Transport in a grooved perfusion flat-bed bioreactor for cell therapy applications.

Abstract

This study considers the transport of oxygen (a growth-associated solute) and lactate (a metabolic byproduct) in a flat-bed perfusion chamber modified to retain cells through the addition of grooves, perpendicular to the direction of flow, at the chamber bottom. The chamber has been successfully applied to hematopoietic cell culture and may be useful for other basic and applied biomedical applications. The objective of this study is to characterize the culture environment in terms of solute transport under various operational conditions. This will allow one to improve the design and operating strategy of the perfusion system for maximizing cell numbers. The system is numerically simulated using the finite element package FIDAP. The reaction kinetics describing oxygen uptake by cells are simplified to zero order to give an upper bound for the oxygen consumption. A flat-bed chamber without grooves is considered here as a benchmark. We show that the growth environment is not oxygen limited (local oxygen concentration above 10 microM) for a variety of flow rates and culture conditions (qO2 = 0.1 micromol/(10(6) cells h)). With a medium flow rate of 2.5 mL/min through the reactor, the model predicts that the 29-cm2 reactor can support at least 33.4 x 10(6) total cells when the inlet medium is in equilibrium with high (20%) oxygen concentration. The culture becomes oxygen limited however for the same flow rate for low (5%) oxygen concentration and can only support 7.2 x 10(6) total cells. Comparison of grooved vs nongrooved chambers reveals that the presence of grooves only affects solute transport on a local scale. This result is attributed to the small size (200 microgram) of the cavities relative to the chamber dimensions. The comparison also yields an empirical relation that allows for rapid estimation of oxygen and lactate concentrations in the grooves using only the numerical simulation of the simpler nongrooved chamber. Finally, our investigation shows that, while decreasing the spacing between cavities decreases the total number of cells the reactor can support, the efficiency of the reactor is increased by 25% (on an area basis) without growth restriction.