Characterization of mixing in a novel wavy-walled bioreactor for tissue engineering

The wavy-walled bioreactor (WWB) possesses a novel geometry comprised of walls with sinusoidal waves that mimic baffles in an effort to promote mixing. This geometry provides a unique hydrodynamic environment suitable for the cultivation of mammalian cells and tissues and the investigation of fluid mechanical effects on cell and tissue growth and development. In the present study, mixing in WWB was characterized and compared to that in a conventional spinner flask (SF). The key parameters included in this characterization were mixing time, residence time distribution (RTD), and dissolved oxygen concentration during engineered cartilage tissue cultivation. Factors that influenced mixing in WWB included wave amplitude, agitation rate, and the ratio of the impeller diameter to the tank diameter (D/T). Data obtained from RTD and acid base neutralization studies confirmed the presence of different mixing zones in WWB. A theoretical comparison of WWB to a baffled spinner flask (BSF) using computational fluid dynamics (CFD) modeling predicted that while enhanced mixing was achieved in wavy-walled and BSF bioreactors, the shear stresses applied on tissue constructs were 15% lower in WWB. Improved mixing was achieved in WWB compared to the SF at similar D/T ratios, verified by improved oxygen transport and increased dispersion. However, for lower D/T ratios mixing in WWB was not necessarily improved. This study demonstrated the importance of characterization of mixing by showing the impact of even minor changes in bioreactor geometry and operating conditions.

Characterization of fluid-flow resistance in root cultures with a convective flow tubular bioreactor

Agrobacterium transformed root cultures of Hyoscyamus muticus were grown in a recirculating 2 L tubular bioreactor system. Performance of this convective flow reactor (CFR) was compared to a bubble column (BC) reactor of the same geometry: replicated CFR experiments produced an average tissue concentration of 556 +/- 4 grams fresh weight per liter in 30 d whereas the bubble column produced only 328 +/- 5 grams per liter corresponding to 25.3 +/- 0.0 and 14.3 +/- 0.5 grams dry weight per liter, respectively. Because media nutrient levels were maintained sufficiently high to saturate growth rate, the improved performance of the CFR is attributed to enhanced convective mass transfer. The pressure drops observed for flow through roots grown within the reactors were more than an order of magnitude higher than previously obtained by placing roots grown in shake culture into defined geometries. The experimentally observed flow resistance was much higher than would be predicted from correlations using the root diameter as the characteristic diameter for flow resistance. Several lines of evidence suggest that root hairs are a substantial contributor to the observed high flow resistance in these transformed root cultures. Pressure drop increased nonlinearly with velocity which could not be adequately described by a modified form of the Ergun equation. Kyan et al's (1970) equation, although predicting such curvature, relies almost exclusively on an empirical packing deflection term to describe the hydrodynamic behavior. Implications of these results to the design of submerged reactor systems for root culture are discussed. Copyright 1998 John Wiley & Sons, Inc.

Zymomonas mobilis--science and industrial application

Zymomonas mobilis is undoubtedly one of the most unique bacterium within the microbial world. Known since 1912 under the names Termobacterium mobilis, Pseudomonas linderi, and Zymomonas mobilis, reviews on its uniqueness have been published in 1977 and 1988. The bacterium Zymomonas mobilis not only exhibits an extraordinarily uniqueness in its biochemistry, but also in its growth behavior, energy production, and response to culture conditions, as well as cultivation techniques used. This uniqueness caused great interest in the scientific, biotechnological, and industrial worlds. Its ability to couple and uncouple energy production in favor of product formation, to respond to physical and chemical environment manipulation, as well as its restricted product formation, makes it an ideal microorganism for microbial process development. This review explores the advances made since 1987, together with new developments in the pure scientific and applied commercial areas.

The application of biotechnology to the treatment of wastes produced from the nuclear fuel cycle: biodegradation and bioaccumulation as a means of treating radionuclide-containing streams

Recent concerns on the radiotoxicity and longevity of nuclides have prompted the development of new technologies for their removal from wastes produced from nuclear power programs and nuclear fuel reprocessing activities. Alongside developments from traditional chemical treatment processes, interest has also centered on the application of biotechnology for efficient waste treatment. Many biological techniques have relied on empirical approaches in simple model systems, with scant regard to the nature and volume of actual target wastes; such considerations may limit the application of the new technologies in practice. This review aims to identify some of the likely problems, to discuss the various approaches under current consideration, and to evaluate ways in which either the target waste or the detoxifying biomass may be modified or presented for the most efficient treatment.