Dual redox responsive coassemblies of diselenide-containing block copolymers and polymer lipids

Recent progress and advances in redox-responsive polymers as controlled delivery nanoplatforms

Recent advances and progress in redox-responsive polymeric nanosystems for biomedical applications are discussed in this review article.

Glutathione responsive polymers and their application in drug delivery systems

Materials which respond to biological cues are the subject of intense research interest due to their possible application in smart drug delivery vehicles.

A redox-responsive selenium-containing pillar[5]arene-based macrocyclic amphiphile: synthesis, controllable self-assembly in water, and application in controlled release

A selenium-containing pillar[5]arene-based macrocyclic amphiphile was prepared. This amphiphile self-assembled in water to form vesicles with redox responsiveness. Then, these pillar[5]arene-based vesicles were used in the controlled release of DOX.

Effective and Reversible Switching of Emulsions by an Acid/Base-Mediated Redox Reaction

To develop a fast, effective, and reversible strategy for phase separation and re-emulsification of the surfactant-based emulsions, a strategy for using acid/base-mediated redox reactions was established to switch the emulsions formed from a redox-responsive anionic surfactant of potassium dodecyl seleninate (C₁₂SeO₂K). Upon acidification, C₁₂SeO₂K was reduced by KI to give didodecyl diselenide (C₁₂Se)₂, a state of almost no surface or interfacial activity; upon basification, (C₁₂Se)₂ was oxidized by I₂ to give C₁₂SeO₂K again. The fractional conversion of C₁₂SeO₂K in the reversible switching processes was close to 100%. Consequently, an unusually large change in interfacial tension (ΔIFT) as high as ∼27.1 mN m^-1 was obtained at a wider concentration range starting from the critical micelle concentration of C₁₂SeO₂K; the highest IFT at the oil-water interface was obtained after an almost complete switch-off, giving an oil-aqueous solution interface very similar to that without any emulsifiers, which leads to the effective and fast phase separation of the C₁₂SeO₂K-based switchable emulsions.

Rapid Self-Assembly of Block Copolymers for Flower-Like Particles with High Throughput

The self-assembly of block copolymers has evolved into a foremost bottom-up approach for building polymeric materials. Historical challenges exist within this lively field, including the scalability and elegant simplicity of self-assembled aggregates with predictable structures. Here, we report a generally applicable strategy for the rapid self-assembly of poly(ethylene glycol)-block-poly(l-lactic acid) with the help of a single oil-in-water emulsion. A kind of flower-like polymer particle with filamentous surface branches is rapidly formed after removing the oil phase from the emulsion system. Moreover, the dimension of the branched filaments and the spherical internal core can be controlled through regulating the block ratio and the emulsification conditions. In particular, we propose an explosion theory as a balance between phase separation and interchain interaction for explaining the formation of the branched structures of the flower-like particles. The particles with high throughput are further functionalized with polypyrrole for their use in enhanced photoelectric-sensing applications.

Redox-Controllable Interfacial Properties of Zwitterionic Surfactant Featuring Selenium Atoms

Control of interfacial properties (foaming and emulsification) plays an important role in industry. Here we developed a novel redox-responsive surfactant, 3-(11-benzylselanyl-undecyl)-dimethylammonium acetate (BSeUCB), using selenium atoms as an environmentally sensitive group. In a reduced state, BSeUCB aqueous solution showed good foaming and emulsification abilities as well as conventional betaine surfactants. After oxidization, BSeUCB transformed into a bola-type structure because of the presence of a new hydrophilic group (selenoxide), and thus the critical micellar concentration, equilibrium surface/interfacial tension, and molecular area at the interface correspondingly increase from 0.32 mM, 46.43 mN·m(-1), 5.30 mN·m(-1), and 0.61 nm(2) to 4.98 mM, 59.15 mN·m(-1), 18.29 mN·m(-1), and 1.22 nm(2), respectively, resulting in a greater amount of energy input required to produce foam or emulsion, and a less dense adsorption layer, i.e., poor foaming and emulsification ability. Such a conversion was reversibly controlled by simply adding a trace amount (<0.06 wt % of the dispersion) of oxidant (H2O2) and reductant (Na2SO3). The products of the redox reaction did not interfere in the switchability except at the first cycle. The oxidization was generally time-consuming, whereas the reduction was very fast.

ROS-responsive drug delivery systems

Reactive oxygen species (ROS) play an important role in signal transduction and metabolism. Over-produced ROS in cells or tissues, however, often leads to oxidation stress that has implications in a series of diseases including cancer, aging, atherosclerosis and inflammation. Driven by the need for on-demand drug delivery and fuelled by recent development of ROS-responsive materials and nanomedicine, responsive drug delivery systems (DDSs) have gained increasing research interest. ROS-responsive DDS is designed to release therapeutic agents only in targets of interest that produce excessive ROS, which may lead to both enhanced therapeutic efficiency and reduced side effects. Multiple-stimuli responsive DDSs that are also sensitive to other stimuli can further enhance controlled drug release in sites where multiple stimuli coexist. Beyond drug delivery, multifunctional DDSs have great potential in achieving simultaneous imaging, combinatorial therapy and targeting ability by introducing multifunctional elements such as signal reporter, targeting elements and photosensitizer. This review will summarize the latest development of ROS-responsive DDSs and discuss their design principle and biomedical applications.

Construction of redox/pH dual stimuli-responsive PEGylated polymeric micelles for intracellular doxorubicin delivery in liver cancer

A schematic of the complete process of DOX-loaded mPEG-SS-PNLG micelles uptake into tumor cells and intracellular release of DOX; size distribution of mPEG-SS-PNLG (90%) micelles and in vivo antitumor efficacy.

Well-defined labile diselenide-centered poly(ε-caprolactone)-based micelles for activated intracellular drug release

Diselenide groups were introduced into aliphatic polyesters to develop a novel well-defined reduction-labile biodegradable diselenide-containing polymeric drug delivery system (mPEG–PCL–Se)₂.

Hydrogen peroxide-responsive micelles self-assembled from a peroxalate ester-containing triblock copolymer

A novel copolymer was synthesized by using peroxalate esters as linkages and the formed micelles possessed specific H₂O₂ responsive reactivity.

Preparation of redox-sensitive, core-crosslinked micelles self-assembled from mPEGylated starch conjugates: remarkable extracellular stability and rapid intracellular drug release

Novel diselenide core-crosslinked mPEGylated starch micelles (mPEG-St-SeSe_x) were developed, which had advanced stability in ultra micelle destabilization conditions and could be quickly disunited to release the drug in the presence of 10 mM GSH.

Redox poly(ethylene glycol)-b-poly(L-lactide) micelles containing diselenide bonds for effective drug delivery

Bioreducible polymers have appeared as the ideal drug carriers for tumor therapy due to their properties of high stability in extracellular circulation and rapid drug release in intracellular reducing environment. Recently, the diselenide bond has emerged as a new reduction-sensitive linkage. In this work, the amphiphilic poly(ethylene glycol)-b-poly(L-lactide) containing diselenide bond has been synthesized and used to load anti-tumor drug, docetaxel (DTX), to form the redox micelles. It was found that the redox micelles showed a rapid response to glutataione (GSH), which resulted in a fast release of DTX in the presence of GSH. In contrast, <40 % of DTX was released from the micelles within 72 h under the normal condition (absence of GSH). The DTX-loaded redox micelles showed the significant inhibition effect to MCF-7 cells, and the cytotoxicity was dependent on the intracellular GSH concentrations. Moreover, considering the potentially clinical applications of the micelles through intravenous injection, the blood compatibility was also studied by the hemolysis analysis, activated partial thromboplastin time, prothrombin time and thromboelastography assays. These results confirmed that the redox micelles showed good blood safety, suggesting a potential application in tumor therapy.

Ultrasensitive ROS-Responsive Coassemblies of Tellurium-Containing Molecules and Phospholipids

Reactive oxygen species (ROS) play crucial roles in cell signaling and redox homeostasis and are strongly related to metabolic activities. The increase of the ROS concentration in organisms can result in several diseases, such as cardiovascular diseases and cancer. The concentration of ROS in biologically relevant conditions is typically as low as around tens of micromolars to 100 μM H2O2, which makes it necessary to develop ultrasensitive ROS-responsive systems. A general approach is reported here to fabricate an ultrasensitive ROS-responsive system via coassembly between tellurium-containing molecules and phospholipids, combining the ROS-responsiveness of tellurium and the biocompatibility of phospholipids. By using dynamic light scattering, transmission electron microscopy, scanning electron microscopy, and NMR spectra, coassembly behaviors and the responsiveness of the coassemblies have been investigated. These coassemblies can respond to 100 μM H2O2, which is a biologically relevant ROS concentration, and demonstrate reversible redox properties.

Xerogel-sequestered silanated organochalcogenide catalysts for bromination with hydrogen peroxide and sodium bromide

While H₂O₂ is a powerful oxidant, decomposing into environmentally benign H₂O and O₂, a catalyst is often required for reactions with H₂O₂ to proceed at synthetically useful rates. Organotellurium and organoselenium compounds catalyze the oxidation of halide salts to hypohalous acids using H₂O₂. When sequestered into xerogel monoliths, the xerogel-chalcogenide combinations have demonstrated increased catalytic activity relative to the organochalcogen compound alone in solution for the oxidation of halide salts to hypohalous acids with H₂O₂. Diorganotellurides, diorganoselenides, and diorganodiselenides bearing triethoxysilane functionalities were sequestered into xerogel monoliths and their catalytic activity and longevity were investigated. The longevity of the catalyst-xerogel combinations was examined by isolating and recycling the catalyst-xerogel combination. It was found tellurium-containing catalyst 3 and selenium-containing catalyst 8 maintained their catalytic activity through three recycling trials and adding electron-donating substituents to catalyst 3 also increased the catalytic rate. The presence of organotellurium and organoselenium groups in the +4 oxidation state was determined by X-ray photoelectron spectroscopy.

Encapsulation and covalent binding of molecular payload in enzymatically activated micellar nanocarriers

The high selectivity and often-observed overexpression of specific disease-associated enzymes make them extremely attractive for triggering the release of hydrophobic drug or probe molecules from stimuli-responsive micellar nanocarriers. Here we utilized highly modular amphiphilic polymeric hybrids, composed of a linear hydrophilic polyethylene glycol (PEG) and an esterase-responsive hydrophobic dendron, to prepare and study two diverse strategies for loading of enzyme-responsive micelles. In the first type of micelles, hydrophobic coumarin-derived dyes were encapsulated noncovalently inside the hydrophobic core of the micelle, which was composed of lipophilic enzyme-responsive dendrons. In the second type of micellar nanocarrier the hydrophobic molecular cargo was covalently linked to the end-groups of the dendron through enzyme-cleavable bonds. These amphiphilic hybrids self-assembled into micellar nanocarriers with their cargo covalently encapsulated within the hydrophobic core. Both types of micelles were highly responsive toward the activating enzyme and released their molecular cargo upon enzymatic stimulus. Importantly, while faster release was observed with noncovalent encapsulation, higher loading capacity and slower release rate were achieved with covalent encapsulation. Our results clearly indicate the great potential of enzyme-responsive micellar delivery platforms due to the ability to tune their payload capacities and release rates by adjusting the loading strategy.

Coordination responsive tellurium-containing multilayer film for controlled delivery

A coordination-responsive tellurium-containing film was fabricated to load cisplatin by Te–Pt coordination, and competitive bio-ligands could trigger the release of cisplatin.

PEGylated poly(diselenide-phosphate) nanogel as efficient self-delivery nanomedicine for cancer therapy

A biocompatible, biodegradable and redox-responsive PEGylated poly(diselenide-phosphate) nanogel was synthesized. The nanogel can potently inhibit the proliferation of tumor cells. It is a potentially efficient and self-delivery nanomedicine for cancer therapy.

Oxidation- and thermo-responsive poly(N-isopropylacrylamide-co-2-hydroxyethyl acrylate) hydrogels cross-linked via diselenides for controlled drug delivery

A novel diselenide crosslinked poly(NIPAM-co-HEA) hydrogel was successfully synthesized, which exhibits a dual-stimuli-responsive drug release behaviors,i.e., thermo-induced slow sustained release and oxidation-induced quick burst release.

Reactive oxygen species (ROS)-responsive tellurium-containing hyperbranched polymer

Tellurium-containing hyperbranched polymers form aggregates, which are a new kind of material responsive to reactive oxygen species at a physiological level.