Micellization of Ionic Block Copolymers

Effect of Polymer and Cell Membrane Coatings on Theranostic Applications of Nanoparticles: A Review

The recent decade has witnessed a remarkable surge in the field of nanoparticles, from their synthesis, characterization, and functionalization to diverse applications. At the nanoscale, these particles exhibit distinct physicochemical properties compared to their bulk counterparts, enabling a multitude of applications spanning energy, catalysis, environmental remediation, biomedicine, and beyond. This review focuses on specific nanoparticle categories, including magnetic, gold, silver, and quantum dots (QDs), as well as hybrid variants, specifically tailored for biomedical applications. A comprehensive review and comparison of prevalent chemical, physical, and biological synthesis methods are presented. To enhance biocompatibility and colloidal stability, and facilitate surface modification and cargo/agent loading, nanoparticle surfaces are coated with different synthetic polymers and very recently, cell membrane coatings. The utilization of polymer- or cell membrane-coated nanoparticles opens a wide variety of biomedical applications such as magnetic resonance imaging (MRI), hyperthermia, photothermia, sample enrichment, bioassays, drug delivery, etc. With this review, the goal is to provide a comprehensive toolbox of insights into polymer or cell membrane-coated nanoparticles and their biomedical applications, while also addressing the challenges involved in translating such nanoparticles from laboratory benchtops to in vitro and in vivo applications. Furthermore, perspectives on future trends and developments in this rapidly evolving domain are provided.

Modern Trends in Polymerization-Induced Self-Assembly

Polymerization-induced self-assembly (PISA) is a powerful and versatile technique for producing colloidal dispersions of block copolymer particles with desired morphologies. Currently, PISA can be carried out in various media, over a wide range of temperatures, and using different mechanisms. This method enables the production of biodegradable objects and particles with various functionalities and stimuli sensitivity. Consequently, PISA offers a broad spectrum of potential commercial applications. The aim of this review is to provide an overview of the current state of rational synthesis of block copolymer particles with diverse morphologies using various PISA techniques and mechanisms. The discussion begins with an examination of the main thermodynamic, kinetic, and structural aspects of block copolymer micellization, followed by an exploration of the key principles of PISA in the formation of gradient and block copolymers. The review also delves into the main mechanisms of PISA implementation and the principles governing particle morphology. Finally, the potential future developments in PISA are considered.

Microstructurally tunable pickering emulsions stabilized by poly(ethylene glycol)-b-poly(ε-caprolactone) diblock biodegradable copolymer micelles with predesigned polymer architecture

Poly(ethylene glycol)-b-poly(ε-caprolactone) diblock copolymers (PEG-b-PCL) with predesigned hydrophilic/hydrophobic block length ratios have been synthesized and self-assembled to form micelles, then used to emulsify medium-chain triglycerides with an aqueous phase. The morphologies and sizes of PEG-b-PCL copolymer micelles have been characterized by transmission electron microscopy and dynamic light scattering. Interfacial tension testing between micellar dispersions and oil, combined with water contact angle measurements, have been performed to assess the ability of these micelles to adjust interfacial tension and micellar hydrophobicity, respectively. Relationship between the wettability of PEG-b-PCL copolymer micelles and their emulsification properties has been proved through phase diagram, optical microscopic observation, droplet sizes evolution and phase separation behavior of Pickering emulsion samples. Results show that both oil-in-water and water-in-oil Pickering emulsions, as well as water-in-oil-in-water (W/O/W) double-Pickering emulsions, may be controllably prepared through one-step homogenization. Double microstructure of W/O/W Pickering emulsion has proved to be extremely stable during long-term storage.

Supramolecularly cross-linked nanoassemblies of self-immolative polyurethane from recycled plastic waste: high encapsulation stability and triggered release of guest molecules

Stabilizing noncovalently encapsulated guest molecules inside a nanoassembly constructed from amphiphilic polymers has become a very challenging effort in the area of targeted drug delivery of biomedical applications. The unwanted...

Polymeric Micro/Nanocarriers and Motors for Cargo Transport and Phototriggered Delivery

Smart polymer-based micro/nanoassemblies have emerged as a promising alternative for transporting and delivering a myriad of cargo. Cargo encapsulation into (or linked to) polymeric micro/nanocarrier (PC) strategies may help to conserve cargo activity and functionality when interacting with its surroundings in its journey to the target. PCs for cargo phototriggering allow for excellent spatiotemporal control via irradiation as an external stimulus, thus regulating the delivery kinetics of cargo and potentially increasing its therapeutic effect. Micromotors based on PCs offer an accelerated cargo-medium interaction for biomedical, environmental, and many other applications. This review collects the recent achievements in PC development based on nanomicelles, nanospheres, and nanopolymersomes, among others, with enhanced properties to increase cargo protection and cargo release efficiency triggered by ultraviolet (UV) and near-infrared (NIR) irradiation, including light-stimulated polymeric micromotors for propulsion, cargo transport, biosensing, and photo-thermal therapy. We emphasize the challenges of positioning PCs as drug delivery systems, as well as the outstanding opportunities of light-stimulated polymeric micromotors for practical applications.

Self-Immolative Polyurethane-Based Nanoassemblies: Surface Charge Modulation at Tumor-Relevant pH and Redox-Responsive Guest Release

The self-assembly of a stimuli-responsive amphiphilic polymer has been of great interest in the area of targeted drug delivery applications. In this article, a new amphiphilic polyurethane with a hydrophobic backbone consisting of a redox-responsive self-immolative unit and hydrophilic pendant triethylene glycol, which is periodically grafted on the backbone by a tertiary amine group, has been designed and synthesized. This amphiphilic polymer self-assembles into a micellar nanostructure (investigated by dynamic light scattering and transmission electron microscopy) in an aqueous medium and shows guest encapsulation property. Furthermore, the pH-responsive nature leads to the formation of a positively charged nanoassembly at a tumor-relevant pH (∼6.5-6.8), which is probed by zeta potential measurements. As the backbone was constructed with self-immolative, redox-responsive functionality, degradation of the polymer was observed in the presence of a reducing agent, glutathione (GSH), which results in disassembly of the self-assembled structure followed by guest release as probed by UV-vis spectroscopy. The triggered degradation and pH-specific charge generation (from neutral to positive), we believe, will have implications in the design of biodegradable polymers as supramoleular scaffolds for biomedical applications.

Assembly of Short-Chain Amphiphilic Homopolymers into Well-Defined Particles

Linear homopolymers of norbornene (NBE) derivatives equipped with short-chain alcohol pendant groups were prepared by ring-opening metathesis polymerization (ROMP) and subsequently assembled into well-defined structures in alcohol solvents. The ratios of hydrophobic carbons and hydrophilic alcohol groups at the repeating monomeric unit in these short-chain amphiphilic polymers were found to play an important role in determining the size and distribution of the final globular structures. Unlike the assembly of other linear homo- and copolymers possessing long-chain amphiphilicity, NBE-based linear polymers were readily transformed into spherical particles with a layered conformation, whose sizes range from a few hundred nanometers to micrometers with narrow distributions, simply by controlling the concentration and molecular weights of the linear homopolymers without using any surfactants. In addition, the degree of the intermolecular forces with solvents (e.g., solvation) possessing different surface tensions and polarities highly affected the final diameter and distribution of the polymer particles, implying the importance of the selection of a proper solvent to regulate their structural features. As such, understanding the assembly of these types of short-chain homopolymers into uniform particles can allow for regulating the transformation of diverse linear amphiphilic polymers into precisely controlled structures for various applications.

Solubility and Bioavailability Enhancement of Oridonin: A Review

Oridonin (ORI), an ent-kaurene tetracyclic diterpenoid compound, is isolated from Chinese herb Rabdosia rubescens with various biological and pharmacological activities including anti-tumor, anti-microbial and anti-inflammatory effects. However, the clinical application of ORI is limited due to its low solubility and poor bioavailability. In order to overcome these shortcomings, many strategies have been explored such as structural modification, new dosage form, etc. This review provides a detailed discussion on the research progress to increase the solubility and bioavailability of ORI.

Supramolecularly cross-linked amphiphilic block copolymer assembly by the dipolar interaction of a merocyanine dye

Dipolar interaction driven dimerization of a merocyanine (MC) dye has been exploited to achieve non-covalently crosslinked stable micelles in water and reverse micelles in toluene with emissive properties from a MC-pendant amphiphilic block copolymer.

Self-Assembly of Polymer Blends and Nanoparticles through Rapid Solvent Exchange

Molecular dynamics simulations were performed to study the fabrication of polymeric colloids containing inorganic nanoparticles (NPs) via the flash nanoprecipitation (FNP) technique. During this process, a binary polymer blend, initially in a good solvent for the polymers, is rapidly mixed with NPs and a poor solvent for the polymers that is miscible with the good solvent. The simulations reveal that the polymers formed Janus particles with NPs distributed either on the surface of the aggregates, throughout their interior, or aligned at the interface between the two polymer domains, depending on the NP-polymer and NP-solvent interactions. The loading and surface density of NPs can be controlled by the polymer feed concentration, the NP feed concentration, and their ratio in the feed streams. Selective localization of NPs by incorporating electrostatic interactions between polymers and NPs has also been investigated, and was shown to be an effective way to enhance NP loading and surface density as compared to the case with only van der Waals attractions. This work demonstrates that the FNP process is promising for the production of structured and hybrid nanocolloids in a continuous and scalable way, with independent control over particle properties such as size, NP location, loading, and surface density. Our results provide useful guidelines for experimental fabrication of such hybrid nanoparticles.

Synthesis and controllable self-assembly of 3D amphiphilic organoplatinum(ii) metallacages in water

A 3D amphiphilic supramolecular coordination metallacycle M1 was designed and fabricated using a new method called “coordination driven self-assembly”. It can self-assemble into well-defined vesicles and further assemble into nanofibres and hybrid vesicles. Importantly, the hybrid vesicles can be applied in photocatalysis in water.

Effect of Composition and Molecular Structure of Poly(l-lactic acid)/Poly(ethylene oxide) Block Copolymers on Micellar Morphology in Aqueous Solution

The effect of the hydrophobic block length in diblock (PLLA _x- b-PEO₁₁₃, x = 64, 166, 418) and triblock (PLLA _y- b-PEO₉₁- b-PLLA _y, y = 30, 52, 120) copolymers of l-lactic acid and ethylene oxide on the structure of micelles prepared by dialysis was studied by wide- and small-angle X-ray scattering in dilute aqueous solution, dynamic light scattering, transmission electron microscopy, atomic force microscopy, and force spectroscopy. It was found that the size of the crystalline PLLA core is weakly dependent on the PLLA block length. In addition to individual micelles, a number of their micellar clusters were detected with characteristic distance between adjacent micelle cores decreasing with an increase in PLLA block length. This effect was explained by the change in the conformation of PEO chains forming the micellar corona because of their overcrowding. Force spectroscopy experiments also reveal a more stretched conformation of the PEO chains for the block copolymers with a shorter PLLA block. A model describing the structure of the individual micelles and their clusters was proposed.

Polymeric Micelles of Biodegradable Diblock Copolymers: Enhanced Encapsulation of Hydrophobic Drugs

Polymeric micelles are potentially efficient in encapsulating and performing the controlled release of various hydrophobic drug molecules. Understanding the fundamental physicochemical properties behind drug⁻polymer systems in terms of interaction strength and compatibility, drug partition coefficient (preferential solubilization), micelle size, morphology, etc., encourages the formulation of polymeric nanocarriers with enhanced drug encapsulating capacity, prolonged circulation time, and stability in the human body. In this review, we systematically address some open issues which are considered to be obstacles inhibiting the commercial availability of polymer-based therapeutics, such as the enhancement of encapsulation capacity by finding better drug⁻polymer compatibility, the drug-release kinetics and mechanisms under chemical and mechanical conditions simulating to physiological conditions, and the role of preparation methods and solvents on the overall performance of micelles.

Solution Self-Assemblies of Sequence-Defined Ionic Peptoid Block Copolymers

A series of amphiphilic ionic peptoid block copolymers where the total number (1 or 3) and position of ionic monomers along the polymer chain are precisely controlled have been synthesized by the submonomer method. Upon dissolution in water at pH = 9, the amphiphilic peptoids self-assemble into small spherical micelles having hydrodynamic radius in ∼5-10 nm range and critical micellar concentration (CMC) in the 0.034-0.094 mg/mL range. Small-angle neutron scattering (SANS) analysis of the micellar solutions revealed unprecedented dependence of the micellar structure on the number and position of ionic monomers along the chain. It was found that the micellar aggregation number ( N_agg) and the micellar radius ( R_m) both increase as the ionic monomer is positioned progressively away from the junction of the hydrophilic and hydrophobic segments along the polymer chain. By defining an ionic monomer position number ( n) as the number of monomers between the junction and the ionic monomer, N_agg exhibited a power law dependence on n with an exponent of ∼1/3 and ∼3/10 for the respective singly and triply charged series. By contrast, R_m exhibited a weaker dependence on the ionic monomer position by a power law relationship with an exponent of ∼1/10 and ∼1/20 for the respective singly and triply charged series. Furthermore, R_m was found to scale with N_agg in a power-law relationship with an exponent of 0.32 for the singly charged series, consistent with a weakly charged ionic star-like polymer model in the unscreened regime. This study demonstrated a unique method to precisely tailor the structure of small spherical micelles based on ionic block copolymers by controlling the sequence and position of the ionic monomer.

Triblock copolymers of styrene and sodium methacrylate as smart materials: synthesis and rheological characterization

Well-defined amphiphilic triblock poly(sodium methacrylate)-polystyrene-poly(sodium methacrylate) (PMAA-b-PS-b-PMAA) copolymers characterized by a different length of either the hydrophilic or the hydrophobic block have been synthesized by ATRP. In solution the micelle-like aggregates consist of a collapsed PS core surrounded by stretched charged PMAA chains. The micelles are kinetically ‘frozen’ and as a consequence the triblock copolymers do not show a significant surface activity. The hydrophilic block length has a major influence on the rheology, the shortest PMAA blocks yielding the strongest gels (at the same total weight concentration). The hydrophobic block length has only a minor influence until a certain threshold, below which the hydrophobic interactions are too weak resulting in weak gels. A mathematical model is used to describe the micelle radius and the results were in good agreement with the experimentally found radius in transmission electron microscopy. The influences of the ionic strength, pH and temperature on the rheology has also been investigated, showing the potential of these polymers as smart hydrogels. The change in conformation of the hydrophilic corona from the collapsed state to the stretched state by changing the pH was quantified with zeta-potential measurements. To the best of our knowledge, this is the first systematic investigation of this kind of triblock copolymers in terms of their rheological behavior in water.

Mixed poly(vinyl pyrrolidone)-based drug-loaded nanomicelles shows enhanced efficacy against pancreatic cancer cell lines

We report in this paper on the enhanced efficacy of a physical mixture of two single anti-cancer loaded nanomicelles against PANC-1 and BxPC-3. Poly(vinyl pyrrolidone-b-polycaprolactone) (PVP-b-PCL) and poly(vinyl pyrrolidone-b-poly(dioxanone-co-methyl dioxanone)) (PVP-b-P(DX-co-MeDX)) were synthesized and successfully loaded with various anti-cancer drugs - gemcitabine (GEM), doxorubicin.HCl (DOX.HCl), doxorubicin.NH₂ (DOX), 5-fluorouracil (5-FU) and paclitaxel (PTX). Spherical micelles of size 160-477 nm were obtained as characterized by DLS while sizes determined by TEM were in the range 140-250 nm. The hydrophobic drugs had a higher loading percentage efficiency compared to hydrophilic drugs in the trend PTX>DOX>5-FU>GEM>DOX.HCl whereas the drug release pattern followed the reverse trend in accordance with decreased polymer-drug interaction as quantified by the binding constant and micellar drug location. Cellular uptake studies showed that nanomicelles are taken up by pancreatic cancer cells into the cytoplasm and nucleus. The free nanomicelles were confirmed to be non-cytotoxic. A physical mixture of GEM loaded micelles and DOX.HCl loaded micelles of comparable size showed significantly higher cytotoxicity than either the free drug mixture or the individual single drug loaded micelles as confirmed by their IC₅₀ values.

Soft nanoparticles: nano ionic networks of associated ionic polymers

Directing the formation of nanostructures that serve as building blocks of membranes presents an immense step towards engineering controlled polymeric ion transport systems. Using the exquisite atomic detail captured by molecular dynamics simulations, we follow the assembly of a co-polymer that consists of polystyrene sulfonate tethered symmetrically to hydrophobic blocks, realizing a new type of long lived solvent-responsive soft nanoparticle.

Adsorption of Small Cationic Nanoparticles onto Large Anionic Particles from Aqueous Solution: A Model System for Understanding Pigment Dispersion and the Problem of Effective Particle Density

The present study focuses on the use of copolymer nanoparticles as a dispersant for a model pigment (silica). Reversible addition-fragmentation chain transfer (RAFT) alcoholic dispersion polymerization was used to synthesize sterically stabilized diblock copolymer nanoparticles. The steric stabilizer block was poly(2-(dimethylamino)ethyl methacrylate) (PDMA) and the core-forming block was poly(benzyl methacrylate) (PBzMA). The mean degrees of polymerization for the PDMA and PBzMA blocks were 71 and 100, respectively. Transmission electron microscopy (TEM) studies confirmed a near-monodisperse spherical morphology, while dynamic light scattering (DLS) studies indicated an intensity-average diameter of 30 nm. Small-angle X-ray scattering (SAXS) reported a volume-average diameter of 29 ± 0.5 nm and a mean aggregation number of 154. Aqueous electrophoresis measurements confirmed that these PDMA71-PBzMA100 nanoparticles acquired cationic character when transferred from ethanol to water as a result of protonation of the weakly basic PDMA chains. Electrostatic adsorption of these nanoparticles from aqueous solution onto 470 nm silica particles led to either flocculation at submonolayer coverage or steric stabilization at or above monolayer coverage, as judged by DLS. This technique indicated that saturation coverage was achieved on addition of approximately 465 copolymer nanoparticles per silica particle, which corresponds to a fractional surface coverage of around 0.42. These adsorption data were corroborated using thermogravimetry, UV spectroscopy and X-ray photoelectron spectroscopy. TEM studies indicated that the cationic nanoparticles remained intact on the silica surface after electrostatic adsorption, while aqueous electrophoresis confirmed that surface charge reversal occurred below pH 7. The relatively thick layer of adsorbed nanoparticles led to a significant reduction in the effective particle density of the silica particles from 1.99 g cm-3 to approximately 1.74 g cm-3, as judged by disk centrifuge photosedimentometry (DCP). Combining the DCP and SAXS data suggests that essentially no deformation of the PBzMA cores occurs during nanoparticle adsorption onto the silica particles.

Adding a solvophilic comonomer to the polymerization-induced self-assembly of block copolymer and homopolymer: a cooperative strategy for preparing large compound vesicles

We report a RAFT dispersion polymerization of styrene and 4-vinylpyridine in methanol/water at 70 °C. The polymerization was mediated by a binary mixture of DDMAT and mPEG₄₅-DDMAT.

Dual-sensitive and biodegradable core-crosslinked HPMA copolymer–doxorubicin conjugate-based nanoparticles for cancer therapy

The nanoplatform of biosafe crosslinked copolymer-NPs efficiently delivers anticancer drugs to tumor cellsviablood circulation.

An insight into aqueous photoinitiated polymerization-induced self-assembly (photo-PISA) for the preparation of diblock copolymer nano-objects

Photoinitiated polymerization-induced self-assembly (photo-PISA) is utilized to investigate the sole effect of reaction temperature on PISA.

Optimization and evaluation of Oridonin-loaded Soluplus®-Pluronic P105 mixed micelles for oral administration

In this study, a new type of mixed micelles was developed using Soluplus^® (SOL) and Pluronic^® P105 (P105) for the encapsulation of Oridonin (ORN). Oridonin-loaded micelles (ORN-M) were simply prepared using solvent evaporation and characterized for particle size, particle morphology, encapsulation efficiency, and drug loading. In addition, the in vitro drug release behavior of ORN-M was assessed using the widely applied dialysis bag technique. The pharmacokinetic property of ORN was explored in rats after oral administration of ORN-M. Optimized ORN-M were of a small size (137.2±1.65nm) and spherical shape when the ratio of SOL:P105 was 3:1, with entrapment efficiency 90.48±1.85% and drug loading 15.08±0.38%. Oral absorption capacity of ORN was greatly enhanced with a relative bioavailability of 210.55% in comparison to that of in-house suspensions, which suggests that ORN-M shows significantly improved bioavailability and drug absorption characteristics. Overall, the optimized SOL-P105 dual mixed micelles show great potential for use as oral drug carriers for cancer treatment.

Preparation of Thermosensitive Gel for Controlled Release of Levofloxacin and Their Application in the Treatment of Multidrug-Resistant Bacteria

Levofloxacin is a synthetic broad-spectrum antibacterial agent for oral or intravenous administration. Chemically, levofloxacin is the levorotatory isomer (L-isomer) of racemate ofloxacin, a fluoroquinolone antibacterial agent. Quinolone derivatives rapidly and specifically inhibit the synthesis of bacterial DNA. Levofloxacin has in vitro activity against a broad range of aerobic and anaerobic Gram-positive and Gram-negative bacteria. However, formulation of combined poloxamers thermoregulated (as Pluronic® F127) and levofloxacin for use in multiresistant bacterial treatment were poorly described in the current literature. Thus, the aim of the present work is to characterize poloxamers for levofloxacin controlled release and their use in the treatment of multidrug bacterial resistance. Micelles were produced in colloidal dispersions, with a diameter between 5 and 100 nm, which form spontaneously from amphiphilic molecules under certain conditions as concentration and temperature. Encapsulation of levofloxacin into nanospheres showed efficiency and enhancement of antimicrobial activity against Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae when compared with only levofloxacin. Furthermore, all formulations were not cytotoxic for NIH/3T3 cell lineage. In conclusion, poloxamers combined with levofloxacin have shown promising results, better than alone, decreasing the minimal inhibitory concentration of the studied bacterial multiresistance strains. In the future, this new formulation will be used after being tested in animal models in patients with resistant bacterial strains.

Drug-loading of poly(ethylene glycol methyl ether methacrylate) (PEGMEMA)-based micelles and mechanisms of uptake in colon carcinoma cells

In this study polymeric micelles formed from poly(poly(ethylene glycol) methyl ether methacrylate)-block-poly(methyl methacrylate) (P(PEGMEMA75)-b-PMMA80) block copolymer of approximately 25nm in diameter were used to encapsulate the model drug, Nile Red, with a loading efficiency of 0.08wt% and a chemotherapeutic drug, doxorubicin (DOX), with an efficiency of 2.75wt%. The release of DOX from the micelles was sufficient to be cytotoxic to human colon carcinoma cells, WiDr, while Nile Red and the unloaded micelles were found not to be cytotoxic when exposed to the cells at polymer concentrations up to 200μg/mL. Nile Red loaded micelles were used to analyze uptake of the micelles into the cells which were rapidly internalized within minutes of exposure. The three major endocytotic pathways were involved in the internalization of micelles; however other passive mechanisms were also at play as the addition of inhibitors to all three pathways did not completely inhibit the uptake of these nanoparticles. These data demonstrate the potential of the P(PEGMEMA)75-b-PMMA80 block copolymer micelles to be rapidly internalized by carcinoma cells and deliver low doses of drugs intracellularly for controlled drug release.