PEG-stabilized core-shell nanoparticles: impact of linear versus dendritic polymer shell architecture on colloidal properties and the reversibility of temperature-induced aggregation

Theory of Brushes Formed by Ψ-Shaped Macromolecules at Solid-Liquid Interfaces

We present a theoretical analysis targeted to describe the structural properties of brushes formed by Ψ-shaped macromolecules tethered by terminal segment of stem to planar surface while exposing multiple free branches to the surrounding solution. We use an analytical self-consistent field approach based on the strong stretching approximation, and the assumption of Gaussian elasticity for linear chain fragments of the tethered macromolecules. The effect of weak and strong polydispersity of branches is analyzed. In the case of weakly polydisperse macromolecules, variations in length of branches lead to a more uniform polymer density distribution with slight increase in the brush thickness compared to the case of monodisperse chains with the same degree of polymerization. We demonstrate that in contrast to linear chains, strong polydispersity of Ψ-shaped macromolecules does not necessarily lead to strong perturbations in polymer density distribution. In particular, mixed brushes of the so-called "mirror" dendrons (in which number of stem monomers in one component coincides with number of monomers in a branch of the other component, and vice versa) give rise to a unified polymer density distribution with shape independent of the brush composition. The predictions of analytical theory are systematically compared to the results of numerical self-consistent field modeling based on the Scheutjens-Fleer approach.

Charge-controlled nanoprecipitation as a modular approach to ultrasmall polymer nanocarriers: making bright and stable nanoparticles

Ultrasmall polymer nanoparticles are rapidly gaining importance as nanocarriers for drugs and contrast agents. Here, a straightforward modular approach to efficiently loaded and stable sub-20-nm polymer particles is developed. In order to obtain ultrasmall polymer nanoparticles, we investigated the influence of one to two charged groups per polymer chain on the size of particles obtained by nanoprecipitation. Negatively charged carboxylate and sulfonate or positively charged trimethylammonium groups were introduced into the polymers poly(d,l-lactide-co-glycolide) (PLGA), polycaprolactone (PCL), and poly(methyl methacrylate) (PMMA). According to dynamic light scattering, atomic force and electron microscopy, the presence of one to two charged groups per polymer chain can strongly reduce the size of polymer nanoparticles made by nanoprecipitation. The particle size can be further decreased to less than 15 nm by decreasing the concentration of polymer in the solvent used for nanoprecipitation. We then show that even very small nanocarriers of 15 nm size preserve the capacity to encapsulate large amounts of ionic dyes with bulky counterions at efficiencies >90%, which generates polymer nanoparticles 10-fold brighter than quantum dots of the same size. Postmodification of their surface with the PEG containing amphiphiles Tween 80 and pluronic F-127 led to particles that were stable under physiological conditions and in the presence of 10% fetal bovine serum. This modular route could become a general method for the preparation of ultrasmall polymer nanoparticles as nanocarriers of contrast agents and drugs.

Kinetics of aggregation in liquids with dispersed nanoparticles

The process of attaching molecules of liquid media by dispersed nanoparticles is modeled and numerically studied. The growth rate of the resulting nanoparticle-induced aggregates is determined by assuming the preferential attachment rule according to which the effectiveness of the connection of a new molecular unit to aggregates is determined by their size. It is shown that, depending on a specific functional form of the growth rate, the size distribution of aggregates can display very different shapes, including various multimodal structures. This can explain experimentally obtained complex size distributions of inhomogeneous aggregates appearing as a consequence of the adsorption of molecules by nanoparticles or as a consequence of the self-assembling of active dispersants on surfaces of nanoparticles. The time evolution and the stationarity of the size distribution are also analyzed, gaining an insight into the long-time behavior of systems with dispersed nanoparticles.

Cisplatin release from dual-responsive magnetic nanocomposites

BACKGROUND

The combination of hyperthermia and controlled drug delivery is a very promising recent effort in cancer therapy. The aim of this study is to synthesize and characterize a dual pH/thermal-responsive composite nanoparticle that acts as a cisplatin carrier, and to evaluate its release profile at different pH and temperature conditions relevant to the physiological and cancerous environment during hyperthermia.

METHODS

Poly (n-isopropyl acrylamide-methacrylic acid-hydroxy ethyl methacrylate) (P (NIPAAM-MAA-HEM)) was synthesized by emulsion polymerization. Fe3O4 magnetic nanoparticles (MNPs) and cisplatin were loaded onto the nanogel, by the swelling method and the conjugation of cisplatin with the -COOH group of MAA, respectively. The chemical and morphological properties of the drug-loaded composite nanoparticle and its profile of drug release at pH levels of 7.4 (physiological pH), 6.8 (tumor extracellular pH), and 5.3 (endosomal pH), and at temperatures of 37°C (physiological) and 43°C (hyperthermia), were studied.

RESULTS

The result shows that the synthesized nanogel and nanocomposite were almost pure and were of an appropriate size and stability. Magnetic saturation was at a position appropriate for the production of enough heat during hyperthermia. A high level of drug release under conditions of low pH and high temperature was observed.

CONCLUSION

This result suggests that the dual pH/temperature-responsive P (NIPAAM-MAA-HEM) magnetic nanocomposite can be very effective in hyperthermia and controlled cisplatin delivery.

Nanoparticle-cored dendrimers: functional hybrid nanocomposites as a new platform for drug delivery systems

Nanoparticle-cored dendrimers (NCDs) are now offering themselves as versatile carriers because of their colloidal stability, tunable membrane properties and ability to encapsulate or integrate a broad range of drugs and molecules. This kind of hybrid nanocomposite aims to combine the advantages of stimuli-responsive dendritic coatings, in order to regulate the drug release behaviour under different conditions and improve the biocompatibility and in vivo half-time circulation of the inorganic nanoparticles. Size, surface chemistry and shape are key nanocarrier properties to evaluate. Here, we have reviewed the most recent advances of NCDs in drug delivery systems, compared their behaviour with non-dendritic stabilized nanoparticles and highlighted their challenges and promising applications in the future.

Dendrimer–nanoparticle conjugates in nanomedicine

Nanomedicine can take advantage of the recent developments in nanobiotechnology research areas for the creation of platforms with superior drug carrier capabilities, selective responsiveness to the environment, unique contrast enhancement profiles and improved accumulation at the disease site. Colloidal inorganic nanoparticles (NPs) have been attracting considerable interest in biomedicine, from drug and gene delivery to imaging, sensing and diagnostics. It is essential to modify the NPs surface to have enhanced biocompatibility and reach multifunctional systems for the in vitro and in vivo applications, especially in delivering drugs locally and recognizing overexpressed biomolecules. This paper describes the rational design for dendrimer–nanoparticle conjugates elaboration and reviews their state-of-the-art uses as efficient nanomedicine tools.

A multiscale approach to the adsorption of core-shell nanoparticles at fluid interfaces

Self-assembly of colloidal particles at liquid-liquid interfaces is a process with great potential for the creation of controlled structures, due to the trapping of the particles in the plane of the interface combined with their lateral mobility. Here we present a multiscale characterisation of the adsorption and interfacial behaviour of core-shell iron oxide-poly(ethylene glycol) nanoparticles at a water-n-decane interface using three complementary, in situ, methods, which span many different length scales. First, dynamic interfacial measurements are taken to follow the adsorption of particles from the bulk aqueous phase to the interface. The mechanical properties of the interface are then probed using micron-sized tracers in probe-particle tracking and nano-tracers in fluorescence correlation spectroscopy. The results show that the rate of particle adsorption to the interface scales with the square of bulk concentration, as predicted by a recent model. In addition, we show that despite full monolayers of nanoparticles forming, the interface remains unexpectedly fluid, with only a slowing of tracer particle mobility but no evidence of interface jamming as seen for hard nanoparticles. Our results illustrate that nanoparticles stabilised by soft, extended polymeric shells, display distinct features at fluid interfaces that can be harnessed for the fabrication of functional materials.

Validation of a dendron concept to tune colloidal stability, MRI relaxivity and bioelimination of functional nanoparticles

A dendritic coating induces colloidal stability of nanoparticles through electrostatic and steric interactions.

Supramolecular anticancer drug delivery systems based on linear–dendritic copolymers

The combination of two generations of polymers as linear–dendritic copolymers leads to hybrid systems with unique properties, which are of great interest for many applications. Herein, recent advances in anticancer drug delivery systems based on linear–dendritic copolymers have been reviewed.

Soft repulsive interactions, particle rearrangements and size selection in the self-assembly of nanoparticles at liquid interfaces

In the adsorption of nanoparticles at liquid interfaces, soft and short ranged repulsive effective interactions between the nanoparticles at the interface may eventually induce crowding, slow dynamics and jamming at high surface coverage. These phenomena can interfere during the adsorption process, significantly slowing down its kinetics. Here, by means of numerical simulations, we find that modifying the effective interactions, which can be achieved for example by grafting differently functionalized polymer shells on the bare nanoparticles, may qualitatively change such interplay. In particular our results suggest that, in the presence of ultrasoft particle interactions such as the ones described by a Gaussian Core Model potential, a small size polydispersity can be sufficient to decouple the adsorption kinetics from the slow dynamics that develops at the interface, due to a qualitative change from an irreversible adsorption controlled by particle rearrangements at the interface to one dominated by size selection mechanisms. These findings may be useful to achieve higher surface coverages and faster adsorption kinetics.

Antibiofouling polymer interfaces: poly(ethylene glycol) and other promising candidates

This review highlights antibiofouling polymer interfaces with emphasis on the latest developments using poly(ethylene glycol) and the design new polymeric structures.

Quantitative mechanical analysis of thin compressible polymer monolayers on oxide surfaces

A clear understanding of the mechanical behavior of nanometer thick films on nanostructures, as well as developing versatile approaches to characterize their mechanical properties, are of great importance and may serve as the foundation for understanding and controlling molecular interactions at the interface of nanostructures. Here we report on the synthesis of thin, compressible polyethylene glycol (PEG) monolayers with a wet thickness of <20 nm on tin dioxide (SnO2) nanofibers through silane-based chemistries. Nanomechanical properties of such thin PEG films were extensively investigated using atomic force microscopy (AFM). In addition, tip-sample interactions were carefully studied, with different AFM tip modifications (i.e., hydrophilic and hydrophobic) and in different ionic solutions. We find that the steric forces dominate the tip-sample interactions when the polymer film is immersed in solution with salt concentrations similar to biological media (e.g., 1x phosphate buffer solution), while van der Waals and electrostatic forces have minimal contributions. A Dimitriadis thin film polymer compression model shows that the linear elastic regime is reproducible in the initial 50% indentation of these films which have tunable Young's moduli ranging from 5 MPa for the low molecular weight films to 700 kPa for the high molecular weight PEG films. Results are compared with the same PEG films deposited on silicon substrates which helped quantify the structural properties and understand the relationship between the structural and the mechanical properties of PEG films on the SnO2 fibers.

Composite-walled magnetic microcapsules at the water-toluene interface by ligand polymerization

The liquid-liquid interface has been exploited as a platform for devising gold and iron oxide nanoparticle (NP)-decorated composite microcapsules (MCs) by cross-linking between -OH groups of poly(ethylene glycol) (PEG) attached to the iron oxide (Fe3O4) nanoparticle surface and starch attached to the gold (Au) nanoparticle surface in the presence of terephthaloyl chloride as a cross-linker. These nanoparticle-decorated capsules form a shell of both types of nanoparticles with water as the minor phase and toluene as the major phase. The morphology of these capsules has been characterized by optical, transmission, and scanning electron microscopy images, and the polymerization reaction has been established by UV-vis and FTIR spectroscopic studies. The magnetic behavior of the capsules has been illustrated by using an external magnetic field to tailor the magnetic control of the capsules. The encapsulated phase was impregnated with dye molecules of three different sizes, viz., fluorescein isothiocyanate and its dextran conjugates, to investigate the permeability of the capsule wall by fluorescence spectroscopy. Interestingly, the microcapsules exhibit size-selective permeability across the capsule wall that points to their plausible applications in controlled encapsulation and release.

Synthesis of core-shell graphitic carbon@silica nanospheres with dual-ordered mesopores for cancer-targeted photothermochemotherapy

Tumor site-directed multifunctional therapeutic platforms such as photothermochemotherapy that respond to tumor-focused physical and biological stimuli are highly demanded for effective cancer therapy. Herein, targeting peptide-conjugated core–shell graphitic carbon@silica nanospheres with dual-ordered mesopores (MMPS) were successfully fabricated and developed as antitumoral doxorubicin (DOX) delivery system (MMPSD) for synergistic targeted photothermal chemotherapy of breast cancer. The hydrophilic mesoporous silica shell guarantees good water dispersity of MMPSD. The hydrophobic graphitic mesoporous carbon core provides excellent hydrophobic drug loading, immediate contact between the drug and photothermal hotspots, and high NIR photothermal conversion efficiency. SP13 peptide facilitates MMPSD for targeted and enhanced delivery of DOX within HER2-positive SK-BR-3 breast cancer cells, while PEGylation ensures biocompatibility. Thus, the MMPSD system exhibited efficient drug loading capacity, high targeting ability, sensitive NIR/pH-responsive DOX release, sustained release, and excellent combined antitumor activity.

Multicore iron oxide mesocrystals stabilized by a poly(phenylenepyridyl) dendron and dendrimer: role of the dendron/dendrimer self-assembly

We report the formation of multicore iron oxide mesocrystals using the thermal decomposition of iron acetyl acetonate in the presence of the multifunctional and rigid poly(phenylenepyridyl) dendron and dendrimer. We thoroughly analyze the influence of capping molecules of two different architectures and demonstrate for the first time that dendron/dendrimer self-assembly leads to multicore morphologies. Single-crystalline ordering in multicore NPs leads to cooperative magnetic behavior: mesocrystals exhibit ambient blocking temperatures, allowing subtle control over magnetic properties using a minor temperature change.

Folic acid-conjugated iron oxide porous nanorods loaded with doxorubicin for targeted drug delivery

Iron oxide porous nanorods (IOPNR) with lengths ranging from 40nm to 60nm and pore diameters ranging from 5nm to 10nm were prepared, and further modified with NH2-PEG-FA (FA-PEG-IOPNR) for ligand targeting and modified with NH2-PEG-OCH3 (PEG-IOPNR) as a control. Instead of chemical bonding, doxorubicin (DOX), a low water solubility anticancer drug, was loaded in the pores of the modified IOPNR because of their porous structure and high porosity. The release of DOX in acidic PBS solution (pH 5.3) was faster than that in neutral (pH 7.4) solution. The analysis results from TEM, inductively coupled plasma emission spectroscopy, confocal laser scanning microscopy, and flow cytometry analyses indicated that the presence of FA on the surface of the nanorods increase the cellular uptake of nanorods in the case of HeLa cells, a folate receptor (FR)-positive cell line. In contrast, for COS 7 cells, a FR-negative cell line, FA ligand on the surface of the nanorods showed no effect on the cellular uptake. MTT assay indicated that the cytotoxicity of DOX loaded in FA-PEG-IOPNR to HeLa cells was higher than that of DOX in PEG-IOPNR. In the case of COS 7 cells, no significant difference between the cytotoxicity of DOX loaded in FA-PEG-IOPNR and PEG-IOPNR was found. These results suggested that FA-PEG-IOPNR had the potential for target delivery of chemotherapeutic into cancer cells.

Endocytosis and exocytosis of nanoparticles in mammalian cells

Engineered nanoparticles that can be injected into the human body hold tremendous potential to detect and treat complex diseases. Understanding of the endocytosis and exocytosis mechanisms of nanoparticles is essential for safe and efficient therapeutic application. In particular, exocytosis is of significance in the removal of nanoparticles with drugs and contrast agents from the body, while endocytosis is of great importance for the targeting of nanoparticles in disease sites. Here, we review the recent research on the endocytosis and exocytosis of functionalized nanoparticles based on various sizes, shapes, and surface chemistries. We believe that this review contributes to the design of safe nanoparticles that can efficiently enter and leave human cells and tissues.

Layer-by-layer nanoencapsulation of camptothecin with improved activity

160 nm nanocapsules containing up to 60% of camptothecin in the core and 7-8 polyelectrolyte bilayers in the shell were produced by washless layer-by-layer assembly of heparin and block-copolymer of poly-l-lysine and polyethylene glycol. The outer surface of the nanocapsules was additionally modified with polyethylene glycol of 5 kDa or 20 kDa molecular weight to attain protein resistant properties, colloidal stability in serum and prolonged release of the drug from the capsules. An advantage of the LbL coated capsules is the preservation of camptothecin lactone form with the shell assembly starting at acidic pH and improved chemical stability of encapsulated drug at neutral and basic pH, especially in the presence of albumin that makes such formulation more active than free camptothecin. LbL nanocapsules preserve the camptothecin lactone form at pH 7.4 resulting in triple activity of the drug toward CRL2303 glioblastoma cell.

Assembly of nanoparticles at liquid interfaces: crowding and ordering

Experiments with the self-assembly of nanoparticles at liquid interfaces suggest that cooperative and slow dynamical processes due to particle crowding at the interface govern the adsorption and properties of the final assembly. Here we report a numerical approach to studying nonequilibrium adsorption, which elucidates these experimental observations. The analysis of particle rearrangements shows that local ordering processes are directly related to adsorption events at high interface coverage. Interestingly, this feature and the mechanism coupling local ordering to adsorption do not seem to change qualitatively upon increasing particle size polydispersity, although the latter changes the interface microstructure and its final properties. Our results indicate how adsorption kinetics can be used for the fabrication of 2D nanocomposites with controlled microstructure.

Adsorption energies of poly(ethylene oxide)-based surfactants and nanoparticles on an air-water surface

The self-assembly of polymer-based surfactants and nanoparticles on fluid-fluid interfaces is central to many applications, including dispersion stabilization, creation of novel 2D materials, and surface patterning. Very often these processes involve compressing interfacial monolayers of particles or polymers to obtain a desired material microstructure. At high surface pressures, however, even highly interfacially active objects can desorb from the interface. Methods of directly measuring the energy which keeps the polymer or particles bound to the interface (adsorption/desorption energies) are therefore of high interest for these processes. Moreover, though a geometric description linking adsorption energy and wetting properties through the definition of a contact angle can be established for rigid nano- or microparticles, such a description breaks down for deformable or aggregating objects. Here, we demonstrate a technique to quantify desorption energies directly, by comparing surface pressure-density compression measurements using a Wilhelmy plate and a custom-microfabricated deflection tensiometer. We focus on poly(ethylene oxide)-based polymers and nanoparticles. For PEO-based homo- and copolymers, the adsorption energy of PEO chains scales linearly with molecular weight and can be tuned by changing the subphase composition. Moreover, the desorption surface pressure of PEO-stabilized nanoparticles corresponds to the saturation surface pressure for spontaneously adsorbed monolayers, yielding trapping energies of ∼10(3) k(B)T.

Fluid interface-mediated nanoparticle membrane as an electrochemical sensor

A poly(ethyleneglycol)-stabilised magnetic Fe₃O₄ nanoparticle decorated ultra-thin membrane has been devised at the water/CCl₄ interface by ligand cross-linking with terephthaloyl chloride and the membrane was exploited as an electrochemical sensor for the detection of l-Dopa up to nanomolar concentration.

Arsonic acid as a robust anchor group for the surface modification of Fe3O4

In order to use iron oxide nanoparticles (Fe3O4) in various applications, a surface modification that provides colloidal stability and additional functionality to the nanoparticles is necessary. For the modification of the nanoparticle surface with ligand molecules, the ligand molecule should contain an anchor group that has a strong affinity for the surface. However, currently used anchor groups have shown some problems such as low affinity and stability as well as reactivity with the surface. In this study, arsonic acid (RAsO(OH)2) was investigated as a novel anchor group. It was possible to introduce azide groups on the surface of iron oxide nanoparticles using 4-azidophenylarsonic acid, and the desired functional molecules could be chemically attached to the surface via copper-catalyzed azide-alkyne cycloaddition (click chemistry). By quantifying and comparing the amount of attached anchors on the surface, it was found that arsonic acid displays better affinity than other currently used anchors (catechol, carboxylic acid). Furthermore, we examined the binding reversibility, long-term anchoring stability, and anchoring stability at various pH values. It was revealed that arsonic acid is a stable anchor in various conditions.

Tuning the mechanical properties of glass fiber-reinforced bismaleimide-triazine resin composites by constructing a flexible bridge at the interface

We demonstrate a new method that can simultaneously improve the strength and toughness of the glass fiber-reinforced bismaleimide-triazine (BT) resin composites by using polyethylene glycol (PEG) to construct a flexible bridge at the interface. The mechanical properties, including the elongation, ultimate tensile stress, Young's modulus, toughness and dynamical mechanical properties were studied as a function of the length of PEG molecular chain. It was found that the PEG molecule acts as a bridge to link BT resin and glass fiber through covalent and non-covalent bondings, respectively, resulting in improved interfacial bonding. The incorporation of PEG produces an increase in elongation, ultimate tensile stress and toughness. The Young's modulus and T_g were slightly reduced when the length of the PEG molecular chain was high. The elongation of the PEG-modified glass fiber-reinforced composites containing 5 wt% PEG-8000 increased by 67.1%, the ultimate tensile stress by 17.9% and the toughness by 78.2% compared to the unmodified one. This approach provides an efficient way to develop substrate material with improved strength and toughness for integrated circuit packaging applications.

Recent advances in surface chemistry strategies for the fabrication of functional iron oxide based magnetic nanoparticles

The synthesis of superparamagnetic nanostructures, especially iron-oxide based nanoparticles (IONPs), with appropriate surface functional groups has been intensively researched for many high-technological applications, including high density data storage, biosensing and biomedicine. In medicine, IONPs are nowadays widely used as contrast agents for magnetic resonance imaging (MRI), in hyperthermia therapy, but are also exploited for drug and gene delivery, detoxification of biological fluids or immunoassays, as they are relatively non-toxic. The use of magnetic particles in vivo requires IONPs to have high magnetization values, diameters below 100 nm with overall narrow size distribution and long time stability in biological fluids. Due to the high surface energies of IONPs agglomeration over time is often encountered. It is thus of prime importance to modify their surface to prevent aggregation and to limit non-specific adsorption of biomolecules onto their surface. Such chemical modifications result in IONPs being well-dispersed and biocompatible, and allow for targeted delivery and specific interactions. The chemical nature of IONPs thus determines not only the overall size of the colloid, but also plays a significant role for in vivo and in vitro applications. This review discusses the different concepts currently used for the surface functionalization and coating of iron oxide nanoparticles. The diverse strategies for the covalent linking of drugs, proteins, enzymes, antibodies, and nucleotides will be discussed and the chemically relevant steps will be explained in detail.

Comparative advantages and limitations of the basic metrology methods applied to the characterization of nanomaterials

Fabrication of modern nanomaterials and nanostructures with specific functional properties is both scientifically promising and commercially profitable. The preparation and use of nanomaterials require adequate methods for the control and characterization of their size, shape, chemical composition, crystalline structure, energy levels, pathways and dynamics of physical and chemical processes during their fabrication and further use. In this review, we discuss different instrumental methods for the analysis and metrology of materials and evaluate their advantages and limitations at the nanolevel.

PEG-Polypeptide Dual Brush Block Copolymers: Synthesis and Application in Nanoparticle Surface PEGylation

Amphiphilic polypeptide-containing hybrid dual brush block copolymers with controlled molecular weights and narrow molecular weight distributions were synthesized in one pot via ring-opening metathesis polymerization of sequentially added norbornyl-PEG and N-(2-((trimethylsilyl)amino)ethyl)-5-norbornene-endo-2,3-dicarboximide (M1) followed by ring-opening polymerization of amino acid N-carboxyanhydrides. Polylactide nanoparticles coated with these am phiphilic dual brush block copolymers showed significantly improved stability in PBS solution compared to those coated with amphiphilic linear block copolymers such as PEG-polylactide and PEG-polypeptides.