Asymmetric flow field-flow fractionation in the field of nanomedicine

A DNA aptamer for binding and inhibition of DNA methyltransferase 1

DNA methyltransferases (DNMTs) are enzymes responsible for establishing and maintaining DNA methylation in cells. DNMT inhibition is actively pursued in cancer treatment, dominantly through the formation of irreversible covalent complexes between small molecular compounds and DNMTs that suffers from low efficacy and high cytotoxicity, as well as no selectivity towards different DNMTs. Herein, we discover aptamers against the maintenance DNA methyltransferase, DNMT1, by coupling Asymmetrical Flow Field-Flow Fractionation (AF4) with Systematic Evolution of Ligands by EXponential enrichment (SELEX). One of the identified aptamers, Apt. #9, contains a stem-loop structure, and can displace the hemi-methylated DNA duplex, the native substrate of DNMT1, off the protein on sub-micromolar scale, leading for effective enzymatic inhibition. Apt. #9 shows no inhibition nor binding activity towards two de novo DNMTs, DNMT3A and DNMT3B. Intriguingly, it can enter cancer cells with over-expression of DNMT1, colocalize with DNMT1 inside the nuclei, and inhibit the activity of DNMT1 in cells. This study opens the possibility of exploring the aptameric DNMT inhibitors being a new cancer therapeutic approach, by modulating DNMT activity selectively through reversible interaction. The aptamers could also be valuable tools for study of the functions of DNMTs and the related epigenetic mechanisms.

Advanced nanomedicine characterization by DLS and AF4-UV-MALS: Application to a HIV nanovaccine

Nanoformulations are complex systems where physicochemical properties determine their therapeutic efficacy and safety. In the case of nanovaccines, particle size and shape play a crucial role on the immune response generated. Furthermore, the antigen's integrity is also a key aspect to control when producing a nanovaccine. The determination of all those physicochemical properties is still an analytical challenge and the lack of well-established methods hinders the access of new therapeutics to the market. In this work, robust methods for the characterization of a novel HIV nanoparticle-based vaccine produced in good manufacturing practice (GMPs)-like environment were developed. With slightly polydisperse particles (< 0.2) close to 180 nm of size, batch-mode Dynamic Light Scattering (DLS) was validated to be used as a quality control technique in the pilot production plant. In addition, a high size resolution method using Asymmetrical Flow Field Flow Fractionation (AF4) demonstrated its ability to determine not only size and size distribution but also shape modification across the size and accurate quantification of the free active ingredient. Results showed a monomodal distribution of particles from 60 to 700 nm, most of them (> 90%) with size lower than 250 nm, consistent with more traditional techniques, and revealed a slight change in the structure of the particles induced by the presence of the antigen. Finally, a batch to batch variability lower than 20% was obtained by both DLS and AF4 methods indicating that preparation method was highly reproducible.

Asymmetrical Flow Field-Flow Fractionation on Virus and Virus-Like Particle Applications

Asymmetrical flow field-flow fractionation (AF4) separates sample components based on their sizes in the absence of a stationary phase. It is well suited for high molecular weight samples such as virus-sized particles. The AF4 experiment can potentially separate molecules within a broad size range (~10³−10⁹ Da; particle diameter from 2 nm to 0.5−1 μm). When coupled to light scattering detectors, it enables rapid assays on the size, size distribution, degradation, and aggregation of the studied particle populations. Thus, it can be used to study the quality of purified viruses and virus-like particles. In addition to being an advanced analytical characterization technique, AF4 can be used in a semi-preparative mode. Here, we summarize and provide examples on the steps that need optimization for obtaining good separation with the focus on virus-sized particles.

Protein Interactions with Nanoparticle Surfaces: Highlighting Solution NMR Techniques

In the last decade, nanoparticles (NPs) have become a key tool in medicine and biotechnology as drug delivery systems, biosensors and diagnostic devices. The composition and surface chemistry of NPs vary based on the materials used: typically organic polymers, inorganic materials, or lipids. Nanoparticle classes can be further divided into sub-categories depending on the surface modification and functionalization. These surface properties matter when NPs are introduced into a physiological environment, as they will influence how nucleic acids, lipids, and proteins will interact with the NP surface. While small-molecule interactions are easily probed using NMR spectroscopy, studying protein-NP interactions using NMR introduces several challenges. For example, globular proteins may have a perturbed conformation when attached to a foreign surface, and the size of NP-protein conjugates can lead to excessive line broadening. Many of these challenges have been addressed, and NMR spectroscopy is becoming a mature technique for in situ analysis of NP binding behavior. It is therefore not surprising that NMR has been applied to NP systems and has been used to study biomolecules on NP surfaces. Important considerations include corona composition, protein behavior, and ligand architecture. These features are difficult to resolve using classical surface and material characterization strategies, and NMR provides a complementary avenue of characterization. In this review, we examine how solution NMR can be combined with other analytical techniques to investigate protein behavior on NP surfaces.

Toward Functional Synthetic Cells: In-Depth Study of Nanoparticle and Enzyme Diffusion through a Cross-Linked Polymersome Membrane

Understanding the diffusion of nanoparticles through permeable membranes in cell mimics paves the way for the construction of more sophisticated synthetic protocells with control over the exchange of nanoparticles or biomacromolecules between different compartments. Nanoparticles postloading by swollen pH switchable polymersomes is investigated and nanoparticles locations at or within polymersome membrane and polymersome lumen are precisely determined. Validation of transmembrane diffusion properties is performed based on nanoparticles of different origin-gold, glycopolymer protein mimics, and the enzymes myoglobin and esterase-with dimensions between 5 and 15 nm. This process is compared with the in situ loading of nanoparticles during polymersome formation and analyzed by advanced multiple-detector asymmetrical flow field-flow fractionation (AF4). These experiments are supported by complementary i) release studies of protein mimics from polymersomes, ii) stability and cyclic pH switches test for in polymersome encapsulated myoglobin, and iii) cryogenic transmission electron microscopy studies on nanoparticles loaded polymersomes. Different locations (e.g., membrane and/or lumen) are identified for the uptake of each protein. The protein locations are extracted from the increasing scaling parameters and the decreasing apparent density of enzyme-containing polymersomes as determined by AF4. Postloading demonstrates to be a valuable tool for the implementation of cell-like functions in polymersomes.

Measuring particle size distribution of nanoparticle enabled medicinal products, the joint view of EUNCL and NCI-NCL. A step by step approach combining orthogonal measurements with increasing complexity

The particle size distribution (PSD) and the stability of nanoparticles enabled medicinal products (NEP) in complex biological environments are key attributes to assess their quality, safety and efficacy. Despite its low resolution, dynamic light scattering (DLS) is the most common sizing technique since the onset of NEP in pharmaceutical technologies. Considering the limitations of the existing sizing measurements and the challenges posed by complex NEPs both scientists and regulators encourage the combination of multiple orthogonal high-resolution approaches to shed light in the NEP sizing space (e.g. dynamic light scattering, electron microscopy, field flow fractionation coupled to online sizing detectors, centrifugal techniques, particle tracking analysis and tunable resistive pulse sensing). The pharmaceutical and biotechnology developers are now challenged to find their own pragmatic characterisation approaches, which should be fit for purpose and minimize costs at the same time, in a complicated landscape where only a few standards exist. In order to support the community, the European Nanomedicine Characterisation Laboratory (EUNCL) and the US National Cancer Institute Nanotechnology Characterization Laboratory (NCI-NCL) have jointly developed multiple standard operating procedures (SOPs) for NEP assessment, including the measurements of particle size distribution, and are offering wide access to their 'state of the art' characterisation platforms, in addition to making SOPs publicly available. This joint perspective article would like to present the NCI-NCL and EUNCL multi-step approach of incremental complexity to measure particle size distribution and size stability of NEPs, consisting of a quick preliminary step to assess sample integrity and stability by low resolution techniques (pre-screening), followed by the combination of complementary high resolution sizing measurements performed both in simple buffers and in complex biological media. Test cases are presented to demonstrate: i) the need for employing at least one high-resolution sizing technique, ii) the importance of selecting the correct sizing techniques for the purpose, and iii) the robustness of utilizing orthogonal sizing techniques to study the physical properties of complex NEP samples.

Recovery, overloading, and protein interactions in asymmetrical flow field-flow fractionation

In asymmetrical flow field-flow fractionation (AF4), similar to other separation techniques, mass recovery and overloading require special attention in order to obtain quantitative results. We conducted a systematic study with five globular proteins of different molecular weight (36.7–669 kDa) and isoelectric point (4.0–6.5), and ultrafiltration membranes that are commonly used in aqueous AF4, regenerated cellulose (RC) and polyethersulfone (PES). Phosphate-buffered saline (PBS) with ionic strength 0.15 M and pH 7.2 was used as the carrier liquid in this study. The actual molecular weight cutoff (MWCO) was found to be higher than the nominal value and varied between membranes of different chemistry but the same nominal MWCO. Adsorption on the membrane was found to be dependent on the membrane chemistry (RC had lower adsorption compared to PES), and independent of the protein standard for the examined proteins. On the other hand, the mass overloading effects (i.e., higher retention times, peak broadening, and fronting peaks) were significantly more pronounced for γ-globulin than for the other proteins. The overloading effects could be rationalized with the increase of the local viscosity close to the membrane, depending on the properties of the proteins, and we derived theoretical equations that related the dependency of the migration velocity on the protein concentration through this non-ideal viscosity effect.

Impact of a Heat Shock Protein Impurity on the Immunogenicity of Biotherapeutic Monoclonal Antibodies

Purpose

Anti-drug antibodies can impair the efficacy of therapeutic proteins and, in some circumstances, induce adverse health effects. Immunogenicity can be promoted by aggregation; here we examined the ability of recombinant mouse heat shock protein 70 (rmHSP70) - a common host cell impurity - to modulate the immune responses to aggregates of two therapeutic mAbs in mice.

Methods

Heat and shaking stress methods were used to generate aggregates in the sub-micron size range from two human mAbs, and immunogenicity assessed by intraperitoneal exposure in BALB/c mice.

Results

rmHSP70 was shown to bind preferentially to aggregates of both mAbs, but not to the native, monomeric proteins. Aggregates supplemented with 0.1% rmHSP70 induced significantly enhanced IgG2a antibody responses compared with aggregates alone but the effect was not observed for monomeric mAbs. Dendritic cells pulsed with mAb aggregate showed enhanced IFNγ production on co-culture with T cells in the presence of rmHSP70.

Conclusion

The results indicate a Th1-skewing of the immune response by aggregates and show that murine rmHSP70 selectively modulates the immune response to mAb aggregates, but not monomer. These data suggest that heat shock protein impurities can selectively accumulate by binding to mAb aggregates and thus influence immunogenic responses to therapeutic proteins.

Electronic supplementary material

The online version of this article (10.1007/s11095-019-2586-7) contains supplementary material, which is available to authorized users.

Comparative study of chikungunya Virus-Like Particles and Pseudotyped-Particles used for serological detection of specific immunoglobulin M

The incidence of chikungunya virus (CHIKV) infection has increased dramatically in recent decades. Effective diagnostic methods must be available to optimize patient management. IgM-capture Enzyme-Linked Immunosorbent Assay (MAC-ELISA) is routinely used for the detection of specific CHIKV IgM. This method requires inactivated CHIKV viral lysate (VL). The use of viral bioparticles such as Virus-Like Particles (VLPs) and Pseudotyped-Particles (PPs) could represent an alternative to VL. Bioparticles performances were established by MAC-ELISA; physico-chemical characterizations were performed by field-flow fractionation (HF5) and confirmed by electron microscopy. Non-purified PPs give a detection signal higher than for VL. Results suggested that the signal difference observed in MAC-ELISA was probably due to the intrinsic antigenic properties of particles. The use of CHIKV bioparticles such as VLPs and PPs represents an attractive alternative to VL. Compared to VL and VLPs, non-purified PPs have proven to be more powerful antigens for specific IgM capture.

Measuring Particle Size Distribution by Asymmetric Flow Field Flow Fractionation: A Powerful Method for the Preclinical Characterization of Lipid-Based Nanoparticles

Particle size distribution and stability are key attributes for the evaluation of the safety and efficacy profile of medical nanoparticles (Med-NPs). Measuring particle average size and particle size distribution is a challenging task which requires the combination of orthogonal high-resolution sizing techniques, especially in complex biological media. Unfortunately, despite its limitations, due to its accessibility, low cost, and easy handling, batch mode dynamic light scattering (DLS) is still very often used as the only approach to measure particle size distribution in the nanomedicine field. In this work the use of asymmetric flow field flow fractionation coupled to multiangle light scattering and dynamic light scattering detectors (AF4-MALS-DLS) was evaluated as an alternative to batch mode DLS to measure the physical properties of lipid-based nanoparticles. A robust standard operating procedure (SOPs) developed by the Nanomedicine Characterization Laboratory (EUNCL) was presented and tested to assess size stability, batch to batch consistency, and the behavior of the lipid-based nanoparticles in plasma. Orthogonal sizing techniques, such as transmission electron microscopy (TEM) and particle tracking analysis (PTA) measurements, were performed to support the results. While batch mode DLS could be applied as a fast and simple method to provide a preliminary insight into the integrity and polydispersity of samples, it was unsuitable to resolve small modifications of the particle size distribution. The introduction of nanoparticle sorting by field-flow fractionation coupled to online DLS and MALS allowed assessment of batch to batch variability and changes in the size of the lipid nanoparticles induced by the interaction with serum proteins, which are critical for quality control and regulatory aspects. In conclusion, if a robust SOP is followed, AF4-MALS-DLS is a powerful method for the preclinical characterization of lipid-based nanoparticles.

Nanoparticle heterogeneity: an emerging structural parameter influencing particle fate in biological media?

Drug nanocarriers' surface chemistry is often presumed to be uniform. For instance, the polymer surface coverage and distribution of ligands on nanoparticles are described with averaged values obtained from quantification techniques based on particle populations. However, these averaged values may conceal heterogeneities at different levels, either because of the presence of particle sub-populations or because of surface inhomogeneities, such as patchy surfaces on individual particles. The characterization and quantification of chemical surface heterogeneities are tedious tasks, which are rather limited by the currently available instruments and research protocols. However, heterogeneities may contribute to some non-linear effects observed during the nanoformulation optimization process, cause problems related to nanocarrier production scale-up and correlate with unexpected biological outcomes. On the other hand, heterogeneities, while usually unintended and detrimental to nanocarrier performance, may, in some cases, be sought as adjustable properties that provide NPs with unique functionality. In this review, results and processes related to this issue are compiled, and perspectives and possible analytical developments are discussed.

Preservation of the soft protein corona in distinct flow allows identification of weakly bound proteins

Nanocarriers that are used for targeted drug delivery come in contact with biological liquids and subsequently proteins will adsorb to the nanocarriers' surface to form the so called 'protein corona'. The protein corona defines the biological identity and determines the biological response towards the nanocarriers in the body. To make nanomedicine safe and reliable it is required to get a better insight into this protein corona and, therefore, the adsorbed proteins have to be characterized. Currently, centrifugation is the common method to isolate the protein corona for further investigations. However, with this method it is only possible to investigate the strongly bound proteins, also referred to as 'hard protein corona'. Therefore, we want to introduce a new separation technique to separate nanoparticles including the soft protein corona containing also loosely bound proteins for further characterization. The used separation technique is the asymmetric flow field-flow fractionation (AF4). We were able to separate the nanoparticles with proteins forming the soft protein corona and were able to show that in our system only the hard protein corona directly influenced the cell uptake behavior.

STATEMENT OF SIGNIFICANCE

Currently, there is an ongoing debate whether only strongly bound proteins (hard corona) or also loosely bound proteins (soft corona) contribute to the biological identity of nanocarriers, because up to now isolation of the soft corona was not possible. Here, asymmetric flow field-flow fractionation was used to isolate nanoparticles with a preserved soft corona from the biological medium. This enabled the characterization of the soft corona composition and to evaluate its influence on cellular uptake. For our system we found that only the strongly bound proteins (hard corona) determined cell internalization. This method can now be used to evaluate the impact of the soft corona further and to characterize nanomaterials that cannot be separated from blood plasma by other means.

Soluble Aβ aggregates can inhibit prion propagation

Mammalian prions cause lethal neurodegenerative diseases such as Creutzfeldt–Jakob disease (CJD) and consist of multi-chain assemblies of misfolded cellular prion protein (PrP^C). Ligands that bind to PrP^C can inhibit prion propagation and neurotoxicity. Extensive prior work established that certain soluble assemblies of the Alzheimer's disease (AD)-associated amyloid β-protein (Aβ) can tightly bind to PrP^C, and that this interaction may be relevant to their toxicity in AD. Here, we investigated whether such soluble Aβ assemblies might, conversely, have an inhibitory effect on prion propagation. Using cellular models of prion infection and propagation and distinct Aβ preparations, we found that the form of Aβ assemblies which most avidly bound to PrP in vitro also inhibited prion infection and propagation. By contrast, forms of Aβ which exhibit little or no binding to PrP were unable to attenuate prion propagation. These data suggest that soluble aggregates of Aβ can compete with prions for binding to PrP^C and emphasize the bidirectional nature of the interplay between Aβ and PrP^C in Alzheimer's and prion diseases. Such inhibitory effects of Aβ on prion propagation may contribute to the apparent fall-off in the incidence of sporadic CJD at advanced age where cerebral Aβ deposition is common.

How to measure release from nanosized carriers?

Novel drug delivery systems exhibit great potential in the formulation of poorly soluble compounds but have also been applied to reduce side effects of highly active drug molecules. Despite all efforts, there are only few technologies available to investigate the in vitro release of next-generation nanotherapeutics. In the following, different approaches for testing the drug release from nanoparticles in the fields of formulation development and quality control will be discussed. A variety of methods is available, starting from dialysis-based equipment, in situ measurements, flow-through devices and sample and separate setups. If possible, these methods should enable a more rapid formulation development and quality control of nanosized carriers as well as improve the prediction of in vivo performance and clinical outcomes.

Inline Coupling of Electrokinetic Preconcentration Method to Taylor Dispersion Analysis for Size-Based Characterization of Low-UV-Absorbing Nanoparticles

The inline coupling of the field-amplified sample injection (FASI) to Taylor dispersion analysis (TDA) was used to characterize low-UV absorbing carboxylated silica nanoparticles (cNPs). The hydrodynamic diameters (D_h) were measured by using a commercial capillary electrophoresis instrument. The proposed methodology did not require any complicated instruments or chromophoric dye to increase the detection sensitivity. A practical method based on a half-Gaussian fitting was proposed for the data processing. The results obtained by this method were compared with those derived from dynamic light scattering (DLS) and transmission electron microscopy (TEM) analyses. From these results, it appeared that the size derived by TDA is in excellent agreement with those measured by DLS and TEM, as demonstrated by stable nanoparticles with narrow size distributions. Intermediate precision relative standard deviations less than 5% were obtained by FASI-TDA. The effect of the FASI-induced cNP peak dispersion on the reliability of the results was discussed in detail.

Are existing standard methods suitable for the evaluation of nanomedicines: some case studies

The use of nanotechnology in medical products has been demonstrated at laboratory scale, and many resulting nanomedicines are in the translational phase toward clinical applications, with global market trends indicating strong growth of the sector in the coming years. The translation of nanomedicines toward the clinic and subsequent commercialization may require the development of new or adaptation of existing standards to ensure the quality, safety and efficacy of such products. This work addresses some identified needs, and illustrates the shortcomings of currently used standardized methods when applied to medical-nanoparticles to assess particle size, drug loading, drug release and in vitro safety. Alternative physicochemical, and in vitro toxicology methods, with the potential to qualify as future standards supporting the evaluation of nanomedicine are provided.

Comparative Evaluation of U.S. Brand and Generic Intravenous Sodium Ferric Gluconate Complex in Sucrose Injection: Physicochemical Characterization

The objective of this study was to evaluate physicochemical equivalence between brand (i.e., Ferrlecit) and generic sodium ferric gluconate (SFG) in sucrose injection by conducting a series of comparative in vitro characterizations using advanced analytical techniques. The elemental iron and carbon content, thermal properties, viscosity, particle size, zeta potential, sedimentation coefficient, and molecular weight were determined. There was no noticeable difference between brand and generic SFG in sucrose injection for the above physical parameters evaluated, except for the sedimentation coefficient determined by sedimentation velocity analytical ultracentrifugation (SV-AUC) and molecular weight by asymmetric field flow fractionation-multi-angle light scattering (AFFF-MALS). In addition, brand and generic SFG complex products showed comparable molecular weight distributions when determined by gel permeation chromatography (GPC). The observed minor differences between brand and generic SFG, such as sedimentation coefficient, do not impact their biological activities in separate studies of in vitro cellular uptake and rat biodistribution. Coupled with the ongoing clinical study comparing the labile iron level in healthy volunteers, the FDA-funded post-market studies intended to illustrate comprehensive surveillance efforts ensuring safety and efficacy profiles of generic SFG complex in sucrose injection, and also to shed new light on the approval standards on generic parenteral iron colloidal products.

Synthesis and characterization of metallo-supramolecular polymers

The incorporation of metal centers into the backbone of polymers has led to the development of a broad range of organometallic and coordination compounds featuring properties that are relevant for potential applications in diverse areas of research, ranging from energy storage/conversion to bioactive or self-healing materials. In this review, the basic concepts and synthetic strategies leading to these types of materials as well as the scope of available characterization techniques will be summarized and discussed.

Quantitative In Vitro Assessment of Liposome Stability and Drug Transfer Employing Asymmetrical Flow Field-Flow Fractionation (AF4)

PURPOSE

In the present study we introduce an efficient approach for a size-based separation of liposomes from plasma proteins employing AF4. We investigated vesicle stability and release behavior of the strongly lipophilic drug temoporfin from liposomes in human plasma for various incubation times at 37°C.

METHODS

We used the radioactive tracer cholesteryl oleyl ether (COE) or dipalmitoyl-phosphocholine (DPPC) as lipid markers and (14)C-labeled temoporfin. First, both lipid labels were examined for their suitability as liposome markers. Furthermore, the influence of plasma origin on liposome stability and drug transfer was investigated. The effect of membrane fluidity and PEGylation on vesicle stability and drug release characteristics was also analyzed.

RESULTS

Surprisingly, we observed an enzymatic transfer of (3)H-COE to lipoproteins due to the cholesterol ester transfer protein (CETP) in human plasma in dependence on membrane rigidity and were able to inhibit this transfer by plasma preincubation with the CETP inhibitor torcetrapib. This effect was not seen when liposomes were incubated in rat plasma. DPPC labels suffered from hydrolysis effects during preparation and/or storage. Fluid liposomes were less stable in human plasma than their PEGylated analogues or a rigid formulation. In contrast, the transfer of the incorporated drug to lipoproteins was higher for the rigid formulations.

CONCLUSIONS

The observed effects render COE-labels questionable for in vivo studies using CEPT-rich species. Here, choline labelled (14)C-DPPC was found to be the most promising alternative. Bilayer composition has a high influence on stability and drug release of a liposomal formulation in human plasma.

Size-based characterization of nanoparticle mixtures by the inline coupling of capillary electrophoresis to Taylor dispersion analysis

Separation of closely related nanoparticles is still a challenging issue for the characterization of complex mixtures for industrial/research applications or regulatory purposes. In this work, the remarkable separating performances of CE were complemented with the absolute size-based determination provided by Taylor dispersion analysis (TDA) for the characterization of nanoparticle mixtures. The inline hyphenation of CE to TDA was successfully implemented for the baseline separation followed by a size-based characterization of a bimodal mixture containing two closely size-related nanolatexes (70nm and 56nm radii). A pixel sensor UV area imager providing three detection points along the capillary was used for a differential measurement of the peak broadening during the Taylor dispersion step. Comparison of this new technique with dynamic light scattering and hydrodynamic chromatography is also discussed.

Controllable Supramolecular Polymerization through Host-Guest Interaction and Photochemistry

A new method for controllable supramolecular polymerization based on ABBA type monomer and cucurbit[8]uril monomer through host-guest interaction and photochemistry is reported. The molecular weight and polydispersity of supramolecular polymers can be well controlled by tuning the molar ratio of these host and guest monomers or by tuning the isomer ratio of azobenzene groups in the guest monomers upon the competitive irradiation of lights. This research provides a general methodology for the control of supramolecular polymerization and the structure of supramolecular polymers.

A tapered aluminium microelectrode array for improvement of dielectrophoresis-based particle manipulation

In this work, the dielectrophoretic force (F_DEP) response of Aluminium Microelectrode Arrays with tapered profile is investigated through experimental measurements and numerical simulations. A standard CMOS processing technique with a step for the formation of a tapered profile resist is implemented in the fabrication of Tapered Aluminium Microelectrode Arrays (TAMA). The F_DEP is investigated through analysis of the Clausius-Mossotti factor (CMF) and cross-over frequency (f_xo). The performance of TAMA with various side wall angles is compared to that of microelectrodes with a straight cut sidewall profile over a wide range of frequencies through FEM numerical simulations. Additionally, electric field measurement (EFM) is performed through scanning probe microscopy (SPM) in order to obtain the region of force focus in both platforms. Results showed that the tapered profile microelectrodes with angles between 60° and 70° produce the highest electric field gradient on the particles. Also, the region of the strongest electric field in TAMA is located at the bottom and top edge of microelectrode while the strongest electric field in microelectrodes with straight cut profile is found at the top corner of the microelectrode. The latter property of microelectrodes improves the probability of capturing/repelling the particles at the microelectrode’s side wall.

Supramolecular polymers synthesized by thiol–ene click polymerization from supramonomers

This communication describes supramolecular polymers fabricated by thiol–ene click polymerization from supramonomers.

Core cross-linked nanogels based on the self-assembly of double hydrophilic poly(2-oxazoline) block copolymers

The synthesis of poly(2-oxazoline)-based block copolymers consisting of a cationic and a hydrophilic segment is described.