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Ciuciu A.I.,CNR Institute of Neuroscience | Cywinski P.J.,Fraunhofer Institute for Applied Polymer Research
RSC Advances | Year: 2014

Hydrogels are cross-linked water-containing polymer networks that are formed by physical, ionic or covalent interactions. In recent years, they have attracted significant attention because of their unique physical properties, which make them promising materials for numerous applications in food and cosmetic processing, as well as in drug delivery and tissue engineering. Hydrogels are highly water-swellable materials, which can considerably increase in volume without losing cohesion, are biocompatible and possess excellent tissue-like physical properties, which can mimic in vivo conditions. When combined with highly precise manufacturing technologies, such as two-photon polymerization (2PP), well-defined three-dimensional structures can be obtained. These structures can become scaffolds for selective cell-entrapping, cell/drug delivery, sensing and prosthetic implants in regenerative medicine. 2PP has been distinguished from other rapid prototyping methods because it is a non-invasive and efficient approach for hydrogel cross-linking. This review discusses the 2PP-based fabrication of 3D hydrogel structures and their potential applications in biotechnology. A brief overview regarding the 2PP methodology and hydrogel properties relevant to biomedical applications is given together with a review of the most important recent achievements in the field. This journal is © the Partner Organisations 2014.

Zehm D.,University of Sheffield | Zehm D.,Fraunhofer Institute for Applied Polymer Research | Ratcliffe L.P.D.,University of Sheffield | Armes S.P.,University of Sheffield
Macromolecules | Year: 2013

Various poly(2-hydroxyethyl methacrylate-b-benzyl methacrylate) (PHEMA n-PBzMAm) and poly(2-hydroxypropyl methacrylate-b-benzyl methacrylate) (PHPMAn-PBzMAm) nano-objects have been prepared via reversible addition-fragmentation chain transfer (RAFT) alcoholic dispersion polymerization. Using either a PHPMA or PHEMA macro-CTA as a steric stabilizer, chain extension with BzMA was conducted in methanol, ethanol, or isopropanol. In each case, in situ self-assembly is driven by the growing PBzMA chains, which become insoluble in lower alcohols above a certain critical chain length. Empirically, PHPMA macro-CTA proved to be much more effective than PHEMA macro-CTA in such syntheses, since the former conferred higher colloidal stability in alcohol. By constructing two detailed phase diagrams, the final nanoparticle morphology is shown to be sensitive to the DP of the core-forming block (PBzMA), the total solids content, and also the mean DP of the stabilizer block (PHPMA). The latter effect is readily demonstrated for PHPMA macro-CTAs possessing mean DPs of 48 and 63. Using PHPMA48 as a steric stabilizer, a range of nano-objects (spheres, worms or vesicles) can be accessed simply by tuning the DP of the core-forming PBzMA block. In contrast, using the PHPMA63 stabilizer only produces spherical morphologies. Presumably this is because the latter confers more effective steric stabilization, which prevents the efficient fusion of spheres to form worms. Nevertheless the PHPMA63-PBzMAn formulation may still be useful, since it allows access to spherical nanoparticles with tunable mean diameters of 29-100 nm. Such phase diagrams are essential for the reproducible targeting of copolymer morphologies, since they enable mixed phase regions to be avoided and allow the predictable synthesis of pure spheres, worms, or vesicles at a given concentration. Finally, a block copolymer "jellyfish" was observed during these PISA syntheses, which suggests that such intermediates are most likely a generic feature of the in situ conversion of worms into vesicles. © 2012 American Chemical Society.

Laschewsky A.,Fraunhofer Institute for Applied Polymer Research | Laschewsky A.,University of Potsdam
Current Opinion in Colloid and Interface Science | Year: 2012

Recent developments in the synthesis of polyelectrolytes are highlighted, with respect to the nature of the ionic groups, the polymer backbones, synthetic methods, and additional functionality given to the polyelectrolytes. In fact, the synthesis of new polyelectrolytes is mostly driven by material aspects, currently. The article pays particular attention to strong polyelectrolytes, and the new methods of controlled polymerization. These methods and the so-called click reactions have enabled novel designs of polyelectrolytes. Nevertheless, the polymerization of unprotected ionic monomers is still challenging and limits the synthetic possibilities. The structural aspects are complemented by considerations with respect to the aspired uses of the new polyelectrolytes. © 2011 Elsevier Ltd.

Lutz J.-F.,Fraunhofer Institute for Applied Polymer Research
Polymer Chemistry | Year: 2010

The aim of this short perspective article is to sensitize polymer chemists to the importance of controlling comonomer sequences. During the last twenty years, our scientific community has made impressive progress in controlling the architecture of synthetic macromolecules (i.e. chain length, shape and composition). In comparison, our tools for controlling polymer microstructures (i.e. sequences and tacticity) are still very rudimentary. However, as learned from Nature, sequence-controlled polymers are most likely the key toward functional sub-nanometric materials. © 2010 The Royal Society of Chemistry.

Lutz J.-F.,Charles Sadron Institute | Schmidt B.V.K.J.,Fraunhofer Institute for Applied Polymer Research | Pfeifer S.,Fraunhofer Institute for Applied Polymer Research
Macromolecular Rapid Communications | Year: 2011

In the present Feature Article, a kinetic strategy for controlling the microstructure of synthetic polymer chains prepared via a radical chain-growth polymerization process is presented. This approach was recently developed in our laboratory and relies on the controlled kinetic addition of ultrareactive N-substituted maleimides during the atom transfer radical polymerization of styrene. This method is experimentally straightforward and can be applied to a broad library of functional N-substituted maleimides. Thus, this platform allows synthesis of unprecedented polymer materials such as 1D macromolecular arrays. The basic kinetic requirements, the experimental conditions, and the synthetic scope of this approach are discussed in details herein. The controlled radical copolymerization of styrene with N-substituted maleimides allows preparation of unique polymer microstructures. Indeed, we reported in recent years that small amounts of N-substituted maleimides can be placed at specific locations in linear polystyrene chains. Herein, we describe in details this research advance. The kinetic concept, the experimental conditions and the scope of this novel strategy are discussed in this feature article. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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