Publications by Urs von Stockar

Chat with Graph Search

Ask any question about EPFL courses, lectures, exercises, research, news, etc. or try the example questions below.

DISCLAIMER: The Graph Chatbot is not programmed to provide explicit or categorical answers to your questions. Rather, it transforms your questions into API requests that are distributed across the various IT services officially administered by EPFL. Its purpose is solely to collect and recommend relevant references to content that you can explore to help you answer your questions.

Real-time data reconciliation of concentration estimates of process analytes and biomass in microbial fermentations is investigated. A Fourier-transform mid-infrared spectrometer predicting the concentrations of process metabolites is used in parallel with ...

The feasibility of removing water from azeotropic mixts. is explored. Although the selectivity of membrane distn. processes is largely detd. by vapor liq. equil. (VLE), differences in diffusion rates across the membrane and an eventual addnl. gas gap may shift the selectivity away from unity, the value expected for azeotropes. Expts. in a plate-and-frame membrane distn. module, with azeotropic mixts. of HCl/H2O and of propionic acid/H2O, yielded retention selectivities of the solute 0.6-0.8. They could be d

In the present study, the optimal medium perfusion rate to be used for the continuous culture of a recombinant CHO cell line in a packed-bed bioreactor made of Fibra-Cel disk carriers was detd. A first-generation process had originally been designed with a high perfusion rate, in order to rapidly produce material for pre-clin. and early clin. trials. It was originally operated with a perfusion of 2.6 vvd during prodn. phase in order to supply the high cell d. (.apprx.2.5*107 cell ml-1 of packed-bed) with su

An anti-Rhesus D antibody was produced in various cell-lines and cell-types which were either stable or transient transfected and grown under varying culture conditions. Glycosylation anal. of the IgG1 was carried out mainly by HPAEC methods. The antibody was N-glycosylated only at the conserved glycosylation site at Asn-297 carrying complex type N-glycans as usually present on IgG. The core structure was entirely fucosylated and did not carry intersecting G1cNAc for all antibodies analyzed. Prodn. in SP2/0

Calcium alginate beads were thermally treated at temps. ranging from 25 DegC to 130 DegC for periods of up to 30 min. Important modifications to the structure of the alginate beads were shown to be a function of the temp. and period of incubation at each temp. Modifications to the alginate beads included redn. in size, mech. resistance, and mol. wt. cut-off with increasing temp. and incubation period. Thus, heating 700 mm calcium alginate beads for 20 min at 130 DegC resulted in a 23% redn. in diam., 70% in

A pH method is described for the detn. of the wettability of membranes used in membrane distn. modules. The wettability factor that varies 0-1 is defined. With aq. EtOH, effects of dynamic overpressure and membrane stretching are shown to affect pore size and wettability of flat membranes. By this technique, the EtOH concn. for onset of membrane wetting (with Durapore 0.22 mm membranes) is 180 g/L as compared with the 235 g/L for penetrating-drop method. [on SciFinder (R)]

The following paper describes how pressurized CO2 under near-crit. and supercrit. conditions affects the survival of a range of yeast and bacterial cells. Kluyveromyces fragilis was found to be the most resistant of the test organisms studied with relative viabilities of >70% under near-crit. conditions. The growth history of the cells before treatment was the major factor affecting survivability with up to 100-fold higher viabilities for cells treated from the stationary phase of batch growth compared with

To meet the need for studies of anaerobic microbial and animal cell cultures involving much lower heat effects as compared to aerobic microbial cultures, a bench scale calorimeter, Bio-RCl, has been improved for achieving a higher long-term sensitivity. This newly improved Bio-RCl was used for heat measurement of anaerobic growth of Lactobacillus helveticus. The results showed that the bench-scale calorimetry has powerful potential for online monitoring and control of anaerobic bioprocesses as well as funda

Continuous cultures of a hybridoma cell line (Zac3) were performed with 2 14C-labeled substrates: glucose and glutamine. A simplified network was used to describe cell metab. This simple network gave a good idea of the main fluxes into the cell, esp. for catabolic reactions. The use of 14C-labeled glucose and glutamine enabled the metabolic routes to be described with great accuracy, esp. CO2 prodn. rate. [on SciFinder (R)]

At high growth rates, the biomass yield of baker's yeast (Saccharomyces cerevisiae) decreases due to the prodn. of ethanol. For this reason, it is std. industrial practice to use a fed-batch process whereby the specific growth rate, m, is fixed at a level below the point of ethanol prodn., i.e., mcrit. Optimally, growth should be maintained at mcrit, but in practice, this is difficult because mcrit is dependent upon strain and culture conditions. In this work, growth was maintained at a point just above mcr

Over the past decade the interest for bioprocess monitoring using non-invasive IR spectroscopic sensors has increased considerably. This is mainly due to their rapid simultaneous multi-analyte detn. ability, in-situ sterilizability, and low need for maintenance during operation. Most of the components in culture media absorb in the MID-IR region. The complex spectra obtained can be deconvoluted using numerical methods such as Partial Least-Squares. In order to do this, a calibration model for each component

Gas absorption in packed columns was modelled, taking into account all heat effects for phys. gas absorption. Multicomponent diffusion effects were incorporated in terms of the film-factor concept. An algorithm of very stable convergence behavior was obtained by simulating the start-up procedure of the column dynamically in order to evaluate the steady-state operation. The importance of rigorous design calcns. was assessed by comparing the rigorous soln. with simplified hand calcns. for a large no. of cases

Synchronized oscillating cultures of Saccharomyces cerevisiae CBS 426 exhibit periodic oxidoreductive metab. The changing metab. is detectable by in situ heat-flux calorimetry in the BSC 81, which was operated as a chemostat in these expts. The measured metabolic heat flux oscillated in phase and with the same period as the other monitored process variables (CER, The authors', and DO) at the diln. rates studied (0.12 and 0.14 h-1). There was a difference of 2 W L-1 between the min. and max. of the oscillati

A chemically-defined protein-free medium (FMX-Turbodoma) has been improved for the production of monoclonal IgA antibodies by hybridoma cells, using a systematic method. Cell growth rate, IgA production, activity and molecular weight pattern have been used as optimization criteria. Of potentially important supplements, glucose, glutamine, Pluronic acid F-68 as well as several amino acids had significant beneficial effects. A determination of amino acids profiles via HPLC analysis allowed the formulation of

The influence of substrate compn. on the yield, nature, and compn. of exopolysaccharides (EPS) produced by the food-grade strain G. xylinus I-2281 was investigated during controlled cultivations on mixed substrates contg. acetate and either glucose, sucrose, or fructose. Enzymic activity anal. and acid hydrolysis revealed that 2 EPS, gluconacetan and levan, were produced by G. xylinus. In contrast to other acetic acid strains, no exocellulose formation has been measured. Considerable differences in metaboli

M. thermoautotrophicum was grown on a defined mineral salts medium under strictly anaerobic conditions with H2 and CO2 as the sole energy and C sources, resp. The cultivation medium was optimized with respect to non-org. components, including Se(IV), W(VI), N, Ni(II), Fe(II), Co(II), and Mo(VI). S2- concn. in the medium was maintained const. using an online regulatory system by the addn. of 0.5M Na2S. A max. supply rate of 0.6 vvm of a mixt. of 80% H2 and 20% CO2 was achieved for the gaseous substrates. Und

Mid-IR (MIR) spectroscopy in combination with partial least-squares (PLS) regression anal. was used to monitor the concns. of glucose, lactate, ammonia, and asparagine in situ during bioreactor cultivation of CHO/SSF3 cells. Simple PLS calibration models were established using referenced in situ collected single-beam spectra of one immobilized culture. The models were applied to another immobilized culture and one suspension culture. In general, glucose predictions were unbiased for both culture types. Appl

Isothermal reaction calorimetry was employed on the bench scale to measure the enthalpy efficiency and O2 efficiency of growth of several microbial strains cultured on a range of substrates with varying degrees of redn. The obsd. values of these energetic efficiency factors agreed well with simple theor. predictions based solely on the degree of redn. of the substrates as independent variable. Calorimetry is thus shown to be a useful tool for investigations of microbial growth energetics. Measuring heat dis

The bioconversion of L-phenylalanine (L-Phe) to 2-phenylethanol (PEA) by the yeast Saccharomyces cerevisiae is limited by the toxicity of the product. PEA extn. by a sep. org. phase in the fermenter is the ideal in situ product recovery (ISPR) technique to enhance productivity. Oleic acid was chosen as org. phase for two-phase fed-batch cultures, although it interfered to some extent with yeast viability. There was a synergistic inhibitory impact toward S. cerevisiae in the presence of PEA, and therefore a

Aq. solns. of formic acid were exptl. investigated in a modified sweeping gas membrane distn. (SGMD) configuration. A thermostated sweeping gas was used in order to enhance the mass transfer performance. A new tubular module was designed and built for this purpose. The effects of the relevant process parameters on the permeate flux and selectivity were studied. Expts. with pure water and pure formic acid were used to est. certain parameters in the model. From these mass transfer coeffs., the fluxes and sele

Urs von Stockar

Chat with Graph Search

Data Reconciliation of Concentration Estimates from Mid-Infrared and Dielectric Spectral Measurements for Improved On-Line Monitoring of Bioprocesses

Azeotropic mixtures may be broken by membrane distillation

Optimization of the medium perfusion rate in a packed-bed bioreactor charged with CHO cells

The effect of cell line, transfection procedure and reactor conditions on the glycosylation of recombinant human anti-rhesus D IGG1

Low-temperature electron microscopy for the study of polysaccharide ultrastructures in hydrogels. II. Effect of temperature on the structure of Ca2+-alginate beads

New method for the determination of wettability in a membrane distillation process

Effect of a near-critical and supercritical fluid on the viability ratio of microbial cells

Anaerobic calorimetry of the growth of Lactobacillus helveticus using a highly sensitive bio-RCl

Metabolic network analysis of a hybridoma cell line using mass balances and 14C-labeled glucose and glutamine

Control of yeast fed-batch process through regulation of extracellular ethanol concentration

Experimental versus simulated calibration mdels for in situ FTIR monitoring of bioprocesses

Rigorous and short-cut design calculations for gas absorption involving large heat effects. 1. A new computational method for packed gas absorbers

Monitoring synchronized oscillating yeast cultures by calorimetry

Systematic improvement of a chemically-defined protein-free medium for hybridoma growth and monoclonal antibody production

Influence of nutritional factors on the nature, yield, and composition of exopolysaccharides produced by Gluconacetobacter xylinus I-2281

Improved growth and methane production conditions for Methanobacterium thermoautotrophicum

Mid-infrared spectroscopic monitoring of animal cell culture bioreactor processes

A calorimetric study of microbial growth energetics

Extractive Bioconversion of 2-Phenylethanol from L-Phenylalanine by Saccharomyces cerevisiae

Separation of binary mixtures by thermostatic sweeping gas membrane distillation II. Experimental results with aqueous formic acid solutions