Calculation of fermentation parameters from the results of a batch test taking account of the volume of biomass in the fermenting medium
The values of fermentation parameters calculated from the measured concentrations of substrates and/or products may be significantly affected by the volume of biomass in the fermenting medium. Corrections proposed in this paper should be evaluated and, depending on their magnitude, considered in order to obtain more representative results.
Fed-batch operational strategies for recombinant Fab production with Pichia pastoris using the constitutive GAP promoter
Abstract Carbon source and growth rate are two major parameters affecting recombinant protein production in Pichia pastoris. The effect of the most commonly used carbon sources (glycerol or glucose) and the specific growth rate (μ) has been studied on the production of a human antigen-binding fragment (Fab) in this cell factory under the constitutive GAP promoter in fed-batch cultures. Glycerol for batch phase and glucose for fed-batch phase was the most successful carbon source combination. During batch phase, by-products were detected when glucose was used, despite maintaining DO at values higher than 35%. Also, the presence of cell aggregates was detected affecting the reproducibility and operability of the bioprocess. Conversely, glucose was the best substrate for fed-batch phase. When working at C-limiting conditions, neither by-products nor aggregates were detected and Fab production levels were comparable to those obtained with glycerol. In addition, the lower heat yield (YQ/X) and oxygen to biomass yield ( Y O 2 / X ) for glucose-supported cultures made this substrate the best alternative from an industrial operational point of view. In addition, the effect of specific growth rate on fed-batch Fab production was studied. Medium and high μ (0.10 and 0.15 h−1) set-points showed similar Fab production yield. However, in terms of total and volumetric productivity, higher μ was the best process condition.
Thermal incompatibility analysis of metal-ceramic systems based on flexural displacement data.
The feasibility of simple tests or analytical methods for prediction of residual stress states in metal-ceramic (MC) prostheses has not been demonstrated. Biomaterial metal-ceramic strips have been proposed to provide sensitive measures of transient and residual stress states through the measurement of midpoint deflection after cooling from the ceramic sintering temperature. The objective of this study was to apply the elastic-viscoelastic analogy to calculate transient and residual midpoint deflections in MC biomaterial strips and to compare these values with deflections measured with a beam-bending viscometer (BBV). Calculations and measurements were made for five MC systems that were found from a clinical study to be "thermally compatible" systems. Metal strips, 64 mm in length, 3 mm wide, and either 0.5 mm, 1.0 mm, or 2.0 mm in thickness, were veneered with four 0.25-mm thick layers of opaque porcelain. Midpoint deflection of the MC strips (ceramic oriented in the posterior position) was measured during cooling from an initial temperature of 700 degrees C. In general, the directions of the measured residual deflections did not agree with the "textbook" convention that negative deflections are associated with positive thermal contraction mismatch (alpha(M) - alpha(c) > 0) regardless of metal thickness. For a metal thickness of 0.5 mm, the residual midpoint deflection for all thermal contraction mismatch cases, except one, was positive (upward deflection) whereas the residual midpoint deflections were all negative when the metal thickness was increased to 1 or 2 mm, independent of the thermal contraction mismatch. The best agreement between calculated and measured values of residual midpoint deflection (+16 microns vs. +14 +/- 2.3 microns, respectively was obtained for MC biomaterial strips with a Ni-Cr alloy (0.5 mm thick) while the largest difference (+346 microns vs. +61 +/- 43.8 microns) was obtained for MC bimaterial strips with a Au-Pd allow (0.5 mm thick). In all but one case, changes in deflection direction as a function of metal thickness were correctly predicted by the viscoelastic analysis. The results of this study indicate that a viscoelastic model is useful for estimating thermal compatibility conditions of MC systems.