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Biomedical subjects

Andreas Fery

Publications and source records attributed to Andreas Fery.

10 recordsLinked to original sources
PubMed2006

Freestanding polyelectrolyte films as sensors for osmotic pressure.

Freestanding ultrathin polyelectrolyte-multilayer membranes, transferred to topographically structured polydimethylsiloxane (PDMS), are used as mechanical sensors. Due to the membranes' semipermeability, high-molecular-weight molecules can be either entrapped inside them or excluded, thus generating an osmotic pressure. This leads to a deformation. We investigate the deformation as a function of the osmotic pressure and present an analytical theory that fully describes the data. Thus, osmotic pressures can be determined quantitatively. The individual osmotic-sensitive elements have only microscopic dimensions, and arrays can be easily produced.

Chemistry, Physical↗
PubMed2006

Surface immobilization and mechanical properties of catanionic hollow faceted polyhedrons.

We report here for the first time on surface immobilization of hollow faceted polyhedrons formed from catanionic surfactant mixtures. We find that electrostatic interaction with the substrate dominates their adhesion behavior. Using polyelectrolyte coated surfaces with tailored charge densities, polyhedrons can thus be immobilized without complete spreading, which allows for further study of their mechanical properties using AFM force measurements. The elastic response of individual polyhedrons can be locally resolved, showing pronounced differences in stiffness between faces and vertexes of the structure, which makes these systems interesting as models for structurally similar colloidal scale objects such as viruses, where such effects are predicted but cannot be directly observed due to the smaller dimensions. Elastic constants of the wall material are estimated using shell and plate deformation models and are found to be a factor of 5 larger than those for neutral lipidic bilayers in the gel state. We discuss the molecular origins of this high stiffness.

Journal Article↗
PubMed2006

Polyelectrolyte films based on polysaccharides of different conformations: effects on multilayer structure and mechanical properties.

Ultrathin films were prepared with cationic poly(allylamine hydrochloride) (PAH) and two anionic polysaccharides, iota- and lambda-carrageenan, of similar chemical composition but different conformations using the layer-by-layer (LbL) technique. The study of aqueous solutions of carrageenans confirms that iota-carrageenan is at room temperature in helical conformation while lambda-carrageenan is in random coil conformation. Characterization of the multilayers by ellipsometry, circular dichroism, and AFM revealed that iota-carrageenan keeps its helical conformation within the films while lambda-carrageenan chains are in random coil conformation. Investigation of the mechanical properties of the films by performing nanoindentation experiments using force spectroscopy showed clear differences between the two films based on carrageenans of different conformations.

Carbohydrate Conformation↗
PubMed2005

Reversible light and air-driven lithography by singlet oxygen.

Monolayers and thin films of diphenylanthracene react in the presence of a singlet oxygen sensitizer by irradiation on air to the corresponding endoperoxides and reconvert to the starting compounds upon heating. This reaction has been applied to create 2D fluorescent pattern structures. Motifs which are written by this technique can be erased and replaced by new images.

Journal Article↗
PubMed2005

Encapsulated living cells on microstructured surfaces.

The immobilization of cells in defined arrays (cell patterning) is a key step towards cell-based biosensors or other cell-based devices. While cell patterning is usually achieved by modifying the surface on which only the cells should adhere and leaving the cells unmodified, we present here a different approach in which cells are first coated with polyelectrolytes and subsequently immobilized on patterned surfaces. By coating, the cells are protected and their interactions with the substrate are modified such that patterning is simplified. We used microcontact printing of polyelectrolytes to structure surfaces such that regions of opposite charges and the same charge as the cell coating were present and found that we can thus achieve patterning of the coated yeast cells. In accordance with prior work, we find that coating does not kill the cells and coated GFP-expressing cells still function after immobilization, which we checked by fluorescence microscopy.

Cell Adhesion↗
PubMed2005

Recrystallization of bacterial S-layers on flat polyelectrolyte surfaces and hollow polyelectrolyte capsules.

Polyelectrolyte multilayer (PE) deposition and S-layer technology have been combined to make novel robust biomimetic surfaces and membranes. Isolated subunits of the bacterial cell surface layer from Bacillus sphaericus CCM2177 SbpA was self-assembled on PE multilayer supports, with the composition of the multilayer playing a crucial role in determining the structure of the resulting supported protein layers. Flat substrates were studied using atomic force microscopy and neutron reflectometry; protein on suitable PE combinations showed a crystalline structure with lattice constants equal to those found in vivo on bacterial surfaces. The mechanical stability of the S-layer is higher when recrystallized on PEs than directly on silicon supports. The recrystallization process was subsequently used to coat colloidal particles, permitting the determination of zeta potentials before and after coating. Hollow capsules could also be coated in the same way, as proven by various techniques. Our results suggest that electrostatic interactions via divalent cations are important for the assembly process. The results also demonstrate that the versatility of the PE multilayer membranes can be successfully combined with the well-defined surface chemistry and structure of 2D protein crystals.

Bacillus↗
PubMed2004

Tuning of microcapsule adhesion by varying the capsule-wall thickness.

The adhesion area and topology of spherical hollow polyelectrolyte shells adhering to flat glass or polyelectrolyte-covered glass surfaces are studied. Strong adhesion is found for anionic poly(sodium 4-styrenesulfonate)-terminated shells on cationic poly(ethylene imine)-covered glass, while no adhesion of those shells on uncoated glass is found. The adhering shells are deformed and obtain a truncated sphere topology with a circular adhesion disk. The radius of the adhesion disks can reach up to 50% of the shell radius for shells of several tens of microns. The dependency of the size of adhesion areas on the capsule radius and capsule wall thickness is also investigated. Remarkably, the size of the adhesion areas is found to depend strongly on the wall thickness, which offers interesting perspectives for controlling capsule adhesion properties. A model based on the energy balance of deformation and wetting energies is presented that explains the observed trends.

Journal Article↗
PubMed2004

Microstructuring of polyelectrolyte coated surfaces for directing capsule adhesion.

We use microcontact printing (microCP) of polyelectrolytes (PEs) onto flat substrates for creating surfaces with regions of negative and positive surface charge. Subsequent incubation of these surfaces with solutions containing hollow PE capsules leads to preferential adsorption of the capsules on regions of opposite charge, while regions of like charge are passivated against adhesion. As well, adsorption of fluorescently labeled PEs is found to be directed toward oppositely charged regions at neutral pH. This approach could lead to novel functional surfaces for combinatorial chemistry or sensor applications and could also be expanded toward cell immobilization.

Adsorption↗