Single-chain Nanoparticles Research Articles

Designing Enhanced Entropy Binding in Single-Chain Nanoparticles.

Single-chain nanoparticles (SCNPs) are a new class of bio- and soft-matter polymeric objects in which a fraction of the monomers are able to form equivalently intra- or interpolymer bonds. Here we numerically show that a fully entropic gas-liquid phase separation can take place in SCNP systems. Control over the discontinuous (first-order) change-from a phase of independent diluted (fully-bonded) polymers to a phase in which polymers entropically bind to each other to form a (fully-bonded) polymer network-can be achieved by a judicious design of the patterns of reactive monomers along the polymer chain. Such a sensitivity arises from a delicate balance between the distinct entropic contributions controlling the binding.

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.

Equilibrium and Dynamic Surface Tension Behavior in Colloidal Unimolecular Polymers (CUP).

Studies of the interfacial behavior of pure aqueous nanoparticles have been limited due tothe difficulty of making contaminant-free nanoparticles while also providing narrow size distribution. Colloidal unimolecular polymers (CUPs) are a new type of single-chain nanoparticle with a particle size ranging from 3 to 9 nm, which can be produced free of surfactants and volatile organic contents (VOCs). CUP particles of different sizes and surface charges were made. The surface tension behavior of these CUP particles in water was studied using a maximum bubble pressure tensiometer. The equilibrium surface tension decreased with increasing concentration and the number of charges present on the surface of the CUP particles influences the magnitude of the interfacial behavior. The effect of electrostatic repulsion between the particles on the surface tension was related. At higher concentrations, surface charge condensation started to dominate the surface tension behavior. The dynamic surface tension of CUP particles shows the influence of the diffusion of the particles to the interface on the relaxation time. The relaxation time of the CUP polymer was 0.401 s, which is closer to the diffusion-based relaxation time of 0.133s for SDS (sodium dodecyl sulfate).

Scalable Synthesis of Photoluminescent Single‐Chain Nanoparticles by Electrostatic‐Mediated Intramolecular Crosslinking

We report the large-scale synthesis of photoluminescent single-chain nanoparticles (SCNPs) by electrostatic-mediated intramolecular crosslinking in a concentrated solution of 40 mg mL-1 by continuous addition of the free radical initiator. Poly(vinyl benzyl chloride) was charged by quaternization with vinyl-imidazolium for the intramolecular crosslinking by using 2,2-dimethoxy-2-phenylacetophenone (DMAP) as the radical initiator. Under the electrostatic repulsion thus interchain isolation, the intrachain crosslinking experiences the transition from coil through pearl-necklace to globular state. The SCNPs demonstrate strong photoluminescence in the visible range when the non-emissive units are confined thereby. Composition and microstructure of the SCNPs are tunable. The photoluminescent tadpole-like Janus SCNP can be used to selectively illuminate interfacial membranes while stabilizing the emulsions.

Scalable Synthesis of Photoluminescent Single‐Chain Nanoparticles by Electrostatic‐Mediated Intramolecular Crosslinking

AbstractWe report the large‐scale synthesis of photoluminescent single‐chain nanoparticles (SCNPs) by electrostatic‐mediated intramolecular crosslinking in a concentrated solution of 40 mg mL−1 by continuous addition of the free radical initiator. Poly(vinyl benzyl chloride) was charged by quaternization with vinyl‐imidazolium for the intramolecular crosslinking by using 2,2‐dimethoxy‐2‐phenylacetophenone (DMAP) as the radical initiator. Under the electrostatic repulsion thus interchain isolation, the intrachain crosslinking experiences the transition from coil through pearl‐necklace to globular state. The SCNPs demonstrate strong photoluminescence in the visible range when the non‐emissive units are confined thereby. Composition and microstructure of the SCNPs are tunable. The photoluminescent tadpole‐like Janus SCNP can be used to selectively illuminate interfacial membranes while stabilizing the emulsions.

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.

Solvent Remodeling in Single-Chain Amphiphilic Heteropolymer Systems.

This work demonstrates the remodeling of single-chain nanoparticles (SCNPs) upon a transition to organic solvent through molecular dynamics simulations. Methacrylate-based random heteropolymers (RHPs), assembled via transient noncovalent linkages in water, have shown promise in an assortment of applications that harness their bio-inspired properties. While their molecular behavior has been broadly characterized in aqueous environments, many newer applications include the use of organic solvent rather than bio-mimetic conditions. The polymer assemblies, typically driven by the hydrophobic effect in water, are less well understood in nonaqueous solution. Here, a specific RHP system is examined which forms compact globular morphologies in highly polar or highly nonpolar environments while adopting extended conformations in solvents of intermediate polarity. The pivotal role of electrostatic interactions between charge groups in low dielectric mediums is also observed. Finally, high temperature anneal cycles are compared to room temperature transformations to illuminate barriers to remodeling upon environmentalchanges.

Orange-Light-Induced Photochemistry Gated by pH and Confined Environments.

We introduce a new photochemically active compound, i.e., pyridinepyrene (PyPy), entailing a pH-active moiety that effects a significant halochromic shift into orange-light (λ = 590 nm) activatable photoreactivity while concomitantly exerting control over its reaction pathways. With blue light (λ = 450 nm) in neutral to basic pH, a [2 + 2] photocycloaddition can be triggered to form a cyclobutene ring in a reversible fashion. If the pH is decreased to acidic conditions, resulting in a halochromic absorption shift, photocycloaddition on the small-molecule level is blocked due to repulsive interactions and exclusive trans-cis isomerization is observed. Through implementation of PyPy into the confined environment of a single-chain nanoparticle (SCNP) design, one can overcome the repulsive forces and exploit the halochromic shift for orange light (λ = 590 nm)-induced cycloaddition and formation of macromolecular three-dimensional (3D) architectures.

Acid-responsive PEGylated branching PLGA nanoparticles integrated into dissolving microneedles enhance local treatment of arthritis

• Calcium carbonate-hybridized nanocarrier achieved acid-responsive release of cargo. • PEGylated multi-armed PLGA has high drug loading and immune escape functions. • The improvement in arthritis involved regulating the VEGF, JAK2 and STAT3 pathways. • Peach gum will become an alternative for dissolving microneedle substrates. • Functionalized nanoparticles integrated with microneedles enhanced drug delivery. The low drug-loading and permeation enhancement abilities of PLGA nanoparticles limit their use as transdermal delivery vehicles. We recently designed PEGylated star-shaped PLGA, which hybridized with calcium carbonate to form nanoparticles [6 s-NPs (CaCO 3 )] with immune stealth and acid-responsive properties, which increased the loading of tetrandrine (Tet), a poorly soluble antiarthritis active ingredient, by 3.26-fold compared with that of single-chain PLGA nanoparticles. The 6 s-NPs (CaCO 3 ) resulted in acid-responsive release of more cargo in both in vitro release medium (pH 5.5) and fibroblast-like synoviocytes (FLSs) ( p < 0.0001), thereby inducing stronger cytotoxic effects of the loaded Tet on the TNF-α-induced abnormal proliferation of FLSs than Tet-loaded 6 s-NPs (no CaCO 3 ) and Tet aqueous dispersion (Free Tet) ( p < 0.0001). However, the number of 6 s-NPs (CaCO 3 ) incorporated by RAW264.7 cells was significantly lower than that of PLGA nanoparticles without PEGylation-endowed immune escape function. Furthermore, the nanoparticles were integrated into peach gum-fabricated dissolving microneedles with higher mechanical hardness and better physical stability than hyaluronic acid-formed microneedles. This integrated delivery strategy dramatically increased synovial uptake of Tet via the transdermal route and was further enhanced by the cofunctionalization with stealth escape from phagocytes and inflammatory acidity-triggered release. The observed improvement in adjuvant-induced arthritis involved stronger regulation of the VEGF, JAK2/p-JAK2, and STAT3/p-STAT3 pathways, which was superior to deleting certain currently designed delivery capacities. This newly fabricated multifunctional transdermal vehicle is therefore a promising therapeutic approach for protecting against local inflammation.

Disentangling Component Dynamics in an All-Polymer Nanocomposite Based on Single-Chain Nanoparticles by Quasielastic Neutron Scattering.

We have investigated an all-polymer nanocomposite (NC) consisting of single-chain nanoparticles (SCNPs) immersed in a matrix of linear chains of their precursors (25/75% composition in weight). The SCNPs were previously synthesized via “click” chemistry, which induces intramolecular cross-links in the individual macromolecules accompanied by a slight shift (5–8 K) of the glass transition temperature toward higher values and a broadening of the dynamic response with respect to the raw precursor material. The selective investigation of the dynamics of the NC components has been possible by using properly isotopically labeled materials and applying quasielastic neutron scattering techniques. Results have been analyzed in the momentum transfer range where the coherent scattering contribution is minimal, as determined by complementary neutron diffraction experiments with polarization analysis. We observe the development of dynamic heterogeneity in the intermediate scattering function of the NC components, which grows with increasing time. Local motions in the precursor matrix of the NC are accelerated with respect to the reference bulk behavior, while the displacements of SCNPs’ hydrogens show enhanced deviations from Gaussian and exponential behavior compared with the pure melt of SCNPs. The resulting averaged behavior in the NC coincides with that of the pure precursor, in accordance with the macroscopic observations by differential scanning calorimetry (DSC) experiments.

Stable Vesicles Formed by a Single Polyelectrolyte in Salt Solutions

The conformation of polyelectrolyte (PE) affects a wealth of structural and dynamic properties of PE solutions and is also fundamental to the study of the folding and aggregation of proteins. Here, we theoretically investigate the classical problem of the conformation of a single homogeneous PE in salt solutions. We predict the formation of a stable vesicle structure at intermediate salt concentrations which is beyond the well-accepted framework of globule to pearl-necklace transition. The vesicle formed by a single PE is electrostatic in origin where salt ions play the role of surfactant. We demonstrate that the transitions from vesicle to both spherical globule and pearl-necklace are discontinuous; the latter involves a two-step nucleation with an intermediate vesicle-necklace state. We also calculate the full diagram of state and show the existence of a critical quadruple point that is uniquely determined for PE with a given chain length. The vesicle structure can be well-controlled by the external salt concentration, which facilitates the design of ionic-responsive single-chain nanoparticles.

A method to estimate the size of single-chain nanoparticles under severe crowding conditions.

Single-chain nanoparticles (SCNPs) result from the folding of isolated polymer chains via intramolecular interactions. Currently, there is no theory able to rationalize the astonishing conformational behaviour of SCNPs under severe crowding conditions (e.g., highly concentrated solutions, all-polymer nanocomposites) and, specifically, the significant size reduction observed in highly crowded solutions of covalent-bonded SCNPs and all-polymer nanocomposites containing SCNPs. Herein, we propose a valuable method to estimate the size of SCNPs under crowding. The method – which is based on combining MD simulations results with scaling concepts – is also useful for ring polymers and nanostructured Janus-shaped SCNPs.

Enzyme-like catalysis by single chain nanoparticles that use transition metal cofactors.

We report a modular approach in which a noncovalently cross-linked single chain nanoparticle (SCNP) selectively binds catalyst "cofactors" and substrates to increase both the catalytic activity of a Cu-catalyzed alkyne-azide cycloaddition reaction and the Ru-catalyzed cleavage of allylcarbamate groups compared to the free catalysts.

Red light induced folding of single polymer chains

We pioneer the photochemical generation of single chain nanoparticles (SCNPs) at the to-date mildest reported wavelength of 625 nm by exploiting the photochemical uncaging of methylene blue protected amines. The protected amines are tethered to polymers prepared via reversible addition-fragmentation chain transfer (RAFT) polymerisation, and subsequently undergo intrachain crosslinking by amide formation.

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.

Cytosolic Delivery of Single-Chain Polymer Nanoparticles.

Cytosolic delivery of therapeutic agents is key to improving their efficacy, as the therapeutics are primarily active in specific organelles. Single-chain polymer nanoparticles (SCNPs) are a promising nanocarrier platform in biomedical applications due to their unique size range of 5-20 nm, modularity, and ease of functionalization. However, cytosolic delivery of SCNPs remains challenging. Here, we report the synthesis of active ester-functional SCNPs of approximately 10 nm via intramolecular thiol-Michael addition cross-linking and their functionalization with increasing amounts of tertiary amines 0 to 60 mol % to obtain SCNPs with increasing positive surface charges. No significant cytotoxicity was detected in bEND.3 cells for the SCNPs, except when SCNPs with high amounts of tertiary amines were incubated over prolonged periods of time at high concentrations. Cellular uptake of the SCNPs was analyzed, presenting different uptake behavior depending on the degree of functionalization. Confocal microscopy revealed successful cytosolic delivery of SCNPs with high degrees of functionalization (45%, 60%), while SCNPs with low amounts (0% to 30%) of tertiary amines showed high degrees of colocalization with lysosomes. This work presents a strategy to direct the intracellular location of SCNPs by controlled surface modification to improve intracellular targeting for biomedical applications.