Effect of pore size, shear rate, and harvest time during the constant permeate flux microfiltration of CHO cell culture supernatant

Abstract

The influence of the shear rate, the membrane pore size, and the age of the culture at time of harvest on transmembrane pressure (TMP) increase and membrane fouling during the microfiltration of a Chinese Hamster Ovary (CHO) cell culture supernatant was investigated. A hollow fiber microfiltration system operated at constant permeate flux was used. The highest TMP increase with filtration time was observed for the small membrane pore size (0.20 microm) operated at the higher shear rate (8,000 s(-1)). Furthermore, the high overall fouling observed with the small membrane pore size was also associated with the highest irreversible fouling and the most significant decrease of predicted open pore area. The predicted reduction in open pore area obtained with the combined pore blockage and cake formation mechanism could explain the observed TMP profiles. Based on the overall membrane fouling, the long-term irreversible fouling and the initial fouling rate, derived from an empirical curve fitting, no effect of the time of harvest was observed but a dependence of the initial fouling rate on the shear rate was identified. Treatment of the fouled membrane with water showed the presence of a more significant reversible fouling at high shear rates and increased irreversible fouling with smaller membrane pore size. It is recommended to use the large membrane pore size (0.45 microm) and the low shear rate (4,000 s(-1)) to minimize fouling associated with the soluble components of serum-free CHO cell culture supernatant.

Understanding and modeling alternating tangential flow filtration for perfusion cell culture

“…Interestingly, the (anti)sticking factor for the pressure phase ( α cells_pressure‐phase ) increased by the same degree, resulting in the same net sticking factor ( α cells_net‐cycle, from Figure ) at the beginning of an experiment (i.e., where cycle‐averaged TMP is low) beginning) as at the end of an experiment (i.e., where cycle‐averaged TMP is higher). Larger pressure‐phase (anti)sticking factors, seen near the end of the experiments, correspond to an enhanced rate of removal of biological deposits from the membrane which is consistent with Stressman's observation that the removal rate of deposited biological solids from a membrane surface as a result of crossflow (during TFF) increases when there is more material deposited on the membrane. The increase in deposition rate during the exhaust cycle (i.e., α cells_exhaust‐phase ) near the end of the experiments is more difficult to explain, and might be a result of existing biological deposits on the membrane surface facilitating deposition of additional deposits.…”

“…For TFF and ATF, there is a crossflow velocity that minimizes the tendency to foul a membrane, and transmembane pressure (TMP; not Δ P ) indicates the pressure drop driving permeate flow across the membrane. Stressman and Moresoli suggested that the rate of formation of open pore area is a result of the crossflow, and correlated mathematically to a constant (that is a function of crossflow velocity) multiplied by the total amount of biomaterial currently on the membrane. Belfort and Zydney suggest that biomaterial can be “peeled off” the membrane by crossflow due to an inertial lift force which increases as the square of the tangential shear rate and the cube of the particle size.…”

Computational fluid dynamic modeling of alternating tangential flow filtration for perfusion cell culture

“…Reversible and irreversible fouling membrane resistances were the highest for the membrane exposed to 0.70 m·s −1 feed cross flow velocity followed by 0.22 and 0.11 m·s −1 feed cross flow rate. Stressmann and Moresoli () showed a similar trend with supernatant solution and a membrane operating under the constant flux mode. These observations may not be intuitively obvious as high shear stress applied to the liquid at the membrane surface reduces the cake layer build‐up and could be considered beneficial in reducing membrane fouling (Silva, Reeve, Husain, Rabie, & Woodhouse, ).…”

“…Previously, ATF has been modeled using a series of empirically derived equations where important parameters such as local velocity, pressure drop, and permeate flux are lumped into single average values (Kelly et al, ). The CFD approach presented in this study provided the basis for improved understanding of the impact of operating conditions on factors such as product sieving (Wang et al, ) and membrane utilization (Stressmann & Moresoli, ). A 2D axisymmetric CFD model was developed using experimental membrane resistance as an input for the simulations.…”

“…The hydraulic filtration resistances were measured based on established methods (Hwang & Sz, ; Stressmann & Moresoli, ) and calculated using Darcy’s equation below: where J is permeate flux (m/s), TMP is transmembrane pressure (kg/m s 2 ), μ is filtrate viscosity (kg/m s), R t (m −1 ) is total membrane resistance during operation, R rm (m −1 ) is intrinsic membrane resistance, R rev (m −1 ) is reversible fouling resistance, and R irev (m −1 ) is irreversible fouling resistance. The clean membrane resistance, R m , was obtained by flowing deionized water through the membrane at a set TMP value.…”