Biomedical subjects

Karina Grundke

Publications and source records attributed to Karina Grundke.

10 recordsLinked to original sources

PubMed2007

In-situ investigation of the adsorption of globular model proteins on stimuli-responsive binary polyelectrolyte brushes.

Binary brushes constituted from two incompatible polymers can be used in the form of ultrathin polymeric layers as a versatile tool for surface engineering to tune physicochemical surface characteristics such as wettability, surface charge, chemical composition, and morphology and furthermore to create responsive surface properties. Mixed brushes of oppositely charged weak polyelectrolytes represent a special case of responding surfaces that are sensitive to changes in the pH value of the aqueous environment and therefore represent interesting tools for biosurface engineering. The polyelectrolyte brushes used for this study were composed of two oppositely charged polyelelctrolytes poly(2-vinylpyridine) (P2VP) and poly(acrylic acid) (PAA). The in-situ properties and surface characteristics such as as surface charge, surface tension, and extent of swelling of these brush layers are functions of the pH value of the surrounding aqueous solution. To test the behavior of the mixed polylelctrolyte brushes in contact with biosystems, protein adsorption experiments with globular model proteins were performed at different pH values and salt concentrations (confinement of counterions) of the buffer solutions. The influence of the pH value, buffer salt concentration, and isoelectric points (IEP) of the brush and protein on the adsorbed amount and the interfacial tension during protein adsorption as well as the protein adsorption mechanism postulated in reference to recently developed theories of protein adsorption on polyelectrolyte brushes is discussed. In the salted regime, protein adsorption was found to be similar to the often-described adsorption at hydrophobic surfaces. However, in the osmotic regime the balance of electrostatic repulsion and a strong entropic driving force, "counterion release", was found to be the main influence on protein adsorption.

Acrylic Resins↗

PubMed2006

The similarity of electric double-layer interaction from the general Poisson-Boltzmann theory.

We studied electric double-layer (EDL) interactions in electrolytes with different valence combinations. Our results show that the interactions are similar for electrolytes with the same co-ion valences and concentrations and such similarity increases with the co-ion valence and surface potential. A scaled surface potential was defined and found to be useful in characterizing the difference in EDL interaction. These results show that co-ions play a more important role than counterions in determining EDL potential and interaction in an electrolyte solution, especially for systems with high co-ion valence and/or high surface potentials.

Colloids↗

PubMed2006

Stick-slip of the three-phase line in measurements of dynamic contact angles.

Contact angles of a series of n-alkanes (i.e., n-heptane to n-hexadecane) are studied on two functionalized maleimide copolymers (i.e., poly(ethene-alt-N-(4-(perfluoroheptylcarbonyl)aminobutyl)maleimide) (ETMF) and poly(octadecene-alt-N-(4-(perfluoroheptylcarbonyl)aminobutyl)maleimide) (ODMF)). On the homogeneous ETMF films, all liquids show a smooth motion of the three-phase line. In contrast, on ODMF surfaces that are found to consist of mainly fluorocarbons and small patches of hydrocarbons, short-chain n-alkanes show a stick-slip pattern. By increasing the chain length of the probe liquids, stick-slip is reduced significantly. The phenomenon is discussed in the framework of the Cassie equation. It is found that the upper limit of contact angles in the stick-slip pattern is given by the advancing angle that would be obtained on the pure fluorocarbon surface, whereas the lower limit of the stick-slip pattern is given by the Cassie angle.

Journal Article↗

PubMed2005

Characterization of maleic acid/anhydride copolymer films by low-rate dynamic liquid-fluid contact angle measurements using axisymmetric drop shape analysis.

Thin films of alternating maleic acid/anhydride copolymers (poly(octadecene-alt-maleic acid/anhydride), POMA; poly(propene-alt-maleic acid/anhydride), PPMA; poly(styrene-alt-maleic acid/anhydride), PSMA) were studied to unravel the influence of the comonomer characteristics in the backbone on the surface-energetic properties of the copolymer films in the dry state and in contact with aqueous solutions. Water contact angle measurements revealed a graduation of the wettability of the dry hydrolyzed and annealed copolymer films that was dependent on the comonomer unit. It ranged from moderately hydrophilic (PPMA, annealed gamma(sv) = 39.9 mJ/m2) to very hydrophobic (POMA, annealed, gamma(sv) = 18.4 mJ/m2) surfaces. Liquid-fluid contact angle measurements using captive air bubbles were performed in different aqueous media (pure water, phosphate-buffered saline, and 10(-)(3) M KCl of two different pH values (pH = 3 and pH = 10) to study the copolymer films in their hydrated states relevant for biointerfacial phenomena. It was found that the graduation of the wettability of the copolymer films in the dry state is overall maintained upon immersion in aqueous solutions. The dependence of the wettability on the pH value of the aqueous medium could be related to the (de)protonation of the carboxylic groups.

Hydrogen-Ion Concentration↗

PubMed2004

Influence of hyperbranched polyesters on the surface tension of polyols.

The influence of hyperbranched polyesters with different functional end groups on the surface tension of mixtures with an oligo(ester diol) was investigated. The temperature dependence of the surface tension of the pure components and of the mixtures was measured by a modified Wilhelmy balance technique. The results indicate that the surface tension of the pure hyperbranched polyesters strongly depends on the functionality of the end groups. The functionalization of the hydroxyl end groups by short alkyl chains (methyl, tert-butyl) reduced the surface tension depending on the degree of substitution. The surface tension of the mixtures with the hydroxyl-terminated hyperbranched polyester was slightly increased at higher concentrations of the hyperbranched polymer compared to the surface tension of the pure ester diol. On the other hand, the surface tension of mixtures could be considerably decreased using 1% of hyperbranched polyester polyols partially substituted with short alkyl chains. In that case, the modified hyperbranched polyesters act as surface active agents. On the molecular level, the enrichment of the modified hyperbranched polyester in the surface region was proven by X-ray photoelectron spectroscopy measurements.

Molecular Structure↗

PubMed2004

Constrained sessile drop as a new configuration to measure low surface tension in lung surfactant systems.

Existing methodology for surface tension measurements based on drop shapes suffers from the shortcoming that it is not capable to function at very low surface tension if the liquid dispersion is opaque, such as therapeutic lung surfactants at clinically relevant concentrations. The novel configuration proposed here removes the two big restrictions, i.e., the film leakage problem that is encountered with such methods as the pulsating bubble surfactometer as well as the pendant drop arrangement, and the problem of the opaqueness of the liquid, as in the original captive bubble arrangement. A sharp knife edge is the key design feature in the constrained sessile drop that avoids film leakage at low surface tension. The use of the constrained sessile drop configuration in conjunction with axisymmetric drop shape analysis to measure surface tension allows complete automation of the setup. Dynamic studies with lung surfactant can be performed readily by changing the volume of a sessile drop, and thus the surface area, by means of a motor-driven syringe. To illustrate the validity of using this configuration, experiments were performed using an exogenous lung surfactant preparation, bovine lipid extract surfactant (BLES) at 5.0 mg/ml. A comparison of results obtained for BLES at low concentration between the constrained sessile drop and captive bubble arrangement shows excellent agreement between the two approaches. When the surface area of the BLES film (0.5 mg/ml) was compressed by about the same amount in both systems, the minimum surface tensions attained were identical within the 95% confidence limits.

Animals↗

PubMed2003

Unusual wetting dynamics of aqueous surfactant solutions on polymer surfaces.

Static and dynamic contact angles of aqueous solutions of three surfactants--anionic sodium dodecyl sulfate (SDS), cationic dodecyltrimethylammonium bromide (DTAB), and nonionic pentaethylene glycol monododecyl ether (C(12)E(5))--were measured in the pre- and micellar concentration ranges on polymer surfaces of different surface free energy. The influence of the degree of substrate hydrophobicity, concentration of the solution, and ionic/nonionic character of surfactant on the drop spreading was investigated. Evaporation losses due to relatively low humidity during measurements were taken into account as well. It was shown that, in contrast to the highly hydrophobic surfaces, contact angles for ionic surfactant solutions on the moderately hydrophobic surfaces strongly depend on time. As far as the nonionic surfactant is considered, it spreads well over all the hydrophobic polymer surfaces used. Moreover, the results obtained indicate that spreading (if it occurs) in the long-time regime is controlled not only by the diffusive transport of surfactant to the expanding liquid-vapor interface. Obviously, another process involving adsorption at the expanding solid-liquid interface (near the three-phase contact line), which goes more slowly than diffusion, has to be active.

Journal Article↗

PubMed2003

Two-level structured self-adaptive surfaces with reversibly tunable properties.

We report a route to fabricate two-level structured self-adaptive surfaces (SAS) of polymer materials. The first level of structure is built by a rough polymer film that consists of needlelike structures of micrometer size. The second level of structure is formed by the nanoscopic self-assembled domains of a demixed polymer brush irreversibly grafted onto the needles. By exposing the surface to solvents that are selective to one of the components of the brush, we reversibly tune the surface properties. The large-scale surface structure amplifies the response and enables us to control wettability, adhesion, and chemical composition of the surface over a wide range.

Journal Article↗

PubMed2002

Suitability of hyperbranched polyester for sensoric applications--investigation with reflectometric interference spectroscopy.

Hyperbranched polyesters (HBP) with different end groups (P-OH, P-COOH, P-OAc) were prepared as thin films. Their surface properties were investigated using zeta potential and contact angle measurements. The differences in surface properties between P-OH and P-COOH, on the one hand, and P-OAc, on the other hand, predicted different behavior in sensoric applications. Therefore, the vapor of the homologous series of alcohols from methanol to pentanol was exposed to the thin films. Changes in thickness were observed with reflectometric interference spectroscopy (RIfS). First investigations in a current analytical problem for the detection and discrimination of refrigerants (freons) using P-OH as sensitive layer have been shown. Polydimethylsiloxane (PDMS) and poly(ether urethane) (PUT) were used as reference sensor materials for the RIfS measurements.

Journal Article↗

PubMed2002

Influence of aqueous electrolytes on the wetting behavior of hydrophobic solid polymers-low-rate dynamic liquid/fluid contact angle measurements using axisymmetric drop shape analysis.

The interaction of inorganic ions with low-energy hydrophobic surfaces was examined using model systems of solid polymers without ionizable functional surface groups in aqueous electrolyte solutions. Low-rate dynamic contact angle measurements with captive bubbles in conjunction with axisymmetric drop shape analysis (ADSA) were performed to study the influence of electrolyte ions (in the aqueous test solutions) on the wettability of the polymers. When various types of ions were used, no significant change in advancing and receding contact angles was observed. The contact angle hysteresis was small. The zeta potential of the model polymers in aqueous electrolyte solutions was determined from streaming potential measurements. The variation of the zeta potential at different pH levels indicates preferential adsorption of hydroxyl ions at this interface. However, the presence of electrolytes at the interface between water and the different model polymers did not influence the macroscopic contact angle. The results may suggest the absence of any specific interaction between the ions and the solid polymer, as this should result in changes of hydrophobicity. Similar to the air/water interface, the composition and the potential of the polymer/water interface are obviously determined predominantly by the aqueous phase with only slight influence from the solid phase.

Journal Article↗