Time filter

Source Type

Märstetten-Dorf, Switzerland

Deng C.,Soochow University of China | Wu J.,Soochow University of China | Cheng R.,Soochow University of China | Meng F.,Soochow University of China | And 3 more authors.
Progress in Polymer Science

Polypeptides derived from naturally occurring α-amino acids have emerged as a unique and versatile family of bio-inspired biomaterials that can be tailor-made for varying biomedical applications such as controlled drug release, gene delivery, tissue engineering and regenerative medicine. In contrast to traditional biodegradable polymers such as aliphatic polyesters and polycarbonates, polypeptides are inherently functional, allow precise control over polarity and charges, show excellent stability against hydrolysis, and are prone to rapid biodegradation in vivo by specific enzymes. Ring-opening polymerization (ROP) of α-amino acid N-carboxyanhydrides (NCAs) is the most straightforward and practical approach for large-scale production of high molecular weight polypeptides. In the past decade, a remarkable progress has been made in controlled NCA polymerization, which offers an unprecedented access to precision polypeptide and hybrid materials by combining with living radical polymerization, click chemistry, and/or post-polymerization modification. Notably, several micellar anti-cancer drugs based on poly(ethylene glycol)-polypeptides have been already advanced to the clinical evaluation. In this review paper, we give an overview on de novo design, controlled synthesis and emerging biomedical applications of functional polypeptide and hybrid materials. © 2013 Elsevier Ltd. All rights reserved. Source

Paripovic D.,Institute des Materiaux | Klok H.-A.,Institute des Materiaux
Macromolecular Chemistry and Physics

Hydrophilic polymer brushes grown via surface-initiated ATRP from silicon oxide surfaces are susceptible to detachment via hydrolytic cleavage of the anchoring siloxane bond. This paper investigates the influence of the structure of the ATRP initiator on the stability of these brushes and seeks for strategies to further enhance their stability. It is found that increasing the hydrophobicity of the organosilane modified ATRP initiator reduces the susceptibility of the brushes toward cleavage. Robust, hydrophilic polymer brushes are prepared, which are obtained by introducing a short, hydrophobic PMMA or PEHMA block between the silicon oxide substrate and the hydrophilic polymer brush. Hydrolytic cleavage of the anchoring siloxane bond limits the stability and durability of hydrophilic polymer brushes grown from silicon oxide surfaces functionalized with dimethylchlorosilane modified ATRP initiators. The stability of the brushes can be enhanced by increasing the hydrophobicity of the surface-tethered ATRP initiator, or, more effectively, by introducing a short hydrophobic block between the silicon oxide substrate and the polymer brush. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Coad B.R.,University of South Australia | Bilgic T.,Institute des Materiaux | Klok H.-A.,Institute des Materiaux

A new method for generating a surface density gradient of polymer chains is presented. A substrate-independent polymer deposition technique was used to coat materials with a chemical gradient based on plasma copolymerization of 1,7-octadiene and allylamine. This provided a uniform chemical gradient to which initiators for atom transfer radical polymerization (ATRP) were immobilized. After surface-initiated atom transfer radical polymerization (SI-ATRP), poly(2-hydroxyethyl methacrylate) (PHEMA) chains were grafted from the surface and the measured thickness profiles provided direct evidence for how surface crowding provides an entropic driving force resulting in chain extension away from the surface. Film thicknesses were found to increase with the position along the gradient surface, reflecting the gradual transition from collapsed to more extended surface-tethered polymer chains as the grafting density increased. The method described is novel in that the approach provides covalent linkages from the polymer coating to the substrate and is not limited to a particular surface chemistry of the starting material. © 2014 American Chemical Society. Source

Friedli J.,Institute des Materiaux | Fife J.L.,Institute des Materiaux | Fife J.L.,Paul Scherrer Institute | Di Napoli P.,Institute des Materiaux | Rappaz M.,Institute des Materiaux
IOP Conference Series: Materials Science and Engineering

Recently, Gonzales and Rappaz [Met. Mat. Trans. A37:2797, 2006] showed the influence of an increasing zinc content on the growth directions of aluminum dendrites. 100 and 110 dendrites were observed below 25wt.% and above 55wt.% zinc, respectively, whereas textured seaweeds and 320 dendrites were observed at intermediate compositions. Considering the complexity of these structures, it is necessary to first characterize them in further details and second, to model them using the phase field method. The so-called Dendrite Orientation Transition (DOT) was thus reinvestigated in quenched Bridgman solidification samples. The combination of X-ray tomographic microscopy and electron backscattered diffraction (EBSD) analysis on a whole range of compositions, from 5 to 90wt.% Zn, allowed insights with unprecedented details about texture, growth directions and mechanisms of the aforementioned structures. We show that seaweeds rather than dendrites are found at all intermediate compositions. Their growth was confirmed to be constrained within a (100) symmetry plane. However, new findings indicate that the observed macroscopic texture does not necessarily correspond to the actual growth directions of the microstructure. Further, it seems to operate by an alternating growth direction mechanism and could be linked to the competition between the 100 and 110 characters of regular dendrites observed at the limits of the DOT. These characters, as well as 3D seaweeds, are observed in phase-field simulations of equiaxed growth and directional solidification, respectively. This study emphasizes the importance of accurate experimental data to validate numerical models and details the progress that such combinations provide for the understanding of growth mechanisms. © Published under licence by IOP Publishing Ltd. Source

Drezet J.-M.,Institute des Materiaux | Sistaninia M.,Institute des Materiaux | Rappaz M.,Institute des Materiaux
Materiaux et Techniques

Hot tearing or solidification cracking is a flaw that appears during casting and welding of metals and alloys. Hot tearing initiates during solidification i.e. when the liquid phase is still present and under tensile deformations acting upon the remaining liquid films. The cracks are always intergranular except in single crystals, and its fracture surfaces appear as dendritic. The present paper aims at giving a state of the art in the understanding and modelling of hot tearing. The key challenge lies in coupling microscopic phenomena such as grain coalescence, solid phase percolation and strain localisation with macroscopic phenomena such as heat transfer and strain build up at the scale of the work piece. Mesoscopic granular models appear to be suitable to capture such coupling. © EDP Sciences, 2010. Source

Discover hidden collaborations