Supramolecular assemblies of amphiphilic homopolymers

Thiol-epoxy 'click' chemistry: a focus on molecular attributes in the context of polymer chemistry

Base-catalyzed ring-opening reaction of epoxides with the thiol nucleophiles is useful in the preparation and post-polymerization modification of synthetic polymers. Due to its many beneficial characteristics, this process is referred to as the thiol-epoxy 'click' reaction. In this article, our aim is to discuss the fundamental attributes of this process by tracing our own steps in the field. We initially address the aspects of efficiency, regio-selectivity, stoichiometry, and reaction conditions with the help of linear, hyperbranched, graft, dendritic, and cross-linked poly(β-hydroxy thioether)s. A special emphasis is placed on hydrogel synthesis and photopolymerization on surfaces. Subsequently, quenching of the alkoxide anion is considered which is a critical step in the formation of the β-hydroxy thioether linkage upon completion of reaction. The amenability of further reaction on the hydroxy and thioether groups through esterification and sulfur alkylation is then discussed. Initially, post-gelation/fabrication modification of sulfide linkages is considered to obtain cationic sulfonium hydrogels and zwitterionic photopatterned networks with antibacterial and antibiofouling properties, respectively. A post-synthesis functionalization strategy is then described to access same centered and segregated main-chain poly(β-hydroxy sulfonium)s as potent antibacterial materials. In side-chain polysulfides, the sequential post-synthesis modifications involving poly(glycidyl methacrylate) scaffolds can lead to the formation of amphiphilic homopolymers. The application of such materials is discussed in the arena of siRNA delivery. Finally, concerns relating to the formation of disulfide defects and open research goals such as study of the orthogonality of the reaction are addressed.

Self-assembly of hydrophobic-amphiphilic diblock copolymers in solution

Thermoresponsive polymers are usually characterized by a locally amphiphilic chain structure and their self-assembly in solution is controlled, in particular, by the surface activity of the monomer units or side chains. We theoretically study the condensed state of a single diblock copolymer molecule consisting of a hydrophobic block and amphiphilic block with hydrophobic groups in the backbone and pendant polar groups. The equilibrium parameters of the polymer globules of different shapes are determined using the mean-field approach to determine the most favorable structure. Morphological diagrams of condensed macromolecules are presented depending on the chain length, amphiphilic block fraction, interaction parameters, and pendant volume and length. The diagrams are compared with those of a copolymer molecule with the same fraction of amphiphilic monomer units which are regularly distributed along the chain. The diblock copolymer molecule is found to form a single spherical or flattened particle, with the core from the hydrophobic block, or a granular micelle consisting of spherical or nearly spherical particles, in agreement with the experimental data in the literature. The optimal chain parameters for self-assembly into a stable single core-shell particle are predicted.

Hyperbranched vs. linear poly(disulfide) for intracellular drug delivery

This communication reports comparative studies between amphiphilic hyperbranched and linear poly(disulfide) with regard to their aggregation and glutathione-responsive intracellular drug delivery.

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...

Preparation and Characterization of Palladium Derivate-Loaded Micelle Formulation in Vitro as an Innovative Therapy Option against Non-Small Cell Lung Cancer Cells

Nanoparticles have been used in cancer treatments to target tumor and reduce side effects. In this study, we aimed to increase the effectiveness of palladium(II) complex [PdCl(terpy)](sac) ⋅ 2H₂ O, which previously showed anticancer potential, by preparing the nanoparticle formulation. An inhalable micellar dispersion containing a palladium(II) complex (PdNP) was prepared and its physicochemical characteristics were evaluated using in vitro tests. Morphology, size and surface charges of particle and loading/encapsulation efficiency of PdNP were analyzed by scanning electron microscopy, zeta sizer and inductively coupled plasma mass spectrometry while aerosol properties of PdNP were measured by the next generation impactor. A549 and H1299 non-small lung cancer cell types were used for cytotoxicity using SRB and ATP assays. Fluorescent staining and M30 antigen assay were carried out for cell death evaluation. Apoptosis was confirmed by flow cytometry analyses. SEM, particle size, and zeta potential results showed the particles have inhalable properties. The amount of the palladium(II) complex loaded into the particles was quantified which indicated high encapsulation efficiencies (97 %). The micellar dispersion expected to reach the alveolar region and the brachial region was determined 35 % and 47 %, respectively. PdNP showed an anti-growth effect by increasing reactive oxygen species that is followed by the induction of mitochondria-dependent apoptosis that is evidenced by pyknotic nuclei and M30 antigen level increments and disruption of polarization of membrane in mitochondria (Δψm). The results show that PdNP might be a promising inhalable novel complex to be used in non-small cell lung cancer, which warrants animal studies in further.

Self-assembly of protein-polymer conjugates for drug delivery

Protein-polymer conjugates are a class of molecules that combine the stability of polymers with the diversity, specificity, and functionality of biomolecules. These bioconjugates can result in hybrid materials that display properties not found in their individual components and can be particularly relevant for drug delivery applications. Engineering amphiphilicity into these bioconjugate materials can lead to phase separation and the assembly of high-order structures. The assembly, termed self-assembly, of these hierarchical structures entails multiple levels of organization: at each level, new properties emerge, which are, in turn, influenced by lower levels. Here, we provide a critical review of protein-polymer conjugate self-assembly and how these materials can be used for therapeutic applications and drug delivery. In addition, we discuss central bioconjugate design questions and propose future perspectives for the field of protein-polymer conjugate self-assembly.

Dimension control on self-assembly of a crystalline core-forming polypeptoid block copolymer: 1D nanofibers versus 2D nanosheets

The balance between the crystallization and solubility of the block copolymer dominates the nanostructures.

Self-assembly behavior of oligo(ethylene glycol) substituted polycaprolactone homopolymers

In this work, non-ionic amphiphilic oligo(ethylene glycol)-substituted polycaprolactone homopolymers readily self-assembled to form micelles in a polar environment, which allowed the encapsulation of a hydrophobic molecule.

Multichain adsorption at fluid interfaces: Amphiphilic homopolymers vs copolymers

HYPOTHESIS

At selective liquid-liquid interface, amphiphilic homopolymers, having groups with different affinity for the liquids in each monomer unit, would demonstrate higher occupation of the interfacial layer than copolymers with various distributions of groups and be advantageous as interface stabilizers.

EXPERIMENTS

By means of Langevin dynamics computer simulation, conformations of multiple chains of amphiphilic macromolecules adsorbed at the liquid-liquid interface were studied. Monomer units having different affinity for the liquids were distributed variously along the polymer chains. Homopolymers, amphiphilic at the level of an individual monomer unit, and copolymers with random, altermating and multiblock distribution of groups were considered. The surface coverage, structure of the layer, and spatial distribution of monomer units were investigated depending on the polymer concentration.

FINDINGS

Compared to copolymers with random, alternating and multiblock distributions of the groups, the interfacial layer concentration of amphiphilic homopolymer is about 1.5 times higher, the adsorbed layer is remarkably thinner, has membrane-like structure and is asymmetric with respect to interface boundary. Also, the adsorbed amphiphilic homopolymers form fewer loops and tails, most located on one side of the interface. This combination of properties is promising for practical application in modern self-assembling molecular devices.

Tuning Size and Morphology of mPEG-b-p(HPMA-Bz) Copolymer Self-Assemblies Using Microfluidics

The careful design of nanoparticles, in terms of size and morphology, is of great importance to developing effective drug delivery systems. The ability to precisely tailor nanoparticles in size and morphology during polymer self-assembly was therefore investigated. Four poly(ethylene glycol)-b-poly(N-2-benzoyloxypropyl methacrylamide) mPEG-b-p(HPMA-Bz) block copolymers with a fixed hydrophilic block of mPEG 5 kDa and a varying molecular weight of the hydrophobic p(HPMA-Bz) block (A: 17.1, B: 10.0, C: 5.2 and D: 2.7 kDa) were self-assembled into nanoparticles by nanoprecipitation under well-defined flow conditions, using microfluidics, at different concentrations. The nanoparticles from polymer A, increased in size from 55 to 90 nm using lower polymer concentrations and slower flow rates and even polymer vesicles were formed along with micelles. Similarly, nanoparticles from polymer D increased in size from 35 to 70 nm at slower flow rates and also formed vesicles along with micelles, regardless of the used concentration. Differently, polymers B and C mainly self-assembled into micelles at the different applied flow rates with negligible size difference. In conclusion, this study demonstrates that the self-assembly of mPEG-b-p(HPMA-Bz) block copolymers can be easily tailored in size and morphology using microfluidics and is therefore an attractive option for further scaled-up production activities.

Polyselenonium salts: synthesis through sequential selenium-epoxy 'click' chemistry and Se-alkylation

With the help of amphiphilic homopolymers, this work explores three new avenues in polymer chemistry: (i) the 'click' nature of the selenium-epoxy reaction, (ii) alkylation of the seleno-ethers as a means to prepare cationic polyelectrolytes, and (iii) the antibacterial activity of polyselenonium salts.

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.

Guanidinylated Amphiphilic Polycarbonates with Enhanced Antimicrobial Activity by Extending the Length of the Spacer Arm and Micelle Self-Assembly

Nine guanidinylated amphiphilic polycarbonates are rationally designed and synthesized. Each polymer has the same biodegradable backbone but different side groups. The influence of the hydrophobic/hydrophilic effect on antimicrobial activities and cytotoxicity is systematically investigated. The results verify that tuning the length of the spacer arm between the cationic guanidine group and the polycarbonate backbone is an efficient design strategy to alter the hydrophobic/hydrophilic balance without changing the cationic charge density. A spacer arm of six methylene units (CH₂ )₆ shows the best antimicrobial activity (minimum inhibitory concentration, MIC = 40 µg mL^-1 against Escherichia coli, MIC = 20 µg mL^-1 against Staphylococcus aureus, MIC = 40 µg mL^-1 against Candida albicans) with low hemolytic activity (HC₅₀ > 2560 µg mL^-1 ). Furthermore, the guanidinylated polycarbonates exhibit the ability to self-assemble and present micelle-like nanostructure due to their intrinsic amphiphilic macromolecular structure. Transmission electron microscopy and dynamic light scattering measurements confirm polymer micelle formation in aqueous solution with sizes ranging from 82 to 288 nm.

Unusual Structures of Interpolyelectrolyte Complexes: Vesicles and Perforated Vesicles

By means of computer simulation and analytical theory, we first demonstrated that the interpolyelectrolyte complexes in dilute solution can spontaneously form hollow spherical particles with thin continuous shells (vesicles) or with porous shells (perforated vesicles) if the polyions forming the complex differ in their affinity for the solvent. The solvent was considered good for the nonionic groups of one macroion and its quality was varied for the nonionic groups of the other macroion. It was found that if the electrostatic interactions are weak compared to the attraction induced by the hydrophobicity of the monomer units, the complex in poor solvent tends to form "dense core-loose shell" structures of different shapes. The strong electrostatic interactions favor the formation of the layered, the hollow, and the filled structured morphologies with the strongly segregated macroions. Vesicles with perforated walls were distinguished as the intermediate between the vesicular and the structured solid morphologies. The order parameter based on the spherical harmonics expansion was introduced to calculate the pore distribution in the perforated vesicles depending on the solvent quality. The conditions of the core-shell and hollow vesicular-like morphologies formation were determined theoretically via the calculations of their free energy. The results of the simulation and theoretical approaches are in good agreement.

Tumor microenvironment-activated self-recognizing nanodrug through directly tailored assembly of small-molecules for targeted synergistic chemotherapy

Carrier-free nanodrug via small-molecule assembly is a promising alternative strategy for tumor therapy. Thus, developing a self-recognizing carrier-free nanodrug without introduction of foreign ligand is very attractive to meet both targeting and therapeutic requirements while reducing structural complexity. Here we fabricated a tumor microenvironment-activated self-targeting nanodrug, via co-assembly of hydroxycamptothecin (HCPT) and bi-functional methotrexate (MTX, not only has antitumor effect but also shows innate affinity towards folate receptors) followed by surface covering through acidity-responsive polyethylene glycol (PEG). Notably, the morphology and size of MTX-HCPT nanodrug could be tuned by varying the drug-to-drug ratio and assembly time. The PEG shell of our nanodrug could be detached in response to acidic tumor microenvironment, and then MTX could be exposed for self-targeting to enhance tumor cell uptake. Subsequently, the shell-detached nanodrug could be dissociated in relatively stronger acidic lysosomal environment, resulting in burst release of both drugs. Further in vitro and in vivo studies demonstrated that our nanodrug showed a ~2.98-fold increase in cancer cell uptake, a ~1.25-fold increase in drug accumulation at tumor site, a significantly lower CI₅₀ value of ~0.3, a ~27.3% improvement in tumor inhibition comparing with the corresponding non-responsive nanodrug. Taken together, the here reported tumor microenvironment-activated self-recognizing nanodrug might be an extremely promising strategy for synergistically enhancing chemotherapy efficiency with minimized side effects.

Hierarchical self-assembled nanostructures of lactone-derived thiobarbiturate homopolymers for stimuli-responsive delivery applications

Hierarchical self-assembled nanostructures of lactone-derived thiobarbiturate homopolymers for stimuli-responsive delivery applications are shown.

Thermoresponsive Poly(ß-hydroxyl amine)s: Synthesis of a New Stimuli Responsive Amphiphilic Homopolymer Family through Amine-Epoxy 'Click' Polymerization

A new synthesis of amphiphilic homopolymers is described. In this synthesis, commercially available and inexpensive primary amines and di-epoxide molecules are utilized as AA- and BB-types of monomers in an amine-epoxy ‘click’ polymerization process. This process can be carried out in water and at room temperature. It does not require a catalyst or inert conditions and forms no byproducts. Therefore, the polymer synthesis can be carried out in open-air and bench-top conditions and a post-synthesis purification step is not required. The modularity of the synthesis, on the other hand, allows for facile structural modulation and tuning of the thermally triggered aggregation process in the temperature range of 7 to 91 °C. Finally, the underlying principles can be translated from linear architectures to polymer networks (hydrogels).

Lamellae and parking garage structures in amphiphilic homopolymer brushes with different grafting densities

This article is devoted to the study of polymer layers of amphiphilic homopolymers tightly grafted to a flat surface at the nodes of a square lattice. It was shown that, due to the amphiphilicity of monomer units containing groups with different affinities, in a selective solvent, such layers form lamellae perpendicular to the grafting surface. The period of the lamellae depends on the grafting density and the quality of the solvent. The results are presented in the form of a state diagram in variables "the energy of attraction of the side groups" (effective solvent quality) and "the distance between the grafting points" (inversely proportional to the square root of the grafting density). The diagram contains the regions of stability of lamellae with significantly different periods, and a transitional area with a parking garage structure. The diagram is constructed by calculating the layer-by-layer structure factor and the angle of inclination of the lamellae in the slice. The calculations were performed for different sizes of the simulation box, and the most commensurate size was determined by a special procedure for each grafting density. The results may be interesting not only to specialists in polymer science but also to all those who investigate the processes of self-organization and rearrangement in dense systems.

Sequential Nucleophilic "Click" Reactions for Functional Amphiphilic Homopolymers

Amphiphilic homopolymers with high densities of functional groups are synthetically challenging. Thiol-yne nucleophilic click reactions have been investigated to introduce multiple functional groups in polymers with high density. An electron deficient alkyne group bearing methacrylate monomer was polymerized using reversible addition-fragmentation chain-transfer (RAFT) polymerization. Subsequently, the electron deficient alkyne group on polymer side chain was readily reacted with a thiol reagent using triethylamine (TEA) as the organocatalyst. This reaction was found to be very efficient under mild conditions. The resultant homopolymer bearing thiol vinyl ether functional groups could perform a second thiol addition with a stronger base, such as triazabicyclodecene (TBD), to prepare multifunctional homopolymers. This stepwise addition process was monitored by 1H NMR as well as gel permeation chromatography. The fidelity of this method was demonstrated by attaching four different functionalities, including both hydrophobic and hydrophilic moieties. Furthermore, these dual functionalized polymers bearing dithio-acetal groups are sensitive to reactive oxygen species (ROS), which compromises the host-guest properties of the assembly in response to this stimulus. The ROS responsive polymers reported here may have potential use in therapeutic delivery.

Effect of Formulation and Processing Parameters on the Size of mPEG- b-p(HPMA-Bz) Polymeric Micelles

Micelles composed of block copolymers of poly(ethylene glycol)- b-poly( N-2-benzoyloxypropyl methacrylamide) (mPEG- b-p(HPMA-Bz)) have shown great promise as drug-delivery carriers due to their excellent stability and high loading capacity. In the present study, parameters influencing micelle size were investigated to tailor sizes in the range of 25-100 nm. Micelles were prepared by a nanoprecipitation method, and their size was modulated by the block copolymer properties such as molecular weight, their hydrophilic-to-hydrophobic ratio, homopolymer content, as well as formulation and processing parameters. It was shown that the micelles have a core-shell structure using a combination of dynamic light scattering and transmission electron microscopy analysis. By varying the degree of polymerization of the hydrophobic block ( N_B) between 68 and 10, at a fixed hydrophilic block mPEG_5k ( N_A = 114), it was shown that the hydrophobic core of the micelle was collapsed following the power law of ( N_B × N_agg)^1/3. Further, the calculated brush height was similar for all the micelles examined (10 nm), indicating that crew-cut micelles were made. Both addition of homopolymer and preparation of micelles at lower concentrations or lower rates of addition of the organic solvent to the aqueous phase increased the size of micelles due to partitioning of the hydrophobic homopolymer chains to the core of the micelles and lower nucleation rates, respectively. Furthermore, it was shown that by using different solvents, the size of the micelles substantially changed. The use of acetone, acetonitrile, ethanol, tetrahydrofuran, and dioxane resulted in micelles in the size range of 45-60 nm after removal of the organic solvents. The use of dimethylformamide and dimethylsulfoxide led to markedly larger sizes of 75 and 180 nm, respectively. In conclusion, the results show that by modulating polymer properties and processing conditions, micelles with tailorable sizes can be obtained.

Effect of the Surface Hydrophobicity Degree on the In Vitro Release of Polar and Non-Polar Drugs from Polyelectrolyte Matrix Tablets

This work is the continuation of a series of studies focused on establishing the relationship between the surface thermodynamic properties of polyelectrolyte matrix tablets and drug release mechanisms. In this case, two model drugs with different polarity features, such as carbamazepine (non-polar) and metoprolol succinate (polar) were used in combination with polymeric material hydroxypropyl-methyl cellulose (HPMC) and two polyelectrolytes derived from maleic anhydride corresponding to the sodium salts of poly(maleic acid-alt-ethylene) and poly(maleic acid-alt-octadecene) named PAM-0Na and PAM-18Na, respectively. The polymers were obtained and characterized as reported previously. Surface studies were performed by the sessile drop method, whilst the surface free energy was determined through Owens, Wendt, Rable and Kaeble (OWRK) semi-empirical model. By contrast, the drug release studies were performed by in vitro dissolution tests, where data were analyzed through dissolution efficiency. The results showed that, depending on the drug polarity, type and polymer proportion, surface properties and drug release processes are significantly affected.

Solvent switchable nanostructures and the function of a π-amphiphile

This manuscript reports solvent tunable functional nano-assemblies of an unsymmetrical bola-shaped π-amphiphile (NDI-PY) which consists of a hydrophobic naphthalene-diimide (NDI) chromophore connected to a non-ionic hydrophilic wedge and a pyridine group at its two opposite arms. Importantly, it contains a hydrazide group located at the hydrophobic domain between the NDI-chromophore and the hydrophilic-wedge to drive the supramolecular assembly by directional H-bonding. NDI-PY exhibits spontaneous assembly in water as well as in a highly non-polar solvent like tetra-chloroethylene (TCE) by the synergistic effect of H-bonding and π-stacking interaction. Spectroscopy studies reveal almost identical self-assembly features in water and TCE with critical aggregation concentrations in the range of 0.3 mM, which matches the values obtained from the isothermal calorimetry (ITC) dilution experiment. Differential scanning calorimetry (DSC) experiments reveal a single endothermic peak at 31 °C (ΔH = -12.3 kJ mol^-1) and 40 °C (ΔH = -5.35 kJ mol^-1) for water and TCE, respectively, indicating marginally higher thermal stability in TCE, which is consistent with the FT-IR data, suggesting stronger H-bonding in TCE. Although the molecular assembly features appear to be similar, NDI-PY produces distinctly different mesoscopic structures in water and TCE. In water, it forms vesicles (D_h = 150-180 nm) with the pyridine groups displayed at the outer surface, while in TCE it generates a transparent gel (CGC = 8.0 mM) with a nanotubular (width ∼50 nm, wall thickness ∼10 nm) morphology. Powder X-ray diffraction studies show clearly different packing structures; in water a single sharp peak at the low angle (d = 19.3 Å, a little shorter than the extended length of the molecule) suggests the formation of a monolayer membrane, while in TCE several sharp peaks appear with the d values maintaining a ratio of 1 : 1/√3 : 1/2 : 1/√7 : 1/3 : 1/√12, indicating the formation of a 2D hexagonal lattice. Photoconductivity measurements reveal moderate electronic conduction in both cases. However, it shows a remarkable enhancement of the life time of the charge-carriers for the nanotubular structure compared to the vesicular morphology. On the other hand, the vesicles in water display antimicrobial activity against Gram-positive S. aureus with a highly promising MIC_LB value of 29.4 μg mL^-1. In contrast, it does not lyse human red blood cells even at as high a concentration as 2.5 mg mL^-1 (HC₅₀ > 2.5 mg mL^-1), implying high selectivity of the NDI-PY vesicles towards bacterial cells over mammalian cells. Display of the pyridine groups at the outer surface of the membrane enables molecular recognition by complementary H-bonding with a carboxylic acid group and thereby facilitates uptake of the attached pyrene chromophores in the NDI-membrane by charge-transfer interaction between the NDI acceptor and the pyrene donor. In fact a Job's plot experiment reveals maximum uptake at a 1 : 1 ratio of the NDI-PY and the pyrene guest, indicating all the pyridine groups are accessible at the vesicular surface.

Improving anti-melanoma effect of curcumin by biodegradable nanoparticles

Melanoma is known as the most common malignant cutaneous cancer. Curcumin, a natural component, has been shown to have various activities such as anti-oxidant, anti-septic, anti-inflammatory, anti-biotic, anti-amyloid and anti-thrombosis. However, there is a greatest obstacle in the administration of curcumin due to its hydrophobicity and low oral bioavailability. In this study, we formulated curcumin-loaded MPEG-PLA (Curcumin/MPEG-PLA) micelles aiming to improve its solubility in aqueous solution and investigated anti-tumor effect on melanoma in vitro and in vivo. The spherical curcumin/MPEG-PLA micelles were completely dispersed in normal saline and could release curcumin in a sustained manner in vitro. In addition, we demonstrated that curcumin/MPEG-PLA micelles had stronger cytotoxicity and induced a higher percentage of apoptosis in B16 and A375 cancer cells than free curcumin in vitro. The immunohistochemical study revealed that curcumin/MPEG-PLA micelles induced more melanoma cell apoptosis than free curcumin and inhibited neovascularization in tumor tissues. In conclusion, the curcumin/MPEG-PLA micelles have potential clinical application for melanoma.

Programmable Nanoassemblies from Non-Assembling Homopolymers Using Ad Hoc Electrostatic Interactions

Robust nanostructures were obtained from polymers that otherwise do not assemble by using a novel approach based on electrostatic self-assembly. The essence of this strategy involves the use of divalent counterions to temporarily perturb the packing features of the ionic groups in a homopolymer, which results in a vesicle-like structure that is captured in situ through a simple crosslinking reaction. The fidelity of the assembly has been tested for molecular transport across the nanomembrane, both for the molecules encapsulated in the lumen and for those trapped in the membrane itself. The membranes are addressable for robust multifunctionalization of their surfaces and for tunable transmembrane molecular transport.

Triple-stimuli-responsive ferrocene-containing homopolymers by RAFT polymerization

This article presents a new type of well-defined ferrocene-containing homopolymer obtained from RAFT polymerization, showing pH/CO₂ and redox responsiveness.

Modular and rapid access to amphiphilic homopolymers via successive chemoselective post-polymerization modification

A modular and simplified post-polymerization modification strategy is developed for the synthesis of amphiphilic homopolymers.

Aptamer-Mediated Targeted Delivery of Therapeutics: An Update

The selective delivery of drugs in a cell- or tissue-specific manner represents the main challenge for medical research; in order to reduce the occurrence of unwanted off-target effects. In this regard, nucleic acid aptamers have emerged as an attractive class of carrier molecules due to their ability to bind with high affinity to specific ligands; their high chemical flexibility; as well as tissue penetration capability. To date, different aptamer-drug systems and aptamer-nanoparticles systems, in which nanoparticles function together with aptamers for the targeted delivery, have been successfully developed for a wide range of therapeutics, including toxins; peptides; chemotherapeutics and oligonucleotides. Therefore, aptamer-mediated drug delivery represents a powerful tool for the safe and effective treatment of different human pathologies, including cancer; neurological diseases; immunological diseases and so on. In this review, we will summarize recent progress in the field of aptamer-mediated drug delivery and we will discuss the advantages, the achieved objectives and the challenges to be still addressed in the near future, in order to improve the effectiveness of therapies.

Cooperation of Amphiphilicity and Crystallization for Regulating the Self-Assembly of Poly(ethylene glycol)-block-poly(lactic acid) Copolymers

Tuning the amphiphilicity of block copolymers has been extensively exploited to manipulate the morphological transition of aggregates. The introduction of crystallizable moieties into the amphiphilic copolymers also offers increasing possibilities for regulating self-assembled structures. In this work, we demonstrate a detailed investigation of the self-assembly behavior of amphiphilic poly(ethylene glycol)-block-poly(l-lactic acid) (PEG-b-PLLA) diblock copolymers with the assistance of a common solvent in aqueous solution. With a given length of the PEG block, the molecular weight of the PLA block has great effect on the morphologies of self-assembled nanoaggregates as a result of varying molecular amphiphilicity and polymer crystallization. Common solvents including N,N-dimethylformamide, dioxane, and tetrahydrofuran involved in the early stage of self-assembly led to the change in chain configuration, which further influences the self-assembly of block copolymers. This study expanded the scope of PLA-based copolymers and proposed a possible mechanism of the sphere-to-lozenge and platelet-to-cylinder morphological transitions.

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.