Synthesis, Self-Assembly, and Photoresponsive Behavior of Tadpole-Shaped Azobenzene Polymers

Thermo- and Light-Responsive Polymer-Coated Magnetic Nanoparticles as Potential Drug Carriers

A series of thermo- and light-responsive copolymers of poly (N-isopropylacrylamide) (PNIPAM) and 6-[4-(4-methoxy phenyl azo)-phenoxyl-hexyl methacrylate) (AzoMA) (PNIPAM-b-PAzoMA) were synthesized via reversible addition–fragmentation chain transfer (RAFT) radical polymerization. The resulting copolymers had a narrow molecular weight distribution range of 1.06–1.24, in which Mn changed regularly with the monomer concentration. Subsequently, the diblock copolymers were successfully modified on the surface of iron oxide nanoparticles through the interaction between the chemical bonds to prepare Fe3O4@(PNIPAM-b-PAzoMA) nanoparticles. The size of fabricated nanoparticles with excellent thermo-sensitivity and photo-sensitivity was controlled at about 40–50 nm. Cell viability assays suggested that the nanoparticles showed no significant cytotoxicity and potential drug delivery in the tumor microenvironment.

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.

Dual-Stimuli Responsive Single-Chain Polymer Folding via Intrachain Complexation of Tetramethoxyazobenzene and β-Cyclodextrin

We synthesize and characterize a triblock polymer with asymmetric tetramethoxyazobenzene (TMAB) and β-cyclodextrin functionalization, taking advantage of the well-characterized azobenzene derivative-cyclodextrin inclusion complex to promote photoresponsive, self-contained folding of the polymer in an aqueous system. We use ¹H NMR to show the reversibility of (E)-to-(Z) and (Z)-to-(E) TMAB photoisomerization, and evaluate the thermal stability of (Z)-TMAB and the comparatively rapid acid-catalyzed thermal (Z)-to-(E) isomerization. Important for its potential use as a functional material, we show the photoisomerization cyclability of the polymeric TMAB chromophore and calculate isomerization quantum yields by extinction spectroscopy. To verify self-inclusion of the polymeric TMAB and cyclodextrin, we use two-dimensional ¹H NOESY NMR data to show proximity of TMAB and cyclodextrin in the (E)-state only; however, (Z)-TMAB is not locally correlated with cyclodextrin. Finally, the observed decrease in photoisomerization quantum yield for the dual-functionalized polymer compared to the isolated chromophore in an aqueous solution confirms TMAB and β-cyclodextrin not only are in proximity to one another, but also form the inclusion complex.

Synthesis and antifouling performance of tadpole-shaped poly(N-hydroxyethylacrylamide) coatings

Linear poly(N-hydroxyethylacrylamide) (PHEAA) is regarded as one of the most promising antifouling materials because of its excellent antifouling properties and good hemocompatibility. However, the antifouling performance of topological PHEAAs remains largely unknown. Herein, the preparation of antifouling surfaces based on a tadpole-shaped PHEAA coating is reported for the first time, and how the tadpole-shaped PHEAA architecture affects antifouling performance is investigated. It is shown that the tadpole-shaped PHEAA-modified surfaces exhibit better antifouling performance than linear copolymer precursor-modified surfaces with identical molar masses and chemical compositions. This may be primarily attributed to the presence of cyclic PHEAA head chain segments in the tadpole-shaped PHEAA copolymer, and the absence of interchain entanglements can facilitate the formation of smoother and densely packed grafts, which result in better antifouling properties.

The self-assembly of single chain Janus nanoparticles from azobenzene-containing block copolymers and reversible photoinduced morphology transitions

Azobenzene-containing liquid crystalline single chain Janus nanoparticles (LC-SCJNPs) were employed as building blocks to construct assemblies showing a reversible photoinduced morphology transition.

Current Trends of Targeted Drug Delivery for Oral Cancer Therapy

Oral cancer is an aggressive tumor that invades the local tissue and can cause metastasis and high mortality. Conventional treatment strategies, e.g., surgery, chemotherapy, and radiation therapy alone or in combinations, possess innegligible issues, and significant side and adverse effects for the clinical applications. Currently, targeting drug delivery is emerging as an effective approach for oral delivery of different therapeutics. Herein we provide a state-of-the-art review on the current progress of targeting drug delivery for oral cancer therapy. Variously oral delivery systems including polymeric/inorganic nanoparticles, liposomes, cyclodextrins, nanolipids, and hydrogels-based forms are emphasized and discussed, and biomimetic systems with respect to oral delivery like therapeutic vitamin, exosomes, proteins, and virus-like particles are also described with emphasis on the cancer treatment. A future perspective is also provided to highlight the existing challenges and possible resolution toward clinical translation of current oral cancer therapies.

Light: A Magical Tool for Controlled Drug Delivery

Light is a particularly appealing tool for on-demand drug delivery due to its noninvasive nature, ease of application and exquisite temporal and spatial control. Great progress has been achieved in the development of novel light-driven drug delivery strategies with both breadth and depth. Light-controlled drug delivery platforms can be generally categorized into three groups: photochemical, photothermal, and photoisomerization-mediated therapies. Various advanced materials, such as metal nanoparticles, metal sulfides and oxides, metal-organic frameworks, carbon nanomaterials, upconversion nanoparticles, semiconductor nanoparticles, stimuli-responsive micelles, polymer- and liposome-based nanoparticles have been applied for light-stimulated drug delivery. In view of the increasing interest in on-demand targeted drug delivery, we review the development of light-responsive systems with a focus on recent advances, key limitations, and future directions.

Recent Advances on Synthetic and Polysaccharide Adhesives for Biological Hemostatic Applications

Rapid hemostasis and formation of stable blood clots are very important to prevent massive blood loss from the excessive bleeding for living body, but their own clotting process cannot be completed in time for effective hemostasis without the help of hemostatic materials. In general, traditionally suturing and stapling techniques for wound closure are prone to cause the additional damages to the tissues, activated inflammatory responses, short usage periods and inevitable second operations in clinical applications. Especially for the large wounds that require the urgent closure of fluids or gases, these conventional closure methods are far from enough. To address these problems, various tissue adhesives, sealants and hemostatic materials are placed great expectation. In this review, we focused on the development of two main categories of tissue adhesive materials: synthetic polymeric adhesives and naturally derived polysaccharide adhesives. Research of the high performance of hemostatic adhesives with strong adhesion, better biocompatibility, easy usability and cheap price is highly demanded for both scientists and clinicians, and this review is also intended to provide a comprehensive summarization and inspiration for pursuit of more advanced hemostatic adhesives for biological fields.

Dual stimuli-responsive nano-structure transition of three-arm branched amphiphilic polymers containing ferrocene (Fc) and azobenzene (Azo) moieties in aqueous solution

Amphiphilic polymers can self-assemble into various nanostructures in solution, which can find applications in many fields such as nanotechnology, drug delivery, and template synthesis. Herein, we report the controlled self-assembly and dual stimuli-responsive nanostructure transition of a class of three-arm branched amphiphilic polymers (AzoFcPEO) containing ferrocene (Fc) and azobenzene (Azo) moieties in aqueous solution. These amphiphilic polymers were synthesized by an esterification reaction of a variety of polyethylene oxide methyl ethers (Me-PEO) with 3-(6-ferrocenyhexyloxyl)-5-(6-azobenzenehexyloxy) benzoic acid. Both the isomerization of Azo and redox of Fc moieties can respectively change the amphiphilicity of these polymers to different degrees. Consequently, these amphiphilic polymers in aqueous solution can self-assemble into various nanostructures, such as spherical micelle, worm-like micelle, spherical compound micelle, rod-like compound micelle and vesicle dependent on the PEO molecular weight, applied stimuli, and polymer concentration. This work can offer tremendous possibilities not only for the fundamental science of the controlled self-assembly but also for establishing a suitable method for regulating the nanostructures of amphiphilic polymers in aqueous solution.

Fabrication of Customized Nanogel Carriers From a UV-Triggered Dynamic Self-Assembly Strategy

Recent advances in self-assembled nanogel carriers have allowed precise design of hierarchical structures by a low-cost solution-phase approach. Typically, photochemical strategy on the tailor of morphology and dimension has emerged as a powerful tool, because light-trigger has exceptional advantages of an instant "on/off" function and spatiotemporal precision at arbitrary time. Herein, we report a tunable manipulation of sequentially morphological transition via a "living" thiol-disulfide exchange reaction from a UV-tailored hierarchical self-assembly strategy. By varying the irradiation time, the photochemical method can easily fabricate and guide a series of attractively architectural evolution in dilute aqueous solutions, by which the improving hydrophobicity and sensitive redox-responsiveness endowed these disulfide-linked nanoparticles with remarkable capacities of abundant encapsulation, effective separation, and controlled release of hydrophobic cargoes. Notably, once the exchange reaction is suspended at any point of time by removing the UV lamp, these active sites within the nanogel carriers are instantaneous deactivated and the correspondingly structural transformations are also not conducted any more. However, if the stable inert sites are reactivated as needed by turning on the UV light, the interrupting morphology evolution can continue its previous steps, which may provide a simple and novel approach to fabricating the desired self-assemblies in solutions. With regard to this advanced functionality, various nanogel carriers with customizable structures and properties have been yielded and screened for cancer therapy. Thus, this "living" controlled self-assembled method to program morphology evolution in situ is a universal strategy that will pave novel pathways for creating sequential shape-shifting and size-growing nanostructures and constructing uniform nanoscopic functional entities for advanced bio-applications.

Controllable Self-Assembly of Amphiphilic Tadpole-Shaped Polymer Single-Chain Nanoparticles Prepared through Intrachain Photo-cross-linking

We report the use of intramolecular cross-linking chemistry as a tool to control the self-assembly of amphiphilic diblock copolymers (di-BCPs). Two amphiphilic di-BCPs of poly( N, N'-dimethylacrylamide)- block-polystyrene (PDMA- b-PS) with photo-cross-linkable cinnamoyl groups in either hydrophobic or hydrophilic blocks were prepared using reversible addition-fragmentation chain transfer polymerization. Intramolecular photo-cross-linking of cinnamoyl groups led to the formation of tadpole-shaped polymer single-chain nanoparticles (SCNPs) consisting of a self-collapsed block as the "head" and an un-cross-linked block as the "tail". When intramolecular photo-cross-linking was carried out in hydrophobic PS blocks, a clear morphological transition from branched cylindrical micelles (for the linear di-BCP) to completely spherical micelles at a dimerization degree of ∼63% was observed. A pattern of morphological transitions from cylindrical micelles to spherical micelles is observed through stepwise downsizing the length of cylindrical micelles when increasing the self-collapse degree of PS blocks, whereas, in case of photo-cross-linking carried out in hydrophilic PDMA blocks, the size of micelles showed a dramatic increase due to the shift of hydrophobic-to-hydrophilic balance. When the cross-linking degree of PDMA blocks reached >60%, tadpole-shaped SCNPs assembled into nonconventional aggregates with a nonsmooth surface. Our results illustrate the impact of chain topologies on the self-assembly outcomes of amphiphilic di-BCPs, which likely opens a door to control the micellar morphologies from just one parent linear di-BCP, rather than resynthesizing BPCs with different volume fractions of the two blocks.

Recent advances in stimuli-responsive polymeric micelles via click chemistry

Stimuli-responsive polymeric micelles via click chemistry are divided into six major sections (temperature, light, ultrasound, pH, enzymes, and redox).

Preparation of reversible photoresponsive N-hydroxyethyl spiropyran/polyacrylonitrile fiber materials with mechanical stability by electrospinning for regulating wettability and humidity automatically

Novel photoresponsive N-hydroxyethyl spiropyran (SP-OH)/polyacrylonitrile (PAN) fiber materials with reversible changes in wettability and humidity were prepared by electrospinning in this work. SP-OH and PAN were mixed through a physical doping method. The wettability and humidity regulation of the electrospun films can be reversibly manipulated by the simple change of ultraviolet (UV)-visible (UV-Vis) light irradiation due to the photoisomerization mechanism of the spiropyran chromophore. Under UV light irradiation, SP-OH molecules exhibit a colored polar open-ring status, resulting in electrostatic attraction with water. However, under visible light irradiation, they are colorless and nonpolar and lose the attraction effect. Wettability and ambient humidity were regulated by this repeated transformation between polar surface and nonpolar surface. The tensile strength and the reversible change ranges of wettability and humidity under UV-Vis irradiation are all closely related to the doping amount of SP-OH. Electrospinning is a promising method to achieve large-scale production that can put such a material into practical application.

Self-Assembly and Applications of Amphiphilic Hybrid POSS Copolymers

Understanding the mechanism of molecular self-assembly to form well-organized nanostructures is essential in the field of supramolecular chemistry. Particularly, amphiphilic copolymers incorporated with polyhedral oligomeric silsesquioxanes (POSSs) have been one of the most promising materials in material science, engineering, and biomedical fields. In this review, new ideas and research works which have been carried out over the last several years in this relatively new area with a main focus on their mechanism in self-assembly and applications are discussed. In addition, insights into the unique role of POSSs in synthesis, microphase separation, and confined size were encompassed. Finally, perspectives and challenges related to the further advancement of POSS-based amphiphilics are discussed, followed by the proposed design considerations to address the challenges that we may face in the future.

Dynamic and programmable morphology and size evolution via a living hierarchical self-assembly strategy

Recent advances in the preparation of shape-shifting and size-growing nanostructures are hot topics in development of nanoscience, because many intelligent functions are always relied on their shape and dimension. Here we report a tunable manipulation of sequential self-assembled transformation in situ via a hierarchical assembly strategy based on a living thiol-disulfide exchange reaction. By tailoring the external stimuli, the reactive points can be generated at the ends of initially unimolecular micelles, which subsequently drive the pre-assemblies to periodically proceed into the hierarchically micellar connection, axial growth, bending, and cyclization processes from nanoscopic assemblies to macroscopic particles. Of particular interest would be systems that acquired the shape control and size adjustment of self-assemblies after termination or reactivation of disulfide reshuffling reaction by regulating external stimuli whenever needed. Such a hierarchical strategy for self-assembled evolution is universally applicable not only for other disulfide-linked dendritic polymers but also for exploitation of biological applications.

Controlled Self-Assembly of Multiple-Responsive Superamphiphilc Polymers Based on Host-Guest Inclusions of a Modified PEG with β-Cyclodextrin

Superamphiphilic polymers (SAPs) constructed by host-guest inclusion can self-assemble into various nanostructures in solution, which can find applications in many fields such as nanodevices, drug delivery, and template synthesis. Herein, we report the controlled self-assembly of multiple-responsive SAP based on a selective host-guest inclusion of β-cyclodextrin (β-CD) with a modified poly(ethylene glycol) (PEG) (FcC₁₁AzoPEG) consisting of a ferrocene (Fc) end group, a C₁₁ alkyl chain, an azobenzene (Azo) block, and a poly(ethylene glycol)methyl ether (PEG) chain. These SAPs can self-assemble into interesting nanostructures in water upon exposure to different stimuli because β-CD can be selectively included with different guests, such as Fc, Azo, and C₁₁ alkyl chain, under different stimuli. The inclusion complex of Fc with β-CD (Fc@β-CD SAP) can form nanowire micelles in aqueous solution. The nanowire micelles can be transformed into spindle micelles with the addition of oxidant because the majority of β-CDs dissociated from the complex Fc@β-CD SAP due to a conversion of Fc to Fc⁺ and will preferentially include with Azo group to form another dominant inclusion complex (Azo@β-CD SAP). After UV irradiation, the spindle micelles can be further transformed into spherical micelles because most of β-CDs are excluded from the complex Azo@β-CD SAP due to a trans- to cis-Azo conversion and then form a dominant inclusion complex with C₁₁ alkyl chains (C₁₁@β-CD SAP). This work not only demonstrates the selective host-guest inclusion of stimuli-responsive groups modified PEG with β-CD but also provides a useful approach for construction of diverse morphologies.

Fabrication of POSS-embedded supramolecular hyperbranched polymers with multi-responsive morphology transitions

We demonstrate a simple approach to prepare POSS-embedded supramolecular hyperbranched polymers with multiple stimulus morphology transitions driven by triple supramolecular driving forces in selective solvents.

Rationally designed hyperbranched azopolymer with temperature, photo and pH responsive behavior

A novel hyperbranched azopolymer, HPAzoAMAM-star-EG₃, was synthesized and it could self-assemble into uniform large compound micelles with multi-stimuli responsive behavior.

Fabrication of multi-stimuli responsive supramolecular hydrogels based on host–guest inclusion complexation of a tadpole-shaped cyclodextrin derivative with the azobenzene dimer

Multi-responsive supramolecular hydrogels, based on host–guest complexation of tadpole-shaped cyclodextrin with the azobenzene dimer, possess reversible sol–gel transition behaviors and better biocompatibility.

Synthesis and characterization of visible-light-activated Azo hyperbranched polymers

All visible-light-activated Azo polymer photoswitches were efficiently synthesized via combination of the AuNP-catalyzed photocatalytic method and the A₃ monomer strategy.

Self-assembly of upconversion nanoclusters with an amphiphilic copolymer for near-infrared- and temperature-triggered drug release

The hybrid colloidal clusters were prepared by self-assembly of multiresponsive copolymer with hydrophobic nanocrystals, and which was able to near-infrared light and temperature triggered drug release.

Facile creation of FRET systems from a pH-responsive AIE fluorescent vesicle

We demonstrate a facile approach to constructing aggregation induced emission (AIE) fluorescent vesicles for creation of FRET systems.

Fe3O4@nanogel via UOx/HRP initiated surface polymerization for pH sensitive drug delivery

This study describes a new strategy to fabricate core–shell nanogels by surface free-radical polymerization initiated by the cascade reaction of UOx and HRP, which showed excellent biocompatible, high loading capacity and pH-responsive drug release.

Facile preparation of pH-responsive AIE-active POSS dendrimers for the detection of trivalent metal cations and acid gases

AIE-active POSS dendrimers, exhibiting AIE effects and pH-responsive properties, were employed as sensitive fluorescent probes for trivalent metal cations and acid gases.

Photoresponsive assemblies of linear-dendritic copolymers containing azobenzene in the dendron interior: the effect of the dendron structure on dye encapsulation and release

Linear-dendritic copolymers show differential dye encapsulation and photoinduced dye release based on the number and positions of azobenzenes in the dendritic backbone as well as substituents on the dendron periphery.