Graduation Year

2021

Document Type

Thesis

Degree

M.S.B.E.

Degree Name

MS in Biomedical Engineering (M.S.B.E.)

Degree Granting Department

Biomedical Engineering

Major Professor

Mark Jaroszeski, Ph.D.

Committee Member

Richard Heller, Ph.D.

Committee Member

William Lee, Ph.D.

Committee Member

Timothy Fawcett, Ph.D.

Keywords

Bioreactor, COMSOL Multiphysics, Perfusion culture

Abstract

Perfusion bioreactors are used for cell production for cell therapies. The system uses cell separation devices such as centrifuge to facilitate cell growth by separating cells and spent media and allows constant media replacement. However, current cell separation technologies can increase shear stress, are generally not continuous processes, and are not as efficient as desired. These limit the amount of media replaced per unit time. Therefore, there is a need for a new system or a method that operates continuously to minimize cell damage, yield high cell concentration, and exchange media effectively. A set of research questions was formulated: (1) develop a computer simulation model for the known cell concentrating dynamics of an industry-standard Centritech Lab III centrifuge as a semi-continuous device, (2) develop a model of a Centritech Lab III centrifuge for continuous operation, and (3) use a developed model to characterize cellular separation in two novel centrifuge designs with respect to feasibility.

Two types of models were made with COMSOL Multiphysics, (1) Centritech Lab III type models and (2) new continuous operation models. Study 1 modeled the throughput and efficiency of a Centritech Lab III. This model was tested with two different culture types: semi-continuous use in study 1-1 and fully continuous use in study 1-2. Study 2 simulated a new continuous operation model, and two new models were created in study 2-1. Theory-based assessment was performed in study 2-2. Flow velocity stability and shear rate were evaluated in study 2-3.

As a result, in study 1-1, a computer simulation model of a Centritech Lab III centrifuge as a semi-continuous device was developed. This model moved cells downward by centrifugal force and could increase cell concentration in the lower area of the bladder in a semi-continuous manner. In study 1-2, a Centritech Lab III centrifuge model for the continuous operation was developed. However, any tested flow settings couldn’t carry the cells from the inlet to the exit stream, and it was found out that this system couldn’t be adapted for continuous operation.

In study 2, a developed model was used to characterize cellular separation in two novel centrifuge designs with respect to feasibility. Two new models were created based on structure and media property tests: the OC model and the No-OC model. The OC model was challenging to increase the cell concentration, but based on the theory of Fd = Fcfg, adjusting flow velocity effectively reduced the possible cell stagnation. Some OC model test cases, considered supernatant removal, allowed removing a high volume of supernatant without losing many cells. The No-OC model yielded a greater cell concentration than the OC model and achieved high supernatant removal. These No-OC tests provided a possibility to use as a benchtop size continuous operation device, though it needed to consider additional cell collection devices. The flow velocity stability and the shear rate in the created model were assessed, and the high pressure and high shear rate were found in the narrow area of the models. Verification by computer simulation was considered to be meaningful.

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