Light-Responsive Self-Assembled Materials by Supramolecular Post-Functionalization via Hydrogen Bonding of Amphiphilic Block Copolymers

Fast and Reversible Photoresponsive Self-Assembly Behavior of Rosin-Based Amphiphilic Polymers

Designing stimulus-responsive amphiphilic polymers with a fast photoresponsive self-assembly behavior remains a challenge. Two series of rosin-terminated and azobenzene-terminated amphiphilic polymers (PAM_n and PMA_n) with fast and reversible photoresponsive properties were prepared using rosin-based azobenzene groups and polyethylene glycol, respectively. Under 5-10 s of UV irradiation, the polymers showed trans-to-cis isomerization and reached a photosteady state. For the PAM_n polymer, the absorbance of the absorption peak at 325 nm recovered to more than 95% of the initial value under visible light for 5-10 s, whereas that of the PMA_n polymer recovered completely. Notably, the PAM_n and PMA_n polymers initially self-assembled to vesicles or spherical micelles, and various morphological changes were achieved by manipulating UV irradiation time, with the initial morphology again recovered under dark conditions or visible-light irradiation. Remarkably, vesicles of the PAM₃₄ and PMA₃₄ polymers presented an intermediate open-vesicle state before being completely deformed under UV irradiation because of the existence of a π-π interaction. Finally, the ability of PAM₃₄ and PMA₃₄ polymer vesicles to perform the controlled release and reversible loading of a fluorescent probe was evaluated.

Microfluidic Synthesis of Block Copolymer Micelles: Application as Drug nanocarriers and as Photothermal Transductors When Loading Pd Nanosheets

The synthesis of polymeric nanoparticles from a block copolymer based on poly(ethylene glycol) and a polymethacrylate containing the nucleobase analogue 2,6-diacylaminopyridine has been optimized by microfluidics to obtain homogeneous spherical micelles. Loading and delivery properties have been studied using naproxen as a model. The incorporation of a Pd precursor in the polymer organic solution fed into the micromixer allows the preparation of Pd(II) precursor-polymer hybrid systems, and the subsequent reduction with CO lead to the in-situ synthesis of Pd nanosheets inside of the hydrophobic core of the polymeric micelles. This methodology is highly efficient to yield all polymeric nanoparticles loaded with Pd nanosheets as detected by electron microscopy and energy-dispersive X-ray spectroscopy. The cell viability of these Pd nanosheets-containing polymeric nanoparticles has been evaluated using five cell lines, showing a high cytocompatibility at the tested concentrations without detrimental effects in cell membrane and nuclei. Furthermore, the use of these hybrid polymeric nanoparticles as photothermal transductors has been evaluated using NIR as irradiation source, as well as its application in photothermal therapy using different cell lines demonstrating a high efficiency in all cell cultures. This article is protected by copyright. All rights reserved.

Photo-controlled self-assembly behavior of novel amphiphilic polymers with a rosin-based azobenzene group

Novel ‘bola’ rosin-based photo-responsive amphiphilic polymers PMPn show an extremely high photoresponsive efficiency and various assembly morphological changes.

Polymeric nanostructures based on azobenzene and their biomedical applications: synthesis, self-assembly and stimuli-responsiveness

Amphiphilic polymers can self-assemble to form nanoparticles with different structures under suitable conditions. Polymer nanoparticles functionalized with aromatic azo groups are endowed with photo-responsive properties. In recent years, a variety of photoresponsive polymers and nanoparticles have been developed based on azobenzene, using different molecular design strategies and synthetic routes. This article reviews the progress of this rapidly developing research field, focusing on the structure, synthesis, assembly and response of photo-responsive polymer assemblies. According to the molecular structure, photo-responsive polymers can be divided into linear polymers containing azobenzene in a side chain, linear polymers containing azobenzene in the main chain, linear polymers containing azobenzene in an end group, branched polymers containing azobenzene and supramolecular polymers containing azobenzene. These systems have broad biomedical application prospects in the field of drug delivery and imaging applications.

Ordered Conformation-Regulated Vesicular Membrane Permeability

In nature, the folding and conformation of proteins can control the cell or organelle membrane permeability and regulate the life activities. Here we report the first example of synthetic polypeptide vesicles that regulate their permeability via ordered transition of secondary conformations, in a manner similar to biological systems.  The polymersomes undergo a β-sheet to α-helix transition in response to reactive oxygen species (ROS), leading to wall thinning without loss of vesicular integrity. The change  of membrane structure increases the vesicular permeability and enables specific transport of payloads with different molecular weights.The change of membrane structure increases the vesicular permeability.  As a proof-of-concept, the polymersomes encapsulating enzymes could serve as nanoreactors and carries for glucose-stimulated insulin secretion in vivo inspired by human glucokinase, resulting in safe and effective treatment of type 1 diabetes mellitus in mouse models. This study will help understand the biology of biomembranes and facilitate the engineering of nanoplatforms for biomimicry, biosensing, and controlled delivery applications.

Recent advances in supramolecular block copolymers for biomedical applications

Supramolecular block copolymers (SBCs) have received considerable interest in polymer chemistry, materials science, biomedical engineering and nanotechnology owing to their unique structural and functional advantages, such as low cytotoxicity, outstanding biodegradability, smart environmental responsiveness, and so forth. SBCs comprise two or more different homopolymer subunits linked by noncovalent bonds, and these polymers, in particular, combine the dynamically reversible nature of supramolecular polymers with the hierarchical microphase-separated structures of block polymers. A rapidly increasing number of publications on the synthesis and applications of SBCs have been reported in recent years; however, a systematic summary of the design, synthesis, properties and applications of SBCs has not been published. To this end, this review provides a brief overview of the recent advances in SBCs and describes the synthesis strategies, properties and functions, and their widespread applications in drug delivery, gene delivery, protein delivery, bioimaging and so on. In this review, we aim to elucidate the general concepts and structure-property relationships of SBCs, as well as their practical bioapplications, shedding further valuable insights into this emerging research field.

Supramolecular Functionalizable Linear-Dendritic Block Copolymers for the Preparation of Nanocarriers by Microfluidics

Hybrid linear-dendritic block copolymers (LDBCs) having dendrons with a precise number of peripheral groups that are able to supramolecular bind functional moieties are challenging materials as versatile polymeric platforms for the preparation of functional polymeric nanocarriers. PEG2k-b-dxDAP LDBCs that are based on polyethylene glycol (PEG) as hydrophilic blocks and dendrons derived from bis-MPA having 2,6-diacylaminopyridine (DAP) units have been efficiently synthesized by the click coupling of preformed blocks, as was demonstrated by spectroscopic techniques and mass spectrometry. Self-assembly ability was first checked by nanoprecipitation. A reproducible and fast synthesis of aggregates was accomplished by microfluidics optimizing the total flow rate and phase ratio to achieve spherical micelles and/or vesicles depending on dendron generation and experimental parameters. The morphology and size of the self-assemblies were studied by TEM, Cryogenic Transmission Electron Microscopy (cryo-TEM), and Dynamic Light Scattering (DLS). The cytotoxicity of aggregates synthesized by microfluidics and the influence on apoptosis and cell cycle evaluation was studied on four cell lines. The self-assemblies are not cytotoxic at doses below 0.4 mg mL-1. Supramolecular functionalization using thymine derivatives was explored for reversibly cross-linking the hydrophobic blocks. The results open new possibilities for their use as drug nanocarriers with a dynamic cross-linking to improve nanocarrier stability but without hindering disassembly to release molecular cargoes.

Hydrogen-bonding mediated self-assembly of amphiphilic ABA triblock copolymers into well-defined giant vesicles

A straightforward and efficient access towards the generation of well-defined giant vesicles (∼3 μm in diameters), featured by Hydrogen-bonded DAP–DAP dimerization, and the amphiphilic interactions is reported.

Micellar Nanocarriers from Dendritic Macromolecules Containing Fluorescent Coumarin Moieties

The design of efficient drug-delivery vehicles remains a big challenge in materials science. Herein, we describe a novel class of amphiphilic hybrid dendrimers that consist of a poly(amidoamine) (PAMAM) dendritic core functionalized with bisMPA dendrons bearing cholesterol and coumarin moieties. Their self-assembly behavior both in bulk and in water was investigated. All dendrimers exhibited smectic A or hexagonal columnar liquid crystal organizations, depending on the generation of the dendrimer. In water, these dendrimers self-assembled to form stable spherical micelles that could encapsulate Nile Red, a hydrophobic model compound. The cell viability in vitro of the micelles was studied in HeLa cell line, and proved to be non-toxic up to 72 h of incubation. Therefore, these spherical micelles allow the encapsulation of hydrophobic molecules, and at the same time provided fluorescent traceability due to the presence of coumarin units in their chemical structure, demonstrating the potential of these dendrimers as nanocarriers for drug-delivery applications.

Photosensitive hydrogels: from structure, mechanisms, design to bioapplications

Hydrogel is a smart material with a three-dimensional network structure and has been widely used in various fields due to its good biodegradability, biocompatibility, and modification. Photosensitive hydrogel is a smart hydrogel, and its amenability to remote, precise control, and flexible and convenient regulation of stimulating factors make it an ideal candidate for use in fields such as biological materials, drug carriers, and sensors. In this review, we discuss the structure, mechanisms, design principles, and bioapplications of photosensitive hydrogels as developed in recent years. Finally, their potential for development and potential future challenges are outlined.

Liquid Crystalline Copolymers Containing Sulfonic and Light-Responsive Groups: From Molecular Design to Conductivity

In the search for novel smart multifunctional liquid crystalline materials, we report the synthesis, thermal and structural characterisation, and the conductivity, of a set of new block and statistical copolymers, containing light-responsive mesogenic groups (MeOAzB), polar sulfonic acids (AMPS), and methyl(methacrylate) groups (MMA). By using a cascade of reversible addition-fragmentation chain polymerisations, RAFT, we have tailored different side-chain polymeric structures by controlling monomer composition (MeOAzB/AMPS/MMA) and configuration. We have yielded simultaneous liquid crystalline behaviour and appreciable conductivity in polymers with low concentrations of polar acid groups, by the formation of smectic phases in narrow aggregates. The light-responsiveness of the polymers, via reversible trans-to-cis photoisomerization of azobenzene groups, and the local activation of conductivity at relatively low temperatures, opens the possibility to prepare polymer electrolytes for energy conversion and storage, whose conductivity could be controlled and optimised by external stimuli, including light irradiation.

Novel amphiphilic graft block azobenzene-containing copolymer with polypeptide block: synthesis, self-assembly and photo-responsive behavior

Well-defined amphiphilic graft block azobenzene-containing copolymer with polypeptide block was synthesized via a combination of copper-mediated atom transfer radical polymerization (ATRP), ring-opening polymerization and click reaction. The alkyne-terminated poly[6-(4-methoxy-azobenzene-4′-oxy)hexyl methacrylate] (PAzoMA) was synthesized by ATRP with a bromine-containing alkyne bifunctional initiator, and the azido-terminated poly(γ-2-chloroethyl-l-glutamate) (PCELG) was synthesized by ROP of γ-2-chloroethyl-l-glutamate-N-carboxyanhydride (CELG-NCA), then the two homopolymers were conjugated by click reaction to afford block azobenzene-containing copolymer PAzoMA-b-PCELG. The chloro groups in PCELG block were transformed into azido groups via azide reactions, and the alkyne-terminated MPEG was grafted to the polypeptide block to afford the final product PAzoMA-b-poly((l-glutamate)-graft-methoxy poly(ethylene glycol)) (PAzoMA-b-(PELG-g-MPEG)) by click reaction. Giant vesicles (micrometer size) were obtained from the amphiphilic graft block copolymer PAzoMA-b-(PELG-g-MPEG) through a solution self-assembly due to the rigid PAzoMA chains and polypeptide chains with the α-helical structure. The investigation of the photo-isomerization behavior of PAzoMA-b-(PELG-g-MPEG) in solution and in vesicular solution showed trans–cis isomerization in solution was quicker than that in vesicular solution and azobenzene J-aggregates in the vesicle solution were only observed. The formation mechanisms of the vesicles were also explored. The research results may provide guidelines for the study of complex copolymers containing different types of rigid chains.

Giant vesicles (micrometer size) were prepared from novel amphiphilic graft block azobenzene-containing copolymer with polypeptide block synthesized via a combination of ATRP, ROP and click reaction.

Polymeric Self-Assemblies Based on tetra-ortho-Substituted Azobenzene as Visible Light Responsive Nanocarriers

Most of reported polymeric light-responsive nanocarriers make use of UV light to trigger morphological changes and the subsequent release of encapsulated cargoes. Moving from UV- to visible-responsive units is interesting for the potential biomedical applications of these materials. Herein we report the synthesis by ring opening polymerization (ROP) of a series of amphiphilic diblock copolymers, into which either UV or visible responsive azobenzenes have been introduced via copper(I) catalyzed azide-alkyne cycloaddition (CuAAC). These copolymers are able to self-assemble into spherical micelles or vesicles when dispersed in water. The study of the response of the self-assemblies upon UV (365 nm) or visible (530 or 625 nm) light irradiation has been studied by Transmission Electron Microscopy (TEM), Cryogenic Transmission Electron Microscopy (Cryo-TEM), and Dynamic Light Scattering (DLS) studies. Encapsulation of Nile Red, in micelles and vesicles, and Rhodamine B, in vesicles, and its light-stimulated release has been studied by fluorescence spectroscopy and confocal microscopy. Appreciable morphological changes have been induced with green light, and the subsequent release of encapsulated cargoes upon green light irradiation has been confirmed.

Synthesis and Self-Assembly of Multistimulus-Responsive Azobenzene-Containing Diblock Copolymer through RAFT Polymerization

This paper gathered studies on multistimulus-responsive sensing and self-assembly behavior of a novel amphiphilic diblock copolymer through a two-step reverse addition-fragmentation transfer (RAFT) polymerization technique. N-Isopropylacrylamide (NIPAM) macromolecular chain transfer agent and diblock copolymer (poly(NIPAM-b-Azo)) were discovered to have moderate thermal decomposition temperatures of 351.8 and 370.8 °C, respectively, indicating that their thermal stability was enhanced because of the azobenzene segments incorporated into the block copolymer. The diblock copolymer was determined to exhibit a lower critical solution temperature of 34.4 °C. Poly(NIPAM-b-Azo) demonstrated a higher photoisomerization rate constant (kt = 0.1295 s-1) than the Azo monomer did (kt = 0.088 s-1). When ultraviolet (UV) irradiation was applied, the intensity of fluorescence gradually increased, suggesting that UV irradiation enhanced the fluorescence of self-assembled cis-isomers of azobenzene. Morphological aggregates before and after UV irradiation are shown in scanning electron microscopy (SEM) and dynamic light scattering (DLS) analyses of the diblock copolymer. We employed photoluminescence titrations to reveal that the diblock copolymer was highly sensitive toward Ru3+ and Ba2+, as was indicated by the crown ether acting as a recognition moiety between azobenzene units. Micellar aggregates were formed in the polymer aqueous solution through dissolution; their mean diameters were approximately 205.8 and 364.6 nm at temperatures of 25.0 and 40.0 °C, respectively. Our findings contribute to research on photoresponsive and chemosensory polymer material developments.

Metallacycle-Cored Supramolecular Polymers: Fluorescence Tuning by Variation of Substituents

Herein, we present a method for the preparation of supramolecular polymers with tunable fluorescence via the combination of metal-ligand coordination and phenanthrene-21-crown-7 (P21C7)-based host-guest interactions. A suite of rhomboidal metallacycles with different substituents were prepared via the coordination-driven self-assembly of a P21C7-based 60° diplatinum(II) acceptor and 120° dipyridyl donors. Upon variation of the substituents on the dipyridyl donors, the metallacycles exhibit emission wavelengths spanning the visible region (λmax = 427-593 nm). Metallacycle-cored supramolecular polymers were obtained via host-guest interactions between bis-ammonium salts and P21C7. The supramolecular polymers exhibit emission wavelengths similar to those of the individual metallacycles and higher fluorescent efficiency in solution and thin films. Utilizing a yellow-emitting supramolecular polymer thin film with high quantum yield (0.22), a white-light-emitting LED was fabricated by painting the thin film onto an ultraviolet LED. This study presents an efficient approach for tuning the properties of fluorescent supramolecular polymers and the potential of the metallacycle-cored supramolecular polymers as a platform for the fabrication of light-emitting materials with good processability and tunability.

Molecular Recognition via Hydrogen Bonding in Supramolecular Complexes: A Fourier Transform Infrared Spectroscopy Study

We assess the assembly of supramolecular complexes by hydrogen bonding between azocompounds and a diacylaminopyridine monomer by temperature-dependent Fourier transform infrared spectroscopy (FT-IR) and density functional theory (DFT) calculations. The electronic delocalisation in the supramolecular rings formed by multiple hydrogen bonds stabilises the complexes, which coexist with dimeric species in temperature-dependent equilibria. We show how the application of readily available molecular modelling and spectroscopic techniques can predict the stability of new supramolecular entities coexisting in equilibria, ultimately assessing the success of molecular recognition.

Photo/pH-controlled host-guest interaction between an azobenzene-containing block copolymer and water-soluble pillar[6]arene as a strategy to construct the "compound vesicles" for controlled drug delivery

Herein, dual stimuli-responsive compound vesicles were constructed based on host-guest interaction between a water-soluble pillar[6]arene (WP6) and an amphiphilic azobenzene-containing block copolymers (BCP). Reversible morphological transformation between compound vesicles and solid aggregates was achieved by repeated pH- and photo-stimuli. These compound vesicles were then applied in the controlled release of water-soluble anticancer drug, doxorubicin hydrochloride (DOX · HCl). Upon external stimuli, the DOX · HCl displayed a faster release rate than that without stimuli. Moreover, the compound vesicles showed an excellent cytocompatibility toward the human breast cancer cells (Michigan Cancer Foundation-7, MCF-7), and the drug-loaded compound vesicles exhibited lower cytotoxicity than free drug. The drug-loaded compound vesicles could be taken up by MCF-7 cells and can release the DOX · HCl in cancer cells due to the acid environment, which was important for applications in the therapy of cancers as a controlled-release drug carrier.

Micellization of Photo-Responsive Block Copolymers

This review focuses on block copolymers featuring different photo-responsive building blocks and self-assembly of such materials in different selective solvents. We have subdivided the specific examples we selected: (1) according to the wavelength at which the irradiation has to be carried out to achieve photo-response; and (2) according to whether irradiation with light of a suitable wavelength leads to reversible or irreversible changes in material properties (e.g., solubility, charge, or polarity). Exemplarily, an irreversible change could be the photo-cleavage of a nitrobenzyl, pyrenyl or coumarinyl ester, whereas the photo-mediated transition between spiropyran and merocyanin form as well as the isomerization of azobenzenes would represent reversible response to light. The examples presented cover applications including drug delivery (controllable release rates), controlled aggregation/disaggregation, sensing, and the preparation of photochromic hybrid materials.

Hypoxia inducible factor (HIF) as a model for studying inhibition of protein-protein interactions

The state of the art in identifying protein–protein interaction inhibitors of hypoxia inducible factor – a promising target for anticancer drug design – is described.

The modulation of protein–protein interactions (PPIs) represents a major challenge in modern chemical biology. Current approaches (e.g. high-throughput screening, computer aided ligand design) are recognised as having limitations in terms of identification of hit matter. Considerable success has been achieved in terms of developing new approaches to PPI modulator discovery using the p53/hDM2 and Bcl-2 family of PPIs. However these important targets in oncology might be considered as “low-hanging-fruit”. Hypoxia inducible factor (HIF) is an emerging, but not yet fully validated target for cancer chemotherapy. Its role is to regulate the hypoxic response and it does so through a plethora of protein–protein interactions of varying topology, topography and complexity: its modulation represents an attractive approach to prevent development of new vasculature by hypoxic tumours.

Synthesis of photoresponsive main-chain oligomers with azobenzene moieties via ADMET oligomerization and their micellization properties

We report the synthesis of azobenzene functionalized linear unsaturated/saturated polyolefin-oligomers.