Search Results
Biocatalytic Self-Cleaning Polymer Membranes
2015, Schulze, Agnes, Stoelzer, Astrid, Striegler, Karl, Starke, Sandra, Prager, Andrea
Polymer membrane surfaces have been equipped with the digestive enzyme trypsin. Enzyme immobilization was performed by electron beam irradiation in aqueous media within a one-step method. Using this method, trypsin was covalently and side-unspecific attached to the membrane surface. Thus, the use of preceding polymer functionalization and the use of toxic solvents or reagents can be avoided. The resulting membranes showed significantly improved antifouling properties as demonstrated by repeated filtration of protein solutions. Furthermore, the biocatalytic membrane can be simply “switched on” to actively degrade a fouling layer on the membrane surface and regain the initial permeability. The membrane pore structure (pore size and porosity) was neither damaged by the electron beam treatment nor blocked by the enzyme loading, ensuring a stable membrane performance.
Surface Functionalization by Stimuli-Sensitive Microgels for Effective Enzyme Uptake and Rational Design of Biosensor Setups
2018, Sigolaeva, Larisa V., Pergushov, Dmitry V., Oelmann, Marina, Schwarz, Simona, Brugnoni, Monia, Kurochkin, Ilya N., Plamper, Felix A., Fery, Andreas, Richtering, Walter
We highlight microgel/enzyme thin films that were deposited onto solid interfaces via two sequential steps, the adsorption of temperature- and pH-sensitive microgels, followed by their complexation with the enzyme choline oxidase, ChO. Two kinds of functional (ionic) microgels were compared in this work in regard to their adsorptive behavior and interaction with ChO, that is, poly(N-isopropylacrylamide-co-N-(3-aminopropyl)methacrylamide), P(NIPAM-co-APMA), bearing primary amino groups, and poly(N-isopropylacrylamide-co-N-[3-(dimethylamino) propyl]methacrylamide), P(NIPAM-co-DMAPMA), bearing tertiary amino groups. The stimuli-sensitive properties of the microgels in the solution were characterized by potentiometric titration, dynamic light scattering (DLS), and laser microelectrophoresis. The peculiarities of the adsorptive behavior of both the microgels and the specific character of their interaction with ChO were revealed by a combination of surface characterization techniques. The surface charge was characterized by electrokinetic analysis (EKA) for the initial graphite surface and the same one after the subsequent deposition of the microgels and the enzyme under different adsorption regimes. The masses of wet microgel and microgel/enzyme films were determined by quartz crystal microbalance with dissipation monitoring (QCM-D) upon the subsequent deposition of the components under the same adsorption conditions, on a surface of gold-coated quartz crystals. Finally, the enzymatic responses of the microgel/enzyme films deposited on graphite electrodes to choline were tested amperometrically. The presence of functional primary amino groups in the P(NIPAM-co-APMA) microgel enables a covalent enzyme-to-microgel coupling via glutar aldehyde cross-linking, thereby resulting in a considerable improvement of the biosensor operational stability.
Charge Separating Microfiltration Membrane with pH-Dependent Selectivity
2018-12-20, Breite, Daniel, Went, Marco, Prager, Andrea, Kuehnert, Mathias, Schulze, Agnes
Membrane filters are designed for selective separation of components from a mixture. While separation by size might be the most common approach, other characteristics like charge can also be used for separation as presented in this study. Here, a polyether sulfone membrane was modified to create a zwitterionic surface. Depending on the pH value of the surrounding solution the membrane surface will be either negatively or positively charged. Thus, the charged state can be easily adjusted even by small changes of the pH value of the solution. Charged polystyrene beads were used as model reagent to investigate the pH dependent selectivity of the membrane. It was found that electrostatic forces are dominating the interactions between polystyrene beads and membrane surface during the filtration. This enables a complete control of the membrane’s selectivity according to the electrostatic interactions. Furthermore, differently charged beads marked with fluorescent dyes were used to investigate the selectivity of mixtures of charged components. These different components were successfully separated according to their charged state proving the selectivity of the invented membrane.
Selective Grafting of Polyamines to Polyether Ether Ketone Surface during Molding and Its Use for Chemical Plating
2018, Nagel, Jürgen, Zimmermann, Philipp, Schwarz, Simona, Schlenstedt, Kornelia
We present a new approach of surface functionalization of polyether ether ketone (PEEK) that is carried out during the molding step. Thin films of polymers with different functional groups were applied to the surface of a mold and brought in close contact with a PEEK melt during injection molding. The surfaces of the produced parts were characterized after solidification. Only those PEEK surfaces that were in contact with polymers bearing primary amino groups exhibited a wettability for water. Obviously, the thin polymer film was grafted to the surface by a chemical reaction initiated by the high melt temperature. The formation of azomethine bonds between PEEK and the polyamine by coupling to the ketone groups was proposed. The other amino groups in the molecule were still in function after the molding process. They adsorbed different anionic molecules and anionic charged nanoparticles from aqueous solutions. The surfaces could be chemically plated by copper and nickel with high adhesion.
Effects of Particle Size and Surface Chemistry on the Dispersion of Graphite Nanoplates in Polypropylene Composites
2018, Santos, Raquel M., Mould, Sacha T., Formánek, Petr, Paiva, Maria C., Covas, José A.
Carbon nanoparticles tend to form agglomerates with considerable cohesive strength, depending on particle morphology and chemistry, thus presenting different dispersion challenges. The present work studies the dispersion of three types of graphite nanoplates (GnP) with different flake sizes and bulk densities in a polypropylene melt, using a prototype extensional mixer under comparable hydrodynamic stresses. The nanoparticles were also chemically functionalized by covalent bonding polymer molecules to their surface, and the dispersion of the functionalized GnP was studied. The effects of stress relaxation on dispersion were also analyzed. Samples were removed along the mixer length, and characterized by microscopy and dielectric spectroscopy. A lower dispersion rate was observed for GnP with larger surface area and higher bulk density. Significant re-agglomeration was observed for all materials when the deformation rate was reduced. The polypropylene-functionalized GnP, characterized by increased compatibility with the polymer matrix, showed similar dispersion effects, albeit presenting slightly higher dispersion levels. All the composites exhibit dielectric behavior, however, the alternate current (AC) conductivity is systematically higher for the composites with larger flake GnP.
Bio-Inspired Polymer Membrane Surface Cleaning
2017-3-9, Schulze, Agnes, Breite, Daniel, Kim, Yongkyum, Schmidt, Martin, Thomas, Isabell, Went, Marco, Fischer, Kristina, Prager, Andrea
To generate polyethersulfone membranes with a biocatalytically active surface, pancreatin was covalently immobilized. Pancreatin is a mixture of digestive enzymes such as protease, lipase, and amylase. The resulting membranes exhibit self-cleaning properties after “switching on” the respective enzyme by adjusting pH and temperature. Thus, the membrane surface can actively degrade a fouling layer on its surface and regain initial permeability. Fouling tests with solutions of protein, oil, and mixtures of both, were performed, and the membrane’s ability to self-clean the fouled surface was characterized. Membrane characterization was conducted by investigation of the immobilized enzyme concentration, enzyme activity, water permeation flux, fouling tests, porosimetry, X-ray photoelectron spectroscopy, and scanning electron microscopy.