Archive for the ‘Paper of the Week’ Category

Paper of the week: Variable conformation pH responsive block copolymers for drug delivery

Polymeric carriers offer many advantages for controlled release applications, drug delivery and nanomedicine. These systems need to be water-soluble, non-toxic and non-immunogenic, as well as compatible with serum components. For most applications, polymer based delivery systems must also be capable of being either degraded to harmless breakdown products or eliminated entirely from the body. Furthermore, these carriers need functional groups that allow them to interact with or encapsulate a drug of interest, and preferably should contain recognition motifs, which target disease-related antigens or receptors. Not surprisingly, the combination of these factors is hard to achieve with existing materials, leading to an urgent need for new highly functional and active biomedical polymers.

Graphical abstract: Synthesis and characterization of variable conformation pH responsive block co-polymers for nucleic acid delivery and targeted cell entry

In this article, Vicent, Salmaso, Alexander and co-workers prepared a modular and effective controlled release system, based on polymers designed to respond to the pH-changes that occur in tissues affected by peculiar disease. The individual blocks were composed of (a) permanently hydrophilic chains with neutral functionality and (b) acrylate polymers with weakly basic side-chains. Variation in co-monomer content, molar mass and block ratios/compositions led to a range of pH-responses, manifested through reversible self-assembly into micelles and/or polymersomes. These transitions were tuned to achieve environmental responses in a pH range from 5–7. The ability of the systems assembled with these polymers to act as pH-responsive containers was shown by DNA encapsulation and release studies, and their potential for application as vehicle for drug delivery was proved by cell metabolic activity and cell uptake measurements.

Synthesis and characterization of variable conformation pH responsive block co-polymers for nucleic acid delivery and targeted cell entry by Teresa Matini, Nora Francini, Anna Battocchio, Sebastian G. Spain, Giuseppe Mantovani, Maria J. Vicent, Joaquin Sanchis, Elena Gallon, Francesca Mastrotto, Stefano Salmaso, Paolo Caliceti and Cameron Alexander Polym. Chem. 2014, 5, 1626-1636.

Julien Nicolas is a web-writer and advisory board member for Polymer Chemistry. He currently works at Univ. Paris-Sud (FR) as a CNRS researcher.

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Paper of the week: Facile synthesis of thiol-functionalized amphiphilic polylactide–methacrylic diblock copolymers

Block copolymers based on the same type of monomer (e.g., either vinyl or cyclic monomers) are traditionally prepared using a single “living” polymerization technique. Recently, novel block copolymers with interesting properties have been prepared by combining two or more “living” polymerization chemistries to copolymerize dissimilar monomers. Sequential polymerizations are most commonly used for such syntheses. In principle, simultaneous polymerization can also lead to the synthesis of block copolymers. In practice, there are some examples in the literature for which incompatibility problems have been overcome to combine different polymerization techniques for the synthesis of well-defined block copolymers in a single step.

Graphical abstract: Facile synthesis of thiol-functionalized amphiphilic polylactide–methacrylic diblock copolymers

In this publication, Themistou, Battaglia and Armes reported on the one-pot metal-free ring-opening polymerization (ROP)–reversible addition–fragmentation chain transfer (RAFT) synthesis of biocompatible linear and branched amphiphilic diblock copolymers based on a biodegradable aliphatic polyester (PLA) and methacrylic monomers (such as 2-(dimethylamino)ethyl methacrylate (DMA) or oligo(ethylene glycol) methacrylate (OEGMA)), using a novel hydroxyl-functionalized trithiocarbonate-based chain transfer agent. These amphiphilic diblock copolymers self-assembled in dilute aqueous solution, leading to various copolymer morphologies depending on the block compositions. Two novel disulfide-functionalized PLA-branched block copolymers were also synthesized using simultaneous ROP of LA and RAFT copolymerization of OEGMA or DMA with a disulfide-based dimethacrylate. The disulfide bonds were reductively cleaved using tributyl phosphine to generate reactive thiol groups. Thiol–ene chemistry was utilized for further derivatization with thiol-based biologically important molecules and heavy metals for tissue engineering or bioimaging applications, respectively.

Facile synthesis of thiol-functionalized amphiphilic polylactide–methacrylic diblock copolymers by Efrosyni Themistou, Giuseppe Battaglia and Steven P. Armes Polym. Chem. 2014, 5, 1405-1417.

Julien Nicolas is a web-writer and advisory board member for Polymer Chemistry. He currently works at Univ. Paris-Sud (FR) as a CNRS researcher.

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Paper of the week: Biohybrid structures consisting of biotinylated glycodendrimers and proteins

The design of versatile nanostructured biohybrid materials has gained increasing attention over the past decades due to their potentially extraordinary and synergetic properties and functions. The combination of components of synthetic and natural origins allows an applicability going far beyond the biomedical field including diverse matters such as bio-sensors, artificial enzymes, light harvesting systems, photonics and nanoelectronic devices.

Graphical abstract: Biohybrid structures consisting of biotinylated glycodendrimers and proteins: influence of the biotin ligand's number and chemical nature on the biotin–avidin conjugation

In this study, Voit, Appelhans and co-workers demonstrated the successful fabrication of biohybrid structures tailored by non-covalent interactions for potential biochemical applications. Using avidin-biotin conjugation as the deciding non-covalent interaction step, different nanometer-sized biohybrid structures can be established by using different molar interaction ratios between mono-, bi- and tetravalent biotinylated glycodendrimers and avidin.  The biotin ligand’s spacer length, its chemical structure and the degree of biotin functionalization were shown to be essential parameters in the formation of nanostructures with avidin having a controlled composition and size dimension up to 100 nm. Biohybrid structures with avidin as a central unit required monovalent glycodendrimers with PEG-linked biotin, while bi- and tetravalent glycodendrimers with short alkyl-linked biotin ligands were more efficient than their counterparts with longer PEG–biotin ligands in the fabrication of defined biohybrid structures (diameters up to 100 nm) with avidin as a bridging unit.  Not only does this study elucidate the formation of biohybrid structures between avidin and biotinylated glycodendrimers in the conjugation solution, but it also provides deeper insight into these supramolecular (bio)polymeric structures from a general point of view.

Biohybrid structures consisting of biotinylated glycodendrimers and proteins: influence of the biotin ligand’s number and chemical nature on the biotin–avidin conjugation by Franka Ennen, Susanne Boye, Albena Lederer, Mihaela Cernescu, Hartmut Komber, Bernhard Brutschy, Brigitte Voit and Dietmar Appelhans Polym. Chem. 2014, 5, 1323-1339.

Julien Nicolas is a web-writer and advisory board member for Polymer Chemistry. He currently works at Univ. Paris-Sud (FR) as a CNRS researcher.

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Paper of the week: Self-healing polymer networks via the photodissociation of alkoxyamine junctions

The development of self-healing polymers has been the subject of a tremendous amount of research over the last decade. When self-healing materials are mechanically damaged, either internally (crack) or externally (scratch), these materials are capable of restoring their original shape and/or recovering their properties. Various approaches have been investigated to achieve polymers exhibiting such behavior.

Graphical abstract: Introduction of self-healing properties into covalent polymer networks via the photodissociation of alkoxyamine junctions

In this study, Poly, Lalevée, Matyjaszewski and co-workers reported on a new approach for the synthesis of dynamic covalent networks exhibiting self-healing properties under UV irradiation. The procedure combined ATRP and click chemistry as two versatile synthetic tools for the design of well-defined peripherally functionalized star-like oligomers followed by their covalent bonding with responsive alkoxyamine crosslinking agents. The incorporation of alkoxyamine linkages into the junctions between the stars enabled their subsequent cleavage under irradiation. Beyond self-healing materials, the concept developed in the present study might be of interest regarding aging issues of polymeric materials due to UV radiation.

Introduction of self-healing properties into covalent polymer networks via the photodissociation of alkoxyamine junctions by Siham Telitel, Yoshifumi Amamoto, Julien Poly, Fabrice Morlet-Savary, Olivier Soppera, Jacques Lalevée and Krzysztof Matyjaszewski Polym. Chem. 2014, 5, 921-930.

Julien Nicolas is a web-writer and advisory board member for Polymer Chemistry. He currently works at Univ. Paris-Sud (FR) as a CNRS researcher.

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Paper of the week: Spontaneous shape changes in polymersomes via polymer/polymer segregation

To elucidate the molecular basis and role of lipid surface domains in cellular processes, giant unilamellar vesicles (GUV, 10–100 μm) have been widely studied as a simple model system. Due to the large average diameter of these giant liposomes, the phase separation of different lipid mixtures – usually as a result of mismatch between the phospholipid chains – can be readily investigated with optical microscopy. With GUVs it was shown that raft formation in some cases leads to local membrane curvature at the domain boundaries or to complete shape deformation. Lipid raft formation is a great source of inspiration for the creation of complex artificial systems like polymer-based vesicles. Polymeric vesicles, known as polymersomes, are the more robust analogues of liposomes; they are composed of high molecular weight amphiphilic block copolymers instead of low molecular weight phospholipids and therefore consist of a membrane exhibiting superior physical and chemical stability. Despite this toughness, polymersomes are capable of domain formation when two or more distinct block copolymers are blended within one membrane. However, the number of studies reporting domain formation in nanoscaled polymersomes is limited because the characterization of polymer/polymer segregation in nanoscale vesicular structures remains a challenge to date.

Graphical abstract: Spontaneous shape changes in polymersomes via polymer/polymer segregation

In this study, van Hest and co-workers demonstrated that nanometer-sized polymersomes assembled from two dissimilar diblock copolymers can undergo shape changes, driven by strong lateral polymer/polymer segregation within the membrane. The two particular block copolymers consisted of identical hydrophobic fragments to stimulate co-assembly, while their hydrophilic segments were either neutrally or negatively charged. It was hypothesized that demixing of the two types of polymer amphiphiles within the bilayer was caused by the different hydrophilic polymer fractions exhibiting intrinsically different interfacial curvatures upon self-assembly. Given the potentially unlimited number of possible hybrid polymersome systems, the local polymer/polymer separation phenomenon could be easily exploited further in the construction of new polymersome morphologies, with potential applications in both nanoscience and biomedical fields.

Spontaneous shape changes in polymersomes via polymer/polymer segregation by Silvie A. Meeuwissen, Stéphanie M. C. Bruekers, Yingchao Chen, Darrin J. Pochan and Jan C. M. van Hest Polym. Chem. 2014, 5, 489-501.

Julien Nicolas is a web-writer and advisory board member for Polymer Chemistry. He currently works at Univ. Paris-Sud (FR) as a CNRS researcher.

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Paper of the week: Polymer patchy colloids with sticky patches

Patchy particles (PPs) are colloidal particles with a chemically or physically patterned surface. The patchy domains may provide specific and directional interactions with other particles or surfaces and therefore PPs can self- and direct-assemble into novel suprastructures which can find applications in the delivery of drugs or other chemicals, electronic devices, photonic crystals, and sensors. Currently, the preparation of PPs mainly focuses on templating or chemical patterning, glancing angle deposition, particle lithography, capillary fluid flow, and self-assembly of pre-synthesized block copolymers. These approaches, however, are difficult to scale up because of demanding synthetic routes or owing to intrinsic limitations related to the preparation process, and therefore hamper the study and development of PPs.

Graphical abstract: Polymer patchy colloids with sticky patches

In this study, Crespy and co-workers developed an easy, low-cost and mild strategy to fabricate PPs in large quantities without using block copolymers. Polymerization-induced phase separation was found to be the reason for the formation of the PPs. The size of the patches could be easily tuned by controlling the monomer conversion or by changing the composition of the nanoparticles. The atomic force microscopy analysis revealed that the patches were sticky and embedded in a harder polymer matrix. Moreover, the patchy structure could be locked by cross-linking the sticky patches. Their approach could be extended to prepare large libraries of different PPs by choosing other polymer/monomer pairs and/or by post-functionalizing the patchy area.

Polymer patchy colloids with sticky patches by Yi Zhao, Rüdiger Berger, Katharina Landfester and Daniel Crespy Polym. Chem. 2014, 5, 365-371.

Julien Nicolas is a web-writer and advisory board member for Polymer Chemistry. He currently works at Univ. Paris-Sud (FR) as a CNRS researcher.

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Paper of the week: Binding and supramolecular organization of homo- and heterotelechelic oligomers in solutions

Supramolecular chemistry, defined as the chemistry of noncovalent bonds (such as hydrogen bonding, π–π stacking, hydrophobic interactions, etc.), is a promising tool to create functional materials. Indeed, noncovalent bonds introduce reversibility and stimuli-responsiveness to materials. Therefore, compared to high-molecular-weight covalent polymers, processing and recycling of supramolecular polymers could be easier. Furthermore, incorporating noncovalent bonds into materials can impart original properties, such as self-healing. The simplest situation occurs when oligomers are equipped with complementary or self-complementary functional end-groups. They can in principle associate to form linear chain supramolecular polymers. The strength of the association constant controls the length of the polymer. Furthermore, supramolecular organizations at mesoscopic scales often appear and they lead to a richer and interesting behavior in comparison with classical covalent polymers. Complex mesoscopic organizations were observed both in the bulk and in solution.

Graphical abstract: Binding and supramolecular organization of homo- and heterotelechelic oligomers in solutions

In this study, Leibler and co-workers reported on the subtle influence of solvent on the organization of supramolecular polymers. They synthesized homotelechelic and heterotelechelic oligomers of poly(propylene oxide) (PPO) equipped with complementary hydrogen bonding functional ends, thymine (Thy) and diaminotriazine (DAT). In a solvent that dissociates Thy–DAT hydrogen bonds, such as DMSO, the viscosity was low for all functional telechelic oligomers. In non-dissociative solvents, the addition of functional oligomers increased the viscosity. For both the homotelechelic blends and the heterotelechelics, the viscosity in toluene was about two times higher than that in chloroform. Additionally, the Thy–DAT association constant was 22 times higher. Carbon relaxation times measured by NMR and viscosity variation for solutions of different concentrations suggest a distinct supramolecular organization in chloroform and toluene: linear and cyclic supramolecular chains in chloroform and small π-stacked objects with a PPO shell and a Thy, DAT core in toluene. One might expect that when the materials are obtained by solvent evaporation, the organization in the bulk is solvent dependent as this is often the case for ABC block copolymers.

Binding and supramolecular organization of homo- and heterotelechelic oligomers in solutions by Jessalyn Cortese, Corinne Soulié-Ziakovic and Ludwik Leibler Polym. Chem. 2014, 5, 116-125.

Julien Nicolas is a web-writer and advisory board member for Polymer Chemistry. He currently works at Univ. Paris-Sud (FR) as a CNRS researcher.

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Paper of the week: All-carbon composite paper and its application in supercapacitors

Flexible papers, which utilize graphene (G) sheets as building blocks in vacuum-assisted self-assembly, have already been developed as binder-free flexible electrodes for supercapacitors due to their excellent mechanical flexibilities and electrical conductivities. Nevertheless, in most cases, the large specific surface area of the closely-packed and oriented G sheets throughout the G papers is inevitably lost which significantly reduces their potential application as supercapacitor electrodes. Thus, it is still a great challenge to develop a feasible and effective way to fabricate G-based hybrid papers as flexible electrodes with relatively high capacitances and without the sacrifice of their good cyclic stabilities.

Graphical abstract: All-carbon composite paper as a flexible conducting substrate for the direct growth of polyaniline particles and its applications in supercapacitors

In this study, Liu and co-workers reported a new strategy for the synthesis of polyaniline (PANI) nanostructures on a flexible G–carbon nanotube (G-CNT) composite paper substrate, which can be directly used as flexible electrodes possessing both electric double layer (EDL) capacitance and pseudocapacitance. The ternary hybrid paper exhibited a reversible capacity of up to 432 F g-1 at a discharge rate of 0.5 A g-1, which was much larger than that of bare G–CNT composite paper (172.4 F g-1); and its cyclic performance was dramatically enhanced, sustaining greater than 96% of its original capacitance after 600 charge–discharge cycles. Besides, the good electrical conductivity of the G–CNT composite paper provided improved conductive pathways for charge transfer at the electrodes thus resulting in superior capacitance during charge–discharge processes. Therefore, the method reported here provides a simple and efficient approach to fabricating G–CNT–PANI ternary hybrid papers with designed hierarchical nanostructures, and may be easily extended to the design of next generation high performance flexible supercapacitors.

All-carbon composite paper as a flexible conducting substrate for the direct growth of polyaniline particles and its applications in supercapacitors by Chao Zhang, Weng Weei Tjiu and Tianxi Liu Polym. Chem. 2013, 4, 5785-5792.

Julien Nicolas is a web-writer and advisory board member for Polymer Chemistry. He currently works at Univ. Paris-Sud (FR) as a CNRS researcher.

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Paper of the week: A CeO2/PVDC hybrid latex mediated by a phosphonated macro-RAFT agent

Combining organic matter with divided inorganic matter (nanoparticles, clays, nanofibers, etc.) is one of the main current trends to bring about new properties to polymer films. More specifically, emulsion polymerization allows the elaboration of waterborne hybrid films by incorporating mineral fillers into polymer particles to create hybrid latexes. Hence, when such latexes are directly applied as a coating, mineral entities are well distributed within the polymer matrix. Cerium oxide nanoparticles possess valuable properties, such as catalytic oxidation activity, relatively high ionic conductivity, and great potential as UV stabilizers. However, to benefit from the specific properties provided by nanoceria, a preliminary step is required in order to compatibilize the mineral phase with the polymer phase.

Graphical abstract: A CeO<sub>2</sub>/PVDC hybrid latex mediated by a phosphonated macro-RAFT agent

In their paper, Lacroix-Desmazes and co-workers reported the synthesis of a CeO2/poly(vinylidene chloride) (PVDC) hybrid latex carried out via the functionalization of CeO2 nanoparticles by reversible addition-fragmentation chain transfer (RAFT) polymerization from a phosphonated macro-RAFT agent, with very efficient formation of hybrid structures (neither free ceria nanoparticles nor free latex particles). This hybrid latex, obtained by emulsion polymerization with a reasonably high solid content (25%), represents a good candidate for the elaboration of high performance coatings. Furthermore, the authors also considered the use of such hybrid latexes as templates for the preparation of functional organic or inorganic porous materials with CeO2 nanoparticles (or other nanoparticles) evenly distributed in the porous matrix.

A CeO2/PVDC hybrid latex mediated by a phosphonated macro-RAFT agent by Jérôme Warnant, Jérôme Garnier, Alex van Herk, Pierre-Emmanuel Dufils, Jérôme Vinas and Patrick Lacroix-Desmazes Polym. Chem. 2013, 4, 5656-5663.

Julien Nicolas is a web-writer and advisory board member for Polymer Chemistry. He currently works at Univ. Paris-Sud (FR) as a CNRS researcher.

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Paper of the week: Water-soluble BODIPY-conjugated glycopolymers as fluorescent probes for live cell imaging

Fluorescent probes have attracted significant attention in targeted imaging and early detection of tumor cells. Detection of real biomarkers in physiological fluid samples can dramatically impair fluorescent agent sensitivity and specificity because of biofouling and nonspecific binding. These uncertainties and drawbacks have limited the practical use of fluorescent agents in a clinical environment for medical diagnostics. Hence, the development of novel fluorescent materials with high cellular internalization efficiency, good photostability, and high specificity for tumor cell staining is in urgent demand.

Graphical abstract: Water-soluble BODIPY-conjugated glycopolymers as fluorescent probes for live cell imaging

In this article, Zhang, Li and co-workers synthesized by Atom Transfer Radical Polymerization (ATRP) a highly water-soluble, multivalent and highly specific BODIPY-conjugated glycopolymer for direct tumor cell imaging, which showed good photostability. The cell viability of BODIPY-conjugated glycopolymers against HepG2 and NIH3T3 cells was more than 80%, indicating that the glycopolymers have low cytotoxicity to living cells. Moreover, simple incubation of living cells with a BODIPY-conjugated glycopolymer led to efficient internalization into HepG2 and clear visualization in cytoplasm, due to the high brightness of BODIPY and good specificity between HepG2 and galactose as compared to NIH3T3 cells. These results suggest that BODIPY-conjugated glycopolymers have potential use as fluorescent probes in live cell imaging.

Water-soluble BODIPY-conjugated glycopolymers as fluorescent probes for live cell imaging by Zhentan Lu, Lin Mei, Xinge Zhang, Yanan Wang, Yu Zhao and Chaoxing Li Polym. Chem. 2013, 4, 5743-5750.

Julien Nicolas is a guest web-writer and advisory board member for Polymer Chemistry. He currently works at Univ. Paris-Sud (FR) as a CNRS researcher.

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