 nm to mostly 100–150 nm upon ionization of BA-moieties with lactate, base, and glucose. Poly(DMA)96-b-(3-BAPhA)62 gave ∼ 500 nm long worms and lamellae under basic conditions, which transitioned to irregular spheres and rods upon addition of glucose. Self-assembly for triblock copolymers with BA-binding gave worms and fused spherical micelle rod-like structures.

Gas-to-nanotextile: high-performance materials from floating 1D nanoparticles.

Suspended in the gas phase, 1D inorganic nanoparticles (nanotubes and nanowires) grow to hundreds of microns in a second and can be thus directly assembled into freestanding network materials. The corresponding process continuously transforms gas precursors into aerosols into aerogels into macroscopic nanotextiles. By enabling the assembly of very high aspect ratio nanoparticles, this processing route has translated into high-performance structural materials, transparent conductors and battery anodes, amongst other embodiments. This paper reviews progress in the application of such manufacturing process to nanotubes and nanowires. It analyses 1D nanoparticle growth through floating catalyst chemical vapour deposition (FCCVD), in terms of reaction selectivity, scalability and its inherently ultra-fast growth rates (107-108 atoms per second) up to 1000 times faster than for substrate CVD. We summarise emerging descriptions of the formation of aerogels through percolation theory and multi-scale models for the collision and aggregation of 1D nanoparticles. The paper shows that macroscopic ensembles of 1D nanoparticles resemble textiles in their porous network structure, high flexibility and damage-tolerance. Their bulk properties depend strongly on inter-particle properties and are dominated by alignment and volume fraction. Selected examples of nanotextiles that surpass granular and monolithic materials include structural fibres with polymer-like toughness, transparent conductors, and slurry-free composite electrodes for energy storage.

Production routes to tailor the performance of cellulose nanocrystals

Cellulose nanocrystals (CNCs) are bio-based, high aspect ratio nanoparticles that are industrially produced in tonne-per-day quantities across the globe. CNCs can be used to improve the performance of a large range of materials such as emulsions and foams, biomedical devices, electronics and sensors, high-viscosity fluids and polymer composites. Their ability to do so, however, is highly dependent on the way they are produced. In this Review, we assess the properties of CNCs from more than 30 production routes and 40 biomass sources to help CNC users select the right material for their desired application. CNCs produced by various methods are evaluated against three target properties: colloidal stability, size and crystallinity index. Alternative production routes and/or starting materials are suggested to overcome challenges associated with CNC use, including increasing compatibility with hydrophobic materials, resistance to thermal degradation and colloidal stability in high ionic strength environments. Additionally, we discuss industrial production of CNCs, as well as considerations for increasing the yield and reducing the environmental impact of these processes. Overall, this Review guides researchers and CNC users towards a deeper understanding of how production processes can be modified to control CNC properties and subsequently tailor their performance. Cellulose nanocrystals are rigid rod-shaped nanoparticles that show promise as additives in composites, emulsions, foams and biomedical devices and as rheological modifiers. In this Review, the authors guide end users towards selecting cellulose sources and production routes that optimize the performance of cellulose nanocrystals in their intended application.

Synthesis of early transition metal oxide nanomaterials and their conversion to nitrides

The synthesis of nanorods and nanowires of early transition metal oxides by hydrothermal methods and the conversion of some bulk oxides to nitrides in NH3 flow are both well established. However, the conversion of such oxide nanostructures to nitrides is not as well explored but could be a valuable method of producing nanowires, nanorods, and other asymmetric or high aspect ratio nanoparticles of the highly conductive metal nitrides. In this work, nanostructures of TiO2, V2O5, MoO3, and WO3 and mixtures thereof were synthesized by hydrothermal reactions, and conversion into nitride was attempted by heating the oxide material under NH3 flow with or without N2 flow. It was found that slow heating produces the best shape retention, but the nitridized products are porous in even the most favorable cases. The products were characterized by X-ray powder diffraction and scanning electron microscopy. Two-point conductivity measurements were done on the nitride materials, and optical measurements to characterize the plasmon absorption were done in favorable cases.

Facile decoding of quantitative signatures from magnetic nanowire arrays

Magnetic nanoparticles have been proposed as contact-free minimal-background nanobarcodes, and yet it has been difficult to rapidly and reliably decode them in an assembly. Here, high aspect ratio nanoparticles, or magnetic nanowires (MNWs), are characterized using first-order reversal curves (FORC) to investigate quantitative decoding. We have synthesized four types of nanowires (differing in diameter) that might be used for barcoding, and identified four possible “signature” functions that might be used to quickly distinguish them. To test this, we have measured the signatures of several combination samples containing two or four different MNW types, and fit them to linear combinations of the individual type signatures to determine the volume ratios of the types. We find that the signature which determines the ratios most accurately involves only the slope of each FORC at its reversal field, which requires only 2–4 data points per FORC curve, reducing the measurement time by a factor of 10 to 50 compared to measuring the full FORC.

Nonspherical Nanoparticles in Block Copolymer Composites: Nanosquares, Nanorods, and Diamonds

A hybrid block copolymer(BCP) nanocomposite computational model is proposed to study nanoparticles(NPs) with a generalised shape including squares, rectangles and rhombus. Simulations are used to study the role of anisotropy in the assembly of colloids within BCPs, ranging from NPs that are compatible with one phase, to neutral NPs. The ordering of square-like NPs into grid configurations within a minority BCP domain was investigated, as well as the alignment of nanorods in a lamellar-forming BCP, comparing the simulation results with experiments of mixtures of nanoplates and PS-\textit{b}-PMMA BCP. The assembly of rectangular NPs at the interface between domains resulted in alignment along the interface. The aspect ratio is found to play a key role on the aggregation of colloids at the interface, which leads to a distinct co-assembly behaviour for low and high aspect ratio NPs.

Physicochemical parameters - hydration performance relationship of the new endodontic cement MTA Repair HP.

BackgroundTo characterize the chemical composition and textural parameters of the MTA Repair HP precursor powder and their influence to hydration performance.Material and MethodsUn-hydrated precursor material was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray fluorescence (XRF), laser diffraction (LD), N2 physisorption and field emission gun scanning electron microscopy (FEG-SEM). Setting time was assessed according to ASTM specification C 266. Hydrated material was analysed by XRD, FT-IR, energy dispersive X-ray (EDX) analysis and FEG-SEM.ResultsCa3SiO5 and Ca2SiO4, in addition to CaWO4 as radiopacifier are the main compositional phases. Other measured parameter indicates high specific surface area of 4.8 m2 g-1, high aluminium content of 1.7 wt.% and low initial and final setting times of 12 and 199 min, respectively. Singular microstructural features consisting of high aspect ratio nanoparticles are main constituents of un-hydrated precursor. Besides, FEM-SEM observation shows notably growth of hexagonal shaped plate-like morphologies homogeneously distributed along the sample during hydration process.ConclusionsThe short setting time measured for HP Repair, is correlated with high surface area of precursor powder, high Al content and the absence of compositional sulphate phases. Key words:Bioactive endodontic cements, hydration performance, MTA HP Repair, physicochemical parameters.

Macrophage-Mediated Exocytosis of Elongated Nanoparticles Improves Hepatic Excretion and Cancer Phototherapy.

The introduction of nanoparticle-mediated delivery and therapy has revolutionized cancer treatment approaches. However, there has been limited success in clinical trials because current approaches have not simultaneously satisfied therapeutic efficacy and biosafety criteria to an adequate degree. Here, we employ efficient macrophage-mediated exocytosis of elongated nanoparticles to facilitate their localization in tumor cells for cancer therapy and their transport to hepatocytes for hepatobiliary excretion. In vitro studies show that PEGylated high-aspect ratio gold nanoparticles exit macrophages more rapidly and remain in tumor cells longer, compared with low-aspect ratio and spherical nanoparticles. In tumors, high-aspect ratio nanoparticles tend to stay in tumor cells and escape from tumor-associated macrophages when they are taken up by those cells. In the liver, high-aspect ratio nanoparticles cleared by Kupffer cells mostly take the hepatobiliary excretion pathway through efficient Kupffer cell-hepatocyte transfer. Furthermore, we demonstrate that time-dependent localization of elongated gold nanoparticles toward tumor cells in tumor tissues enhances the overall phototherapeutic outcome. Engineering nanoparticles to modulate their exocytosis provides a new approach to improve cancer nanomedicine and pave the way toward clinical translation.

Shape memory polyurethane nanocomposites with porous architectures for enhanced microwave shielding

Thermoplastic Polyurethanes (TPU) are versatile smart materials exhibiting shape memory property and have wide usage in the field of microwave shielding through incorporation of microwave active nanoparticles. The incorporation of high aspect ratio particles into the shape memory polymer matrix may however lead to increase in stiffness and thereby loss of shape memory property. To successfully incorporate high aspect ratio nanoparticles in the polymer matrix, porous polyurethane membranes were prepared by phase inversion technique using polyethylene glycol (PEG) as pore forming agent. The pore sizes were tuned to be of the order of 1–3 µm in size by varying the PEG concentration in the dope solution to facilitate the vacuum filtration of an aqueous nanoparticles solution through the porous structure. This technique helped to preserve the shape memory property of PU which would otherwise be disturbed if nanoparticles were incorporated into the polymer matrix. From the results obtained it was clear that this strategy of coating nanoparticles onto the porous membranes helped in achieving good shielding effectiveness at relatively lower membrane thickness without compromising much on the shape memory property of the membranes which otherwise is impeded at higher filler content. When stacked to form a sandwich structure of about 400 µm thickness, the membranes showed a high shielding effectiveness of −32 dB manifesting in 99.9% attenuation of electromagnetic radiations.

Mobility of nanofiber, nanorod, and straight-chain nanoparticles in gases

ABSTRACTWith the fast development of nanotechnology, accurate measurement and classification of nanoparticles are in great need. Nanoparticles frequently appear in non-spherical forms such as long aspect ratio nanofibers, nanotubes, and irregular nano-agglomerates. While the well-developed classical studies were mainly in continuum regime with spherical particles, dynamics of the non-spherical nanoparticles is not fully understood. In this study, orientation-averaged mobility of nanofiber and nanorod (with no preferred alignment) is examined by the methods of Brownian diffusion theory, a combination of collision limited reaction rate theory and the bipolar diffusion charging analysis. Comparisons to empirical predictions from the experimental measurements are also made. The study leads to the discovery of a surface-dominated mobility for high aspect ratio nanoparticles with characteristic Knudsen number greater than 5. In view of the extreme relative length scales between particle size and the gas mean fr...

Five years update on relationships between malignant pleural mesothelioma and exposure to asbestos and other elongated mineral particles

ABSTRACTDespite the reduction of global asbestos consumption and production due to the ban or restriction of asbestos uses in more than 50 countries since the 1970s, malignant mesothelioma remains a disease of concern. Asbestos is still used, imported, and exported in several countries, and the number of mesothelioma deaths may be expected to increase in the next decades in these countries. Asbestos exposure is the main risk factor for malignant pleural mesothelioma, but other types of exposures are linked to the occurrence of this type of cancer. Although recent treatments improve the quality of life of patients with mesothelioma, malignant pleural mesothelioma remains an aggressive disease. Recent treatments have not resulted in appreciable improvement in survival, and thus development of more efficient therapies is urgently needed. The development of novel therapeutic strategies is dependent on our level of knowledge of the physiopathological and molecular changes that mesothelial cells acquired during the neoplastic process. During the past 5 years, new findings have been published on the etiology, epidemiology, molecular changes, and innovative treatments of malignant pleural mesothelioma. This review aims to update the findings of recent investigations on etiology, epidemiology, and molecular changes with a focus on (1) attributable risk of asbestos exposure in men and women and (2) coexposure to other minerals and other elongated mineral particles or high aspect ratio nanoparticles. Recent data obtained on genomic and gene alterations, pathways deregulations, and predisposing factors are summarized.

Formation of Well-Defined, Functional Nanotubes via Osmotically Induced Shape Transformation of Biodegradable Polymersomes.

Polymersomes are robust, versatile nanostructures that can be tailored by varying the chemical structure of copolymeric building blocks, giving control over their size, shape, surface chemistry, and membrane permeability. In particular, the generation of nonspherical nanostructures has attracted much attention recently, as it has been demonstrated that shape affects function in a biomedical context. Until now, nonspherical polymersomes have only been constructed from nondegradable building blocks, hampering a detailed investigation of shape effects in nanomedicine for this category of nanostructures. Herein, we demonstrate the spontaneous elongation of spherical polymersomes comprising the biodegradable copolymer poly(ethylene glycol)-b-poly(d,l-lactide) into well-defined nanotubes. The size of these tubes is osmotically controlled using dialysis, which makes them very easy to prepare. To confirm their utility for biomedical applications, we have demonstrated that, alongside drug loading, functional proteins can be tethered to the surface utilizing bio-orthogonal “click” chemistry. In this way the present findings establish a novel platform for the creation of biocompatible, high-aspect ratio nanoparticles for biomedical research.

Study of thermal, flammability and mechanical properties of intumescent flame retardant PP/kenaf nanocomposites

ABSTRACTDetrimental physical and mechanical properties are common problems for composites when their flame retardancy is improved through filler additions. An increased interest of the synergistic nanoparticle addition to improve the flame retardancy of natural fiber composites is the aim of this work. The paper investigates the synergistic effect of two different nanoparticles (halloysite nanotubes (HNTs) and montmorillonite (MMT) nanoclay) on the flame and mechanical properties in an intumescent ammonium polyphosphate (APP)-based polypropylene (PP)/kenaf composite system. First, the nature of nanoparticle dispersion in PP through X-ray diffraction (XRD) and transmission electron microscopy (TEM) reveals that under twin screw compounding process, the partial exfoliation and intercalation have taken place within the nanocomposites. An increase in the decomposition temperature was observed under thermogravimetric analysis (TGA), with the presence of HNT. However, MMT tends to lower the maximum decomposition temperature under inert atmosphere. The flammability analysis in an intumescent flame retardant (IFR) system shows that the suitable amount of high aspect ratio nanoparticles with their exfoliation characteristics effectively helps to reduce the sustained combustion. Even though, improved stiffness properties can be observed with the presence of increased filler content, particle agglomeration tends to reduce the mechanical strengths of these composites due to low compatibilization and crack propagation.

Effect of Hydrodynamic Forces on meso-(4-Sulfonatophenyl)-Substituted Porphyrin J-Aggregate Nanoparticles: Elasticity, Plasticity and Breaking.

The J aggregates of 4-sulfonatophenyl meso-substituted porphyrins are non-covalent polymers obtained by self-assembly that form nanoparticles of different morphologies. In the case of high aspect-ratio nanoparticles (bilayered ribbons and monolayered nanotubes), shear hydrodynamic forces may modify their shape and size, as observed by peak force microscopy, transmission electron microscopy of frozen solutions, small-angle X-ray scattering measurements in a disk-plate rotational cell, and cone-plate rotational viscometry. These nanoparticles either show elastic or plastic behaviour: there is plasticity in the ribbons obtained upon nanotube collapse on solid/air interfaces and in viscous concentrated nanotube solutions, whereas elasticity occurs in the case of dilute nanotube solutions. Sonication and strong shear hydrodynamic forces lead to the breaking of the monolayered nanotubes into small particles, which then associate into large colloidal particles.

Diffusion and Uptake of Tobacco Mosaic Virus as Therapeutic Carrier in Tumor Tissue: Effect of Nanoparticle Aspect Ratio.

Nanoparticle-based technologies, including platforms derived from plant viruses, hold great promise for targeting and delivering cancer therapeutics to solid tumors by overcoming dose-limiting toxicities associated with chemotherapies. A growing body of data indicates advantageous margination and penetration properties of high aspect-ratio nanoparticles, which enhance payload delivery, resulting in increased efficacy. Our lab has demonstrated that elongated rod-shaped and filamentous macromolecular nucleoprotein assemblies from plant viruses have higher tissue diffusion rates than spherical particles. In this study, we developed a mathematical model to quantify diffusion and uptake of tobacco mosaic virus (TMV) in a spheroid system approximating a capillary-free segment of a solid tumor. Model simulations predict TMV concentration distribution with time in a tumor spheroid for different sizes and cell densities. From simulations of TMV concentration distribution, we can quantify the effect of TMV aspect ratio (e.g., nanorod length-to-width) with and without cellular uptake by modulated surface chemistry. This theoretical analysis can be applied to other viral or nonviral delivery systems to complement the experimental development of the next generation of nanotherapeutics.

Distortion of Chain Conformation and Reduced Entanglement in Polymer-Graphene Oxide Nanocomposites.

We study the conformations of polymer chains in polymer-graphene oxide nanocomposites. We show that the chains have a reduced radius of gyration that is consistent with confinement at a solid interface in the melt, as is expected for well-dispersed, high aspect ratio nanoparticles that are much larger than the polymer coil size. We show that confinement of the polymer chains causes a corresponding reduction in interchain entanglements, and we calculate a contribution to the plateau modulus from the distorted polymer network via a simple scaling argument. Our results are a significant step forward in understanding how two-dimensional nanoparticles affect global material properties at low loadings.

Injectable shear-thinning nanoengineered hydrogels for stem cell delivery.

Injectable hydrogels are investigated for cell encapsulation and delivery as they can shield cells from high shear forces. One of the approaches to obtain injectable hydrogels is to reinforce polymeric networks with high aspect ratio nanoparticles such as two-dimensional (2D) nanomaterials. 2D nanomaterials are an emerging class of ultrathin materials with a high degree of anisotropy and they strongly interact with polymers resulting in the formation of shear-thinning hydrogels. Here, we present 2D nanosilicate reinforced kappa-carrageenan (κCA) hydrogels for cellular delivery. κCA is a natural polysaccharide that resembles native glycosaminoglycans and can form brittle hydrogels via ionic crosslinking. The chemical modification of κCA with photocrosslinkable methacrylate groups renders the formation of a covalently crosslinked network (MκCA). Reinforcing the MκCA with 2D nanosilicates results in shear-thinning characteristics, and enhanced mechanical stiffness, elastomeric properties, and physiological stability. The shear-thinning characteristics of nanocomposite hydrogels are investigated for human mesenchymal stem cell (hMSC) delivery. The hMSCs showed high cell viability after injection and encapsulated cells showed a circular morphology. The proposed shear-thinning nanoengineered hydrogels can be used for cell delivery for cartilage tissue regeneration and 3D bioprinting.

Fate of cellulose nanocrystal aerosols deposited on the lung cell surface in vitro.

When considering the inhalation of high-aspect ratio nanoparticles (HARN), the characterization of their specific interaction with lung cells is of fundamental importance to help categorize their potential hazard. The aim of the present study was to assess the interaction of cellulose nanocrystals (CNCs) with a multicellular in vitro model of the epithelial airway barrier following realistic aerosol exposure. Rhodamine-labeled CNCs isolated from cotton (c-CNCs, 237 ± 118 × 29 ± 13 nm) and tunicate (t-CNCs, 2244 ± 1687 × 30 ± 8 nm) were found to display different uptake behaviors due to their length, although also dependent upon the applied concentration, when visualized by laser scanning microscopy. Interestingly, the longer t-CNCs were found to exhibit a lower clearance by the lung cell model compared to the shorter c-CNCs. This difference can be attributed to stronger fiber-fiber interactions between the t-CNCs. In conclusion, nanofiber length and concentration has a significant influence on their interaction with lung cells in vitro.