Claus-Peter Klages

Polyelectrolyte multilayer surface functionalization of poly(dimethylsiloxane) (PDMS) for reduction of yeast cell adhesion in microfluidic devices

Polyelectrolyte multilayers (PEMs) based on the combinations poly(diallyldimethylammonium chloride)∕poly(acrylic acid) (PDADMAC∕PAA) and poly(allylamine hydrochloride)∕PAA (PAH∕PAA) were adsorbed on poly(dimethylsiloxane) (PDMS) and tested for nonspecific surface attachment of hydrophobic yeast cells using a parallel plate flow chamber. A custom-made graft copolymer containing poly(ethylene glycol) (PEG) side chains (PAA-g-PEG) was additionally adsorbed on the PEMs as a terminal layer. A suitable PEM modification effectively decreased the adhesion strength of Saccharomyces cerevisiae DSM 2155 to the channel walls. However, a further decrease in initial cell attachment and adhesion strength was observed after adsorption of PAA-g-PEG copolymer onto PEMs from aqueous solution. The results demonstrate that a facile layer-by-layer surface functionalization from aqueous solutions can be successfully applied to reduce cell adhesion strength of S. cerevisiae by at least two orders of magnitude compared to bare PDMS. Therefore, this method is potentially suitable to promote planktonic growth inside capped PDMS-based microfluidic devices if the PEM deposition is completed by a dynamic flow-through process.

Effects on Silanol Condensation during Low Temperature Silicon Fusion Bonding

This paper presents the results of surface energy measurements performed in situ during annealing of silicon wafers. The method allows conclusions to be drawn about the progress of silanol condensation while surface energy increases. The effects of wafer conditioning by atmospheric pressure plasmas, chemical post-treatments after plasma exposure but before bonding, and annealing temperatures on silanol condensation is investigated. Using nitrogen or nitrogen/oxygen gas mixtures for plasma activation, higher fracture surface energies γ are obtained at room temperature compared with oxygen plasma activation. Upon annealing, an increase in surface energies starts below 100°C. Possible reasons responsible for the effects of nitrogen plasma treatment and post-treatments with ammonia are discussed. Upward bent γ(t) curves are obtained during annealing at 200°C, independently of the type of wafer preconditioning, in contrast with the implications of existing chemical-kinetic models of the bonding process. Aside from a self-enhancement of the process due to facilitated water removal from the interface, the hypothesis of the nucleation and growth of covalently bonded microareas is able to explain the observed behavior qualitatively.

Novel coating systems and surface technologies for continuous processing of steel sheet

In this article, approaches are described to create the technological basics for a new generation of surface coated steel strip products. Important means to reach this aim are the use of new results from basic research (e.g., interfacial and surface chemistry/physics) and the transfer of innovative and non-polluting deposition technologies (e.g., vapor deposition processes such as physical vapor deposition, PVD, and chemical vapor deposition, CVD) to continuous processing of steel strip.

Design and optimization of dielectric barrier discharge microplasma stamps

Microplasma stamps based upon the principle of dielectric barrier discharges are applied to a new type of area-selective surface modification process at atmospheric pressure. This process integrates the surface treatment and lateral microstructuring within one process step. For this purpose the plasma is ignited in cavities which are formed temporarily by compressing the microplasma stamp and the substrate to be treated. In this work we compare different microplasma stamp designs with the objective of minimizing the ignition voltage to the smallest possible value. Several experiments with regard to the ignition voltage have been conducted, operating in air at atmospheric pressure with medium frequency excitation (33 kHz). They contrast the influence of different types of electrical contacts as well as different electrode types and cavity sizes (diameter 100–500 µm) on the ignition voltage. Furthermore the influence of different substrates to be treated and the compression force have been analysed.

Characterization of oxygen transfer in vertical microbubble columns for aerobic biotechnological processes

This paper presents the applicability of a microtechnologically fabricated microbubble column as a screening tool for submerged aerobic cultivation. Bubbles in the range of a few hundred micrometers in diameter were generated at the bottom of an upright‐positioned microdevice. The rising bubbles induced the circulation of the liquid and thus enhanced mixing by reducing the diffusion distances and preventing cells from sedimentation. Two differently sized nozzles (21 × 40 µm2 and 53 × 40 µm2 in cross‐section) were tested. The gas flow rates were adjustable, and the resulting bubble sizes and gas holdups were investigated by image analysis. The microdevice features sensor elements for the real‐time online monitoring of optical density and dissolved oxygen. The active aeration of the microdevice allowed for a flexible oxygen supply with mass transfer rates of up to 0.14 s−1. Slightly higher oxygen mass transfer rates and a better degassing were found for the microbubble column equipped with the smaller nozzle. To validate the applicability of the microbubble column for aerobic submerged cultivation processes, batch cultivations of the model organism Saccharomyces cerevisiae were performed, and the specific growth rate, oxygen uptake rate, and yield coefficient were investigated. Biotechnol. Bioeng. 2014;111: 1809–1819.

Controlling solid lipid nanoparticle adhesion by polyelectrolyte multilayer surface modifications.

This study addresses the tunability of polyelectrolyte multilayers (PEM) toward adsorption of solid lipid nanoparticles (SLN). In SLN production for pharmaceutical applications, repellence from production equipment is desired while targeted adsorption is necessary for the functionalization of surfaces. SLN containing triglyceride/phospholipid or wax matrices were exposed to different PEM (consisting of poly(allylamine hydrochloride) (PAH), poly(diallyldimethylammonium chloride), and poly(acrylic acid)). PEM varied regarding layer architecture and surface properties by means of deposition pH, top layer variation, PEGylation with poly(acrylic acid)-graft-poly(ethylene glycol) copolymer, and thermal crosslinking. FTIR-ATR and SEM revealed SLN adhesion depending on PEM composition. Particle adsorption was tunable toward attraction as well as repellence: PEGylated PEM displayed lowest adsorption while PEM capped with PAH provided the strongest attraction of particles. Examinations at elevated temperatures resembled production conditions of SLN where these are processed as emulsions. Crystalline triglyceride SLN displayed high anisometry and, consequently, a large specific surface area. These platelets were more adherend than spherical droplets from the same formulation as an emulsion. Wax-based nanoparticles showed spherical shape, both in crystalline and molten state. However, adsorption was fostered as the fluidity of the disperse phase increased upon melting. Additionally, coalescence of adsorbed droplets took place, further increasing adsorption.

Vertical microbubble column–A photonic lab-on-chip for cultivation and online analysis of yeast cell cultures

This paper presents a vertically positioned microfluidic system made of poly(dimethylsiloxane) (PDMS) and glass, which can be applied as a microbubble column (μBC) for biotechnological screening in suspension. In this μBC, microbubbles are produced in a cultivation chamber through an integrated nozzle structure. Thus, homogeneous suspension of biomass is achieved in the cultivation chamber without requiring additional mixing elements. Moreover, blockage due to produced carbon dioxide by the microorganisms-a problem predominant in common, horizontally positioned microbioreactors (MBRs)-is avoided, as the gas bubbles are released by buoyancy at the upper part of the microsystem. The patterned PDMS layer is based on an optimized two-lithographic process. Since the naturally hydrophobic PDMS causes problems for the sufficient production of microbubbles, a method based on polyelectrolyte multilayers is applied in order to allow continuous hydrophilization of the already bonded PDMS-glass-system. The μBC comprises various microelements, including stabilization of temperature, control of continuous bubble formation, and two optical configurations for measurement of optical density with two different sensitivities. In addition, the simple and robust application and handling of the μBC is achieved via a custom-made modular plug-in adapter. To validate the scalability from laboratory scale to microscale, and thus to demonstrate the successful application of the μBC as a screening instrument, a batch cultivation of Saccharomyces cerevisiae is performed in the μBC and compared to shake flask cultivation. Monitoring of the biomass growth in the μBC with the integrated online analytics resulted in a specific growth rate of 0.32 h(-1), which is almost identical to the one achieved in the shake flask cultivation (0.31 h(-1)). Therefore, the validity of the μBC as an alternative screening tool compared to other conventional laboratory scale systems in bioprocess development is proven. In addition, vertically positioned microbioreactors show high potential in comparison to conventional screening tools, since they allow for high density of integrated online analytics and therefore minimize time and cost for screening and guarantee improved control and analysis of cultivation parameters.

Nucleophilic Derivatization of Polyethylene Surfaces Treated in Ambient-Pressure N2–H2 DBD Post Discharges

Chemical derivatization analysis of polyethylene surfaces plasma-treated in the afterglow regions of dielectric barrier discharges in mixtures of nitrogen and hydrogen was studied, using nucleophilic instead of electrophilic reagents which have commonly been used in studies of polymer surfaces exposed to discharges in nitrogen or nitrogen-containing gases. Vapors of strongly nucleophilic 2-mercaptoethanol and 4-(trifluoromethyl)-phenylhydrazine (TFMPH), respectively, were used for derivatization. XPS spectroscopy was subsequently applied in order to quantify the amount of sulfur and fluorine, respectively, introduced to the surface due to the presence of electrophilic moieties generated by the plasma treatment. Using FTIR-ATR spectroscopy following TFMPH derivatization, a quantitative determination of the hydrazone groups formed was possible, based on a comparison with spectra of a low-molecular weight model hydrazone. The results of these investigations confirm conclusions from earlier studies showing that the formation of electrophilic groups such as imines on polymers treated in afterglows of nitrogen–hydrogen DBDs must not be disregarded.

Adsorption of Poly(Acrylic Acid)-Graft-Poly(Ethylene Glycol) on Polyelectrolyte Multilayers

Graft copolymers PAA-g-PEG with poly(acrylic acid) (PAA, 200 kDa) backbone and poly(ethylene glycol) (PEG, 5 kDa) side chains with grafting ratios g = 5, adsorbed on stainless steel surfaces, were studied using FTIR-ATR spectroscopy. The amount of adsorbed PAA-g-PEG could strongly be increased with a polyelectrolyte multilayer (PEM) as an interlayer. Two independent calibration methods were used to calculate PEG chain areal densities σPEG or effective thickness values d = σPEG·nEG / ρEG (nEG: number of EG units in the chain, ρEG: assumed volume density of EG units) of the PEG component. With a suitable PEM interlayer a thickness of d = 34 nm, close to the theoretical length of a helical PEG chain with 114 EG units (32 nm), was obtained. In PEM-PEG coatings with appreciable contents of PEG, the dominance of vibrational bands with transition dipole moments parallel to the axis of helical PEG chains indicates that most PEG helices are oriented vertically on the substrate.

P3T – a new technology for the cost and resource efficient inline production of flexible printed circuits, RFID antennas and biosensors

Purpose – The purpose of this paper is to present details of the plasma printing and packaging technology (P3T), a new reel‐to‐reel technology under development for the cost and resource efficient manufacture of flexible printed circuits (FPC).Design/methodology/approach – The first two process steps of P3T include reel‐to‐reel patterned activation of polymer film at ambient pressure in the so‐called plasma‐printing process and subsequent selective electroless plating of the plasma‐activated areas of the polymer film. The concept underlying the P3T project includes processing of flexible films with widths up to 400 mm.Findings – Copper, palladium and nickel metal structures with widths down to less than 100 μm were produced on various polymers. Peel strengths according to the German DIN Standard 53494 of copper on polyimide film reached values in the region of 1 N/mm, sufficient for electronic applications. Sufficient wetting of the solder on copper metallisations and solderability were found.Research lim...