The potential of hydrodynamic damage to animal cells of industrial relevance: current understanding

Abstract

Suspension animal cell culture is now routinely scaled up to bioreactors on the order of 10,000 L, and greater, to meet commercial demand. However, the concern of the 'shear sensitivity' of animal cells still remains, not only within the bioreactor, but also in the downstream processing. As the productivities continue to increase, titer of ~10 g/L are now reported with cell densities greater than 2 × 10(7) cells/mL. Such high, and potentially higher cell densities will inevitably translate to increased demand in mass transfer and mixing. In addition, achieving productivity gains in both the upstream stage and downstream processes can subject the cells to aggressive environments such as those involving hydrodynamic stresses. The perception of 'shear sensitivity' has historically put an arbitrary upper limit on agitation and aeration in bioreactor operation; however, as cell densities and productivities continue to increase, mass transfer requirements can exceed those imposed by these arbitrary low limits. Therefore, a better understanding of how animal cells, used to produce therapeutic products, respond to hydrodynamic forces in both qualitative and quantitative ways will allow an experimentally based, higher, "upper limit" to be created to guide the design and operation of future commercial, large scale bioreactors. With respect to downstream hydrodynamic conditions, situations have already been achieved in which practical limits with respect to hydrodynamic forces have been experienced. This review mainly focuses on publications from both the academy and industry regarding the effect of hydrodynamic forces on industrially relevant animal cells, and not on the actual scale-up of bioreactors. A summary of implications and remaining challenges will also be presented.

Enriching particles on a bubble through drainage: Measuring and modeling the concentration of microbial particles in a bubble film at rupture

“…However, like all models there are limitations, and we anticipate instances where our model may not yield good agreement. For example, the biotechnology industry routinely introduces additives, such as the non-ionic surfactant Pluronic® F-68, to prevent cells from attaching to bubbles, as rupturing bubbles are generally agreed to be the largest cause of damage to the cells being grown in production scale bioreactors (Hu et al, 2011). In this example, we would anticipate the film concentration to be approximately equal to the bulk concentration, as the primary method of initially trapping cells in the film has been inhibited, which effectively reduces the collision efficiency to zero.…”

Applications and optimization of cryopreservation technologies to cellular therapeutics

“…Similar to the production process, recovery could be achieved by transferring these cell constructs into a bioreactor which provides a dynamic environment aiming to mimic the perfusion condition which cells are subjected to in vivo, with more effective mass transfer properties [75]. A number of different types of bioreactors exist (fluidised bed, rotary cell culture system) that can optimally support cell recovery and metabolism whilst minimising cell damage [76][77][78][79]. Such systems can be readily scaled-up for fast recovery of large volumes of cryopreserved cell therapies.…”

Investigation of low viability in sparged bioreactor CHO cell cultures points to variability in the Pluronic F-68 shear protecting component of cell culture media

“…serum), and, more recently, low molecular weight surfactants have been proposed [18][19][20][21][22], only PF-68 remains widely used in cell culture media [19]. PF-68 is a water-soluble copolymer of a block of hydrophobic polypropylene oxide flanked by two blocks of hydrophilic polyethylene oxide with an average molecular weight of 8,400 [23].…”

“…The mechanism of PF-68-mediated protection of cell cultures is now well-understood to be mainly physical and perhaps biophysical. It is widely accepted that PF-68 acts mainly by lowering the surface tension of the cell culture media thus minimizing cellular attachment on bubbles, which causes cell damage as bubbles breakup at the liquid surface [18,19,21,22,24]. With regard to biophysical effects on cells, PF-68 is known to interact with the cell membrane [23] and may even be endocytosed by CHO cells in small amounts [25].…”