Sustained release properties of arborescent polystyrene-graft-poly(2-vinylpyridine) copolymers

Unimolecular Micelles from Randomly Grafted Arborescent Copolymers with Different Core Branching Densities: Encapsulation of Doxorubicin and In Vitro Release Study

A series of amphiphilic arborescent copolymers of generations G1 and G2 with an arborescent poly(γ-benzyl L-glutamate) (PBG) core and poly(ethylene oxide) (PEO) chain segments in the shell, PBG-g-PEO, were synthesized and evaluated as drug delivery nanocarriers. The PBG building blocks were generated by ring-opening polymerization of γ-benzyl L-glutamic acid N-carboxyanhydride (Glu-NCA) initiated with n-hexylamine. Partial or full deprotection of the benzyl ester groups followed by coupling with PBG chains yielded a comb-branched (arborescent polymer generation zero or G0) PBG structure. Additional cycles of deprotection and grafting provided G1 and G2 arborescent polypeptides. Side chains of poly(ethylene oxide) were then randomly grafted onto the arborescent PBG substrates to produce amphiphilic arborescent copolymers. Control over the branching density of G0PBG was investigated by varying the length and the deprotection level of the linear PBG substrates used in their synthesis. Three G0PBG cores with different branching densities, varying from a compact and dense to a loose and more porous structure, were thus synthesized. These amphiphilic copolymers behaved similar to unimolecular micelles in aqueous solutions, with a unimodal number- and volume-weighted size distributions in dynamic light scattering measurements. It was demonstrated that these biocompatible copolymers can encapsulate hydrophobic drugs such as doxorubicin (DOX) within their hydrophobic core with drug loading efficiencies of 42-65%. Sustained and pH-responsive DOX release was observed from the unimolecular micelles, which suggests that they could be useful as drug nanocarriers for cancer therapy.

DPD Modelling of the Self- and Co-Assembly of Polymers and Polyelectrolytes in Aqueous Media: Impact on Polymer Science

This review article is addressed to a broad community of polymer scientists. We outline and analyse the fundamentals of the dissipative particle dynamics (DPD) simulation method from the point of view of polymer physics and review the articles on polymer systems published in approximately the last two decades, focusing on their impact on macromolecular science. Special attention is devoted to polymer and polyelectrolyte self- and co-assembly and self-organisation and to the problems connected with the implementation of explicit electrostatics in DPD numerical machinery. Critical analysis of the results of a number of successful DPD studies of complex polymer systems published recently documents the importance and suitability of this coarse-grained method for studying polymer systems.

Dendronized Systems for the Delivery of Chemotherapeutics

This chapter reviews the use of dendronized systems as nanocarriers for the delivery of chemotherapeutic drugs. Dendronized systems include dendrimers prepared through convergent methods as well as other systems containing dendrons (e.g., polymers, nanoparticles, liposomes). The preparation of such systems is detailed, followed by the various conjugation techniques used for the transport of chemotherapeutic drugs and their specific delivery to tumor cells. In addition, the ability of dendronized systems to provide passive and active targeting to tumors is discussed. The efficacy of drug delivery using dendronized systems is also illustrated through specific examples of kinetic and biological studies. Finally, the newest trends in conjugation of the most common chemotherapeutics to dendronized systems are described. Overall, this chapter highlights dendronized systems as a way to improve the therapeutic efficiency of drugs for the treatment of cancer. All the recent developments in areas, such as biodegradable dendrimers, modifications to enhance biocompatibility, selectively cleavable drug conjugations, ligand-mediated targeting, and the potential for multifunctional properties, show promises for future advances in cancer therapy.

Effect of Architecture on Micelle Formation and Liquid-Crystalline Ordering in Solutions of Block Copolymers Comprising Flexible and Rigid Blocks: Rod-Coil vs Y-Shaped vs Comblike Copolymers

Micelle formation of amphiphilic block copolymers of various architectures comprising both flexible and rodlike blocks were studied in a selective solvent via dissipative particle dynamics (DPD) simulations. Peculiarities of self-assembly of Y-shaped (insoluble rigid block and two flexible soluble arms) and comblike (soluble flexible backbone with insoluble rigid side chains) copolymers are compared with those of equivalent rod-coil diblock copolymers. We have shown that aggregation of the rigid blocks into the dense core of the micelles is accompanied by their nematic ordering. However, the orientation order parameter and aggregation number of the micelles are strongly dependent on macromolecular architecture. Relatively small micelles of pretty high nematic order parameter, S₂ ≈ 0.5-0.8, are the features of the Y-shaped and rod-coil copolymer micelles. They are characterized by different responses to the solvent quality worsening. The aggregation number of the rod-coil diblock copolymer micelles increases and that of the Y-shaped copolymer micelles decreases at the solvent quality worsening. However, the order parameter grows in both cases, achieving a maximum value for the Y-shaped copolymer micelles. Herewith, the core elongates. On the contrary, comblike copolymers self-assemble into bigger spherical micelles whose core possesses a lower nematic order of the rods, S₂ ≈ 0.3-0.4. The aggregation number is shown to depend on the length of the combs (on the number of repeating elements in the architecture). Possible physical reasons for such behavior of the systems are discussed.

Amphiphilic Arborescent Copolymers and Microgels: From Unimolecular Micelles in a Selective Solvent to the Stable Monolayers of Variable Density and Nanostructure at a Liquid Interface

Amphiphilic arborescent block copolymers of two generations (G2 and G3) and polymer microgels, obtained via cross-linking of diblock copolymers, were studied in a selective solvent and at liquid interface via dissipative particle dynamics (DPD) simulations. Depending on the primary structure, single arborescent macromolecules in selective solvent can have both core-corona and multicore structures. Self-assembly of the G2, G3, and microgels in the selective solvent is compared with equivalent linear diblock copolymers. The latter self-assemble into spherical micelles of large enough aggregation number. On the contrary, stability of unimolecular micelles is a feature of the arborescent copolymers and microgels, whereas their ability to aggregate is very low. Adsorption of the single molecules at liquid (oil-water) interface leads to their flattening and segregation of the amphiphilic blocks: hydrophilic and hydrophobic blocks are exposed toward water and oil, respectively. Depending on the character of interactions between monomer units, which can be controlled by temperature or solvent(s) quality, Janus, patchy, and nanosegregated structures can be formed within the macromolecules. Their self-assembly at the interface can lead to the formation of both loose and dense monolayers, which can be homogeneous and nanostructured. The pretty fast adsorption kinetics of G2 macromolecules make them efficient stabilizers of emulsions.

Structural Implications on the Properties of Self-Assembling Supramolecular Hosts for Fluorescent Guests

Nine amphiphilic macromolecules with decyl and oligo(ethylene glycol) side chains, randomly distributed along a common poly(methacrylate) backbone, were synthesized from the radical copolymerization of appropriate methacrylate monomers. The resulting amphiphilic constructs differ in (1) the ratio between their hydrophobic and hydrophilic components, (2) the length of their oligo(ethylene glycol) chains, and/or (3) the molecular weight. When the ratio between hydrophobic and hydrophilic segments is comprised between 6:1 and 1:2, the macromolecules assemble spontaneously into particles with nanoscaled dimensions in neutral buffer and capture hydrophobic borondipyrromethene chromophores in their interior. However, the critical concentration required for the assembly of these supramolecular hosts as well as their hydrodynamic diameter, supramolecular weight, and number of constituent macromolecular building blocks all vary monotonically with the ratio between hydrophobic and hydrophilic components. Specifically, the critical concentration decreases and the other three parameters increase as the relative hydrophobic content raises. Furthermore, an increase in the relative hydrophobic content also discourages interchromophoric interactions between entrapped guests in both ground and excited states as well as delays access of potential quenchers. In fact, these observations demonstrate that the hydrophobic components must be in excess over their hydrophilic counterparts for optimal supramolecular hosts to assemble. Indeed, a ratio of 6:1 between the numbers of decyl and oligo(ethylene glycol) side chains appears to be ideal for this particular structural design. Under these conditions, supramolecular hosts assemble spontaneously even at relatively low polymer concentrations and their fluorescent guests do not escape into the bulk aqueous solution, despite the reversibility of the noncovalent interactions holding the supramolecular container together. Thus, these systematic investigations provide invaluable structural guidelines to design self-assembling supramolecular hosts with optimal composition for the effective encapsulation of fluorescent guests and can lead to ideal delivery vehicles for the transport of imaging probes to target locations in biological samples.

Unimolecular Micelles from Layered Amphiphilic Dendrimer-Like Block Copolymers

In this report, we synthesized layered amphiphilic dendrimer-like block copolymers containing a polystyrene core and poly(p-tert-butoxystyrene)/poly(p-hydroxylstyrene) shell (coded G4-PtBOS/G4-PHOS). The synthetic method is easy involving anionic polymerization, epoxidation, ring-opening reaction and hydrolysis reaction. The hydrolyzed G4-PtBOS was soluble in alkaline water and behaved as unimolecular micelle, as demonstrated by the results of DLS, cryo- and normal TEM, and pyrene entrapping experiment. The stability of the unimolecular micelles was investigated via ζ-potential measurements.

Synthesis in living cells with the assistance of supramolecular nanocarriers

Supramolecular nanocarriers transport complementary reactants inside living cells in consecutive internalization steps to allow their reaction exclusively in the intracellular space with the formation of a fluorescent product.

Energy-Transfer Schemes To Probe Fluorescent Nanocarriers and Their Emissive Cargo

A strategy to probe supramolecular nanocarriers and their cargo in the intracellular space was developed on the basis of fluorescence measurements and energy transfer. It relies on the covalent attachment of an energy donor, or acceptor, to the macromolecular backbone of amphiphilic polymers and the noncovalent encapsulation of a complementary acceptor, or donor, in the resulting micelles. In aqueous environments, these macromolecules self-assemble into nanostructured constructs and bring the complementary chromophores in close proximity to enable efficient energy transfer. These supramolecular assemblies travel from the extracellular to the intracellular space and retain their integrity in the process. Indeed, donors and acceptors remain close to each other after internalization, and excitation of the former chromophores translates into significant intracellular emission from the latter. Furthermore, these supramolecular assemblies exchange their components with fast kinetics in aqueous dispersions because of the reversible character of the noncovalent contacts holding them together. As a result, micelles incorporating exclusively the donors and nanocarriers containing only the acceptors scramble their chromophoric building blocks, upon mixing, to allow the transfer of energy. These dynamic processes can be reproduced in the intracellular environment with the sequential incubation of cells with the two sets of complementary nanostructured assemblies. Thus, these operating principles and choice of supramolecular synthons are particularly valuable to monitor self-assembling nanocarriers and their cargo inside living cells and can facilitate the elucidation of the behavior of these promising delivery vehicles in a diversity of biological specimens.

Supramolecular nanoreactors for intracellular singlet-oxygen sensitization

An amphiphilic polymer with multiple decyl and oligo(ethylene glycol) chains attached to a common poly(methacrylate) backbone assembles into nanoscaled particles in aqueous environments. Hydrophobic anthracene and borondipyrromethene (BODIPY) chromophores can be co-encapsulated within the self-assembling nanoparticles and transported across hydrophilic media. The reversible character of the noncovalent bonds, holding the supramolecular containers together, permits the exchange of their components with fast kinetics in aqueous solution. Incubation of cervical cancer (HeLA) cells with a mixture of two sets of nanoparticles, pre-loaded independently with anthracene or BODIPY chromophores, results in guest scrambling first and then transport of co-entrapped species to the intracellular space. Alternatively, incubation of cells with the two sets of nanocarriers in consecutive steps permits the sequential transport of the anthracene and BODIPY chromophores across the plasma membrane and only then allows their co-encapsulation within the same supramolecular containers. Both mechanisms position the two sets of chromophores with complementary spectral overlap in close proximity to enable the efficient transfer of energy intracellularly from the anthracene donors to the BODIPY acceptors. In the presence of iodine substituents on the BODIPY platform, intersystem crossing follows energy transfer. The resulting triplet state can transfer energy further to molecular oxygen with the concomitant production of singlet oxygen to induce cell mortality. Furthermore, the donor can be excited with two near-infrared photons simultaneously to permit the photoinduced generation of singlet oxygen intracellularly under illumination conditions compatible with applications in vivo. Thus, these supramolecular strategies to control the excitation dynamics of multichromophoric assemblies in the intracellular environment can evolve into valuable protocols for photodynamic therapy.

Flow-directed loading of block copolymer micelles with hydrophobic probes in a gas-liquid microreactor

We investigate the loading efficiencies of two chemically distinct hydrophobic fluorescent probes, pyrene and naphthalene, for self-assembly and loading of polystyrene-block-poly(acrylic acid) (PS-b-PAA) micelles in gas-liquid segmented microfluidic reactors under different chemical and flow conditions. On-chip loading efficiencies are compared to values obtained via off-chip dropwise water addition to a solution of copolymer and probe. On-chip, probe loading efficiencies depend strongly on the chemical probe, initial solvent, water content, and flow rate. For pyrene and naphthalene probes, maximum on-chip loading efficiencies of 73 ± 6% and 11 ± 3%, respectively, are obtained, in both cases using the more polar solvent (DMF), an intermediate water content (2 wt % above critical), and a low flow rate (∼5 μL/min); these values are compared to 81 ± 6% and 48 ± 2%, respectively, for off-chip loading. On-chip loading shows a significant improvement over the off-chip process where shear-induced formation of smaller micelles enables increased encapsulation of probe. As well, we show that on-chip loading allows off-chip release kinetics to be controlled via flow rate: compared to vehicles produced at ∼5 μL/min, pyrene release kinetics from vehicles produced at ∼50 μL/min showed a longer initial period of burst release, followed by slow release over a longer total period. These results demonstrate the necessity to match probes, solvents, and running conditions to achieve effective loading, which is essential information for further developing these on-chip platforms for manufacturing drug delivery formulations.

Self-assembled particles of N-phthaloylchitosan-g-polycaprolactone molecular bottle brushes as carriers for controlled release of indometacin

A series of amphiphilic N-phthaloylchitosan-g-polycaprolactone molecular bottle brushes were prepared by "graft onto" method. The narrow distribution of polycaprolactone macromonomers ensures that the molecular bottle brushes can self-assemble into highly monodisperse particles, which have the ability to get a high loading efficiency of the hydrophobic drug, indometacin (INN). Searching for the effective drug loading ratio, three parameters such as polycaprolactone chain length, the grafting content and concentration of the molecular bottle brushes were tested to entrap INN. These encapsulated drug particles show sustained release of the encapsulated INN, of which 91.7% was released in 22 h at 37 degrees C in phosphate buffered saline. The self-assembled particles of the molecular bottle brushes as carriers for INN can effectively prevent the drug from releasing quickly and prolong the release time, which is a promising candidate for potential clinical applications.