Inverse problem analysis of pluripotent stem cell aggregation dynamics in stirred-suspension cultures

Abstract

The cultivation of stem cells as aggregates in scalable bioreactor cultures is an appealing modality for the large-scale manufacturing of stem cell products. Aggregation phenomena are central to such bioprocesses affecting the viability, proliferation and differentiation trajectory of stem cells but a quantitative framework is currently lacking. A population balance equation (PBE) model was used to describe the temporal evolution of the embryonic stem cell (ESC) cluster size distribution by considering collision-induced aggregation and cell proliferation in a stirred-suspension vessel. For ESC cultures at different agitation rates, the aggregation kernel representing the aggregation dynamics was successfully recovered as a solution of the inverse problem. The rate of change of the average aggregate size was greater at the intermediate rate tested suggesting a trade-off between increased collisions and agitation-induced shear. Results from forward simulation with obtained aggregation kernels were in agreement with transient aggregate size data from experiments. We conclude that the framework presented here can complement mechanistic studies offering insights into relevant stem cell clustering processes. More importantly from a process development standpoint, this strategy can be employed in the design and control of bioreactors for the generation of stem cell derivatives for drug screening, tissue engineering and regenerative medicine.

Current state and perspectives in modeling and control of human pluripotent stem cell expansion processes in stirred‐tank bioreactors

“…Moreover, the same group showed that the aggregation kernel representing aggregation dynamics used in PBE models can be derived from experimental size distributions of cultured ESC clusters as a solution of the inverse problem. 42 Their results revealed that the rate of change of the average aggregate size depends on agitation rates and peaks at the intermediate rate. This analytical framework can be used to derive insights about the cell clustering processes of specific cell types.…”

“…Using a similar strategy implemented for aggregation of platelets, Kehoe et al, applied a mass‐structured population balance equation (PBE) to model the distribution of mESC aggregate sizes in stirred‐tank bioreactors; the prediction made with this model was consistent with experimentally obtained data. Moreover, the same group showed that the aggregation kernel representing aggregation dynamics used in PBE models can be derived from experimental size distributions of cultured ESC clusters as a solution of the inverse problem . Their results revealed that the rate of change of the average aggregate size depends on agitation rates and peaks at the intermediate rate.…”

A scalable and tunable thermoreversible polymer for 3D human pluripotent stem cell biomanufacturing

“…Finally, suspension culture of 3D cell aggregates may offer a potential scalable solution to stem cell manufacturing, as there is low cost of goods and high cell yields ( Hookway et al., 2016 ). However, 3D aggregate suspensions require high shear rates in stir-tank reactors to prevent cell agglomeration, affecting cell viability, and differentiation ( Rostami et al., 2015 ).…”

Estimation of aggregation kernels based on Laurent polynomial approximation

“…The estimation of aggregation kernels was demonstrated by Wright and Ramkrishna (1992), based on the assumption of self-similarity. The latter approach was subsequently used by other groups for determining kernels for stem cell aggregation (Rostami et al, 2015) and sludge flocculation (Torfs et al, 2012). The self-similarity of the particle size distribution depends on the aggregation kernel as well as on the initial conditions and may not be achieved under conditions where aggregation and growth occur simultaneously, as for instance reported by Bramley et al (1997).…”