Senta Reichelt

Functionalization of solid surfaces with hyperbranched polyesters to control protein adsorption.

Thin films of hyperbranched polyesters were studied in dry state and in aqueous buffer solution regarding their swelling behaviour and protein adsorption potential. The influence of the degree of branching, the backbone structure, flexibility as well as the polarity was varied. By changing the backbone structure from aromatic, aromatic-aliphatic to aliphatic the surface properties can be controlled from protein active to protein repelling. The higher adsorption potential observed in comparison to linear polyesters is the result of the large amount of end groups allowing the formation of hydrogen bonds, and the larger swellability of the more flexible linear polymers. The protein adsorption process was studied intensively by in-situ spectroscopic ellipsometry. Different approaches towards a proper optical model for the vis-ellipsometry data evaluation for the determination of the correct layer thickness and refractive index are discussed. IR-ellipsometric measurements using a new in-situ cell gave the full chemical evidence for the formation of thin protein adsorption layer on the polymer films in the aqueous buffer environment.

Biocompatible polysaccharide-based cryogels.

This study focuses on the development of novel biocompatible macroporous cryogels by electron-beam assisted free-radical crosslinking reaction of polymerizable dextran and hyaluronan derivatives. As a main advantage this straightforward approach provides highly pure materials of high porosity without using additional crosslinkers or initiators. The cryogels were characterized with regard to their morphology and their basic properties including thermal and mechanical characteristics, and swellability. It was found that the applied irradiation dose and the chemical composition strongly influence the material properties of the resulting cryogels. Preliminary cytotoxicity tests illustrate the excellent in vitro-cytocompatibility of the fabricated cryogels making them especially attractive as matrices in tissue regeneration procedures.

Electron-beam derived polymeric cryogels

In this study we publish a novel attempt to macroporous, polymeric cryogels (MPCs) by electron-beam (EB) initiated free radical crosslinking polymerization of (meth)acrylates in frozen aqueous media. The EB-process is an environmentally benign fast process (radiation and reaction time about 10–20 min) which allows the initiator-free polymerization of double-bond containing monomers. The MPCs were thoroughly characterized by swelling experiments, SEM, detailed XPS studies, DMA, Hg intrusion porosity and ESEM. The processes during the reaction were studied using ESR experiments. The influences of the reaction parameters like dose, radiation time, freezing conditions, chemical composition and (meth)acrylate concentration on the properties of the MPCs were investigated. The MPCs were synthesized in situ in capillaries or in tubes up to a diameter of 25 mm. The porous structure of the MPCs is mainly controlled by the freezing temperature and the macromonomer/crosslinker concentration and consists of large interconnected pores in the range of 10–70 μm. The crosslinker concentration directly affects the stiffness and the Tg of the materials. The MPCs were successfully modified with poly(allylamine hydrochloride). This straightforward method provides a toolbox for the synthesis of manifold MPCs from various unsaturated substances in large quantities and scale.

Hydrodynamic Parameters of Linear Aromatic Polyester of 3-Phenylglutaric Acid and Bisphenol A

Abstract A series of samples of linear aromatic polyester of 3-phenylglutaric acid and bisphenol A was prepared with molecular weights ranging from 14 700 to 92 700. The polymers were characterized by size exclusion chromatography with triple light-scattering, viscosity, and concentration detection. Hydrodynamic parameters of the chain were determined using the theory of Yoshizaki, Yamakawa, and Nitta modified by Bohdanecký and Netopilík. The chain parameters are a useful reference in the study of aromatic hyperbranched polyesters.

Electron-beam generated porous dextran gels: Experimental and quantum chemical studies

Abstract Purpose: The aim of this work was to investigate the reaction mechanism of electron-beam generated macroporous dextran cryogels by quantum chemical calculation and electron paramagnetic resonance measurements. Methods: Electron-beam radiation was used to initiate the cross-linking reaction of methacrylated dextran in semifrozen aqueous solutions. The pore morphology of the resulting cryogels was visualized by scanning electron microscopy. Quantum chemical calculations and electron paramagnetic resonance studies provided information on the most probable reaction pathway and the chain growth radicals. Results: The most probable reaction pathway was a ring opening reaction and the addition of a C-atom to the double-bond of the methacrylated dextran molecule. Conclusions: First detailed quantum chemical calculation on the reaction mechanism of electron-beam initiated cross-linking reaction of methacrylated dextran are presented.

ADSA-TRIS: a new method to study interfacial phenomena at polymer–aqueous solution interfaces

AbstractAxisymmetric drop shape analysis-profile (ADSA-P) was combined with total reflectometric interference spectroscopy (TRIS) in one experimental setup to study the interfacial phenomena at solid–liquid and liquid–vapor interfaces caused by adsorption/desorption (dissolution) of surface-active substances. Using sessile liquid droplets on polymer film/chromium-coated glass substrates that were optically matched with an immersion oil to a TRIS reflection prism, the optical thickness (product of physical thickness d and refractive index n) of the polymer film can be estimated by evaluating the wavelength-dependent intensity of reflected light. The sessile droplet is analyzed simultaneously by an ADSA setup arranged in a transverse direction to the path of the white-light beam of TRIS. From this analysis, the solid–vapor interfacial tension γlv(t), contact angle θ(t), contact radius r(t), drop volume V(t), and solid–liquid interfacial tension γsl(t) can be monitored as a function of time. The new method was applied to study polystyrene and poly(4-hydroxystyrene) surfaces in contact with aqueous buffer solutions and with protein solutions. The time-dependent changes in the optical film thickness caused by the adsorption of human serum albumin (HSA) and lysozyme (LSZ) were accompanied by changes in the solid–liquid interfacial tension. From the detailed study of both parameters, conclusions can be drawn with regard to the adsorption kinetics of the proteins on the hydrophobic polystyrene surfaces and to conformational changes occurring within the adsorbed protein layers. FigurePhoto of the ADSA-TRIS setup