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391. Mougin, N.; van Rijn, P.; Park, H.; Müller, A.H.E.; Böker, A.: Hybrid Capsules via Self-Assembly of Thermoresponsive and Interfacially Active Bionanoparticle-Polymer Conjugates, Adv. Funct. Mater. 21, 2470 (2011) -- DOI: 10.1002/adfm.201002315
Key words: horse spleen ferritin, ATRP, thermoresponsive materials, Pickering emulsions, capsules

New bionanoparticles have been prepared from Horse Spleen Ferritin by grafting thermo-responsive poly(N-isopropyl acrylamide) (PNIPAAm) and photo-crosslinkable 2-(dimethyl maleinimido)-N-ethyl-acrylamide (DMIAAm) from the protein surface. The 72 addressable amino groups on the exterior of HSF were modified with N-hydroxysuccinimide activated 2-bromo-isobutyrate to form a macro-initiator for atom transfer radical polymerization, which was performed in water/DMF solutions at low temperature. The modification of the HSF and the presence of the polymer shell were confirmed by size exclusion chromatography (SEC), sodium dodecyl sulfate-polyacrylamide gel-electrophoresis, transmission electron microscopy and scanning force microscopy. The thermo-responsive behavior of the ferritin-PNIPAAm conjugates was investigated in solution by UV-Vis spectroscopy showing a phase transition in the form of a cloud point around 32 °C. Further, dynamic light scattering revealed an increasing hydrodynamic radius around this transition, indicating aggregation of the particles at elevated temperatures which was confirmed by transmission electron microscopy. Initial experiments show that the particles are highly surface active, much more than the individual components alone, which was demonstrated by pendant-drop interfacial tension measurements. This leads to the fact that they form stable Pickering emulsions, i.e. emulsion droplets decorated with polymer-modified bionanoparticles which can be cross-linked successively. This allows for the formation of capsules with a thermo-responsiveness for controlled release purposes e.g. in drug delivery.

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