Single-chain Polymeric Nanoparticles Research Articles

Effect of Particle Heterogeneity in Catalytic Copper-Containing Single-Chain Polymeric Nanoparticles Revealed by Single-Particle Kinetics.

Single-chain polymeric nanoparticles (SCPNs) have been extensively explored as a synthetic alternative to enzymes for catalytic applications. However, the inherent structural heterogeneity of SCPNs, arising from the dispersity of the polymer backbone and stochastic incorporation of different monomers as well as catalytic moieties, is expected to lead to variations in catalytic activity between individual particles. To understand the effect of structural heterogeneities on the catalytic performance of SCPNs, techniques are required that permit researchers to directly monitor SCPN activity at the single-polymer level. In this study, we introduce the use of single-molecule fluorescence microscopy to study the kinetics of Cu(I)-containing SCPNs towards depropargylation reactions. We developed Cu(I)-containing SCPNs that exhibit fast kinetics towards depropargylation and Cu-catalyzed azide-alkyne click reactions, making them suitable for single-particle kinetic studies. SCPNs were then immobilized on the surface of glass coverslips and the catalytic reactions were monitored at a single-particle level using total internal reflection fluorescence (TIRF) microscopy. Our studies revealed the interparticle turnover dispersity for Cu(I)-catalyzed depropargylations. In the future, our approach can be extended to different polymer designs which can give insights into the intrinsic heterogeneity of SCPN catalysis and can further aid in the rational development of SCPN-based catalysts.

Imaging Diffusion and Stability of Single-Chain Polymeric Nanoparticles in a Multi-Gel Tumor-on-a-Chip Microfluidic Device.

The performance of single-chain polymeric nanoparticles (SCPNs) in biomedical applications highly depends on their conformational stability in cellular environments. Until now, such stability studies are limited to 2D cell culture models, which do not recapitulate the 3D tumor microenvironment well. Here, a microfluidic tumor-on-a-chip model is introduced that recreates the tumor milieu and allows in-depth insights into the diffusion, cellular uptake, and stability of SCPNs. The chip contains Matrigel/collagen-hyaluronic acid as extracellular matrix (ECM) modelsand is seeded with cancer cell MCF7 spheroids. With this 3D platform, it is assessed how the polymer's microstructure affects the SCPN's behavior when crossing the ECM, and evaluates SCPN internalization in 3D cancer cells. A library of SCPNs varying in microstructure is prepared. All SCPNs show efficient ECM penetration but their cellular uptake/stability behavior depends on the microstructure. Glucose-based nanoparticles display the highest spheroid uptake, followed by charged nanoparticles. Charged nanoparticles possess an open conformation while nanoparticles stabilized by internal hydrogen bonding retain a folded structure inside the tumor spheroids. The 3D microfluidic tumor-on-a-chip platform is an efficient tool to elucidate the interplay between polymer microstructure and SCPN's stability, a key factor for the rational design of nanoparticles for targeted biological applications.

Enhanced Efficiency of Pd(0)-Based Single Chain Polymeric Nanoparticles for in Vitro Prodrug Activation by Modulating the Polymer's Microstructure.

Bioorthogonal catalysis employing transition metal catalysts is a promising strategy for the in situ synthesis of imaging and therapeutic agents in biological environments. The transition metal Pd has been widely used as a bioorthogonal catalyst, but bare Pd poses challenges in water solubility and catalyst stability in cellular environments. In this work, Pd(0) loaded amphiphilic polymeric nanoparticles are applied to shield Pd in the presence of living cells for the in situ generation of a fluorescent dye and anticancer drugs. Pd(0) loaded polymeric nanoparticles prepared by the reduction of the corresponding Pd(II)-polymeric nanoparticles are highly active in the deprotection of pro-rhodamine dye and anticancer prodrugs, giving significant fluorescence enhancement and toxigenic effects, respectively, in HepG2 cells. In addition, we show that the microstructure of the polymeric nanoparticles for scaffolding Pd plays a critical role in tuning the catalytic efficiency, with the use of the ligand triphenylphosphine as a key factor for improving the catalyst stability in biological environments.

Consecutive one-pot alkyne semihydrogenation/alkene dioxygenation reactions by Pt(II)/Cu(II) single-chain nanoparticles in green solvent.

Heterobimetallic Pt(II)/Cu(II) single-chain polymer nanoparticles (SCNPs) were sequentially synthesized from a polymeric precursor featuring both α-diazo-β-ketoester and naked β-ketoester functional groups. Photoactivated carbene generation at λexc = 365 nm from α-diazo-β-ketoester moieities was triggered for bonding Pt(II) ions from dichloro(1,5-cyclooctadiene)Pt(II) to the polymeric precursor, whereas Cu(II) ions were subsequently incorporated via Cu(II)-(β-ketoester)2 complex formation using Cu(II) acetate. Both intrachain Pt(II) bonding and Cu(II) complexation were found to contribute to the folding of the polymeric precursor generating Pt(II)/Cu(II)-SCNPs as evidenced by infrared spectroscopy, size exclusion chromatography and dynamic light scattering. These heterobimetallic SCNPs proved highly efficient as soft nanocatalysts for the consecutive one-pot alkyne semihydrogenation/alkene dioxygenation reactions at room temperature in N-butylpyrrolidone, as a non-toxic alternative solvent to N,N-dimethylformamide.

In vitro activity of novel apramycin-dextran nanoparticles and free apramycin against selected Dutch and Pakistani Klebsiella pneumonia isolates

Klebsiella pneumoniae are bacteria associated with respiratory tract infections and are increasingly becoming resistant to antibiotics, including carbapenems. Apramycin is a veterinary antibiotic that may have the potential to be re-purposed for use in human health, for example, for the treatment of respiratory tract infections after coupling to inhalable nanoparticles. In the present study, the antibiotic apramycin was formulated with single chain polymeric nanoparticles and tested in free and formulated forms against a set of 13 Klebsiella pneumoniae isolates (from the Netherlands and Pakistan) expressing different aminoglycoside resistance phenotypes. Minimum Inhibitory Concentration, Time Kill Kinetics and biofilm experiments were performed providing evidence for the potential efficacy of apramycin and apramycin-based nanomedicines for the treatment of human Klebsiella pneumonia infections.

Preparing cyclic polymers at high concentrations via self-folding cyclization technique by adjusting the contents of hydrophilic units in linear precursors

Cyclic polymers are a class of polymers that feature endless topology, and the synthesis of cyclic polymers has attracted the attention of many researchers. Herein, cyclic polymers were efficiently constructed by self-folding cyclization technique at high concentrations. Linear poly((oligo(ethylene glycol)acrylate)-co-(dodecyl acrylate)) (P(OEGA-co-DDA)) precursors with different ratios of hydrophilic and hydrophobic moieties were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization using a bifunctional chain transfer agent with two anthryl end groups. The amphiphilic linear precursors underwent the self-folding process to generate polymeric nanoparticles in water. By irradiating the aqueous solution of the nanoparticles with 365 nm UV light, cyclic polymers were synthesized successfully via coupling of anthryl groups. The effects of the ratios of hydrophilic and hydrophobic moieties in linear P(OEGA-co-DDA) copolymers and polymer concentration on the purity of the obtained cyclic polymers were explored in detail via1H nuclear magnetic resonance (1H NMR), dynamic light scattering (DLS), UV‒visible (vis) analysis, three-detection size exclusion chromatography (TD-SEC) and transmission electron microscopy (TEM). It was found that by adjusting the content of the hydrophilic segments in linear precursors, single chain polymeric nanoparticles (SCPNs) can be generated at high polymer concentrations. Therefore, cyclic polymers with high purity can be constructed efficiently. This method overcomes the limitation of traditional ring-closure method, which is typically conducted in highly dilute conditions, providing an efficient method for the scalable preparation of cyclic polymers.

Influence of structural dynamics on cell uptake investigated with single-chain polymeric nanoparticles

Influence of structural dynamics on cell uptake investigated with single-chain polymeric nanoparticles

Influence of structural dynamics on cell uptake investigated with single-chain polymeric nanoparticles

Influence of structural dynamics on cell uptake investigated with single-chain polymeric nanoparticles

Simultaneously controlling conformational and operational stability of single-chain polymeric nanoparticles in complex media.

Single-chain polymeric nanoparticles (SCPNs) comprising a solvatochromic pyrazoline adduct show conformational and operational stability in complex media and in cellular compartments; the connectivity of the adduct is crucial in modulating interactions with the surrounding media.

Single-Chain Polymer Nanoparticles Targeting the Ookinete Stage of Malaria Parasites.

Malaria is an infectious disease transmitted by mosquitos, whose control is hampered by drug resistance evolution in the causing agent, protist parasites of the genus Plasmodium, as well as by the resistance of the mosquito to insecticides. New approaches to fight this disease are, therefore, needed. Research into targeted drug delivery is expanding as this strategy increases treatment efficacies. Alternatively, targeting the parasite in humans, here we use single-chain polymer nanoparticles (SCNPs) to target the parasite at the ookinete stage, which is one of the stages in the mosquito. This nanocarrier system provides uniquely sized and monodispersed particles of 5-20 nm, via thiol-Michael addition. The conjugation of succinic anhydride to the SCNP surface provides negative surface charges that have been shown to increase the targeting ability of SCNPs to Plasmodium berghei ookinetes. The biodistribution of SCNPs in mosquitos was studied, showing the presence of SCNPs in mosquito midguts. The presented results demonstrate the potential of anionic SCNPs for the targeting of malaria parasites in mosquitos and may lead to progress in the fight against malaria.

Enhancing Cellular Internalization of Single-Chain Polymer Nanoparticles via Polyplex Formation.

Intracellular delivery of nanoparticles is crucial in nanomedicine to reach optimal delivery of therapeutics and imaging agents. Single-chain polymer nanoparticles (SCNPs) are an interesting class of nanoparticles due to their unique site range of 5-20 nm. The intracellular delivery of SCNPs can be enhanced by using delivery agents. Here, a positive polymer is used to form polyplexes with SCNPs, similar to the strategy of protein and gene delivery. The size and surface charge of the polyplexes were evaluated. The cellular uptake showed rapid uptake of SCNPs via polyplex formation, and the cytosolic delivery of the SCNPs was presented by confocal microscopy. The ability of SCNPs to act as nanocarriers was further explored by conjugation of doxorubicin.

Single-Chain Polymer Nanoparticles for Addressing Morphologies and Functions at the Nanoscale: A Review

This review discusses recent advances concerning morphologies and functions obtained from single-chain nanoparticles (SCNPs). SCNPs are unimolecular, soft nano-objects consisting of individual polymer chains collapsed to a certain degree by means of intramolecular bonding. Many of potential applications of SCNPs rely on their peculiar molecular morphology adopted in solution. SCNPs coming from random or block copolymers can yield ordered structures by self-assembly in a wide range of morphologies including spheres, cylinders, bicontinuous structures, lamellae, vesicles, and many other complex or hierarchical assemblies. These nanocomposites can provide practical applications, still in their infancy, in several fields. The classification of SCNPs according to their morphologies will help to link their function to the specific applications.

CO2-Switchable Single-Chain Polymeric Nanoparticles Enable Gas-Controllable Reaction Separation for Asymmetric Catalysis in Water

Water-soluble single-chain polymeric nanoparticles (SCPNs), which isolated catalytic sites within a hydrophobic interior, made water-incompatible organometallic catalysis highly efficient in water. However, it is still a great challenge to conveniently control their hydrophilicity, so as to combine reactivity and recovery of the catalytic SCPNs in aqueous systems. Herein, we have developed a series of catalytic SCPNs, which possessed CO2-switchable hydrophilic/hydrophobic behavior, to realize the gas-controlled reaction and separation for asymmetric sulfa-Michael addition (SMA) in water. A novel series of CO2-switchable random copolymers were thus synthesized by copolymerization of CO2-responsive amidine derivatives with hydrophobic chiral salen FeIII monomers via reversible addition-fragmentation chain transfer polymerization. Characterization suggested their CO2-controlled self-collapse behavior in water due to CO2-switched change in hydrophilicity/hydrophobicity of the amidine moiety. The resultant CO2-switchable SCPNs provided hydrophobic, catalytic compartments for asymmetric SMA in water upon CO2 addition, giving various chiral β-keto sulfides with almost quantitative yields (90–98%) and high enantioselectivities (93–99%). When CO2 is removed by N2 bubbling, they were collapsed and spontaneously precipitated from the aqueous system for steady reuse. The gas-controlled reaction-separation approach provides an energy-efficient way to combine reactivity and recovery of catalytic SCPNs in aqueous systems, which should be quite practical in large-scale industrial applications.

En Route to Stabilized Compact Conformations of Single-Chain Polymeric Nanoparticles in Complex Media.

Precise control over the folding pathways of polypeptides using a combination of noncovalent and covalent interactions has evolved into a wide range of functional proteins with a perfectly defined 3D conformation. Inspired hereby, we develop a series of amphiphilic copolymers designed to form compact, stable, and structured single-chain polymeric nanoparticles (SCPNs) of defined size, even in competitive conditions. The SCPNs are formed through a combination of noncovalent interactions (hydrophobic and hydrogen-bonding interactions) and covalent intramolecular cross-linking using a light-induced [2 + 2] cycloaddition. By comparing different self-assembly pathways of the nanoparticles, we show that, like for proteins in nature, the order of events matters. When covalent cross-links are formed prior to the folding via hydrophobic and supramolecular interactions, larger particles with less structured interiors are formed. In contrast, when the copolymers first fold via hydrophobic and hydrogen-bonding interactions into compact conformations, followed by covalent cross-links, good control over the size of the SCPNs and microstructure of the hydrophobic interior is achieved. Such a structured SCPN can stabilize the solvatochromic dye benzene-1,3,5-tricarboxamide–Nile Red via molecular recognition for short periods of time in complex media, while showing slow exchange dynamics with the surrounding complex media at longer time scales. The SCPNs show good biocompatibility with cells and can carry cargo into the lysosomal compartments of the cells. Our study highlights the importance of control over the folding pathway in the design of stable SCPNs, which is an important step forward in their application as noncovalent drug or catalyst carriers in biological settings.

Neutralization of ionic interactions by dextran-based single-chain nanoparticles improves tobramycin diffusion into a mature biofilm

The extracellular matrix protects biofilm cells by reducing diffusion of antimicrobials. Tobramycin is an antibiotic used extensively to treat P. aeruginosa biofilms, but it is sequestered in the biofilm periphery by the extracellular negative charge matrix and loses its efficacy significantly. Dispersal of the biofilm extracellular matrix with enzymes such as DNase I is another promising therapy that enhances antibiotic diffusion into the biofilm. Here, we combine the charge neutralization of tobramycin provided by dextran-based single-chain polymer nanoparticles (SCPNs) together with DNase I to break the biofilm matrix. Our study demonstrates that the SCPNs improve the activity of tobramycin and DNase I by neutralizing the ionic interactions that keep this antibiotic in the biofilm periphery. Moreover, the detailed effects and interactions of nanoformulations with extracellular matrix components were revealed through time-lapse imaging of the P. aeruginosa biofilms by laser scanning confocal microscopy with specific labeling of the different biofilm components.

Single-chain polymer nanoparticles-encapsulated chiral bifunctional metal-organic frameworks for asymmetric sequential reactions

• Pd(II) was stably loaded in the channels of MOFs using Pd(II) cross-linked single-chain nanoparticles. • A bifunctional catalyst Pd-SCNP@DUT-67-Pro was prepared by the “one-pot” method. • The catalyst was used for Suzuki coupling/asymmetric aldol sequential reactions. • The catalyst can be used for 3 cycles without activity loss and structural changes. Among multitudinous development methods of the active sites of MOFs, the encapsulation method is widely used. However, metal ions with excellent catalytic performance are not suitable for being directly encapsulated in MOFs. Because metal ions are much smaller than the pore sizes of MOFs, they will move in and out of the channels of MOFs haphazardly rather than being stably loaded in the channels like that of enzymes and metal nanoparticles. Here, to solve the above-mentioned problem, the metal ion Pd(II) was introduced into the single-chain polymer nanoparticles (SCNP) to form Pd(II) cross-linked SCNP (Pd-SCNP). A bifunctional heterogeneous catalyst Pd-SCNP@DUT-67-Pro was prepared by introducing Pd-SCNP and chiral proline into the channels and on the Zr-clusters of DUT-67, respectively. The catalyst displayed excellent enantioselectivity and good coupling performance in Suzuki coupling/asymmetric aldol sequential reactions. Besides, Pd-SCNP@DUT-67-Pro still retained good catalytic activity within three cycles of reuse.

Preparation of AIE Functional Single-Chain Polymer Nanoparticles and Their Application in H2 O2 Detection through Intermolecular Heavy-Atom Effect.

Single-chain polymer nanoparticles (SCNPs) are soft matter constructed by intrachain crosslinks, with promising prospects in detection and catalysis. Herein, a fluorescent core (SCNPs) with aggregation-induced emission (AIE) is prepared, applying for H2 O2 detection through intermolecular heavy-atom effect. In detail, the SCNPs precursors are synthesized by ring-opening copolymerization. Then the SCNPs are prepared by intramolecularly cross-linking via olefin metathesis. Imitating the structure of AIE dots, SCNPs are encapsulated by H2 O2 -responsive polymers. Probably due to the stable secondary structure of SCNPs, the obtained micelles show stable fluorescence performance. Furthermore, as the heavy-atom, tellurium is introduced into the carriers to construct the heavy-atom effect. In this micelle-based system, the SCNPs act as the fluorescent core, and the stimuli-responsive polymer acts as the carrier and the fluorescent switch. The hydrophilicity of the tellurium-containing segment is affected by the concentration of H2 O2 , resulting in a change in the distance from the SCNPs, which ultimately leads to a change in the fluorescence intensity. Furthermore, tellurium is particularly sensitive to H2 O2 , which can detect low concentrations of H2 O2 . The SCNPs are merged with AIE materials, with the hope of exploring new probe designs.

Rapid synthesis of polyester based single-chain polymeric nanoparticles via an intra-molecular aza-Michael addition reaction

An alternative method to produce single-chain polymeric nanoparticles using the aza-Michael addition reaction of a linear polyester containing in-chain reactive triple bonds is introduced.

Control and Characterization of the Compactness of Single-Chain Nanoparticles

Polymers when self-cross-linked into single-chain nanoparticles bear some resemblance to folded proteins; yet proteins have clear energy landscapes that determine precisely folded structures, while single-chain polymer nanoparticles (SCNPs) have more undefined structures. There have been initial reports showing that some structural parameters in SCNPs can be controlled, for example, compactness. Here, we construct SCNPs from poly(allylamine) (Mw ∼ 22 000 Da) with dicarboxylic acids (HOOC–R–COOH) in solvent conditions, where initial chains adopt either extended or collapsed conformation. The spacer groups R that we used were −CH2CH2–, −(CH2S)2–, or −(CH2CH2)3–, whose length can be estimated to vary from ∼4 to ∼12 Å. We present a systematic study that uses several characterization techniques (1H NMR diffusion-ordered spectroscopy (DOSY), viscometry, analytical ultracentrifugation, and 1H NMR T2 relaxation) to show that both initial reaction conditions as well as length of cross-linking molecules determine the final compactness of SCNPs. Specifically, when short cross-linking molecules are applied, short-range loops dominate and the cross-linking process fails to achieve global chain compaction, leading to less compact SCNPs. When the chain is precollapsed (0.1 M water solution of NaCl or 10 vol % ethanol as opposed to DI water), the particles resulting after cross-linking are more compact. Of utmost practical relevance, we show that particles that are essentially chemically identical but differ only in compactness have different toxicity when interacting with HeLa cells, the more compact ones being less toxic.

Elucidating the Stability of Single-Chain Polymeric Nanoparticles in Biological Media and Living Cells.

The controlled folding of synthetic polymer chains into single-chain polymeric nanoparticles (SCPNs) of defined size and shape in water is a viable way to create compartmentalized, nanometer-sized structures for a range of biological applications. Understanding the relationship between the polymer’s microstructure and the stability of folded structures is crucial to achieving desired applications. Here, we introduce the solvatochromic dye Nile red into SCPNs and apply a combination of spectroscopic and microscopic techniques to relate polymer microstructure to nanoparticle stability in complex biological media and cellular environments. Our experimental data show that the polymer’s microstructure has little effect on the stability of SCPNs in biological media and cytoplasm of living cells, but only SCPNs comprising supramolecular benzene-1,3,5-tricarboxamide (BTA) motifs showed good stability in lysosomes. The results indicate that the polymer’s microstructure is vital to ensure nanoparticle stability in highly competitive environments: both hydrophobic collapse and a structured interior are required. Our study provides an accessible way of probing the stability of SCPNs in cellular environments and paves the way for designing highly stable SCPNs for efficient bio-orthogonal catalysis and sensing applications.