Surface-functionalization of plasma-treated polystyrene by hyperbranched polymers and use in biological applications

Plasma Activation of Microplates Optimized for One-Step Reagent-Free Immobilization of DNA and Protein

Activated microplates are widely used in biological assays and cell culture to immobilize biomolecules, either through passive physical adsorption or covalent cross-linking. Covalent attachment gives greater stability in complex biological mixtures. However, current multistep chemical activation methods add complexity and cost, require specific functional groups, and can introduce cytotoxic chemicals that affect downstream cellular applications. Here, we show a method for one-step linker-free activation of microplates by energetic ions from plasma for covalent immobilization of DNA and protein. Two types of energetic ion plasma treatment were shown to be effective: plasma immersion ion implantation (PIII) and plasma-activated coating (PAC). This is the first time that PIII and PAC have been reported in microwell plates with nonflat geometry. We confirm that the plasma treatment generates radical-activated surfaces at the bottom of wells despite potential shadowing from the walls. Comprehensive surface characterization studies were used to compare the PIII and PAC microplate surface composition, wettability, radical density, optical properties, stability, and biomolecule immobilization density. PAC plates were found to have more nitrogen and lower radical density and were more hydrophobic and more stable over 3 months than PIII plates. Optimal conditions were obtained for high-density DNA (PAC, 0 or 21% nitrogen, pH 3-4) and streptavidin (PAC, 21% nitrogen, pH 5-7) binding while retaining optical properties required for typical high-throughput biochemical microplate assays, such as low autofluorescence and high transparency. DNA hybridization and protein activity of immobilized molecules were confirmed. We show that PAC activation allows for high-density covalent immobilization of functional DNA and protein in a single step on both 96- and 384-well plates without specific linker chemistry. These microplates could be used in the future to bind other user-selected ligands in a wide range of applications, for example, for solid phase polymerase chain reaction and stem cell culture and differentiation.

Direct Plasma Deposition of Collagen on 96-Well Polystyrene Plates for Cell Culture

A cold atmospheric plasma unit was used to deposit a biologic, in this case collagen, onto a surface. A collagen coating was applied to 96-well polystyrene plates at a range of powers to determine the effects of the plasma power on the coating structure and viability. Plasma characterization was carried out using voltage, current, and power measurements. Coating characterization was completed using gravimetric measurement, cell growth, water contact angle, as well as spectroscopic analysis and compared to commercial collagen-coated plates. Cell culture studies were also undertaken. The plasma coating matched the performance of the commercial plate but dramatically reduced production time and cost. This method could allow for automated inline production of collagen-coated plates for cell culture applications.

Charge Separating Microfiltration Membrane with pH-Dependent Selectivity

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.

Immobilization of Enzymes on Flexible Tubing Surfaces for Continuous Bioassays

Immobilized enzymes can be used to catalyze biochemical reactions in a batch process, however, it is more difficult to use them in a continuous process. Herein, we develop an enzyme immobilization technique for flexible tubing surfaces, which can be used to catalyze biochemical reactions in a continuous process. In this technique, the tubing is first treated with (3-aminopropyl)triethoxysilane at 50 °C and baked at 100 °C in vacuum to form a network of reactive amine functional group on the inner tubing surface. Subsequently, dextran polyaldehyde, a polymeric cross-linker, is used to immobilize crude protease extract and catalase for hydrolyzing casein and degrading H₂O₂, respectively, in a continuous process. The immobilized proteases are highly stable even after a long-term storage at 4 °C. After 12 weeks of storage, 90% of the original protease activity can be preserved. Meanwhile, the immobilized catalase is able to degrade 0.1% H₂O₂ solution flowing at 5 μL/min. The immobilization technique is potentially useful for bioassays and industrial wastewater treatments when continuous processes are preferred.

Improvement of osteogenesis by a uniform PCL coating on a magnesium screw for biodegradable applications

A polymer coating as polycaprolactone (PCL) is applied to improve the initial corrosion resistance of biodegradable magnesium. In addition, plasma electrolytic oxidation (PEO) is performed to increase adhesion between the polymer and the metal. However, when a complex-shaped material such as a screw is implanted in a bone, the surface coatings are locally damaged, and the protective role of the coating is not sufficiently maintained. In this study, the optimal conditions for producing a polymer coating on a screw were determined by varying the concentration of the PCL and the coating cycles, and were examined in vitro and in vivo. Among various the PCL coating conditions of 2∼6 cycles with 5∼7 wt.% concentrations, the 6 wt.% + 4 cycles group was applied uniformly to the screw thread. In the case of the non-uniform PCL layers, oxides and gases were present between the Mg and the PCL layer because internal magnesium corrosion and the layer peel off. The 6 wt.% + 4 cycles group had a high corrosion resistance due to the low wear on the thread. Denser and thicker bone formed around the PCL-coated screw in rat femur. This difference was due to the high corrosion resistance, which provided sufficient time for bone healing and promoting new bone growth.

Membrane Functionalization with Hyperbranched Polymers

Polymer membranes have been modified with hyperbranched polymers with the aim to generate a high density of hydrophilic functional groups at the membrane surface. For this purpose hyperbranched polymers containing amino, alcohol, and carboxylic acid end groups were used for membrane modification, respectively. Thus, surface potential and charges were changed significantly to result in attractive or repulsive interactions towards three different proteins (albumin, lysozyme, myoglobin) that were used to indicate membrane fouling properties. Our studies demonstrated that hydrophilization alone is not effective for avoiding membrane fouling when charged proteins are present. In contrast, electrostatic repulsion seems to be a general key factor.

The critical zeta potential of polymer membranes: how electrolytes impact membrane fouling

The zeta potential of membrane surfaces and the resulting electrostatic interactions are determining factors of membrane fouling. This publication presents the impact of salt concentration and pH value on these interactions.

Particle adsorption on a polyether sulfone membrane: how electrostatic interactions dominate membrane fouling

This study presents a new method focussing on electrostatic interactions during fouling of microfiltration membranes.

Grafting of poly-L-lysine dendrigrafts onto polypropylene surface using plasma activation for ATP immobilization - Nanomaterial for potential applications in biotechnology

The present work describes a new environmental friendly strategy for the development of surfaces with high amine density via the grafting of native or modified poly-L-lysine dendrigraft (DGL G3) onto plasma activated polypropylene (PP), polystyrene (PS), polyimide, and polytetrafluoroethylene (PTFE) surface. Modified DGL G3 was prepared by replacement of few peripheral amines by various functionalities. Grafting efficiency was determined by wettability measurements, IRTF, XPS, AFM, and by colorimetry using optimized Coomassie Brilliant Blue method tailored for surface analysis. It was shown that a 4-7nm DGL G3 monolayer with 4×10(14)aminecm(-)(2) was covalently grafted onto various surfaces. Immobilization of adenosine triphosphate on the DGL-g-PP material from dilute solution was studied by bioluminescence and proved the ability of the material to interact with polyanionic biological compounds: 1 ATP complex with 5 amine groups. So, this material has a potential use in diagnostic and more widely for biotechnology due to its high capacity for biomolecule immobilization.

Fluorinated Boron-Dipyrromethene (BODIPY) Dyes: Bright and Versatile Probes for Surface Analysis

A family of bright boron-dipyrromethene-type fluorophores with a high number of fluorine atoms (F-BODIPYs) has been developed and characterized by X-ray crystallography and optical spectroscopy. The introduction of 3,5-bis(trifluoromethyl)phenyl and pentafluorophenyl moieties significantly enhances the photostability of such dyes, yielding for instance photostable near-infrared (NIR) fluorophores that show emission maxima>750 nm, when the BODIPY's π system is extended with two (dimethylamino)styryl and (dimethylamino)naphthastyryl moieties, or green-emitting BODIPYs with fluorescence quantum yields of unity. When equipped with a suitable group that selectively reacts for instance with amines, F-BODIPYs can be used as potent dual labels for the quantification of primary amino groups on surfaces by X-ray photoelectron spectroscopy (XPS) and fluorescence, two powerful yet complementary tools for the analysis of organic surface functional groups. The advantage of reactive F-BODIPYs is that they allow a fast and non-destructive mapping of the labelled supports with conventional fluorescence scanners and a subsequent quantification of selected areas of the same sample by the potentially traceable XPS technique. The performance is exemplarily shown here for the assessment of the amino group density on SiO2 supports, one of the most common reactive silica supports, in particular, for standard microarray applications.

Thermocurable hyperbranched polystyrenes for ultrathin polymer dielectrics

Thermocurable hyperbranched polystyrenes were successfully synthesized using atom transfer radical polymerization and exhibited superior ultrathin film formation capabilities in comparison with the linear analogues, as assessed by the minimal film thickness attainable by spin-coating without dewetting. They were suitable as ultrathin film organic dielectrics, with parallel plate specific capacitances as high as ∼680 nF/cm2. Similar to high performance inorganic dielectrics, capacitance measurements pointed to the presence of "dead" interfacial capacitance, which could be accounted for by considering the geometric effect of roughness "incommensurability" between metal electrode and polymer film.