A One-Step Approach to the Highly Efficient Preparation of Core-Stabilized Polymeric Micelles with a Mixed Shell Formed by Two Incompatible Polymers

Formation of n-Hexane-in-DMF Nonaqueous Pickering Emulsions: ABC Triblock Worms versus AB Diblock Worms

Nonaqueous Pickering emulsions exhibit promising applications in many industrial areas but have been relatively less studied in the past. In this study, n-hexane-in-DMF nonaqueous Pickering emulsions stabilized by core cross-linked copolymer worms with mixed shells are demonstrated for the first time. Core cross-linked copolymer worms with mixed shells were prepared by seeded reversible addition-fragmentation chain transfer (RAFT) quasi-solution polymerization. Specifically, polystyrene-poly(4-vinylpyridine) (PS-P4VP) diblock copolymer worms were first prepared via RAFT-mediated dispersion polymerization in toluene under the given conditions using PS as both the macro-CTA and the stabilizer block. After the chemical cross-linking of P4VP cores, PS-P4VP diblock copolymer worms were chain-extended with LMA in DMF/toluene (1:9, weight ratio) mixed solvents, producing core cross-linked PS-P4VP-PLMA worms with PS/PLMA mixed shells. The as-prepared core cross-linked PS-P4VP-PLMA worms with mixed PS/PLMA shells were further utilized as Pickering emulsifiers for the generation of nonaqueous n-hexane-in-DMF Pickering emulsions. The emulsifying performances of mixed-shell copolymer worms were compared with those of their spherical and linear analogues with entirely identical chemical compositions as well as PS-P4VP diblock copolymer worm precursors, respectively.

Using Amphiphilic Polymer Micelles as the Templates of Antisolvent Crystallization to Produce Drug Nanocrystals

Biocompatible and biodegradable amphiphilic polymeric micelles (PLA-CMCS-g-OA) were prepared by surface grafting of oleic acid and polylactic acid onto carboxymethyl chitosan and were used as templates for the crystallization of camptothecin. The camptothecin (CPT) nanocrystals prepared by the novel micelle-templated antisolvent crystallization (mt-ASC) method demonstrated higher crystallinity, narrower particle size distribution, and slower release characteristic than those prepared by conventional antisolvent crystallization (c-ASC) using a high initial concentration and fast addition rate. In particular, the CPT release behavior of mt-ASC products in phosphate buffer solutions presented a pH-responsive characteristic with the increasing release rate of CPT under lower pH conditions. This work confirmed that amphiphilic nanomicelle-templated crystallization was an effective method for preparing drug nanocrystals.

Multifunctional polymeric micellar nanomedicine in the diagnosis and treatment of cancer

Polymeric micelles are a prevalent topic of research for the past decade, especially concerning their fitting ability to deliver drug and diagnostic agents. This delivery system offers outstanding advantages, such as biocompatibility, high loading efficiency, water-solubility, and good stability in biological fluids, to name a few. The multifunctional polymeric micellar architect offers the added capability to adapt its surface to meet the looked-for clinical needs. This review cross-talks the recent reports, proof-of-concept studies, patents, and clinical trials that utilize polymeric micellar family architectures concerning cancer targeted delivery of anticancer drugs, gene therapeutics, and diagnostic agents. The manuscript also expounds on the underlying opportunities, allied challenges, and ways to resolve their bench-to-bedside translation for allied clinical applications.

Stereocomplexed micelle formation through enantiomeric PLA-based Y-shaped copolymer for targeted drug delivery

In this study, a novel stereocomplexed micelle system was prepared from the self-assembly of enantiomeric PLA-based Y-shaped copolymers, i.e. folic acid-adamantane/β-cyclodextrin-b-[poly(D-lactide)]₂ (FA-AD/CD-b-(PDLA)₂) and poly(2-dimethylaminoethyl methacrylate)-b-[poly(L-lactide)]₂ (PDMAEMA-b-(PLLA)₂) in aqueous solution. The newly designed Y-shaped copolymer FA-AD/CD-b-(PDLA)₂ was prepared by a combination of "click" reaction and host guest interaction between FA-AD and CD-b-(PDLA)₂. In addition, enantiomeric Y-shaped PDMAEMA-b-(PLLA)₂ copolymer was synthesized through ring-opening polymerization (ROP) of L-lactide using three-head initiator with bromo and -OH at distal ends, followed by atom transfer radical polymerization (ATRP) of DMAEMA to obtain the desired macromolecular architecture. The resultant copolymers and their intermediates were characterized by ¹H nuclear magnetic resonance (¹H NMR) and gel permeation chromatography (GPC) techniques. Due to the strong stereocomplexation interaction, FA-AD/CD-b-(PDLA)₂ and PDMAEMA-b-(PLLA)₂ mixture could self-assemble into stable mixed micelles in aqueous solution. Further, the stereocomplexed micelles exhibited excellent biocompatibility as revealed in the cytotoxicity assay. Together with the intrinsic biodegradability of PLA, it is envisioned that the stereocomplexed micelles developed in this study can be used as a promising nanocarrier for targeting drug delivery.

Optimization of Weight Ratio for DSPE-PEG/TPGS Hybrid Micelles to Improve Drug Retention and Tumor Penetration

PURPOSE

To enhance therapeutic efficacy and prevent phlebitis caused by Asulacrine (ASL) precipitation post intravenous injection, ASL-loaded hybrid micelles with size below 40 nm were developed to improve drug retention and tumor penetration.

METHODS

ASL-micelles were prepared using different weight ratios of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-polyethyleneglycol-2000 (DSPE-PEG₂₀₀₀) and D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) polymers. Stability of micelles was optimized in terms of critical micelle concentration (CMC) and drug release properties. The encapsulation efficiency (EE) and drug loading were determined using an established dialysis-mathematic fitting method. Multicellular spheroids (MCTS) penetration and cytotoxicity were investigated on MCF-7 cell line. Pharmacokinetics of ASL-micelles was evaluated in rats with ASL-solution as control.

RESULTS

The ASL-micelles prepared with DSPE-PEG₂₀₀₀ and TPGS (1:1, w/w) exhibited small size (~18.5 nm), higher EE (~94.12%), better sustained in vitro drug release with lower CMC which may be ascribed to the interaction between drug and carriers. Compared to free ASL, ASL-micelles showed better MCTS penetration capacity and more potent cytotoxicity. Pharmacokinetic studies demonstrated that the half-life and AUC values of ASL-micelles were approximately 1.37-fold and 3.49-fold greater than that of free ASL.

CONCLUSIONS

The optimized DSPE-PEG₂₀₀₀/TPGS micelles could serve as a promising vehicle to improve drug retention and penetration in tumor.

Solution-Based Thermodynamically Controlled Conversion from Diblock Copolymers to Janus Nanoparticles

Nanosized polymeric Janus particles (NPJPs) have important applications in a variety of theoretical and practical research fields. However, the methods that are versatile and can prepare NPJPs highly efficiently are very limited. Herein, we reported a two-step thermodynamically controlled preparation of NPJPs with a high yield using a diblock copolymer as the precursor. At the first step, A-b-B coassembled in the solution with a partner diblock copolymer C-b-B to form the mixed shell micelles (MSMs) with B core and A/C mixed shell. Then, intramicellarly covalently cross-linking the A block chains resulted in the complete phase separation of A and C chains in the mixed shell, leading to the direct conversion of the MSMs into NPJPs. The first step, diblock copolymer micellization, is known as a thermodynamically controlled process, and we also made the second step, conversion from MSMs to NPJPs, be thermodynamically controlled due to the application of covalent cross-linking. As the result, the conversion efficiency is close to 100%. Besides, it was further confirmed that the method can be applied to different systems and used to tune the Janus balance. Therefore, this conversion should be very significant for the fabrication and application of the NPJPs.

Heteropoly blue doped polymer nanoparticles: an efficient theranostic agent for targeted photoacoustic imaging and near-infrared photothermal therapy in vivo

We report a two-step process to construct heteropoly blue (HPB) doped polymer nanoparticles with efficient near-infrared (NIR) light absorption and photothermal conversion efficiency of ∼23%.

Glutathione-dependent micelles based on carboxymethyl chitosan for delivery of doxorubicin

Novel glutathione (GSH)-dependent micelles based on carboxymethyl chitosan (CMCS) were developed for triggered intracellular release of doxorubicin (DOX). DOX-33'-Dithiobis (N-hydroxysuccinimidyl propionate)-CMCS (DOX-DSP-CMCS) prodrugs were synthesized. DOX was attached to the amino group on CMCS via disulfide bonds and drug-loaded micelles were formed by self-assembly. The micelles formed core-shell structure with CMCS and DOX as the shell and core, respectively, in aqueous media. The structure of the prodrugs was confirmed by IR and proton nuclear magnetic resonance (¹H NMR) spectroscopy. The drug-loading capacity determined by UV spectrophotometry was 4.96% and the critical micelle concentration of polymer prodrugs determined by pyrene fluorescence was 0.089 mg/mL. Micelles were spherical and the mean size of the nanoparticles was 174 nm, with a narrow polydispersity index of 0.106. Moreover, in vitro drug release experiments showed that the micelles were highly GSH-sensitive owing to the reductively degradable disulfide bonds. Cell counting kit (CCK-8) assays revealed that DOX-DSP-CMCS micelles exhibited effective cytotoxicity against HeLa cells. Moreover, confocal laser scanning microscopy (CLSM) demonstrated that DOX-DSP-CMCS micelles could efficiently deliver and release DOX in the cancer cells. In conclusion, the DOX-DSP-CMCS nanosystem is a promising drug delivery vehicle for cancer therapy.

Multicompartment micelles based on hierarchical co-assembly of PCL-b-PEG and PCL-b-P4VP diblock copolymers

Multicompartment micelles with various morphologies were preparedviadirected stepwise self-assembly using pre-assembled subunits, which were first constructed through the co-assembly of two amphiphilic diblock copolymer: PCL-b-PEG and PCL-b-P4VP.

Hierarchical nanostructures self-assembled from a mixture system containing rod-coil block copolymers and rigid homopolymers

Self-assembly behavior of a mixture system containing rod-coil block copolymers and rigid homopolymers was investigated by using Brownian dynamics simulations. The morphologies of formed hierarchical self-assemblies were found to be dependent on the Lennard-Jones (LJ) interaction ε_RR between rod blocks, lengths of rod and coil blocks in copolymer, and mixture ratio of block copolymers to homopolymers. As the ε_RR value decreases, the self-assembled structures of mixtures are transformed from an abacus-like structure to a helical structure, to a plain fiber, and finally are broken into unimers. The order parameter of rod blocks was calculated to confirm the structure transition. Through varying the length of rod and coil blocks, the regions of thermodynamic stability of abacus, helix, plain fiber, and unimers were mapped. Moreover, it was discovered that two levels of rod block ordering exist in the helices. The block copolymers are helically wrapped on the homopolymer bundles to form helical string, while the rod blocks are twistingly packed inside the string. In addition, the simulation results are in good agreement with experimental observations. The present work reveals the mechanism behind the formation of helical (experimentally super-helical) structures and may provide useful information for design and preparation of the complex structures.

Controlled co-delivery nanocarriers based on mixed micelles formed from cyclodextrin-conjugated and cross-linked copolymers

The combination of multiple drugs within a single nanocarrier can provide significant advantages for disease therapy and it is desirable to introduce a second drug based on host-guest interaction in these co-delivery systems. In this study, a core-stabilized mixed micellar system consisting of β-cyclodextrin-conjugated poly(lactic acid)-b-poly(ethylene glycol) (β-CD-PLA-mPEG) and DL-Thioctic acid (TA) terminated PLA-mPEG (TA-PLA-mPEG) was developed for the co-delivery of DOX and fluorescein isothiocyanate labeled adamantane (FA). DOX can be loaded within the hydrophobic segment of PLA and FA may form stable complexation with β-CD in the core. The mixed micelles (MM) are based on well-accepted medical materials and can be easily cross-linked by adding 1,4-dithio-D,L-threitol (DTT), which can enhance the stability of the system. Drug-loaded MM system was characterized in terms of particle size, morphology, drug loading and in vitro release profile. Cytotoxicity test showed that blank MM alone showed negligible cytotoxicity whereas the drug-loaded MM remained relatively high cytotoxicity for HeLa cancer cells. Confocal laser scanning microscopy (CLSM) demonstrated that the MM could efficiently deliver and release DOX and FA in the same tumor cells to effectively improve drugs' bioavailability. These results suggested that the core-stabilized MM are highly promising for intracellular co-delivery of multiple drugs.

A facile synthesis of dynamic, shape-changing polymer particles

We herein report a new facile strategy to ellipsoidal block copolymer nanoparticles that exhibit a pH-triggered anistropic swelling profile. In a first step, elongated particles with an axially stacked lamellae structure are selectively prepared by utilizing functional surfactants to control the phase separation of symmetric polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) in dispersed droplets. In a second step, the dynamic shape change is realized by cross-linking the P2VP domains, thereby connecting glassy PS discs with pH-sensitive hydrogel actuators.

Water in oil emulsion stabilized by tadpole-like single chain polymer nanoparticles and its application in biphase reaction

In this study, tadpole-like single chain polymer nanoparticles (TSCPNs) were efficiently synthesized by intramolecularly cross-linking P4VP block of commercial block polymer of PMMA2250-b-P4VP286 in N,N-dimethylformamide using propargyl bromide as cross-linking agent. The intramolecular cross-linking reaction led to the production of TSCPNs with a linear tail and a cross-linked head. The as-prepared TSCPNs were then applied as emulsifier to stabilize water in chlorobenzene emulsion, and an extremely stabilized water in oil (W/O) emulsion was generated at a low TSCPNs concentration. The TSCPNs concentration was as low as 0.0075 wt % versus total weight of water and chlorobenzene for emulsion formation. The emulsifying performance of TSCPNs was better than that of low molecular surfactant, such as Span-80. The generated W/O emulsion provided an ideal medium for the reduction of oil-soluble p-nitroanisole by water-soluble sulfide to p-anisidine, an effective contact problem between the two reactants with different solubility was well solved through interfacial reaction.

Complex Micelles with Glucose-Responsive Shells for Self-Regulated Release of Glibenclamide

Complex micelles with a hydrophobic poly(ϵ-caprolactone) (PCL) core and a mixed P(Asp-co-AspPBA)/PEG shell were prepared through co-assembly of two block copolymers PCL-b- P(Asp-co-AspPBA) and PEG-b-PCL in basic aqueous solutions. The P(Asp-co-AspPBA) chains (Asp = aspartic acid; AspPBA = aspartamidophenylboronic acid) collapsed and formed a shell layer around the PCL core at neutral pH while the soluble PEG chains stabilised the micelles. The collapsed P(Asp-co-AspPBA) polymer becomes soluble under higher glucose concentration and collapses onto the PCL core reversibly at lower glucose concentration. Self-regulated release of glibenclamide from the complex micelles was achieved based on the reversible change of P(Asp-co-AspPBA) chain mobility in response to the change of glucose concentration. As a result, polymeric micelles with glucose-responsive on-off switches were successfully developed.

In vivo biodistribution of mixed shell micelles with tunable hydrophilic/hydrophobic surface

The miserable targeting performance of nanocarriers for cancer therapy arises largely from the rapid clearance from blood circulation and the major accumulation in the organs of the reticuloendothelial system (RES), leading to inefficient enhanced permeability and retention (EPR) effect after intravenous injection (i.v.). Herein, we reported an efficient method to prolong the blood circulation of nanoparticles and decrease their deposition in liver and spleen. In this work, we fabricated a series of mixed shell micelles (MSMs) with approximately the same size, charge and core composition but with varied hydrophilic/hydrophobic ratios in the shell through spontaneously self-assembly of block copolymers poly(ethylene glycol)-block-poly(l-lysine) (PEG-b-PLys) and poly(N-isopropylacrylamide)-block-poly(aspartic acid) (PNIPAM-b-PAsp) in aqueous medium. The effect of the surface heterogeneity on the in vivo biodistribution was systematically investigated through in vivo tracking of the (125)I-labeled MSMs determined by Gamma counter. Compared with single PEGylated micelles, some MSMs were proved to be significantly efficient with more than 3 times lower accumulation in liver and spleen and about 6 times higher concentration in blood at 1 h after i.v.. The results provide us a novel strategy for future development of long-circulating nanocarriers for efficient cancer therapy.

Orienting block copolymer microdomains with block copolymer brushes

A simple, rapid, and robust technique for controlling the self-assembly of block copolymers (BCPs) with a large segmental interaction parameter, χ, is described using a surface modified with anchored BCP brushes. End-functionalized poly(styrene-b-ethylene oxide)s (PS-b-PEOs), where the fraction of PS (f(PS)) was varied, end-functionalized neat PS, and end-functionalized neat PEO were end-grafted onto Si substrates modifying the surface with polymer brushes. Thin films of cylinder-forming PS-b-PEO were prepared on modified Si substrates and thermally annealed. When neat PS and PEO were used as the anchored brushes, the microdomains of the PS-b-PEO oriented parallel to the substrate upon thermal annealing due to the preferential interactions of one block to the anchored brushes. However, when end-functionalized PS-b-PEOs were used to modify the substrate, hexagonally packed cylindrical PEO microdomains oriented normal to the substrate, having long-range lateral ordering, were obtained over a very wide range of f(PS) (0.32 to 0.77).

Advanced materials for co-delivery of drugs and genes in cancer therapy

With cancer being the major cause of mortality worldwide, the continued development of safe and efficacious treatments is warranted. A better understanding of the molecular mechanism and genetic basis of tumor initiation and progression, coupled with advances in chemistry, molecular biology and engineering have led to discovery of a wide range of therapeutic agents for cancer therapy. However, multidrug-resistance, which is mainly caused by malfunction of genes, has become a major problem in chemotherapy. To overcome this problem, the simultaneous delivery of genes to cancer cells has been proposed to correct the malfunctioned genes to sensitize the cells to chemotherapeutics. This progress report summarizes key advances in drug and gene delivery with focus on the development of polymers, peptides, liposomes and inorganic materials as nanocarriers for co-delivery of small molecular drugs and macromolecular genes or proteins. In addition, challenges and future perspectives in the design of nanocarriers for the co-delivery of therapeutic drugs and genes are discussed.

Core-shell-corona au-micelle composites with a tunable smart hybrid shell

Micelles having a core of polystyrene and a mixed shell of poly(ethylene glycol) and poly(4-vinylpyridine) were formed through self-assembly of a triblock copolymer poly(ethylene glycol)- block-polystyrene- block-poly(4-vinylpyridine) in acidic water (pH 2). Reducing the HAuCl(4)-treated micelle solution leads to the formation of the Au-micelle composites with a core of polystyrene, a hybrid shell of poly(4-vinylpyridine)/Au/poly(ethylene glycol), and a corona of poly(ethylene glycol). The gold nanoparticles with controlled sizes were anchored to poly(4-vinylpyridine) to form the physically cross-linked hybrid shell. In aqueous solution, the hybrid shell is swollen and the swollen degree is sensitive to the pH condition. Under basic conditions, the channel in the hybrid shells of the composite is produced, which renders the composites a good catalytic activity. In addition, the composites also show good stability, unchanged hydrodynamic diameter, and surface plasmon absorption under different pH conditions.

Solvent effect on the aggregation behavior of rod-coil diblock copolymers

The water-induced aggregation behavior of rod-coil diblock copolymers based on poly(ethylene oxide) (PEO) and poly{(+)-2,5-bis[4'-((S)-2-methylbutoxy)phenyl]styrene} (PMBPS), PEO104-b-PMBPS53, was investigated in the common solvent THF and in the selective solvent dioxane. Before adding water, PEO104-b-PMBPS53 stayed as single polymer chains no matter what conformation the PEO block took (i.e., either the random coil conformation in THF or the compact globule conformation in dioxane). The critical water content ( approximately 6 wt %) at which PEO104-b-PMBPS53 began to aggregate was also similar in both solvents, indicating that PMBPS dominated the aggregation process. However, the size, the size distribution, and the morphology of aggregates in THF/water were quite different from those in dioxane/water. Narrowly distributed spheres with Rh approximately 20 nm were observed in dioxane, whereas in THF, a bimodal distribution peaked at 3 and approximately 300 nm, was observed. The results from 2D wide-angle X-ray diffraction and polarized optical microscopy demonstrated that the PMBPS blocks packed in a parallel pattern upon aggregation in dioxane/water. The anisotropic disclike structures observed in THF/water also indicated the orientation of the PMBPS blocks upon forming aggregates in dilute solution.

Soft patchy nanoparticles from solution-phase self-assembly of binary diblock copolymers

The fabrication of highly ordered, defect-free nanostructures is a key challenge in nanotechnology. Bottom-up fabrication approaches require nanobuilding blocks of precisely defined size and shape. In this work we propose a simple approach to obtain one type of building block--soft patchy nanoparticles--suggested by a series of coarse grain molecular dynamics simulations. A binary mixture of two different diblock copolymers with a common hydrophobic block but sufficiently dissimilar hydrophilic blocks reliably self-assembles into a "patchy" spherical micelle in water, with phase separation of the two hydrophilic blocks on the surface of the micelle core. Subsequent crosslinking of the core to solidify the patchy sphere geometry should allow further hierarchical assembly. Altering the hydrophilic versus hydrophobic composition of each polymer yields a change of morphology from "patchy spheres" to "patchy cylinders". Furthermore, by controlling the interaction strength of the blocks with solvent, the patches can be selectively placed either on the outer surface or inside the core of the micelle. The number and size of the patches are found to be largely controlled by the composition of the binary copolymer mixture.

Preparation of PEO-b-P2VPH+-S2O8(2-) micelles in water and their reversible UCST and redox-responsive behavior

We report here the preparation of PEO-b-P2VPH+-S2O8(2-) micelles and their reversible multi-responsive behavior.