Pharmaceutical Technology - May 2018

Pharmaceutical Technology eBook - Biologics and Sterile Drug Manufacturing

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20 Pharmaceutical Technology BIOLOGICS AND STERILE DRUG MANUFACTURING 2018 P h a r mTe c h . c o m Bioreactor Design A bioreactor is a stirred tank designed to grow cell culture. The distribution of oxygen in a bioreactor is one of the main growth-inf luencing factors, along with ample sup- ply of nutrients, uniform concentration, and consistent temperature. Agitators are used in these vessels to distribute the gas, blend the contents of the tank, and drive mass transfer by reducing gas droplet size. Oxygen transfer rate (OTR) is defined in Equation 1: OTR = k L a(C* - C) [Eq. 1] where k L = mass transfer coefficient of the liquid a = interfacial area between the gas and liquid C* = saturated concentration of dissolved gas in the liquid C = operating concentration of dissolved gas in the liquid. The mass transfer coefficient and interfacial area are combined to form k L a given that both are system dependent and the interfacial area is unknown in gas–liquid systems. k L a is commonly referred to as the "mass transfer coefficient" due to the inseparable nature of the two terms. The k L a is calculated according to Equation 2: k L a = A(P⁄ V) α f β [Eq. 2] where A, α, and β = system-dependent coefficients P/V = agitator power input per unit volume f = superficial gas velocity = gas f low rate divided by cross-sec- tional tank area. Impact of Agitator Design on Bioreactor Performance Aaron Strand and Nicolle Courtemanche Aerobic bioprocesses are highly dependent upon the oxygen transfer rate from sparged to dissolved gas. The relatively low solubility of oxygen, however, makes the choice of mixer impeller configuration a critical design factor for the bioreactor vessel. This article describes a series of experiments and computational fluid dynamics simulations to detail the effect of mixer configuration on the efficiency and effectiveness of a bioreactor vessel with respect to blend time and mass transfer. Aaron Strand, PE is a senior research engineer with SPX FLOW, aaron.strand@spxflow. com; Nicolle Courtemanche is a senior application engineer with SPX FLOW, nicolle. CRAFTSMANSHIP/SHUTTERSTOCK.COM

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