Synthesis of double hydrophilic poly(ethylene oxide)-b-poly(2-hydroxyethyl acrylate) by single-electron transfer-living radical polymerization

Poly(ethylene oxide)/Gelatin-Based Biphasic Photocrosslinkable Hydrogels of Tunable Morphology for Hepatic Progenitor Cell Encapsulation

Macroporous hydrogels have great potential for biomedical applications. Liquid or gel-like pores were created in a photopolymerizable hydrogel by forming water-in-water emulsions upon mixing aqueous solutions of gelatin and a poly(ethylene oxide) (PEO)-based triblock copolymer. The copolymer constituted the continuous matrix, which dominated the mechanical properties of the hydrogel once photopolymerized. The gelatin constituted the dispersed phase, which created macropores in the hydrogel. The microstructures of the porous hydrogel were determined by the volume fraction of the gelatin phase. When volume fractions were close to 50 v%, free-standing hydrogels with interpenetrated morphology can be obtained thanks to the addition of a small amount of xanthan. The hydrogels displayed Young's moduli ranging from 5 to 30 kPa. They have been found to be non-swellable and non-degradable in physiological conditions. Preliminary viability tests with hepatic progenitor cells embedded in monophasic PEO-based hydrogels showed rapid mortality of the cells, whereas encouraging viability was observed in PEO-based triblock copolymer/gelatin macroporous hydrogels. The latter has the potential to be used in cell therapy.

Colored Janus Nanocylinders Driven by Supramolecular Coassembly of Donor and Acceptor Building Blocks

Janus nanocylinders exhibit nanometric dimensions, a high aspect ratio, and two faces with different chemistries (Janus character), making them potentially relevant for applications in optics, magnetism, catalysis, surface nanopatterning, or interface stabilization, but they are also very difficult to prepare by conventional strategies. In the present work, Janus nanocylinders were prepared by supramolecular coassembly in water of two different polymers functionalized with complementary assembling units. The originality of our approach consists in combining charge transfer complexation between electron-rich and electron-poor units with hydrogen bonding to (1) drive the supramolecular formation of one-dimensional structures (cylinders), (2) force the two polymer arms on opposite sides of the cylinders independently of their compatibility, resulting in Janus nanoparticles, and (3) detect coassembly through a color change of the solution upon mixing of the functional polymers.

Polymer Brushes via Surface-Initiated Electrochemically Mediated ATRP: Role of a Sacrificial Initiator in Polymerization of Acrylates on Silicon Substrates

Silicon wafers as semiconductors are essential components of integrated circuits in electronic devices. For this reason, modification of the silicon surface is an important factor in the manufacturing of new hybrid materials applied in micro- and nanoelectronics. Herein, copolymer brushes of hydrophilic poly(2-hydroxyethyl acrylate) (PHEA) and hydrophobic poly(tert-butyl acrylate) (PtBA) were grafted from silicon wafers via simplified electrochemically mediated atom transfer radical polymerization (seATRP) according to a surface-initiated approach. The syntheses of PHEA-b-PtBA copolymers were carried out with diminished catalytic complex concentration (successively 25 and 6 ppm of Cu). In order to optimize the reaction condition, the effect of the addition of a supporting electrolyte was investigated. A controlled increase in PHEA brush thickness was confirmed by atomic force microscopy (AFM). Various other parameters including contact angles and free surface energy (FSE) for the modified silicon wafer were presented. Furthermore, the effect of the presence of a sacrificial initiator in solution on the thickness of the grafted brushes was reported. Successfully fabricated inorganic–organic hybrid nanomaterials show potential application in biomedicine and microelectronics devices, e.g., biosensors.

Photo-Cross-Linked Self-Assembled Poly(ethylene oxide)-Based Hydrogels Containing Hybrid Junctions with Dynamic and Permanent Cross-Links

Homogeneous hydrogels were formed by self-assembly of triblock copolymers via association of small hydrophobic end blocks into micelles bridged by large poly(ethylene oxide) central blocks. A fraction of the end blocks were photo-cross-linkable and could be rapidly cross-linked covalently by in situ UV irradiation. In this manner networks were formed with well-defined chain lengths between homogeneously distributed hybrid micelles that contained both permanent and dynamically cross-linked end blocks. Linear rheology showed a single relaxation mode before in situ irradiation intermediate between those of the individual networks. The presence of transient cross-links decreased the percolation threshold of the network rendered permanent by irradiation and caused a strong increase of the elastic modulus at lower polymer concentrations. Large amplitude oscillation and tensile tests showed significant increase of the fracture strain caused by the dynamic cross-links.

Recent Developments in the Synthesis of Biomacromolecules and their Conjugates by Single Electron Transfer-Living Radical Polymerization

Single electron transfer-living radical polymerization (SET-LRP) represents a robust and versatile tool for the synthesis of vinyl polymers with well-defined topology and chain end functionality. The crucial step in SET-LRP is the disproportionation of the Cu(I)X generated by activation with Cu(0) wire, powder, or nascent Cu(0) generated in situ into nascent, extremely reactive Cu(0) atoms and nanoparticles and Cu(II)X₂. Nascent Cu(0) activates the initiator and dormant chains via a homogeneous or heterogeneous outer-sphere single-electron transfer mechanism (SET-LRP). SET-LRP provides an ultrafast polymerization of a plethora of monomers (e.g., (meth)-acrylates, (meth)-acrylamides, styrene, and vinyl chloride) including hydrophobic and water insoluble to hydrophilic and water soluble. Some advantageous features of SET-LRP are (i) the use of Cu(0) wire or powder as readily available catalysts under mild reaction conditions, (ii) their excellent control over molecular weight evolution and distribution as well as polymer chain ends, (iii) their high functional group tolerance allowing the polymerization of commercial-grade monomers, and (iv) the limited purification required for the resulting polymers. In this Perspective, we highlight the recent advancements of SET-LRP in the synthesis of biomacromolecules and of their conjugates.

Cu(0)-mediated living radical polymerization: recent highlights and applications; a perspective

Cu(0)-mediated living radical polymerization or single electron transfer living radical polymerization (Cu(0)-mediated LRP or SET-LRP) is a versatile polymerization technique that has attracted considerable interest during the past few years for the facile preparation of advanced materials.

Aqueous copper(0) mediated reversible deactivation radical polymerization of 2-hydroxyethyl acrylate

Lowering the concentration of adsorbed radicals on the Cu(0) surface, achieved by reducing catalyst and adding NaBr, is the key to the synthesis of well-defined P(HEA) without a high molecular weight shoulder in aqueous solution using two-step Cu(0) in situ mediation.