Tailor-made ligands for biocompatible nanoparticles.
Explore the source record for details and available documents.
Biocompatible Materials↗
Biomedical subjects
Stephan Förster
Publications and source records attributed to Stephan Förster.
pH-induced release from P2VP-PEO block copolymer vesicles.
The pH-induced release of hydrophilic dyes from poly(2-vinylpyridine-b-ethylene oxide) (P2VP-PEO) block copolymer vesicles is investigated. The structure of the vesicles is characterized using small-angle neutron scattering (SANS) and cryo-electron microscopy (cryo-TEM). A decrease of the pH below 5 leads to protonation and dissolution of the poly-2-vinylpyridine blocks which induces rupture and dissolution of the vesicle membrane. Details of the rupture, dissolution, and release process are studied by fluorescence video microscopy, gel electrophoresis, and high-performance ultrafiltration.
Cryoelectron Microscopy↗
Direct preparation and loading of lipid and polymer vesicles using inkjets.
Explore the source record for details and available documents.
Cryoelectron Microscopy↗
Formation of large PEE domains in PEE212-PEO112 diblock copolymer monolayers: shift of the PEO-desorption transition.
PEE212-PEO112 diblock copolymer monolayers are studied at the air/water interface. At large molecular areas, with X-ray reflectivity, PEE domains are observed, which are partly immersed into the water. The domain thickness increases on compression (28 to 40 A). With off-specular X-ray reflectivity, an average domain radius of 750 A is found, but there are also smaller domains. Due to these space constraints, most PEO blocks form a brush beneath the PEE domains. Only a few PEO blocks form a corona surrounding the domains and adsorb flatly onto the air/water interface. The PEO desorption transition is observed at the typical pressure of 9 mN/m, when the flatly adsorbed PEO is compressed at a domain fraction of 95%. It occurs at 6 A2/EO monomer, about half the value found for lipopolymers or diblock copolymers with NPEE approximately NPEO or NPEE < NPEO. Apparently, the thickness of the PEE domains is determined by the forces from the two interfaces, not by the PEO block, for which flat adsorption beneath the domain would be more favorable instead of formation of a PEO brush.
Journal Article↗
CdSe and CdSe/CdS nanorod solids.
We demonstrate the self-organization of CdSe nanorods into nematic, smectic, and crystalline solids. Layered colloidal crystals of CdSe nanorods grow by slow destabilization of a nanocrystal solution upon allowing the diffusion of a nonsolvent into the colloidal solution of nanocrystals. The colloidal crystals of nanorods show characteristic birefringence, which we assign to specific spherulite-like texture of each nanorod assembly. To demonstrate the general character of nanorod self-assembly technique, CdSe/CdS heterostructure nanorods were organized into highly luminescent superlattices.
Journal Article↗
Molecular exchange through vesicle membranes: a pulsed field gradient nuclear magnetic resonance study.
The permeability of block copolymer vesicles is studied using pulsed field gradient nuclear magnetic resonance spectroscopy together with a numerical data analysis procedure. Polyethylene oxide molecules of various molecular masses are used to sample the permeability of the vesicle membrane by observing the trans-membrane exchange process under equilibrium conditions. For shorter polyethylene oxide chains, the analysis yields a nearly linear dependence of the logarithmic trans-membrane exchange rate on the hydrodynamic radius of the sample molecules.
Journal Article↗
Giant hexagonal superstructures in diblock-copolymer membranes.
We have observed polymersomes of high genus with their vesicle wall organized on the micrometer scale either in a double bilayer connected by a lattice of passages or a tubular network with hexagonal symmetry. Experimentally found shape classes are identified within a theoretical phase diagram based on the bending energy of the polymer membrane. Pronounced morphological changes could be induced and controlled by temperature.
Butadienes↗
From self-organizing polymers to nanohybrid and biomaterials.
Block copolymers form a large number of superlattices with characteristic dimensions in the range of a few nanometers up to several micrometers by self-organization. The interplay of supramolecular physics and chemistry opens up new approaches to the production of inorganic, organic, and biological structures and to their integration into functional units. Possible applications in the fields of materials science and molecular biology are being investigated. Block copolymers find numerous applications from the production of inorganic nanoparticles (metals, semiconductors, magnets) and mesoporous materials up to take-up/release systems in chemo- and gene therapy.
Biocompatible Materials↗
The formation of polymer vesicles or "peptosomes" by polybutadiene-block-poly(L-glutamate)s in dilute aqueous solution.
Polybutadiene-block-poly(L-glutamate) copolymers were made by anionic polymerization and subsequent ring-opening polymerization of N-carboxyanhydrides and were characterized by NMR, IR, SEC, and circular dichroism. These polymers, when appropriately designed, form so-called "polymersomes" or "peptosomes", vesicles composed of modified protein units. The size and structure of the vesicles are determined by dynamic light scattering, small-angle neutron scattering, and freeze-fracture electron microscopy. It is also shown that the size of the peptosomes does not depend on the pH; that is, the solvating peptide units can perform a helix-coil transition without serious changes of the vesicle morphology.
Butadienes↗