Formation Of Polymeric Micelles Research Articles

Entropy-Driven Liquid-Liquid Phase Separation Transition to Polymeric Micelles.

In recent years, liquid-liquid phase separation (LLPS) has been recognized to act as a precursor to self-assembly in amphiphilic systems. In this study, we propose the use of entropy-driven LLPS to obtain a tunable precursor for polymeric micelle formation. In this new approach, an oligomer is utilized as a nonselective solvent for the block copolymer, allowing for the tuning of entropy and subsequent LLPS. A comprehensive model was developed using mean-field lattice theory to predict the conditions under which LLPS and micellization occur. The degree of polymerization of the solvent was found to have a significant impact on the phase behavior of the system, outweighing enthalpic contributions such as the interaction between the blocks of the copolymer and the solvent. Our model predicts that using a solvent with a degree of polymerization equal to or greater than 5 for a copolymer such as PEG4kDa-b-PLA2.2kDa will result in LLPS prior to complete micellization, regardless of the values of interaction parameters. It also suggests that phase-separated liquid and polymeric micelles can co-exist in such a mixture. We confirmed our model predictions using dynamic light scattering and phase microscopy when PEG200 was used as the solvent. Micellization for PEG4kDa-b-PLA2.2kDa/PEG200/water mixture occurred at 10-12% w/w water content, consistent with the model predictions. Furthermore, the LLPS-to-micelle transition was shown to be reversible by changing the temperature or water content, indicating that the phase-separated liquid may be in thermodynamic equilibrium with polymeric micelles.

Synthesis approaches of amphiphilic copolymers for spherical micelle preparation: application in drug delivery.

The formation of polymeric micelles in aqueous environments through the self-assembly of amphiphilic polymers can provide a versatile platform to increase the solubility and permeability of hydrophobic drugs and pave the way for their administration. In comparison to various self-assembly-based vehicles, polymeric micelles commonly have a smaller size, spherical morphology, and simpler scale up process. The use of polymer-based micelles for the encapsulation and carrying of therapeutics to the site of action triggered a line of research on the synthesis of various amphiphilic polymers in the past few decades. The extended knowledge on polymers includes biocompatible smart amphiphilic copolymers for the formation of micelles, therapeutics loading and response to external stimuli, micelles with a tunable drug release pattern, etc. Different strategies such as ring-opening polymerization, atom transfer radical polymerization, reversible addition-fragmentation chain-transfer, nitroxide mediated polymerization, and a combination of these methods were employed to synthesize copolymers with diverse compositions and topologies with the proficiency of self-assembly into well-defined micellar structures. The current review provides a summary of the important polymerization techniques and recent achievements in the field of drug delivery using micellar systems. This review proposes new visions for the design and synthesis of innovative potent amphiphilic polymers in order to benefit from their application in drug delivery fields.

Effect of the hydrophobic segment of an amphiphilic block copolymer on micelle formation, zinc phthalocyanine loading, and photodynamic activity

A series of amphiphilic block copolymers, i.e., poly(N-substituted acrylamide)-block-poly(polyethylene glycol monomethyl ether acrylate) (P(R)-b-PPEGA) were prepared via RAFT polymerization and post-polymerization modification, and the formation of polymeric micelles as zinc(II) phthalocyanine (ZnPc) carriers for photodynamic therapy was investigated. The effect of hydrophobic R groups at the hydrophobic segment of the block copolymer on critical micelle concentration, hydrodynamic diameters ZnPc-loading ability, and in vitro photocytotoxicity of the polymer micelles was examined. The hydrodynamic diameters of the polymer micelles were insensitive to R groups and falls in a narrow range between 23 and 25 nm, whereas those of the ZnPc-loaded micelles vary from 167 to 230 nm depending on the R groups. The Q bands in UV–vis spectra of the ZnPc-loaded micelles indicate that the presence of aromatic R groups results in loose ZnPc aggregates, whereas those containing aliphatic R groups are well packed. The photodynamic effect examined in RGK-1 cell lines was also dependent on the R groups; ZnPc-loaded micelles having aromatic R groups exert higher photodynamic effect than those with aliphatic R groups. These findings indicate that aromatic R groups form larger polymeric micelles with loosely packed ZnPc aggregates, leading to enhanced release of ZnPc in cellular environment and therefore higher photodynamic effect.

Facile Synthesis of Amphiphilic Fluorescent Phosphorus Dendron-Based Micelles as Antiproliferative Agents: First Investigations.

We designed and synthesized several families of novel amphiphilic fluorescent phosphorus dendron-based micelles showing relevant antiproliferative activities for use in the field of theranostic nanomedicine. Based on straightforward synthesis pathways, 12 amphiphilic phosphorus dendrons bearing 10 protonated cyclic amino groups (generation one), or 20 protonated amino groups (generation two), and 1 hydrophobic chain carrying 1 fluorophore moiety were created. The amphiphilic dendron micelles had the capacity to aggregate in solution using hydrophilic/hydrophobic interactions, which promoted the formation of polymeric micelles. These dendron-based micelles showed moderate to high antiproliferative activities against a panel of tumor cell lines. This paper presents for the first time the synthesis and our first investigations of new phosphorus dendron-based micelles for cancer therapy applications.

Development and evaluation of polymeric micelle containing tablet formulation for poorly water-soluble drug: tamoxifen citrate

Poor aqueous solubility is one of the key reasons for slow dissolution rate and poor intestinal absorption and finally that causes low therapeutic efficacy of many existing drugs. Tamoxifen citrate (TMX) (BCS Class II drug) with low water solubility has poor oral bioavailability in the range of 20%–30%, therefore, high doses are required for treatment with TMX. Self-assemblage of amphiphilic polymers leads to the formation of polymeric micelles which makes them unique nano-carriers with excellent biocompatibility, low toxicity, enhanced blood circulation time, and solubilization of poorly water-soluble drugs. In this study poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) triblock copolymer, which has been approved by FDA for oral application was used to benefit its micellar solubilization effect. Self-assembled micelles were prepared for the delivery of TMX and this way TMX solubility was increased approximately 60 times. TMX-treated cells showed 38.06 ± 1.5% viability at 50 µM concentration for 24 h; 66.71 ± 11.6% viability at 25 µM concentration for 48 h, at the same conditions TMX-loaded micelles exhibited 24.994 ± 0.25% and 43.36 ± 4.37% cell viability, respectively (p < 0.05). These results showed that the encapsulation of TMX into PEG-PPG-PEG micelles facilitated the cellular uptake, which led to an increased cytotoxicity in MCF-7 cancer cells. Tablet formulation containing lyophilized TMX-loaded micelles was showed an improved dissolution than commercial TMX tablet (Tamoxifen® TEVA). It can be reasonably expected that the obtained drug dissolution rate and increased cytotoxicity to tumor cells will result in an increase of TMX bioavailability and tolerability associated with an important dose reduction and decreased side effects.

Silicon Tetrapyrazinoporphyrazine Derivatives-Incorporated Carbohydrate-Based Block Copolymer Micelles for Photodynamic Therapy.

Developing nonaggregated photosensitizers (PSs) for efficient photodynamic therapy (PDT) using polymeric micelles (PMs) has been challenging. In this study, axially substituted nonaggregated silicon tetrapyrazinoporphyrazine (SiTPyzPz) derivatives in carbohydrate-based block glycopolymer-based PMs were designed and used as PSs for PDT. To achieve the nonaggregated PSs, SiTPyzPz was axially substituted with trihexylsiloxy (THS) groups to form SiTPyzPz-THS, which exhibited highly monomeric behaviors in organic solvents. Moreover, three block copolymers were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. Each copolymer comprised hydrophobic polystyrene blocks and loadable SiTPyzPz-THS, and one or two consisted of two possible hydrophilic blocks, polyethylene glycol or poly(glucosylethyl methacrylate). The self-assembly of SiTPyzPz-THS and the block copolymers in aqueous solvents induced the formation of spherical PMs with core-shell or core-shell-corona structures. The SiTPyzPz-THS in the PMs exhibited monomeric state, intense fluorescence emission, and outstanding singlet oxygen generation; moreover, it did not form aggregates. During the in vitro test, which was performed to investigate the PDT efficiency, the PMs, which consisted of poly(glucosylethyl methacrylate) shells, exhibited high photocytotoxicity and cellular internalization ability. Consequently, the PM systems of nonaggregated PSs and carbohydrate-based block copolymers could become very promising materials for PDT owing to their photophysicochemical properties and considerable selectivity against cancer cells.

Novel amphiphilic chitosan micelles as carriers for hydrophobic anticancer drugs.

Chitosan was grafted with O-methyl-O'-succinylpolyethylene glycol and oleic acid after a two-step carbodiimide coupling. The structural and physicochemical characterization of the compounds confirmed the successful conjugation of the hydrophilic and hydrophobic moieties to the chitosan backbone. The amphiphilic chitosan derivative obtained allowed the formation of polymeric micelles with an average size of 140nm, a polydispersity index <0.234, and a positive superficial charge. Camptothecin, used as a model hydrophobic drug, was successfully carried into the polymeric micelles with an encapsulation efficiency of 78%. The in vitro drug release was evaluated in simulated gastrointestinal fluids, exhibiting a low release of camptothecin in gastric media and a controlled release in intestinal fluids. Furthermore, it was demonstrated that chitosan micelles were able to stabilize camptothecin, protecting up to 75% of the drug from hydrolysis, preserving its active lactone form. This new chitosan amphiphilic system exhibits great potential to load hydrophobic drugs, acting as a promising delivery system.

Ethylene oxide based copolymers functionalized with terminal alkynes: Structure influence on their micelle formation

Copolymers from ethylene oxide (EO) and propylene oxide (PO) functionalized with glycidyl propargyl ether (GPE) are synthesized. The GPE allows further attachment of drugs but its influence on the polymeric micelle formation is unknown. In this work, the influence of the structure of these copolymers on their critical micellar concentration (CMC) in water and in the size and stability of obtained micelles is studied. For this purpose, the presence of GPE, the copolymer type (gradient or block), the EO:PO ratio and the initiator (water or ethanol) are modified. Gradient copolymers can be synthesized in a single step thanks to the different monomers reactivity, simplifying the process and obtaining similar CMC values to the block copolymers. The use of ethanol as initiator decreases the block copolymer CMC and increases the polydispersity. Besides, the presence of the GPE does not impede the micelle formation and has low effect on the copolymer CMCs. Finally, the higher the EO:PO ratio, the higher the CMC and the smaller the size of micelles. Moreover, Z-potential, DLS and HRSEM analyses show that the micelles are stable, spherical, capable to incorporate coumarin (a hydrophobic drug) and with apparent hydrodynamic sizes suitable to be absorbed by target cells.

ATP-Driven Temporal Control over Structure Switching of Polymeric Micelles.

An adenosine triphosphate (ATP)-fueled micellar system in the out-of-equilibrium state was constructed based on 4,5-diamino-1,3,5-triazine (DAT)-containing block copolymer. The block copolymer self-assembled into spherical micelles in equilibrium steady state at pH higher than its p Ka. The pendant DAT residues in protonated form acted as ATP catchers via hydrogen bonding and electrostatic interactions. Activated by ATP fuel, the polymeric micelles spontaneously disrupted into small aggregates of ATP/polymer hybrid complexes. The consumption of ATP energy via the enzymatic hydrolysis led to dissociation of the complexes and reversible formation of polymeric micelles. A transient self-assembly cycle, in which the assembly underwent autonomous division-fusion motion, was created using ATP fuel and enzyme; the switching of assembly structure was sustained by continuous supply of ATP fuel. This DAT-containing block copolymer have good biocompatibility, and drug-loaded micelles display ATP-responsive release behavior. It is expected that this ATP-fueled supramolecular assembly system will provide a functional platform for biomimic chemistry and therapeutic applications.

Hybrid Gold/Silica/Quantum-Dots supramolecular-nanostructures encapsulated in polymeric micelles as potential theranostic tool for targeted cancer therapy

Efficient theranostic tools are today more and more frequently represented by the nano-sized systems. In this paper, polymeric micelles were produced and exploited to encapsulate both an antitumor drug (Doxorubicin) and gold core–shell quantum dots nanoparticles (Au-SiO2/QDs). α,β-poly(N-hydroxyethyl)-dl-aspartamide (PHEA) was functionalized with lipoic acid (LA), polyethylenglycol (PEG), and folic acid (FA) pendant moieties to obtain a synthetic derivative (PHEA-LA-PEG-FA) able to self assemble in aqueous medium giving rise to the formation of polymeric micelles exposing on their surface both targeting groups (FA) and hydrophilic chains (PEG). The drug carrying ability of PHEA-LA-PEG-FA micelles was here studied along with the cytotoxity of the obtained nanostructures toward breast cancer cells employing doxorubicin as a model anticancer drug. Finally, the properties of the gold-shell QDs incorporated into the micelles as cells imaging agent and photothermal anticancer treatment tool were explored.

1052 The improvement on the skin penetration of water insoluble drugs by polymeric micelles

Polymeric micelle is consisted of poly (ethylene glycol) - poly (amino acid) block copolymer formed micelles through the self-assembly of block copolymers. This micelle has been recognized as a systemic nanocarrier in targeted cancer therapy. It is known as the nanoparticle formation for mainly hydrophobic drug encapsulated in the micelles, and has characteristics of increased drug solubility, its sustainable release and tissue distribution. The polymeric micelle shows high stability characterized by low micelle concentration as compared with general surfactants. On the other hand, the local distribution study of such polymeric micelles in the skin has not been well recognized. In this study we investigated the skin distribution of encapsulated hydrophobic drug in polymeric micelle formation. We reported at the 42nd Conference of JSID that the amount of drug penetrated into the skin was depended on the donor concentration of drug, and such penetration was increased by polymeric micelles-improving solubility of water insoluble drug. On this study, we report the pharmacokinetics of encapsulated drug and released drug from the micelle in the skin. We observed that the maximum amount of encapsulated drug in the skin was achieved at 6 hours after administration. However, the drug penetration time into the basal layer of the epidermis was taken approximately 24 hours after the administration. Therefore, we speculated that the drug was gradually penetrated into the deeper layer of the skin after saturating in the stratum corneum. As the result of high efficiency of drug skin penetration, we consider that polymeric micelle formulation is useful approach and one of the best topical dosage forms for drug insoluble in water.

Polyion complex micelle formation from double-hydrophilic block copolymers composed of charged and non-charged segments in aqueous media

Polymeric micelles are representative self-assembly structures of block copolymers and have widely been investigated from both fundamental and applied aspects. In 1995, we discovered polyion complex (PIC) micelles formed from a pair of oppositely charged block copolymers with poly(ethylene glycol) segments through electrostatic interactions in aqueous media, which expanded the concept of polymeric micelle formation in selective solvents. Hereafter, extensive studies have been carried out on PIC micelles, for example, fundamental characterizations as a novel class of self-assembly systems and applications as nanocarrier systems for the delivery of charged molecules with therapeutic efficacies, including nucleic acids and proteins. This review mainly focuses on physicochemical studies on the formation of PIC micelles, particularly the critical molecular factors that have a role to determine the self-assembly scheme of charged block copolymers for micelle structures. This review focuses on the physicochemical characterization of polyion complex (PIC) micelles, particularly addressing the critical molecular factors to determine the self-assembly scheme of double-hydrophilic block copolymers composed of charged and non-charged segments into micelle structures. The process of PIC micelle formation provides new insights on the block copolymer self-assembly in thermodynamically equilibrium condition in aqueous medium, such as chain length recognition and transition from uPIC, which is the PIC of smallest neutralizing unit, to PIC micelle structures.

Polymeric micelles self-assembled from amphiphilic polymers with twin disulfides used as siRNA carriers to enhance the transfection

The sequence-defined polycationic polymers with or without Cys-Arg-Cys motifs conjugated with targeting and shielding segments were synthesized as siRNA carriers via native chemical ligation (NCL) reaction. After purification, the structures and physicochemical characteristics were determined by a variety of experimental techniques. The particle size of siRNA/CRC-polymer polyplex was much smaller than that of polyplex without CRC motifs. The buffer capacity and siRNA binding ability of CRC motifs modified polymers were significantly improved, resulting from the twin disulfides and hexatomic ring formulation. The critical micelle concentrations of the polymers were <10mg/L, indicating formation of polymeric micelles and sufficient stability of the system. The CRC motifs modified polymers with folate targeted ligands exhibited a strongly enhanced cellular uptake than the negative control and the unmodified analogues. The results of gene transfection showed that the folate-PEG-ligated polymer modified with CRC motifs had much better gene transfection compared to the alanine-ended control and other analogues. Furthermore, they showed barely cytotoxicity. By the way, there was no distinctly improvement for pDNA transfection. All above results suggested that folate-PEG-ligated polymers modified with CRC motifs and their self-assembly polymeric micelles could be promising non-viral siRNA carriers.

P2.06-020 A Open-Label Randomised Controlled Trial of First-Line Genexol-PM/CrEL-Based Paclitaxel plus Cisplatin in Advanced NSCLC Patients: Topic: Phase II + NK

Genexol-PM is a novel Cremophor EL(CrEL)-free polymeric micelle formation of paclitaxel.This multicentre study was designed to compare Genexol-PM and CrEL-based paclitaxel in combination with cisplatin in terms of efficacy and safety as first-line therapy in advanced non-small cell lung cancer. Chemonaive patients aged from 18 to 70 years with histologically or cytologically confirmed, locally advanced, metastatic or recurrent advanced NSCLC and an ECOG performance status of 0–1 were randomised 2:1 to the treatment group (Genexol-PM+ cisplatin) and the controll group (paclitaxel+cisplatin). Patients were treated with Genexol-PM 230mg/m2 intravenously without premedication or paclitaxel 175mg/m2 intravenously with premedication plus cisplatin 70mg/m2 on day 1 of a 3-week cycle for up to six cycles. Intrapatient dose escalation of Genexol-PM to 300mg/m2 was carried out in treatment group from the second cycle if the prespecified toxic effects were not observed after the first cycle. 170 patients were randomised into the study. PFS and OS data are not yet mature. This multicenter study is in progress.

Location of Varying Hydrophobicity Zinc(II) Phthalocyanine-Type Photosensitizers in Methoxy Poly(ethylene oxide) and Poly(l-lactide) Block Copolymer Micelles Using 1H NMR and XPS Techniques.

Hydrophobic zinc(II) phthalocyanine-type derivatives, solubilized in polymeric micelles (PMs), provide a befitting group of so-called nanophotosensitizers, suitable for a variety of photodynamic therapy (PDT) protocols. The factors that influence the success of such products in PDT are the location of the active cargo in the PMs and the nanocarrier-enhanced ability to safely interact with biological systems and fulfill their therapeutic functions. Therefore, the aim of this work was to determine the solubilization loci of three phthalocyanines of varying hydrophobicity, i.e., zinc(II) phthalocyanine (ZnPc), along with its tetrasulfonic acid (ZnPc-sulfo4) and perfluorinated (ZnPcF16) derivatives, loaded in polymeric micelles of methoxy poly(ethylene oxide)-b-poly(l-lactide) (mPEG-b-PLLA), by means of 1H nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) combined with ion sputtering. Furthermore, the microenvironment influence upon the chemical and physical status of the solubilized cargo in PMs, expressed by photobleaching and reactive oxygen species (ROS) generation comparing to the same properties of native cargoes in solution, was also evaluated and discussed in regards to the probing location data. The studied phthalocyanine-loaded PMs exhibited good physical stability, high drug-loading efficiency, and a size of less than ca. 150 nm with low polydispersity indices. The formation of polymeric micelles and the solubilization locus were investigated by 1H NMR and XPS. ZnPc localized within the PM core, whereas both ZnPcF16 and ZnPc-sulfo4 - in the corona of PMs. We proved that the cargo locus is crucial for the photochemical properties of the studied phthalocyanines; the increase in photostability and ability to generate ROS in micellar solution compared to free photosensitizer was most significant for the photosensitizer in the PM core. Our results indicate the role of the cargo location in the PM microenvironment and demonstrate that such attempts are fundamental for improving the properties of photosensitizers and their assumed efficiency as nanophotosensitizers in PDT.

Mesoscopic simulation studies on the formation mechanism of drug loaded polymeric micelles

In this work, the formation of polymeric micelles as drug delivery vehicles in an aqueous environment is investigated by dissipative particle dynamics (DPD) simulations. Doxorubicin (DOX) is selected as the model drug, whereas docosahexaenoic acid (DHA) conjugated His10Lys10 (DHA-His10Lys10) as the drug carrier. It is shown from DPD simulation that drug molecules and DHA-His10Lys10 molecules could aggregate and form micelles under a defined composition recipe; drug molecules are homogeneously distributed inside the carrier matrix, on whose surface the stabilizer lysine segments are absorbed. Under different compositions of drug and water, aggregate morphologies of polymeric micelles are observed as spherical, columnar, and lamellar structures. We finally proposed the formation mechanism of drug loaded polymeric micelles and apply it in practice by analyzing the simulated phenomena. All the results can effectively guide the experimental preparation of drug delivery system with desired properties or explore a novel polymeric micelle with high performance.

Microfluidics-Based Self-Assembly of Amphiphilic Random Copolymer P(St-ran-DM)

Styrene monomer (St) and dimethylaminoethyl methacrylate (DM) monomer were used to synthesize the amphiphilic random copolymer P(St-ran-DM) via free radical copolymerization. A Y-shaped microchannel was used enabling a controllable and fast mixing process to assist the formation of polymeric micelles which was triggered by a solvent exchange process when organic solutions of the polymer mixed with water. The effects of flow rate, polymer concentration, and microchannel dimensions on the characteristics of micelle were systematically investigated. The results showed that besides the effect of the flow rate, the chemical environment played an important role in determining the characteristics of the polymeric micelles.

Supramolecular flower micelle formation of polyrotaxane-containing triblock copolymers prepared from macro-chain transfer agents bearing molecular hooks

A precise synthesis of polyrotaxanes (PRX)-containing triblock copolymers was achieved using PRX macro-chain transfer agents with terminal hooks. Also, polymeric micelle formation of them in aqueous solution was investigated.

Controlled block copolymer micelle formation for encapsulation of hydrophobic ingredients

We report on the formation of polymeric micelles in water using triblock copolymers with a polyethylene glycol middle block and various hydrophobic outer blocks prepared with the precipitation method. We form micelles in a reproducible manner with a narrow size distribution. This suggests that during the formation of the micelles the system had time to form micelles under close-to-thermodynamic control. This may explain why it is possible to use an equilibrium self-consistent field theory to predict the hydrodynamic size and the loading capacity of the micelles in accordance with experimental finding. Yet, the micelles are structurally quenched as concluded from the observation of size stability in time. We demonstrate that our approach enables to prepare rather hydrophobic block copolymer micelles with tunable size and loading.

Amphiphilic polyaspartamide copolymer-based micelles for rivastigmine delivery to neuronal cells

A novel polysorbate-80 (PS80)-attached amphiphilic copolymer comprising a hydrophilic α,β-poly(N-2-hydroxyethyl)-d,l-aspartamide (PHEA) backbone and hydrophobic squalenyl-C17 (Sq17) portions was synthesized and characterized; the formation of polymeric micelles was also evaluated. Rivastigmine free-base (Riv), a hydrophobic drug employed to treat Alzheimer’s disease, was chosen as model drug to investigate micelle’s ability to incorporate hydrophobic molecules and target them to neuronal cells. Micelle formation was studied through analyses including fluorescence spectroscopy and 2D 1H-NMR NOESY experiments. Finally, the capacity of Riv-loaded micelles, versus free drug, to penetrate mouse neuroblastoma cells (Neuro2a) was evaluated. 2D 1H-NMR NOESY experiments demonstrated that the PHEA-EDA-Sq17-PS80 copolymer self-assembles into micelle structures in water, with a micelle core formed by hydrophobic interaction between Sq17 alkyl chains. Fluorescence probe studies revealed the CAC of PHEA-EDA-Sq17-PS80 micelles, which was 0.25 mg mL−1. The micelles obtained had a nanometric hydrodynamic diameter with narrow size distribution and negative surface charge. The PHEA-EDA-Sq17-PS80 micelles incorporated a large amount of Riv, and the system maintained the stability of Riv after incubation in human plasma. An in vitro biological assay evidenced no cytotoxic effects of either empty or loaded micelles on the neuronal cell lines tested. Moreover, the micelles are internalized by neuroblastoma cell lines with drug uptake depending on the micelles concentration.