Self-assembly of hyperbranched polymers and its biomedical applications

Charge storage and electron transport properties of gold nanoparticles decorating a urethane-methacrylate comb polymer network

We propose enhanced charge storage capacity of nanoparticles based polymer films. A flat band voltage window varying from 5-7 V is obtained leading to a trapped charge density of the order of 10(13) cm(-2). These results vary for two distinct morphologies obtained due to decoration of a urethane-methacrylate comb polymer (UMCP) network by gold nanoparticles (AuNPs). Films have been further investigated for morphology, optical, charge storage, and electron transport properties using techniques like scanning electron microscopy (SEM), atomic force microscopy (AFM), absorption spectroscopy (UV-Vis), scanning tunneling microscopy/spectroscopy (STM/STS) and capacitance versus voltage (C-V) measurements. SEM and AFM confirm either the deposition of AuNPs inside the UMCP network or the formation of ring like structures depending on the deposition sequence. STS measurements performed on both films are compared with bare UMCP and AuNPs films. Current versus voltage (I-V) characteristics so obtained are discussed in the light of electron transport mechanisms in such materials.

A Facile Route to Functional Hyperbranched Polymers by Combining Reversible Addition-Fragmentation Chain Transfer Polymerization, Thiol-Yne Chemistry, and Postpolymerization Modification Strategies

This contribution reports on the preparation of functional hyperbranched polystyrene-based materials via a combination of reversible addition-fragmentation chain transfer (RAFT) polymerization, thiol-yne chemistry, and postpolymerization modification reactions. The thiol-yne approach allows the rapid preparation of hyperbranched polymers under mild reaction conditions from polymeric chains bearing a thiol group at one chain end and an alkyne moiety at the other. Postpolymerization modifications of the focal thiol and peripheral alkyne functionalities present within the hyperbranched structures were conducted using two highly efficient strategies, i.e., phosphine-catalyzed thiol-ene reaction and copper-catalyzed azide-alkyne cycloaddition (CuAAC), respectively. In addition to introducing functionalities by postpolymerization modification onto the periphery of the hyperbranched polymers, the interior of the globular structure could also be functionalized by taking advantage of the isocyanate chemical handle of a poly(styrene-co-3-isopropenyl-α,α-dimethylbenzyl isocyanate) (P(S-co-TMI)) copolymer. The combination of these strategies provides an elegant tool for the elaboration of a wide variety of multifunctional hyperbranched structures.

Galactose-based amphiphilic block copolymers: synthesis, micellization, and bioapplication

Redox-responsive amphiphilic diblock copolymers, poly(6-O-methacryloyl-D-galactopyranose-co-2-(N,N-dimethylaminoethyl) methacrylate)-b-poly(pyridyl disulfide ethyl methylacrylate) (P(MAGP-co-DMAEMA)-b-PPDSMA) were obtained by deprotection of poly((6-O-methacryloyl-1,2:3,4-di-O-isopropylidene-D-galactopyranose)-co-DMAEMA)-b-PPDSMA [P(MAlpGP-co-DMAEMA)-b-PPDSMA], which were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization of PDSMA using P(MAlpGP-co-DMAEMA) as macro-RAFT agent. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) studies showed that diblock copolymers P(MAGP-co-DMAEMA)-b-PPDSMA can self-assemble into micelles. Doxorubicin (DOX) could be encapsulated by P(MAGP-co-DMAEMA)-b-PPDSMA upon micellization and released upon adding glutathione (GSH) into the micelle solution. The galactose functional groups in the PMAGP block had specific interaction with HepG2 cells, and P(MAGP-co-DMAEMA)-b-PPDSMA can act as gene delivery vehicle. So, this kind of polymer has potential applications in hepatoma-targeting drug and gene delivery and biodetection.

Bio-based hyperbranched polyurethane/Fe3O4 nanocomposites: smart antibacterial biomaterials for biomedical devices and implants

The fabrication of a smart magnetically controllable bio-based polymeric nanocomposite (NC) has immense potential in the biomedical domain. In this context, magneto-thermoresponsive sunflower oil modified hyperbranched polyurethane (HBPU)/Fe3O4 NCs with different wt.% of magnetic nanoparticles (Fe3O4) were prepared by an in situ polymerization technique. Fourier-transform infrared, x-ray diffraction, vibrating sample magnetometer, scanning electron microscope, transmission electron microscope, thermal analysis and differential scanning calorimetric were used to analyze various physico-chemical structural attributes of the prepared NC. The results showed good interfacial interactions between HBPU and well-dispersed superparamagnetic Fe3O4, with an average diameter of 7.65 nm. The incorporation of Fe3O4 in HBPU significantly improved the thermo-mechanical properties along with the shape-memory behavior, antibacterial activity, biocompatibility as well as biodegradability in comparison to the pristine system. The cytocompatibility of the degraded products of the NC was also verified by in vitro hemolytic activity and MTT assay. In addition, the in vivo biocompatibility and non-immunological behavior, as tested in Wistar rats after subcutaneous implantation, show promising signs for the NC to be used as antibacterial biomaterial for biomedical device and implant applications.

Self-association and complexation of the anti-cancer drug doxorubicin with PEGylated hyperbranched polyesters in an aqueous environment

Fully atomistic molecular dynamics simulations were employed in order to examine in detail the self-assembly characteristics and the complexation behavior of the anticancer drug doxorubicin with PEGylated hyperbranched polyesters in an aqueous environment. We have examined two variants of the polymeric compound by altering the length of the hydrophilic poly(ethylene glycol) arms attached to the hydrophobic hyperbranched core. By comparing the clustering properties of the drug molecules in a polymer-free system to those in the polymer-containing models, we were able to assess the effects related to the presence and to the structural features of the polymer moiety. In addition, we have distinguished the effects associated with the neutral and protonated drug molecules separately. It was found that, in the presence of the polymeric material, the drug molecules formed clusters preferentially close to the polymer's periphery, the characteristics of which depended on the structural details of the polymeric host and on the charge of the drug molecules. Hydrogen bonding was found to contribute to the polymer/drug complexation, with the nature of the prevailing donor/acceptor pairs depending on the charge of the drug. Dynamic analysis of the drugs' motion revealed that in the polymer-containing systems the drug molecules experienced a larger degree of confinement within the formed clusters compared to that describing their polymer-free analogues, while the structural coherence of the clusters was found to be more persistent in the system with the larger poly(ethylene glycol) arms. The results described in this work, through the monitoring of both static and dynamic aspects of the self-association and the complexation behavior of the neutral and charged molecules of doxorubicin with the polymeric host, may help toward the elucidation of the key parameters that are involved in the formation of effective polymer-based carriers for drug molecules of the anthracycline family used in cancer chemotherapy.

Surface hybrid self-assembly, mechanism, and crystalline behavior of a carboxyl-ended hyperbranched polyester/platinum complex

The self-assembly of hyperbranched polymers has attracted much attention because of their wide application. In this article, we report a new facile surface self-assembly method for a carboxyl-ended hyperbranched polyester/platinum complex (HTD-3-Pt) and obtain ordered structural microrods with a length of 10-20 μm and a width of 1 μm. The length and diameter of the self-assembled microrods could be increased to 300-600 μm and 4-5 μm, respectively, by hierarchical self-assembly. The main factors affecting the morphology of the self-assemblies, including temperature, time, solvent and solubility parameter, and relative humidity were discussed by transmission/reflection polarizing optical microscopy (TRPOM), SEM, and HRSEM. The indications for the coordination bond (-COOPt) included the appearance of a new peak at 1606 cm(-1) and its shifting to 1634 cm(-1) in the FT-IR spectra, the disappearance of the C 1s peak at about 288.6 eV, and the increase in the O 1s electron binding energy in the XPS spectra. Furthermore, an interesting crystal property of the HTD-3-Pt self-assemblies was discovered and confirmed by XRD. The study results from the surface self-assembly mechanism suggest that the coordination induction of the platinum ion play a key role in driving microphase separation between the intermolecular chains and end groups of the HTD-3-Pt to form the microrod self-assemblies. Another interesting finding was that HTD-3-Pt showed a higher catalytic activity for hydrosilylation than did a traditional homogeneous catalyst.

Bioreducible poly(amido amine)s with different branching degrees as gene delivery vectors

Based on the knowledge that cationic polymers with different topographical structures behave differently in gene transfection process, herein, we synthesized three biodegradable poly(amido amine)s (PAAs) with the same repeating units and molecular weights except for degree of branching: linear PAA (LPAA), low-branched PAA (LBPAA), and high-branched PAA (HBPAA). We found that LBPAA could more effectively compact pDNA into positively charged nanoparticles than both HBPAA and LPAA. LBPAA polyplexes had the highest transfection efficiency among the three PAA polyplexes, and the difference in transfection efficiency is mainly attributed to the endocytosis rate. The cytotoxicity of PAAs was negligible at the transfection doses, probably due to the degradable disulfide bonds. Therefore, we could use branching as a parameter to simply tune a polymer's cellular uptake behavior and transfection efficiency.

Biodegradable hyperbranched polyglycerol with ester linkages for drug delivery

Biodegradable hyperbranched polyglycerols (dHPGs) were synthesized through oxyanionic initiating hybrid polymerization of glycerol and glycidyl methacrylate. Due to the introduction of ester linkages into the hyperbranched polyglycerol backbone, dHPGs showed good biodegradability and low cytotoxicity. Benefiting from the existence of terminal hydroxyls and methacryloyl groups, both the anticancer drug methotrexate (MTX) and fluorescent probe Rhodamine-123 could be conjugated onto the surface of dHPGs easily. The resultant MTX-conjugated polymers (dHPG-MTXs) exhibited an amphiphilic character, resulting in the formation of micelles in an aqueous solution. The release of MTX from micelles was significantly faster at mildly acidic pH of 5.0 compared to physiological pH of 7.4. dHPG-MTX micelles could be efficiently internalized by cancer cells. MTT assay against cancer cells showed dHPG-MTXs micelles had high anticancer efficacy. On the basis of their good biodegradability and low cytotoxicity, dHPGs provide an opportunity to design excellent drug delivery systems.

Nanoceria facilitates the synthesis of poly(o-phenylenediamine) with pH-tunable morphology, conductivity, and photoluminescent properties

Poly(ortho-phenylenediamine) synthesis enabled by the catalytic oxidase-like activity of nanoceria was accomplished for applications in electronics, medicine, and biotechnology. The polymer shows unique morphology, conductivity, and photoluminescence based on pH of the solution during synthesis. The various poly(ortho-phenylenediamine) preparations were characterized by UV-visible spectroscopy, scanning electron microscopy, fluorescence spectroscopy, fluorescence microscopy, high-pressure liquid chromatography, and cyclic voltammetry. Poly(ortho-phenylenediamine) synthesized at pH 1.0 by nanoceria was selected to be extensively studied on the basis of the fast synthetic kinetics and the resulting conductive and photoluminescent properties for various applications.

Spiropyran-based hyperbranched star copolymer: synthesis, phototropy, FRET, and bioapplication

Photo- and pH-responsive amphiphilic hyperbranched star copolymers, poly(6-O-methacryloyl-1,2;3,4-di-O-isopropylidene-d-galactopyranose)[poly(2-(N,N-dimethylaminoethyl) methacrylate)-co-poly(1'-(2-methacryloxyethyl)-3',3'-dimethyl-6-nitro-spiro(2H-1-benzo-pyran-2,2'-indoline))](n)s [HPMAlpGP(PDMAEMA-co-PSPMA)(n)], were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of the DMAEMA and the SPMA using hyperbranched PMAlpGP as a macro RAFT agent. In aqueous solution, the copolymers self-assembled to form core-shell micelles with HPMAlpGP core and PDMAEMA-co-PSPMA shell. The hydrophobic fluorescent dye nitrobenzoxadiazolyl derivative (NBD) was loaded into the spiropyran-containing micelles. The obtained micelles not only have the photochromic properties, but also modulate the fluorescence of NBD through fluorescence resonance energy transfer (FRET), which was also observed in living cells. Slight fluorescence intensity decrease of the spiropyran in merocyanine (ME) form was observed after five UV-visible light irradiation cycles. The cytotoxicity of the HPMAlpGP(PDMAEMA-co-PSPMA)(n) micelles was lower than that of 25k PEI. All the results revealed that these photoresponsive nanoparticles are a good candidate for cell imaging and may find broad applications in biological areas such as biological diagnosis, imaging, and detection.

Hyperbranched Poly(propylene oxide): A Multifunctional Backbone-Thermoresponsive Polyether Polyol Copolymer

Backbone-thermoresponsive hyperbranched poly(propylene oxide)-based polyether polyols have been synthesized by anionic ring-opening copolymerization of glycidol and propylene oxide. The number of functional hydroxyl end groups and the lower critical solution temperature (LCST) can be readily adjusted by varying the comonomer ratio. Molecular weights in the range of 1200-2000 g/mol were achieved. Hyperbranched polyether polyols with LCST values between 24 and 83 °C can be obtained in a convenient one-step reaction.