Microfluidic nutrient gradient-based three-dimensional chondrocyte culture-on-a-chip as an in vitro equine arthritis model.

In this work, we describe a microfluidic three-dimensional (3D) chondrocyte culture mimicking in vivo articular chondrocyte morphology, cell distribution, metabolism, and gene expression. This has been accomplished by establishing a physiologic nutrient diffusion gradient across the simulated matrix, while geometric design constraints of the microchambers drive native-like cellular behavior. Primary equine chondrocytes remained viable for the extended culture time of 3 weeks and maintained the low metabolic activity and high Sox9, aggrecan, and Col2 expression typical of articular chondrocytes. Our microfluidic 3D chondrocyte microtissues were further exposed to inflammatory cytokines to establish an animal-free, in vitro osteoarthritis model. Results of our study indicate that our microtissue model emulates the basic characteristics of native cartilage and responds to biochemical injury, thus providing a new foundation for exploration of osteoarthritis pathophysiology in both human and veterinary patients.

Biogas desulfurization and biogas upgrading using a hybrid membrane system--modeling study.

Membrane gas permeation using glassy membranes proved to be a suitable method for biogas upgrading and natural gas substitute production on account of low energy consumption and high compactness. Glassy membranes are very effective in the separation of bulk carbon dioxide and water from a methane-containing stream. However, the content of hydrogen sulfide can be lowered only partially. This work employs process modeling based upon the finite difference method to evaluate a hybrid membrane system built of a combination of rubbery and glassy membranes. The former are responsible for the separation of hydrogen sulfide and the latter separate carbon dioxide to produce standard-conform natural gas substitute. The evaluation focuses on the most critical upgrading parameters like achievable gas purity, methane recovery and specific energy consumption. The obtained results indicate that the evaluated hybrid membrane configuration is a potentially efficient system for the biogas processing tasks that do not require high methane recoveries, and allows effective desulfurization for medium and high hydrogen sulfide concentrations without additional process steps.

Chemical-oxidative scrubbing for the removal of hydrogen sulphide from raw biogas: potentials and economics.

In the present work chemical-oxidative scrubbing as a novel method for the desulphurisation of raw biogas is presented with a special focus on the process potentials and economics. The selective absorption of hydrogen sulphide from gas streams containing high amounts of carbon dioxide using caustic solutions is not trivial but has been treated in literature. However, the application of this method to biogas desulphurisation has not been established so far. Based on rigorous experimental work, an industrial-scale pilot plant has been designed, erected and commissioned at a biogas plant with biogas upgrading and gas grid injection in Austria. Data collected from the 12-month monitored operation has been used to elaborate performance as well as economic parameters for the novel desulphurisation method. The proposed technology offers significant operational advantages regarding the degree of automation and the flexibility towards fluctuations in process boundary conditions. Furthermore, the economic assessment revealed the high competitiveness of the chemical-oxidative scrubbing process compared with other desulphurisation technologies with the named advantageous operational behaviour.

Design and scale-up of an oxidative scrubbing process for the selective removal of hydrogen sulfide from biogas.

Reliable and selective removal of hydrogen sulfide (H(2)S) is an essential part of the biogas upgrading procedure in order to obtain a marketable and competitive natural gas substitute for flexible utilization. A promising biogas desulfurization technology has to ensure high separation efficiency regardless of process conditions or H(2)S load without the use or production of toxic or ecologically harmful substances. Alkaline oxidative scrubbing is an interesting alternative to existing desulfurization technologies and is investigated in this work. In experiments on a stirred tank reactor and a continuous scrubbing column in laboratory-scale, H(2)S was absorbed from a gas stream containing large amounts of carbon dioxide (CO(2)) into an aqueous solution prepared from sodium hydroxide (NaOH), sodium bicarbonate (NaHCO(3)) and hydrogen peroxide (H(2)O(2)). The influence of pH, redox potential and solution aging on the absorption efficiency and the consumption of chemicals was investigated. Because of the irreversible oxidation reactions of dissolved H(2)S with H(2)O(2), high H(2)S removal efficiencies were achieved while the CO(2) absorption was kept low. At an existing biogas upgrading plant an industrial-scale pilot scrubber was constructed, which efficiently desulfurizes 180m(3)/h of raw biogas with an average removal efficiency of 97%, even at relatively high and strongly fluctuating H(2)S contents in the crude gas.

Towards biochemical reaction monitoring using FT-IR synchrotron radiation.

A lab-on-a-chip device made of CaF2 windows and SU-8 polymer was used for fluid lamination to achieve rapid mixing of two streamlines with a cross section of 300 x 5 microm each. Time resolved measurements of the induced chemical reaction was achieved by applying constant feeding low flow rates and by on-chip measurement at defined distances after the mixing point. Synchrotron IR microscopic detection was employed for direct and label-free monitoring of (bio)chemical reactions. Furthermore, using synchrotron IR microscopy the measurement spot could be reduced to the diffraction limit, thus maximizing time resolution in the experimental set-up under study. Based on computational fluid dynamic simulations the principle of the set-up is discussed. Experimental results on the basic hydrolysis of methyl chloroacetate proved the working principle of the experimental set-up. First results on the interaction between the antibiotic vancomycin and a tripeptide (Ac2KAA) involved in the build up of the membrane proteins of gram-positive bacteria are presented.

Design, simulation and application of a new micromixing device for time resolved infrared spectroscopy of chemical reactions in solution.

We present a novel micromachined fast diffusion based mixing unit for the study of rapid chemical reactions in solution with stopped-flow time resolved Fourier transform infrared spectroscopy (TR-FTIR). The presented approach is based on a chip for achieving lamination of two liquid sheets of 10 microm thickness and approximately 1 mm width on top of each other and operation in the stopped-flow mode. The microstructure is made on infrared transmitting calcium fluoride discs and built up with two epoxy negative photoresist layers and one silver layer in between. Due to the highly laminar flow conditions and the short residence time in the mixer there is hardly any mixing when the two liquid streamlines pass through the mixing unit, which allows one to record a mid-IR transmission spectrum of the analytes prior to reaction. When the flow is stopped, the reactant streams are arrested in the flow-cell and rapidly mixed by diffusion due to the reduced interstream distances and the reaction can be directly followed with hardly any dead time. On the basis of two model reactions-neutralisation of acetic acid with sodium hydroxide as well as saponification of methyl monochloroacetate-the performance of the mixing device was tested revealing proper functioning of the device with a time for complete mixing of less than 100 ms. The experimental results were supported by numerical simulations using computational fluid dynamics (CFD), which allowed a reliable, quantitative analysis of concentration, pressure and flow profiles in the course of the mixing process.