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Scale-up Strategy (scale-up + strategy)
Selected AbstractsModeling the competition between aggregation and self-assembly during virus-like particle processing,BIOTECHNOLOGY & BIOENGINEERING, Issue 3 2010Yong Ding Abstract Understanding and controlling aggregation is an essential aspect in the development of pharmaceutical proteins to improve product yield, potency and quality consistency. Even a minute quantity of aggregates may be reactogenic and can render the final product unusable. Self-assembly processing of virus-like particles (VLPs) is an efficient method to quicken the delivery of safe and efficacious vaccines to the market at low cost. VLP production, as with the manufacture of many biotherapeutics, is susceptible to aggregation, which may be minimized through the use of accurate and practical mathematical models. However, existing models for virus assembly are idealized, and do not predict the non-native aggregation behavior of self-assembling viral subunits in a tractable nor useful way. Here we present a mechanistic mathematical model describing VLP self-assembly that accounts for partitioning of reactive subunits between the correct and aggregation pathways. Our results show that unproductive aggregation causes up to 38% product loss by competing favorably with the productive nucleation of self-assembling subunits, therefore limiting the availability of nuclei for subsequent capsid growth. The protein subunit aggregation reaction exhibits an apparent second-order concentration dependence, suggesting a dimerization-controlled agglomeration pathway. Despite the plethora of possible assembly intermediates and aggregation pathways, protein aggregation behavior may be predicted by a relatively simple yet realistic model. More importantly, we have shown that our bioengineering model is amenable to different reactor formats, thus opening the way to rational scale-up strategies for products that comprise biomolecular assemblies. Biotechnol. Bioeng. 2010;107: 550,560. © 2010 Wiley Periodicals, Inc. [source] The effect of heating rate on Escherichia coli metabolism, physiological stress, transcriptional response, and production of temperature-induced recombinant protein: A scale-down studyBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2009Luis Caspeta Abstract At the laboratory scale, sudden step increases from 30 to 42°C can be readily accomplished when expressing heterologous proteins in heat-inducible systems. However, for large scale-cultures only slow ramp-type increases in temperature are possible due to heat transfer limitations, where the heating rate decreases as the scale increases. In this work, the transcriptional and metabolic responses of a recombinant Escherichia coli strain to temperature-induced synthesis of pre-proinsulin in high cell density cultures were examined at different heating rates. Heating rates of 6, 1.7, 0.8, and 0.4°C/min were tested in a scale-down approach to mimic fermentors of 0.1, 5, 20, and 100 m3, respectively. The highest yield and concentration of recombinant protein was obtained for the slowest heating rate. As the heating rate increased, the yield and maximum recombinant protein concentration decreased, whereas a larger fraction of carbon skeletons was lost as acetate, lactate, and formate. Compared to 30°C, the mRNA levels of selected heat-shock genes at 38 and 42°C, as quantified by qRT-PCR, increased between 2- to over 42-fold when cultures were induced at 6, 1.7, and 0.8°C/min, but no increase was observed at 0.4°C/min. Only small increases (between 1.5- and 4-fold) in the expression of the stress genes spoT and relA were observed at 42°C for cultures induced at 1.7 and 6°C/min, suggesting that cells subjected to slow temperature increases can adapt to stress. mRNA levels of genes from the transcription,translation machinery (tufB, rpoA, and tig) decreased between 40% and 80% at 6, 1.7 and 0.8°C/min, whereas a transient increase occurred for 0.4°C/min at 42°C. mRNA levels of the gene coding for pre-proinsulin showed a similar profile to transcripts of heat-shock genes, reflecting a probable analogous induction mechanism. Altogether, the results obtained indicate that slow heating rates, such as those likely to occur in conventional large-scale fermentors, favored heterologous protein synthesis by the thermo-inducible expression system used in this report. Knowledge of the effect of heating rate on bacterial physiology and product formation is useful for the rational design of scale-down and scale-up strategies and optimum recombinant protein induction schemes. Biotechnol. Bioeng. 2009;102: 468,482. © 2008 Wiley Periodicals, Inc. [source] Combustion of chlorinated hydrocarbons in catalyst-coated sintered metal fleece reactors,JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2-3 2003K Everaert Abstract Incinerators emit chlorinated hydrocarbons, such as polychlorinated benzenes (PCBz) and phenols (PCPh), polychlorinated biphenyls (PCB) and polychlorinated dibenzodioxins and furans (PCDD/F), as very dilute streams. High temperatures (>1000,°C) are required in traditional oxidizers. From an energy-saving perspective and to avoid de novo synthesis of PCDD/F, exhaust gas clean-up must be performed at low temperatures (250,350,°C). Catalytic combustion can be applied in this temperature range and different reactor layouts are used (eg monoliths, honeycomb). The present investigation uses a novel catalyst-coated sintered metal fleece. Thin metal fibers are sintered (non-woven) to fleece of various thickness, structure and porosity. V,Ti,W catalysts are examined. The paper will briefly review the catalyst coating method suitable to provide a structured fleece reactor with adequate characteristics. Experiments were carried out in the temperature range of 260,340,°C with various hydrocarbons injected in a carrier air stream. The experimental investigations demonstrated: (i) that the conversion of the hydrocarbons (volatile organic compounds, VOC) is independent of the oxygen concentration, corresponding to a zero-order dependence of the reaction rate; (ii) that the conversion of the hydrocarbons is a first-order reaction in the VOC; (iii) that the oxidation of the VOC proceeds to a greater extent with increasing temperature, with chlorine substitution enhancing the reactivity, and (iv) that the reaction rate constant follows an Arrhenius-dependence with activation energies between 37.3 and 58.4,kJ,mol,1. An assessment of the results leads to a model expression with kinetic reaction control. This model can be used in a scale-up strategy. © 2003 Society of Chemical Industry [source] Modeling and design of vapor-phase biofiltration for chlorinated volatile organic compoundsAICHE JOURNAL, Issue 9 2002Walter Den A mathematical model was developed for biofilter design and performance prediction with reference to the purification of contaminated gas streams. The model incorporated important aspects such as mass transfer, biodegradation, and adsorption processes. A systematic modeling protocol incorporated the development of a scale-up strategy based on dimensional analysis and similitude. Trichloroethylene (TCE) was employed as the model contaminant for biofiltration testing and model verification. The biokinetic and adsorption parameters for the contaminant were determined independently from a series of minibiofilter and miniadsorber column experiments, specifically designed to simulate the actual biofilter operational regimes in a miniature scale. Bench-scale biofilter experiments employing granular activated carbon columns indicated the good predictive capability of the model for the removal of TCE. Dynamic simulation studies were performed to assess the transient- and steady-state behavior of the model under various operating conditions. Model sensitivity was studied to evaluate the influence of adsorption equilibrium, transport and biological parameters on the biofilter dynamics. The results demonstrated that the biofilter performance was greatly influenced by the Monod coefficients and the biofilm thickness. [source] Scale-up from shake flasks to fermenters in batch and continuous mode with Corynebacterium glutamicum on lactic acid based on oxygen transfer and pHBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2007Juri M. Seletzky Abstract Scale-up from shake flasks to fermenters has been hampered by the lack of knowledge concerning the influence of operating conditions on mass transfer, hydromechanics, and power input. However, in recent years the properties of shake flasks have been described with empirical models. A practical scale-up strategy for everyday use is introduced for the scale-up of aerobic cultures from shake flasks to fermenters in batch and continuous mode. The strategy is based on empirical correlations of the volumetric mass transfer coefficient (kLa) and the pH. The accuracy of the empirical kLa correlations and the assumptions required to use these correlations for an arbitrary biological medium are discussed. To determine the optimal pH of the culture medium a simple laboratory method based on titration curves of the medium and a mechanistic pH model, which is solely based on the medium composition, is applied. The effectiveness of the scale-up strategy is demonstrated by comparing the behavior of Corynebacterium glutamicum on lactic acid in shake flasks and fermenters in batch and continuous mode. The maximum growth rate (µmax,=,0.32 h,1) and the oxygen substrate coefficient (,=,0.0174 mol/l) of C. glutamicum on lactic acid were equal for shake flask, fermenter, batch, and continuous cultures. The biomass substrate yield was independent of the scale, but was lower in batch cultures (YX/S,=,0.36 g/g) than in continuous cultures (YX/S,=,0.45 g/g). The experimental data (biomass, respiration, pH) could be described with a simple biological model combined with a mechanistic pH model. Biotechnol. Bioeng. 2007; 98: 800,811. © 2007 Wiley Periodicals, Inc. [source] | ||||||||||