An overview on field-flow fractionation techniques and their applications in the separation and characterization of polymers

Microfluidic purification of genomic DNA

We describe a microfluidic device to extract DNA from a cell lysate, without the need for centrifuges, magnetic beads, or gels. Instead, separation is driven by transverse migration of DNA, which occurs when a polyelectrolyte solution flowing through a microfluidic channel is subjected to an electric field. The coupling of the weak shearing with the axial electric field is highly selective for long, flexible, charged molecules, of which DNA is the sole example in a typical cell lysate. As a result of migration to the walls, DNA is held near the channel inlet by electrophoresis (there is no flow near the channel walls), while the remaining components are eluted by the much larger (at least 10-fold) convective flow. We have demonstrated the feasibility of the device by recovering up to 40 ng of purified DNA in less than 30 min from 10 μL of Escherichia coli lysate. Gel electrophoresis indicates minimal additional fragmentation during purification, up to the maximum length recorded by the gel (60 kbp). Electropherograms were also obtained for purified mammalian DNA, using a Femto Pulse system (fragment lengths up to 165 kbp). Extracted samples show strong amplification by PCR, while the original lysate does not. Mixtures of λ-DNA and BSA were used to determine the extent of the separation of DNA from a physiological concentration of proteins (30 mg/mL). The protein concentration in the extract (0.3 to 0.5 ng/µL) was reduced by five orders of magnitude from the initial mixture.

Virus-Mimicking Polymer Nanocomplexes Co-Assembling HCV E1E2 and Core Proteins with TLR 7/8 Agonist-Synthesis, Characterization, and In Vivo Activity

Hepatitis C virus (HCV) is a major public health concern, and the development of an effective HCV vaccine plays an important role in the effort to prevent new infections. Supramolecular co-assembly and co-presentation of the HCV envelope E1E2 heterodimer complex and core protein presents an attractive vaccine design strategy for achieving effective humoral and cellular immunity. With this objective, the two antigens were non-covalently assembled with an immunostimulant (TLR 7/8 agonist) into virus-mimicking polymer nanocomplexes (VMPNs) using a biodegradable synthetic polyphosphazene delivery vehicle. The resulting assemblies were characterized using dynamic light scattering and asymmetric flow field-flow fractionation methods and directly visualized in their vitrified state by cryogenic electron microscopy. The in vivo superiority of VMPNs over the individual components and an Alum-formulated vaccine manifests in higher neutralizing antibody titers, the promotion of a balanced IgG response, and the induction of a cellular immunity-CD4+ T cell responses to core proteins. The aqueous-based spontaneous co-assembly of antigens and immunopotentiating molecules enabled by a synthetic biodegradable carrier offers a simple and effective pathway to the development of polymer-based supramolecular nanovaccine systems.

In situ characterization techniques of protein corona around nanomaterials

Nanoparticles (NPs) inevitably interact with proteins upon exposure to biological fluids, leading to the formation of an adsorption layer known as the "protein corona". This corona imparts NPs with a new biological identity, directly influencing their interactions with living systems and dictating their fates in vivo. Thus, gaining a comprehensive understanding of the dynamic interplay between NPs and proteins in biological fluids is crucial for predicting therapeutic effects and advancing the clinical translation of nanomedicines. Numerous methods have been established to decode the protein corona fingerprints. However, these methods primarily rely on prior isolation of NP-protein complex from the surrounding medium by centrifugation, resulting in the loss of outer-layer proteins that directly interact with the biological system and determine the in vivo fate of NPs. We discuss here separation techniques as well as in situ characterization methods tailored for comprehensively unraveling the inherent complexities of NP-protein interactions, highlighting the challenges of in situ protein corona characterization and its significance for nanomedicine development and clinical translation.

Nano-Assembled Polyphosphazene Delivery System Enables Effective Intranasal Immunization with Nipah Virus Subunit Vaccine

The ultimate vaccine against infections caused by Nipah virus should be capable of providing protection at the respiratory tract─the most probable port of entry for this pathogen. Intranasally delivered vaccines, which target nasal-associated lymphoid tissue and induce both systemic and mucosal immunity, are attractive candidates for enabling effective vaccination against this lethal disease. Herein, the water-soluble polyphosphazene delivery vehicle assembles into nanoscale supramolecular constructs with the soluble extracellular portion of the Hendra virus attachment glycoprotein─a promising subunit vaccine antigen against both Nipah and Hendra viruses. These supramolecular constructs signal through Toll-like receptor 7/8 and promote binding interactions with mucin─an important feature of effective mucosal adjuvants. High mass contrast of phosphorus-nitrogen backbone of the polymer enables a successful visualization of nanoconstructs in their vitrified state by cryogenic electron microscopy. Here, we characterize the self-assembly of polyphosphazene macromolecule with biologically relevant ligands by asymmetric flow field flow fractionation, dynamic light scattering, fluorescence spectrophotometry, and turbidimetric titration methods. Furthermore, a polyphosphazene-enabled intranasal Nipah vaccine candidate demonstrates the ability to induce immune responses in hamsters and shows superiority in inducing total IgG and neutralizing antibodies when benchmarked against the respective clinical stage alum adjuvanted vaccine. The results highlight the potential of polyphosphazene-enabled nanoassemblies in the development of intranasal vaccines.

Reaction kinetics of chitosan nanogels crosslinked by genipin

Crosslinking of chitosan chains in dilute solution by natural crosslinker genipin leads to biocompatible nanogels. Here we investigated the reaction kinetics between chitosan and genipin in a 200 mM acetate buffer at 37 °C, and the structural and conformational evolutions of the nanogels during the crosslinking reaction by multi detection asymmetric flow field-flow fractionation (AF4). Upon crosslinking by genipin, the z-average hydrodynamic radius Rhz of the chitosan chains increased from 26 nm to 130 nm, while the weight average molar mass Mw increased from 2.0 × 105 g/mol to 1.8 × 107 g/mol. The crosslinking reaction appeared to be first-order and size-dependent. In particular, the intrachain crosslinking reaction was preferentially for nanogels having the larger size, leading to formation of branched chains/nanogels having a wide range of molar masses between 106 and 108 g/mol but a similar radius of gyration Rg ∼ 40 nm. For the largest nanogel fractions with M > 2.0 × 108 g/mol, both Rg and Rh showed a scaling relation with exponent 1/3 and a structure parameter Rg/Rh = 0.74, as expected for the hard sphere particle. The reaction was accompanied by a reduction of charge density and an increase in hydrophobicity of chitosan nanogels, which plays a key role in the formation of uniform size nanogels with chain density ρ(Rh) up to 0.45 g/cm3.

Monitoring Protein Complexation with Polyphosphazene Polyelectrolyte Using Automated Dynamic Light Scattering Titration and Asymmetric Flow Field Flow Fractionation and Protein Recognition Immunoassay

Polyphosphazenes represent a class of intrinsically flexible polyelectrolytes with potent immunoadjuvant activity, which is enabled through non-covalent self-assembly with antigenic proteins by charge complexation. The formation of supramolecular complexes between polyphosphazene adjuvant, poly[di(carboxylatophenoxy)phosphazene] (PCPP), and a model vaccine antigen, hen egg lysozyme, was studied under physiological conditions using automated dynamic light scattering titration, asymmetric flow field flow fractionation (AF4), enzyme-linked immunosorbent assay (ELISA), and fluorescent quenching methods. Three regimes of self-assembly were observed covering complexation of PCPP with lysozyme in the nano-scale range, multi-chain complexes, and larger aggregates with complexes characterized by a maximum loading of over six hundred protein molecules per PCPP chain and dissociation constant in the micromolar range (Kd = 7 × 10-6 mol/L). The antigenicity of PCPP bound lysozyme, when compared to equivalent lysozyme solutions, was largely retained for all complexes, but observed a dramatic reduction for heavily aggregated systems. Routes to control the complexation regimes with elevated NaCl or KCl salt concentrations indicate ion-specific effects, such that more smaller-size complexes are present at higher NaCl, counterintuitive with respect to PCPP solubility arguments. While the order of mixing shows a prominent effect at lower stoichiometries of mixing, higher NaCl salt reduces the effect all together.

Validated method for polystyrene nanoplastic separation in aqueous matrices by asymmetric-flow field flow fraction coupled to MALS and UV-Vis detectors

Plastics with nanosize (nanoplastics, NPLs) must be characterized, since they can be toxic or act as carriers of organic and inorganic pollutants, but there is a lack of reference materials and validated methods in the nanosize range. Therefore, this study has focused on the development and validation of a separation and size characterization methodology of polystyrene latex nanospheres, by using an asymmetric-flow field flow fraction system coupled to multi-angle light scattering and ultraviolet-visible detectors (AF4-MALS-UV). Hence, this work presents a fully validated methodology in the particle size range 30 to 490 nm, with bias between 95 and 109%, precision between 1 and 18%, LOD and LOQ below 0.2 and 0.3 µg respectively, except for 30-nm standard, for both detectors, and showing stable results for 100 analyses.

Continuous CTC separation through a DEP-based contraction-expansion inertial microfluidic channel

The efficient isolation of viable and intact circulating tumor cells (CTCs) from blood is critical for the genetic analysis of cancer cells, prediction of cancer progression, development of drugs, and evaluation of therapeutic treatments. While conventional cell separation devices utilize the size difference between CTCs and other blood cells, they fail to separate CTCs from white blood cells (WBCs) due to significant size overlap. To overcome this issue, we present a novel approach that combines curved contraction-expansion (CE) channels with dielectrophoresis (DEP) and inertial microfluidics to isolate CTCs from WBCs regardless of size overlap. This label-free and continuous separation method utilizes dielectric properties and size variation of cells for the separation of CTCs from WBCs. The results demonstrate that the proposed hybrid microfluidic channel can effectively isolate A549 CTCs from WBCs regardless of their size with a throughput of 300 μL/min, achieving a high separation distance of 233.4 μm at an applied voltage of 50 Vp-p . The proposed method allows for the modification of cell migration characteristics by controlling the number of CE sections of the channel, applied voltage, applied frequency, and flow rate. With its unique features of a single-stage separation, simple design, and tunability, the proposed method provides a promising alternative to the existing label-free cell separation techniques and may have a wide range of applications in biomedicine.

On the Fractionation and Physicochemical Characterisation of Self-Assembled Chitosan-DNA Polyelectrolyte Complexes

Chitosan is extensively studied as a carrier for gene delivery and is an attractive non-viral gene vector owing to its polycationic, biodegradable, and biocompatible nature. Thus, it is essential to understand the chemistry of self-assembled chitosan-DNA complexation and their structural and functional properties, enabling the formation of an effective non-viral gene delivery system. In this study, two parent chitosans (samples NAS-032 and NAS-075; Mw range ~118-164 kDa) and their depolymerised derivatives (deploy nas-032 and deploy nas-075; Mw range 6-14 kDa) with degrees of acetylation 43.4 and 4.7%, respectively, were used to form polyelectrolyte complexes (PECs) with DNA at varying [-NH3+]/[-PO4-] (N/P) molar charge ratios. We investigated the formation of the PECs using ζ-potential, asymmetric flow field-flow fractionation (AF4) coupled with multiangle light scattering (MALS), refractive index (RI), ultraviolet (UV) and dynamic light scattering (DLS) detectors, and TEM imaging. PEC formation was confirmed by ζ-potential measurements that shifted from negative to positive values at N/P ratio ~2. The radius of gyration (Rg) was determined for the eluting fractions by AF4-MALS-RI-UV, while the corresponding hydrodynamic radius (Rh), by the DLS data. We studied the influence of different cross-flow rates on AF4 elution patterns for PECs obtained at N/P ratios 5, 10, and 20. The determined rho shape factor (ρ = Rg/Rh) values for the various PECs corresponded with a sphere morphology (ρ ~0.77-0.85), which was consistent with TEM images. The results of this study represent a further step towards the characterisation of chitosan-DNA PECs by the use of multi-detection AF4 as an important tool to fractionate and infer aspects of their morphology.

Skin Vaccination with Ebola Virus Glycoprotein Using a Polyphosphazene-Based Microneedle Patch Protects Mice against Lethal Challenge

Ebolavirus (EBOV) infection in humans is a severe and often fatal disease, which demands effective interventional strategies for its prevention and treatment. The available vaccines, which are authorized under exceptional circumstances, use viral vector platforms and have serious disadvantages, such as difficulties in adapting to new virus variants, reliance on cold chain supply networks, and administration by hypodermic injection. Microneedle (MN) patches, which are made of an array of micron-scale, solid needles that painlessly penetrate into the upper layers of the skin and dissolve to deliver vaccines intradermally, simplify vaccination and can thereby increase vaccine access, especially in resource-constrained or emergency settings. The present study describes a novel MN technology, which combines EBOV glycoprotein (GP) antigen with a polyphosphazene-based immunoadjuvant and vaccine delivery system (poly[di(carboxylatophenoxy)phosphazene], PCPP). The protein-stabilizing effect of PCPP in the microfabrication process enabled preparation of a dissolvable EBOV GP MN patch vaccine with superior antigenicity compared to a non-polyphosphazene polymer-based analog. Intradermal immunization of mice with polyphosphazene-based MN patches induced strong, long-lasting antibody responses against EBOV GP, which was comparable to intramuscular injection. Moreover, mice vaccinated with the MN patches were completely protected against a lethal challenge using mouse-adapted EBOV and had no histologic lesions associated with ebolavirus disease.

Size characterization of nanomaterials in environmental and biological matrices through non-electron microscopic techniques

Engineered nanomaterials (ENs) can enter the environment, and accumulate in food chains, thereby causing environmental and health problems. Size characterization of ENs is critical for further evaluating the interactions among ENs in biological and ecological systems. Although electron microscope is a powerful tool in obtaining the size information, it has limitations when studying nanomaterials in complex matrices. In this review, we summarized non-electron microscope-based techniques, including chromatography-based, mass spectrometry-based, synchrotron radiation- and neutron-based techniques for detecting the size of ENs in environmental and biological matrices. The advantages and disadvantages of these techniques were highlighted. The perspectives on size characterization of ENs in complex matrices were also presented.

Polyphosphazene: A New Adjuvant Platform for Cocaine Vaccine Development

Cocaine is a highly addictive drug that has seen a steady uptrend causing severe health problems worldwide. Currently, there are no approved therapeutics for treating cocaine use disorder; hence, there is an urgent need to identify new medications. Immunopharmacotherapeutics is a promising approach utilizing endogenous antibodies generated through active vaccination, and if properly programmed, can blunt a drug's psychoactive and addictive effects. However, drug vaccine efficacy has largely been limited by the modest levels of antibodies induced. Herein, we explored an adjuvant system consisting of a polyphosphazene macromolecule, specifically poly[di(carboxylatoethylphenoxy)-phosphazene] (PCEP), a biocompatible synthetic polymer that was solicited for improved cocaine conjugate vaccine delivery performance. Our results demonstrated PCEP's superior assembling efficiency with a cocaine hapten as well as with the combined adjuvant CpG oligodeoxynucleotide (ODN). Importantly, this combination led to a higher titer response, balanced immunity, successful sequestering of cocaine in the blood, and a reduction in the drug in the brain. Moreover, a PCEP-cocaine conjugate vaccine was also found to function well via intranasal administration, where its efficacy was demonstrated through the antibody titer, affinity, mucosal IgA production, and a reduction in cocaine's locomotor activity. Overall, a comprehensive evaluation of PCEP integrated within a cocaine vaccine established an advance in the use of synthetic adjuvants in the drugs of abuse vaccine field.

Cationic Fluoropolyphosphazenes: Synthesis and Assembly with Heparin as a Pathway to Hemocompatible Nanocoatings

The development of state-of-the-art blood-contacting devices can be advanced through integrating hemocompatibility, durability, and anticoagulant functionalities within engineered nanoscale coatings. To enable all-aqueous assembly of nanocoatings combining omniphobic fluorinated features with the potent anticoagulant activity of hydrophilic heparin, two fluoropolymers containing cationic functionalities were synthesized─poly[(trifluoroethoxy)(dimethylaminopropyloxy)phosphazene], PFAP-O, and poly[(trifluoroethoxy)(dimethylaminopropylamino)phosphazene], PFAP-A. Despite a relatively high content of fluorinated pendant groups─approximately 50% (mol) in each─both polymers displayed solubility in aqueous solutions and were able to spontaneously form stable supramolecular complexes with heparin, as determined by dynamic light scattering and asymmetric flow field-flow fractionation methods. Heparin-containing coatings were then assembled by layer-by-layer deposition in aqueous solutions. Nanoassembled coatings were evaluated for potential thrombogenicity in three important categories of in vitro tests─coagulation by thrombin generation, platelet retention, and hemolysis. In all assays, heparin-containing fluoro-coatings consistently displayed superior performance compared to untreated titanium surfaces or fluoro-coatings assembled using poly(acrylic acid) in the absence of heparin. Short-term stability studies revealed the noneluting nature of these noncovalently assembled coatings.

Archaeal Viruses: Production of Virus Particles and Vesicle-like Viruses and Purification Using Asymmetrical Flow Field-Flow Fractionation

Asymmetrical flow field-flow fractionation (AF4) is a separation method based on hydrodynamic size of the sample components. It can separate a broad size range of components (~10³ to 10⁹ Da; particle diameter from ~1 nm to ~1 μm), but is especially well suited for high molecular weight samples such as virus-sized particles and extracellular vesicles. Separation takes place in an open channel where the flows control sample elution. Separation does not involve stationary phase, allowing gentle separation and good recoveries. The method is compatible with a wide variety of buffers. Coupling to various analytical detectors enables rapid assays on the molecular weight and size and their distribution, degradation, and aggregation of the sample components giving information on the sample quality. In addition to being an advanced analytical method, AF4 can be used in a semipreparative mode for purification. Here, we summarize archaeal virus production methods and virus purification by AF4 and provide examples on the steps that need optimization for obtaining good separation with the focus on halophilic archaeal viruses. Importantly, AF4 method is suitable for a variety of viruses and extracellular vesicles regardless of their host organism.

In silico all-atom approach to thermodiffusion in dilute aqueous solutions

Thermodiffusion (or thermophoresis) is the phenomenon by which the spatial distributions of constituents of liquid or gas phases become inhomogeneous in response to a temperature gradient. It has been evidenced in a variety of systems and has many practical applications as well as implications in the context of the origins of life. A complete molecular picture of thermophoresis is still missing, and phenomenological approaches are often employed to account for the experimental observations. In particular, the amplitude of the resulting concentration-gradients (quantified by the Soret coefficient) depends on many factors that are not straightforwardly rationalized. All-atom molecular dynamics simulations appear as an exquisite tool to shed light on the molecular origins for this phenomenon in molecular systems, but the practical implementation of thermophoretic settings in silico poses significant challenges. Here, we propose a robust approach to tackle thermophoresis in dilute realistic solutions at the molecular level. We rely on a recent enhanced heat-exchange algorithm to generate temperature-gradients. We carefully assess the convergence of thermophoretic simulations in dilute aqueous solutions. We show that simulations typically need to be propagated on long timescales (hundreds of nanoseconds). We find that the magnitude of the temperature gradient and the box sizes have little effect on the measured Soret coefficients. Practical guidelines are derived from such observations. Provided with this reliable setup, we discuss the results of thermophoretic simulations on several examples of molecular, neutral solutes, which we find in very good agreement with experimental measurements regarding the concentration-, mass-, and temperature-dependence of the Soret coefficient.

Nano-Assembly of Quisinostat and Biodegradable Macromolecular Carrier Results in Supramolecular Complexes with Slow-Release Capabilities

Self-assembly of ionically charged small molecule drugs with water-soluble biodegradable polyelectrolytes into nano-scale complexes can potentially offer a novel and attractive approach to improving drug solubility and prolonging its half-life. Nanoassemblies of quisinostat with water-soluble PEGylated anionic polyphosphazene were prepared by gradient-driven escape of solvent resulting in the reduction of solvent quality for a small molecule drug. A study of binding, analysis of composition, stability, and release profiles was conducted using asymmetric flow field flow fractionation (AF4) and dynamic light scattering (DLS) spectroscopy. Potency assays were performed with WM115 human melanoma and A549 human lung cancer cell lines. The resulting nano-complexes contained up to 100 drug molecules per macromolecular chain and displayed excellent water-solubility and improved hemocompatibility when compared to co-solvent-based drug formulations. Quisinostat release time (complex dissociation) at near physiological conditions in vitro varied from 5 to 14 days depending on initial drug loading. Multimeric complexes displayed dose-dependent potency in cell-based assays and the results were analyzed as a function of complex concentration, as well as total content of drug in the system. The proposed self-assembly process may present a simple alternative to more sophisticated delivery modalities, namely chemically conjugated prodrug systems and nanoencapsulation-based formulations.

Conformation and persistence length of chitosan in aqueous solutions of different ionic strengths via asymmetric flow field-flow fractionation

Conformation of chitosan in acidic aqueous solutions is strongly influenced by ionic strength, but the conventional employed size exclusion chromatography is limited to high ionic strength. Here we show that conformation of chitosan in acetate buffer down to millimolar ionic strength can be studied via asymmetric flow field-flow fractionation (AF4), where the separation is governed by the diffusion properties of the chitosan molecules and assisted by the electrostatic repulsion of the polyelectrolyte from the channel membrane. The size of chitosan decreases with ionic strength due to increasing screening of the polyelectrolyte effect. The persistence length of chitosan in the solutions, obtained by fitting the conformation plot by the wormlike chain model, decreases linearly with the Debye screening length from 44.5 nm at a salt concentration of 1.25 mM dominated by the electrostatic contribution to 8.6 nm in 800 mM acetate buffer close to its intrinsic persistence length of 7.7 nm.

A comprehensive analysis in one run - in-depth conformation studies of protein-polymer chimeras by asymmetrical flow field-flow fractionation

Polymer-based protein engineering has enabled the synthesis of a variety of protein-polymer conjugates that are widely applicable in therapeutic, diagnostic and biotechnological industries. Accurate characterizations of physical-chemical properties, in particular, molar masses, sizes, composition and their dispersities are critical parameters that determine the functionality and conformation of protein-polymer conjugates and are important for creating reproducible manufacturing processes. Most of the current characterization techniques suffer from fundamental limitations and do not provide an accurate understanding of a sample's true nature. In this paper, we demonstrate the advantage of asymmetrical flow field-flow fractionation (AF4) coupled with multiple detectors for the characterization of a library of complex, zwitterionic and neutral protein-polymer conjugates. This method allows for determination of intrinsic physical properties of protein-polymer chimeras from a single, rapid measurement.

Field-flow fractionation for nanoparticle characterization

This review presents field-flow fractionation: The elements of theory enable the link between the retention and the characteristics of the nanometer-sized analytes to be highlighted. In particular, the nature of force and its way of being applied are discussed. Four types of forces which determine four types of techniques were considered: hydrodynamic, sedimentation, thermal, and electrical; this is to show the importance of the choice of technique in relation to the characterization objectives. Then the separation performance is presented and compared with other separation techniques: field-flow fractionation has the greatest intrinsic separation capability. The characterization strategies are presented and discussed; on the one hand with respect to the characteristics needed for the description of nanoparticles; on the other hand in connection with the choice of the nature of the force, and also of the detectors used, online or offline. The discussion is based on a selection of published study examples. Finally, current needs and challenges are addressed, and as response, trends and possible characterization solutions.

Characterization of dextran particle size: How frit-inlet asymmetrical flow field-flow fractionation (FI-AF4) coupled online with dynamic light scattering (DLS) leads to enhanced size distribution

Accurate determinations of particle size and particle size distribution (PSD) are essential to achieve the clinical translation of medical nanoparticles (NPs). Herein, dextran-based NPs produced via a water-in-oil emulsification/crosslinking process and developed as nanomedicines were studied. NPs were first characterized using traditional batch-mode techniques as dynamic light scattering (DLS) and laser diffraction. In a second step, their analysis by frit-inlet asymmetrical flow field-flow fractionation (FI-AF4) was explored. The major parameters of the AF4 procedure, namely, crossflow, detector flow, crossflow decay programming and relaxation time were set up. The sizes of the particle fractions eluted under optimized conditions were measured using DLS as an online detector. We demonstrate that FI-AF4 is a powerful method to characterize dextran-NPs in the 200 nm -1 µm range. It provided a more realistic and comprehensive picture of PSD, revealing its heterogenous character and clearly showing the ratio of different populations in the sample, while batch-mode light scattering techniques only detected the biggest particle sizes.

Asymmetric-Flow Field-Flow Fractionation of complex waterborne polymer dispersions: Effect of the concentration of water in the measurement of molar mass distributions

Asymmetric-Flow Field-Flow Fractionation is a very powerful technique for measuring the molar mass distribution of polymers with complex microstructures. The analysis of some samples such as self-crosslinkable latexes requires to directly dissolve the polymer dispersion in the eluent (THF) without drying it, and this work studies the effect of the presence of this water in those analysis. Taking a polystyrene latex as model system, it was observed that the measured molar mass and radius of gyration increased as the concentration of water in the sample increased. This was an effect of a decrease in the compatibility between the solvent mixture (THF and water) and the polymer, which formed aggregates, and could be predicted calculating the polymer-solvent interaction parameter. When the study was extended to poly(methyl methacrylate), poly(n-butyl acrylate) and poly(vinyl acetate) the same general trend was observed, however, the impact of the water was less significant as the hydrophilicity of the polymer increased. Most importantly, if the samples with the highest water content were first dissolved in THF and afterwards dried using MgSO₄ the measured molar mass and radius of gyration values were the same as for the reference sample (dried in the oven), providing a method to analyze samples that cannot be dried into a film and remove the negative effect of the water at the same time.

Facile Synthesis of Unimodal Polymethacrylates with Narrow Dispersity via NIR LED Light-Controlled Bromine-Iodine Transformation Reversible-Deactivation Radical Polymerization

A facile and clean strategy for synthesizing unimodal polymethacrylates with narrow dispersity (Đ < 1.10) is successfully developed by a near-infrared (NIR) light-emitting diode (LED) light (λ_max = 740 nm)-controlled in situ bromine-iodine transformation reversible-deactivation radical polymerization system without the use of NIR dyes and expensive catalysts. In this system, alkyl iodide ethyl α-iodophenylacetate (EIPA) initiator is generated in situ by the nucleophilic substitution reaction between an alkyl bromide compound ethyl α-bromophenylacetate and sodium iodide (NaI). At the same time, excessive NaI is also acted as a highly active catalyst by forming halogen bonds with terminal iodine of the polymer chains in this system to make it capable of precisely synthesizing polymethacrylates with narrow dispersities (Đ = 1.03-1.10). In addition, the strong penetration ability of NIR LED light is illustrated by the successful polymerization even through 11 pieces of A4 paper.

Brownian Sieving Effect for Boosting the Performance of Microcapillary Hydrodynamic Chromatography. Proof of Concept

Microcapillary hydrodynamic chromatography (MHDC) is a well-established technique for the size-based separation of suspensions and colloids, where the characteristic size of the dispersed phase ranges from tens of nanometers to micrometers. It is based on hindrance effects which prevent relatively large particles from experiencing the low velocity region near the walls of a pressure-driven laminar flow through an empty microchannel. An improved device design is here proposed, where the relative extent of the low velocity region is made tunable by exploiting a two-channel annular geometry. The geometry is designed so that the core and the annular channel are characterized by different average flow velocities when subject to one and the same pressure drop. The channels communicate through openings of assigned cut-off length, say A. As they move downstream the channel, particles of size bigger than A are confined to the core region, whereas smaller particles can diffuse through the openings and spread throughout the entire cross section, therein attaining a spatially uniform distribution. By using a classical excluded-volume approach for modeling particle transport, we perform Lagrangian-stochastic simulations of particle dynamics and compare the separation performance of the two-channel and the standard (single-channel) MHDC. Results suggest that a quantitative (up to thirtyfold) performance enhancement can be obtained at operating conditions and values of the transport parameters commonly encountered in practical implementations of MHDC. The separation principle can readily be extended to a multistage geometry when the efficient fractionation of an arbitrary size distribution of the suspension is sought.

Next generation polyphosphazene immunoadjuvant: Synthesis, self-assembly and in vivo potency with human papillomavirus VLPs-based vaccine

Poly[di(carboxylatomethylphenoxy)phosphazene] (PCMP), a new member of polyphosphazene immunoadjuvant family, is synthesized. In vitro assessment of a new macromolecule revealed hydrolytic degradation profile and immunostimulatory activity comparable to its clinical stage homologue PCPP; however, PCMP was characterized by a beneficial reduced sensitivity to the ionic environment. In vivo evaluation of PCMP potency was conducted with human papillomavirus (HPV) virus-like particles (VLPs) based RG1-VLPs vaccine. In contrast with previously reported self-assembly of polyphosphazene adjuvants with proteins, which typically results in the formation of complexes with multimeric display of antigens, PCMP surface modified VLPs in a composition dependent pattern, which at a high polymer-to VLPs ratio led to stabilization of antigenic particles. Immunization experiments in mice demonstrated that PCMP adjuvanted RG1-VLPs vaccine induced potent humoral immune responses, in particular, on the level of highly desirable protective cross-neutralizing antibodies, and outperformed PCPP and Alhydrogel adjuvanted formulations.

Molecular Dynamics-Guided Design of a Functional Protein-ATRP Conjugate That Eliminates Protein-Protein Interactions

Even the most advanced protein-polymer conjugate therapeutics do not eliminate antibody-protein and receptor-protein recognition. Next-generation bioconjugate drugs will need to replace stochastic selection with rational design to select desirable levels of protein-protein interaction while retaining function. The "Holy Grail" for rational design would be to generate functional enzymes that are fully catalytic with small molecule substrates while eliminating interaction between the protein surface and larger molecules. Using chymotrypsin, an important enzyme that is used to treat pancreatic insufficiency, we have designed a series of molecular chimeras with varied grafting densities and shapes. Guided by molecular dynamic simulations and next-generation molecular chimera characterization with asymmetric flow field-flow fractionation chromatography, we grew linear, branched, and comb-shaped architectures from the surface of the protein by atom-transfer radical polymerization. Comb-shaped polymers, grafted from the surface of chymotrypsin, completely prevented enzyme inhibition with protein inhibitors without sacrificing the ability of the enzyme to catalyze the hydrolysis of a peptide substrate. Asymmetric flow field-flow fractionation coupled with multiangle laser light scattering including dynamic light scattering showed that nanoarmor designed with comb-shaped polymers was particularly compact and spherical. The polymer structure significantly increased protein stability and reduced protein-protein interactions. Atomistic molecular dynamic simulations predicted that a dense nanoarmor with long-armed comb-shaped polymer would act as an almost perfect molecular sieve to filter large ligands from substrates. Surprisingly, a conjugate that was composed of 99% polymer was needed before the elimination of protein-protein interactions.

Marine Exopolysaccharide Complexed With Scandium Aimed as Theranostic Agents

(1) Background: Exopolysaccharide (EPS) derivatives, produced by Alteromonas infernus bacterium, showed anti-metastatic properties. They may represent a new class of ligands to be combined with theranostic radionuclides, such as ⁴⁷Sc/⁴⁴Sc. The goal of this work was to investigate the feasibility of such coupling. (2) Methods: EPSs, as well as heparin used as a drug reference, were characterized in terms of molar mass and dispersity using Asymmetrical Flow Field-Flow Fractionation coupled to Multi-Angle Light Scattering (AF4-MALS). The intrinsic viscosity of EPSs at different ionic strengths were measured in order to establish the conformation. To determine the stability constants of Sc with EPS and heparin, a Free-ion selective radiotracer extraction (FISRE) method has been used. (3) Results: AF4-MALS showed that radical depolymerization produces monodisperse EPSs, suitable for therapeutic use. EPS conformation exhibited a lower hydrodynamic volume for the highest ionic strengths. The resulting random-coiled conformation could affect the complexation with metal for high concentration. The LogK of Sc-EPS complexes have been determined and showing that they are comparable to the Sc-Hep. (4) Conclusions: EPSs are very promising to be coupled with the theranostic pair of scandium for Nuclear Medicine.

Intracellular Delivery of Active Proteins by Polyphosphazene Polymers

Achieving intracellular delivery of protein therapeutics within cells remains a significant challenge. Although custom formulations are available for some protein therapeutics, the development of non-toxic delivery systems that can incorporate a variety of active protein cargo and maintain their stability, is a topic of great relevance. This study utilized ionic polyphosphazenes (PZ) that can assemble into supramolecular complexes through non-covalent interactions with different types of protein cargo. We tested a PEGylated graft copolymer (PZ-PEG) and a pyrrolidone containing linear derivative (PZ-PYR) for their ability to intracellularly deliver FITC-avidin, a model protein. In endothelial cells, PZ-PYR/protein exhibited both faster internalization and higher uptake levels than PZ-PEG/protein, while in cancer cells both polymers achieved similar uptake levels over time, although the internalization rate was slower for PZ-PYR/protein. Uptake was mediated by endocytosis through multiple mechanisms, PZ-PEG/avidin colocalized more profusely with endo-lysosomes, and PZ-PYR/avidin achieved greater cytosolic delivery. Consequently, a PZ-PYR-delivered anti-F-actin antibody was able to bind to cytosolic actin filaments without needing cell permeabilization. Similarly, a cell-impermeable Bax-BH3 peptide known to induce apoptosis, decreased cell viability when complexed with PZ-PYR, demonstrating endo-lysosomal escape. These biodegradable PZs were non-toxic to cells and represent a promising platform for drug delivery of protein therapeutics.

Effect of Core-Crosslinking on Protein Corona Formation on Polymeric Micelles

Most nanomaterials acquire a protein corona upon contact with biological fluids. The magnitude of this effect is strongly dependent both on surface and structure of the nanoparticle. To define the contribution of the internal nanoparticle structure, protein corona formation of block copolymer micelles with poly(N-2-hydroxypropylmethacrylamide) (pHPMA) as hydrophilic shell, which are crosslinked-or not-in the hydrophobic core is comparatively analyzed. Both types of micelles are incubated with human blood plasma and separated by asymmetrical flow field-flow fractionation (AF4). Their size is determined by dynamic light scattering and proteins within the micellar fraction are characterized by gel electrophoresis and quantified by liquid chromatography-high-resolution mass spectrometry-based label-free quantitative proteomics. The analyses reveal only very low amounts of plasma proteins associated with the micelles. Notably, no significant enrichment of plasma proteins is detectable for core-crosslinked micelles, while noncrosslinked micelles show a significant enrichment of plasma proteins, indicative of protein corona formation. The results indicate that preventing the reorganization of micelles (equilibrium with unimers) by core-crosslinking is crucial to reduce the interaction with plasma proteins.

In Vivo and In Vitro Potency of Polyphosphazene Immunoadjuvants with Hepatitis C Virus Antigen and the Role of Their Supramolecular Assembly

Two well-defined synthetic polyphosphazene immunoadjuvants, PCPP and PCEP, were studied for their ability to potentiate the immune response to the hepatitis C virus (HCV) E2 glycoprotein antigen in vivo. We report that PCEP induced significantly higher serum neutralization and HCV-specific IgG titers in mice compared to other adjuvants used in the study: PCPP, Alum, and Addavax. PCEP also shifted the response toward the desirable balanced Th1/Th2 immunity, as evaluated by the antibody isotype ratio (IgG2a/IgG1). The in vivo results were analyzed in the context of antigen-adjuvant molecular interactions in the system and in vitro immunostimulatory activity of formulations. Asymmetric flow field flow fractionation (AF4) and dynamic light scattering (DLS) analysis showed that both PCPP and PCEP spontaneously self-assemble with the E2 glycoprotein with the formation of multimeric water-soluble complexes, which demonstrates the role of polyphosphazene macromolecules as vaccine delivery vehicles. Intrinsic in vitro immunostimulatory activity of polyphosphazene adjuvants, which was assessed using a mouse macrophage cell line, revealed comparable activities of both polymers and did not provide an explanation of their in vivo performance. However, PCEP complexes with E2 displayed greater stability against agglomeration and improved in vitro immunostimulatory activity compared to those of PCPP, which is in line with superior in vivo performance of PCEP. The results emphasize the importance of often neglected antigen-polyphosphazene self-assembly mechanisms in formulations, which can provide important insights on their in vivo behavior and facilitate the establishment of a structure-activity relationship for this important class of immunoadjuvants.

A review of microplastics aggregation in aquatic environment: Influence factors, analytical methods, and environmental implications

A large amount of plastic waste released into natural waters and their demonstrated toxicity have made the transformation of microplastics (MPs; < 5 mm) and nanoplastics (NPs; < 100 nm) an emerging environmental concern. Aggregation is one of the most important environmental behaviors of MPs, especially in aquatic environments, which determines the mobility, distribution and bioavailability of MPs. In this paper, the sources and inputs of MPs in aquatic environments were first summarized followed by the analytical methods for investigating MP aggregation, including the sampling, visualization, and quantification procedures of MP' particle sizes. We critically evaluated the sampling methods that still remains a methodological gap. Identification and quantification of MPs were mostly carried out by visual, spectroscopic and spectrometric techniques, and modeling analysis. Important factors affecting MP aggregation in natural waters and environmental implications of the aggregation process were also reviewed. Finally, recommendations for future research were discussed, including (1) conducting more field studies; (2) using MPs in laboratory works representing those in the environment; and (3) standardizing methods of identification and quantification. The review gives a comprehensive overview of current knowledge for MP aggregation in natural waters, identifies knowledge gaps, and provides suggestions for future research.

Polyphosphazene immunoadjuvants: Historical perspective and recent advances

The development of successful vaccines has been increasingly reliant on the use of immunoadjuvants - additives, which can enhance and modulate immune responses to vaccine antigens. Immunoadjuvants of the polyphosphazene family encompass synthetic biodegradable macromolecules, which attain in vivo activity via antigen delivery and immunostimulation mechanisms. Over the last decades, the technology has witnessed evolvement of next generation members, expansion to include various antigens and routes of administration, and progression to clinical phase. This was accompanied by gaining important insights into the mechanism of action and the development of a novel class of virus-mimicking nano-assemblies for antigen delivery. The present review evaluates in vitro and in vivo data generated to date in the context of latest advances in understanding the primary function and biophysical behavior of these macromolecules. It also provides an overview of relevant synthetic and characterization methods, macromolecular biodegradation pathways, and polyphosphazene-based multi-component, nanoparticulate, and microfabricated formulations.

Limitations of Nanoparticles Size Characterization by Asymmetric Flow Field‑Fractionation Coupled with Online Dynamic Light Scattering

The development of reliable protocols suitable for the characterisation of the physical properties of nanoparticles in suspension is becoming crucial to assess the potential biological as well as toxicological impact of nanoparticles. Amongst sizing techniques, asymmetric flow field flow fractionation (AF4) coupled to online size detectors represents one of the most robust and flexible options to quantify the particle size distribution in suspension. However, size measurement uncertainties have been reported for on-line dynamic light scattering (DLS) detectors when coupled to AF4 systems. In this work we investigated the influence of the initial concentration of nanoparticles in suspension on the sizing capability of the asymmetric flow field-flow fractionation technique coupled with an on-line dynamic light scattering detector and a UV–Visible spectrophotometer (UV) detector. Experiments were performed with suspensions of gold nanoparticles with a nominal diameter of 40 nm and 60 nm at a range of particle concentrations. The results obtained demonstrate that at low concentration of nanoparticles, the AF4-DLS combined technique fails to evaluate the real size of nanoparticles in suspension, detecting an apparent and progressive size increase as a function of the elution time and of the concentration of nanoparticles in suspension.

Critical Assessment of the Application of Multidetection SEC and AF4 for the Separation of Single-Chain Nanoparticles

The intramolecular chain collapse of linear precursors with systematic variation of molar mass and ligation group density (5, 15, and 30 mol %) into single-chain nanoparticles (SCNPs) was studied by two different separation approaches. The efficiency of size exclusion chromatography with quadruple detection (SEC-D4) was compared to asymmetrical field flow fractionation hyphenated to quintuple detection (AF4-D5) in organic solvent. The application of the unique combination of advanced detection to different separation principles opens up the opportunity to critically evaluate the determination of molar masses and different types of radii for an in-depth understanding of the structural properties affected by the internal folding process. This is achieved by a detailed comparison of assets, drawbacks, and limitations of these approaches based on the systematical screening of different chain lengths and sizes of the precursors and the SCNPs. Furthermore, an alternative strategy for quantitative determination of intramolecular ligation density by a combination of AF4 and UV detection is introduced.

Insights into the internal structures of nanogels using a versatile asymmetric-flow field-flow fractionation method

Poly(N-isopropylacrylamide) (pNIPAM) nanogels are a highly researched type of colloidal material. In this work, we establish a versatile asymmetric-flow field-flow fractionation (AF4) method that can provide high resolution particle sizing and also structural information on nanogel samples from 65-310 nm in hydrodynamic diameter and so different chemical compositions. To achieve this online multi-angle light scattering and dynamic light scattering detectors were used to provide measurement of the radius of gyration (R _g) and hydrodynamic radius (R _h) respectively. Two different eluents and a range of cross-flows were evaluated in order to provide effective fractionation and high recovery for the different nanogel samples. We found that using 0.1 M NaNO₃ as the eluent and an initial cross-flow of 1 mL min^-1 provided optimal separation conditions for all samples tested. Using this method, we analysed two types of samples, pNIPAM nanogels prepared by free radical dispersion polymerisation with increasing diameters and analysed poly(acrylic acid)-b-pNIPAM crosslinked nanogels prepared by reversible addition-fragmentation chain transfer dispersion polymerisation. We could determine that the differently sized free radical nanogels possessed differing internal structures; shape factors (R _g/R _h) ranged from 0.58-0.73 and revealed that the smallest nanogel had a homogeneous internal crosslinking density, while the larger nanogels had a more densely crosslinked core compared to the shell. The poly(acrylic acid)-b-pNIPAM crosslinked nanogels displayed clear core-shell structures due to all the crosslinking being contained in the core of the nanogel.

Role of Interfacial Entropy in the Particle-Size Dependence of Thermophoretic Mobility

We show that changes in the surface tension of a particle due to the presence of nonionic surfactants and impurities, which alter the interfacial entropy, have an impact on the value of the thermophoretic mobility. We have found the existence of different behaviors of this quantity in terms of particle size which can be summarized through a power law. For particles that are small enough, the thermophoretic mobility is a constant, whereas for larger particles it is linear in the particle radius. These results show the important role of the interfacial entropic effects on the behavior of the thermophoretic mobility.

Polymeric Nanoparticles with Neglectable Protein Corona

The current understanding of nanoparticle-protein interactions indicates that they rapidly adsorb proteins upon introduction into a living organism. The formed protein corona determines thereafter identity and fate of nanoparticles in the body. The present study evaluates the protein affinity of three core-crosslinked polymeric nanoparticles with long circulation times, differing in the hydrophilic polymer material forming the particle surface, namely poly(N-2-hydroxypropylmethacrylamide) (pHPMA), polysarcosine (pSar), and poly(ethylene glycol) (PEG). This includes the nanotherapeutic CPC634, which is currently in clinical phase II evaluation. To investigate possible protein corona formation, the nanoparticles are incubated in human blood plasma and separated by asymmetrical flow field-flow fractionation (AF4). Notably, light scattering shows no detectable differences in particle size or polydispersity upon incubation with plasma for all nanoparticles, while in gel electrophoresis, minor amounts of proteins can be detected in the particle fraction. Label-free quantitative proteomics is additionally applied to analyze and quantify the composition of the proteins. It proves that some proteins are enriched, but their concentration is significantly less than one protein per particle. Thus, most of the nanoparticles are not associated with any proteins. Therefore, this work underlines that polymeric nanoparticles can be synthesized, for which a protein corona formation does not take place.

Supramolecular assembly of Toll-like receptor 7/8 agonist into multimeric water-soluble constructs enables superior immune stimulation in vitro and in vivo

Resiquimod or R848 (RSQD) is a Toll-like receptor (TLR) 7/8 agonist which shows promise as vaccine adjuvant due to its potential to promote highly desirable cellular immunity. The development of this small molecule in the field to date has been largely impeded by its rapid in vivo clearance and lack of association with vaccine antigens. Here, we report a multimeric TLR 7/8 construct of nano-scale size, which results from a spontaneous self-assembly of RSQD with a water-soluble clinical-stage polymer - poly[di(carboxylatophenoxy)phosphazene] (PCPP). The formation of ionically paired construct (PCPP-R) and a ternary complex, which also includes Hepatitis C virus (HCV) antigen, has been demonstrated by dynamic lights scattering (DLS), turbidimetry, fluorescence spectroscopy, asymmetric flow field flow fractionation (AF4), and ¹H NMR spectroscopy methods. The resulting supramolecular assembly PCPP-R enabled superior immunostimulation in cellular assays (mouse macrophage reporter cell line) and displayed improved in vitro hemocompatibility (human erythrocytes). In vivo studies demonstrated that PCPP-R adjuvanted HCV formulation induced higher serum neutralization titers in BALB/c mice and shifted the response towards desirable cellular immunity, as evaluated by antibody isotype ratio (IgG2a/IgG1) and ex vivo analysis of cytokine secreting splenocytes (higher levels of interferon gamma (IFN-γ) single and tumor necrosis factor alpha (TNF-α)/IFN-γ double producing cells). The non-covalent multimerization approach stands in contrast to previously suggested RSQD delivery methods, which involve covalent conjugation or encapsulation, and offers a flexible methodology that can be potentially integrated with other parenterally administered drugs.

Evaluation of Polymeric Materials for Chemical Enhanced Oil Recovery

Polymer flooding is a promising enhanced oil recovery (EOR) technique; sweeping a reservoir with a dilute polymer solution can significantly improve the overall oil recovery. In this overview, polymeric materials for enhanced oil recovery are described in general terms, with specific emphasis on desirable characteristics for the application. Application-specific properties should be considered when selecting or developing polymers for enhanced oil recovery and should be carefully evaluated. Characterization techniques should be informed by current best practices; several are described herein. Evaluation of fundamental polymer properties (including polymer composition, microstructure, and molecular weight averages); resistance to shear/thermal/chemical degradation; and salinity/hardness compatibility are discussed. Finally, evaluation techniques to establish the polymer flooding performance of candidate EOR materials are described.

Thermophoresis of colloids in nematic liquid crystal

Thermophoresis, or the directional motion of colloidal particles in liquids driven by a temperature gradient, is of both fundamental interest and practical use. In this work we explore the thermophoresis of colloids suspended in nematic liquid crystals (LCs). We observe that the motion of these colloids is fundamentally different from that in isotropic systems as a result of elastic distortions in the director fields caused by the colloidal inclusions. In the case of a sufficiently large local temperature and gradient, the elastic energy drives negative thermophoresis of immersed particles, which has a strongly nonlinear dependence on temperature. We develop a theory that incorporates elastic energy minimization into the traditional thermophoretic formulation and demonstrated a good agreement with experimental observations. We also examine the temperature dependence of the effective viscosity of the colloids and highlight the large magnitude of the Soret coefficient (|ST| > 5000), which results from the inherent enhancement in thermophoresis due to elastophoretic considerations and suppression of Brownian diffusion in LC media.