During the first half of 2020, Merck KGaA, Darmstadt, Germany, sponsored the CMMC’s development of a stirred tank bioreactor model. The model serves as a proof-of-concept that novel computational modeling methods can recapitulate laboratory results of direct relevance to the cultivated meat industry.
Once the interactive animation below loads [does not work well from most cell phones], you will see a simple stirred tank bioreactor studied by Croughan et al [1] in the mid 1980s. A spinning cylindrical rotor suspended from above perpetuates fluid flow, propelling tiny spherical microcarriers. On the surface of each microcarrier, even tinier cells adhere and proliferate. The color of a cell represents the stress it endures: a redder color corresponds to higher stress. The stress emanates from two sources: the compressive forces exerted by the cell’s neighbors; and the tensional forces exerted by its adherence junction when propelled faster or slower than the attached microcarrier.
NB: Demo works most smoothly when other video applications are not running (e.g., we recommend quitting out of zoom.) Runs poorly on most phones.
[1] Croughan MS, Hamel JF, Wang DI. Hydrodynamic effects on animal cells grown in microcarrier cultures. Biotechnol Bioeng. 1987;29(1):130-141. doi:10.1002/bit.260290117
To get a sense of what it’s like to be a cell on a microcarrier, once you see the bioreactor image click on the image and type f …
Click on image once loaded. Then ctrl-mouse changes angle of view. move with {w,a,s,d} or (faster) {W,A,S,D}
space-bar toggles pause
+/- speed-up/slow-down the simulation (note that this does not affect the stir speed of the simulation, it will merely increase/decrease the speed at which simulation results are displayed)
f - focuses on "next" microcarrier; u - releases focus when focused, w/a move closer/further from microcarrier.
h - releases focus and returns to initial positionTo create products competitive with butchered meat, the cultivated meat industry must grow massive numbers of cells in vitro at low cost. Cells proliferate fastest when attached to other cells or microcarriers and provided a stable environment rich in nutrients and oxygen. Sustaining availability of these inputs in the presence of cells’ consumption of those same inputs requires that the fluid be mixed. Mixing agitates the cells, creating physical stresses that disrupt cell processes. Instead of proliferating as desired, replication slows; cell adhesions break; and differentiation, quiescence or even death may result. The challenge of maintaining a well-mixed environment without subjecting cells to excessive stress is exacerbated when pursuing economy of scale, both due the increased energy to maintain mixing over larger bioreactor volumes and the increased potential for high viscosity as cell density in those bioreactors grows.
To understand and optimize bioreactors for cultivated meat is prerequisite to the industry’s success. To support the industry in its quest, CMMC is developing new purpose-built modeling tools. One modeling methodology the CMMC is pursuing integrates computational fluid dynamics (CFD) and agent-based modeling (ABM). CFD is used to establish the fluid velocity field within a given bioreactor design operated in a given way with a given viscosity field. ABM is used to determine how this fluid velocity field influences the movement of microcarriers and cells, and how the resulting forces exerted by the fluid impact cell biology, proliferation and death. As of July, 2020, the CMMC has developed a proof-of-concept demonstrating this technology. Taking this forward will involve modeling cultivated meat bioreactor scenarios and ultimately predicting, for example, what rotational speeds optimize biomass production as the number of cells (and therefore viscosity) increases; what geometry and density of microcarriers works best; and what schedules for microcarrier addition or media enhancement work best.