A Novel Biodegradable and Light-Breakable Diblock Copolymer Micelle for Drug Delivery

A facile approach to the preparation of light-responsive copolymer micelles is developed. This approach is based on the attachment of hydrophobic groups to one block of a diblock copolymer via a light-sensitive linkage. The micelles can be dissociated under light irradiation and release the encapsulated pyrene. The obtained polymeric micelles are expected to be of use as drug-delivery vehicles.

Alternating copolymerization of carbon dioxide and propylene oxide by single-component cobalt salen complexes with various axial group

A series of single-component cobalt salen complexes, N,N'-bis(salicylidene)-1,2phenylenediamino cobaltIII X(X = Cl (1a), Br (1b), NO3 (1c), CF3COO (1d), BF4 (le), and N3 (If)) (SalphCoX), were prepared for alternating copolymerization of carbon dioxide and propylene oxide(PO) under mild condition. The axial anion X group of the SalenphCoX played important role in tailoring the catalytic activity, polymeric/cyclic carbonate selectivity, as well as stereochemistry of carbonate unit sequence in the polymer chain. SalenphCoX with an electron-withdrawing axial X group (complex 1c) was an ideal catalyst for the copolymerization of CO2 and PO to selectively produce polycarbonate with similar to 99% carbonate linkage and over 81% head-to-tail structure.

Synthesis of Hyperbranched Polymers with Pendent Norbornene Functionalities via RAFT Polymerization of a Novel Asymmetrical Divinyl Monomer

Hyperbranched polymers with numerous pendent norbornene functionalities have been synthesized via the radical polymerization of a novel asymmetrical divinyl monomer hearing a higher reactivity methacrylate group and it lower reactivity norbornene group. Mediated by a rapid reversible addition-fragmentation chain transfer (RAFT) equilibrium, the concentration of polymeric chain radicals is decreased, and thus the gelation did not occur until higher monomer conversions (ca. 90%). An increase in reaction temperature call also significantly promote the formation of the hyperbranched structure owing to the decreased stability of the intermediate radicals derived from the norbornene group, which was confirmed by a model copolymerization system of two single vinyl monomers with similar structures to the vinyl groups in the asymmetrical divinyl monomer. Furthermore, Tri-SEC and conventional Sin-SEC as well as H-1 NMR.

CNT Templated Regioselective Enzymatic Polymerization of Phenol in Water and Modification of Surface of MWNT Thereby

Carbon nanotubes (CNTs) are used as templates to synthesize regioselective polymers from enzymatic polymerization of phenol in water. About 90% of total polymeric units in the obtained polymers are the highly thermally stable oxyphenylene units. The polymer-yields are dependent on the quantities of CNTs used. On the basis of MWNT-templated enzymatic polymerization of phenol, covalent attachment of polyphenol chains to the surface of MWNT by way of a linking molecule, hydroquinone, is achieved. This approach supplies a novel way for producing high-performance polymers and for functionalization of the surface of CNT.

Folate-Conjugated Micelles and Their Folate-Receptor-Mediated Endocytosis

A folate-conjugated copolymer PEG-PLA-PLL/folate was synthesized and mixed with pure PEG-PLA-PLL and a fluorescent model drug mFITC to prepare folate-conjugated micelles. The distribution of micelles was studied on cancer-cell-bearing mice via frozen slicing. The results show that mFITC is successfully encapsulated into folate(+) and folate(-)micelles; PEG-PLA-PLL micelles the latter can be internalized by both HeLa and CHO cells without selectivity due to their cationic surface charges, while folate(+)micelles exhibit more preferential endocytosis by HeLa cells than by CHO cells. The folate(-)micelles showed retention in both organs and tumors. The folate(+)micelles are a promising active targeting drug delivery system for FR over-expressing cells and they accumulate in tumor beds.

Feasibility of biodegradable PLGA common bile duct stents: An in vitro and in vivo study

The current study investigates the feasibility of using a biodegradable polymeric stent in common bile duct (CBD) repair and reconstruction. Here, poly(l-lactide-co-glycolide) (PLGA, molar ratio LA/GA = 80/20) was processed into a circular tube- and dumbbell-shaped specimens to determine the in vitro degradation behavior in bile. The morphology, weight loss, and molecular weight changes were then investigated in conjunction with evaluations of the mechanical properties of the specimen. Circular tube-shaped PLGA stents with X-ray opacity were subsequently used in common bile duct exploration (CBDE) and primary suturing in canine models. Next, X-ray images of CBD stents in vivo were compared and levels of serum liver enzymes and a histological analysis were conducted after stent transplantation. The results showed that the PLGA stents exhibited the required biomedical properties and spontaneously disappeared from CBDs in 4-5 weeks. The degradation period and function match the requirements in repair and reconstruction of CBDs to support the duct, guide bile drainage, and reduce T-tube-related complications.

Comparative study of paclitaxel physically encapsulated in and chemically conjugated with PEG-PLA

Paclitaxel-loaded poly(ethylene glycol)-b-poly(L-lactide (LA)) (PEG-PLA) micelles were prepared by two methods. One is physical encapsulation of paclitaxel in micelles composed of a PEG-PLA block copolymer and the other is based on a PEG-PLA-paclitaxel conjugate, abbreviated as "conjugate micelles" Their physicochemical characteristics, e.g. critical micelle concentration (CMC), morphology, and micelle size distribution were then evaluated by means of fluorescence spectroscopy, scanning electron microscopy (SEM), and dynamic light scattering (DLS). The results show that the CMC of PEG-PLA-paclitaxel and PEG-PLA are 6.31 x 10(4) and 1.78 x 10(-3) g L-1, respectively. Both micelles assume a spherical shape with comparable diameters and have unimodal size distribution. Moreover, in vitro drug delivery behavior was studied by high performance liquid chromatography (HPLC). The antitumor activity of the paclitaxel-loaded micelles against human liver cancer H7402 cells was evaluated by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) method.

Prostate cancer cell-specific VEGF siRNA delivery system using cell targeting peptide conjugated polyplexes

A polymeric gene carrier was developed to deliver vascular endothelial growth factor (VEGF) small interfering RNA (siRNA) for prostate cancer cells in a target-specific manner. Prostate cancer-binding peptide (PCP) was conjugated with polyethylenimine (PEI) via a poly(ethylene glycol) (PEG) linker (PEI-PEG-PCP). The PEI-PEG-PCP conjugate could effectively condense siRNA to form stable polyelectrolyte complexes (polyplexes) with an average diameter of approximately 150 nm in an aqueous solution. VEGF siRNA/PEI-PEG-PCP polyplexes exhibited significantly higher VEGF inhibition efficiency than PCP-unmodified polycationic carriers (PEI-PEG or PEI) in human prostate carcinoma cells (PC-3 cells). The enhanced gene silencing activity of VEGF siRNA/PEI-PEG-PCP was maintained even under serum conditions, owing to the steric stabilization of the polyplexes with hydrophilic PEG grafts. Confocal microscopic studies revealed that the siRNA/PEI-PEG-PCP polyplexes were delivered into PC-3 cells in a PCP ligand-specific manner.

Biodegradable amphiphilic polymer-drug conjugate micelles

The coupling of drugs to macromolecular carriers received an important impetus from Ringsdorf's notion of polymer-drug conjugates. Several water-soluble polymers, poly(ethylene glycol), poly[N-(2-hydroxypropyl) methacrylamidel, poly(L-glutamic acid) and dextran, are studied intensively and have been utilized successfully in clinical research. The promising results arising from clinical trials with polymer-drug conjugates (e.g., paclitaxel, doxorubicin, camptothecins) have provided a firm foundation for other synthetic polymers, especially biodegradable polymers, used as drug delivery vehicles. This review discusses biodegradable polymeric micelles as an alternative drug-conjugate system. Particular focus is on A-B or B-A-B type biodegradable amphiphilic block copolymer such as polylactide, morpholine-2,5-dione derivatives and cyclic carbonates, which can form a core-shell micellar structure, with the hydrophobic drug-binding segment forming the hydrophobic core and the hydrophilic segment as a hydrated outer shell. Polymeric micelles can be designed to avoid uptake by cells of reticuloendothelial system and thus enhance their blood lifetime via the enhanced permeability and retention effect.

Toward high-performance polymer solar cells: The importance of morphology control

Polymer solar cells have the potential to become a major electrical power generating tool in the 21st century. R&D endeavors are focusing on continuous roll-to-roll printing of polymeric or organic compounds from solution-like newspapers-to produce flexible and lightweight devices at low cost. It is recognized, though, that besides the functional properties of the compounds the organization of structures on the nanometer level-forced and controlled mainly by the processing conditions applied-determines the performance of state-of-the-art polymer solar cells. In such devices the photoactive layer is composed of at least two functional materials that form nanoscale interpenetrating phases with specific functionalities, a so-called bulk heterojunction. In this perspective article, our current knowledge on the main factors determining the morphology formation and evolution is introduced, and gaps of our understanding on nanoscale structure-property relations in the field of high-performance polymer solar cells are addressed. Finally, promising routes toward formation of tailored morphologies are presented.

Confined intra-molecular clustering in orientated polyethylene after annealing

Deuterated polyethylene tracer molecules with small amount of branches (12 C2H5- branches per 1000 backbone carbon atoms) were blended with a hydrogenated polyethylene matrix to form a homogenous mixture. The conformational evolution of the deuterated chains in a stretched semi-cry stall me film was observed via online small angle neutron scattering measurements during annealing at high temperatures close to the melting point. Because the sample was annealed at a temperature closely below its melting point, the crystalline lamellae were only partially molten and the system could not fully relax. The global chain dimensions were preserved during annealing. Recrystallization of released polymeric chain segments allows for local phase separation thus driving the deuterated chain segments into the confining interlamellar amorphous layers giving rise to an interesting intra-molecular clustering effect of the long deuterated chain. This clustering is deduced from characteristic small angle neutron scattering patterns. The confined phase separation has its origin in primarily the small amount of the branches on the deuterated polymers which impede the crystallization of the deuterated chain segments.

Fabrication of conductive metallized nanostructures from self-assembled amphiphilic triblock copolymer templates: Nanospheres, nanowires, nanorings

Various metallized nanostructures (such as rings, wires with controllable lengths, spheres) have been successfully fabricated by coating metallic nanolayers onto soft nanotemplates through simple electroless methods. In particular, bimetallic nanostructures have been obtained by using simple methods. The multiple functional polymeric nanostructures, were obtained through the self-assembly of polystyrene/poly(4-vinyl pyridine) triblock copolymer (P4VP-b-PS-b-P4VP) in selective media by changing the common solvent properties. By combining field emission scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) characterization, it was confirmed that polymer/metal and bimetallic (Au@Ag) core-shell nanostructures could be achieved by chemical metal deposition method.

Transformation from ordered islands to holes in phase-separating P2VP/PS blend films by adding triton X-100

Our previous investigation showed that the ordered hexagonal island pattern in the phase-separating polymeric blend films of polystyrene and poly(2-vinylpyridine) (PS/P2VP) formed due to the convection effect by proper control of PS molecular weight, solvent evaporation rate, and the weight ratio of PS to P2VP. In this paper, we further illustrate that, by adding a proper amount of the surfactant Triton X-100 to the PS/P2VP toluene solution, the ordered hexagonal island pattern can be transformed to the ordered honeycomb pattern. The effects of the amount of Triton X-100 on the surface morphology evolution and the pattern transformation are discussed in terms of the collapse of Triton X-100, phase separation between Triton X-100/P2VP and PS, the interfacial interaction between Triton X-100/P2VP and the mica substrate, and the Benard-Marangoni convection.

Surface morphology evolution of poly (styrene-block-4-vinylpyridine) (PS-b-P4VP)(H+) and poly(methyl methacrylate)-dibenzo-18-crown-6-poly(methyl methacrylate) (PMCMA) supramolecular film

Well-ordered nanostructured polymeric supramolecular thin films were fabricated from the supramolecular assembly of poly(styrene-block-4-vinylpyridine) (PS-b-P4VP)(H+) and poly(methyl methacrylate)-dibenzo-18-crown-6-poly(methyl methacrylate) (PMCMA). A depression Of cylindrical nanodomains was formed by the block of P4VP(H+) and PMCMA associates surrounded by PS. The repulsive force aroused from the incompatibility between the block of P4VP(H+) and PMCMA was varied through changing the molecule weight (M-w) of PMCMA, the volume fraction of the block of P4VP(H+), and annealing the film at high temperature. Increasing the repulsive force led to a change of overall morphology from ordered nanoporous to featureless structures. The effects of solvent nature and evaporation rate on the film morphology were also investigated. Further evolution of surface morphologies from nanoporous to featureless to nanoporous structures was observed upon exposure to carbon bisulfide vapors for different treatment periods. The wettability of the film surface was changed from hydrophilicity to hydrophobicity due to the changes of the film surface microscopic composition.