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Disposable bioreactors
6/18/15

“Kleenex” bioreactors: an economic alternative to stainless steel

The end of the 1990s saw the emergence of “Kleenex” bioreactors as an alternative. In the words of Dominique Toye. “The advantage of these reactors was mainly economical. The absolute necessity for a sterile environment is a real constraint. The cleaning processes for the tanks between two reactions are costly in terms of products, water, energy and time consumption. A lengthy verification process must also be put in place to ensure the absence of debris or lack of sterility in even the tiniest areas… A bioreactor that can be discarded after one use could avoid these kind of complications”. The procedure is relatively simple. There are flexible plastic pockets which are sterilized by radiation, placed in stainless steel supports and are used only once. They have the same peripheral equipment as traditional bioreactors with connections for the measurement probes for the oxygen levels, pH, entry points for regulating the environment inside, sample-taking, and finally, an agitator. These reactors, light and detachable, can then be used to move the cell culture without having to transfer the contents into another container.  

These so-called “Kleenex” reactors have not met with immediate success. The protocols in place in the production line for pharmaceutical products are very strict for obvious reasons. “Transferring equipment which was designed for the manufacture of a particular medicine to another type of equipment is not easy”, explains the researcher. “You have to be able to demonstrate that the conditions for each step involved in manufacturing are equivalent. In addition, there is always a certain distrust of new products. The industrial environment is reluctant to change procedures that work, especially when this involves replacing equipment”. But today, the disposable bioreactors seem to have proved their worth and more and more companies are turning to them. 

A rectangular bioreactor as opposed to a cylindrical one

The main reservation that GSK had about the bioreactor was its shape. This bioreactor has certainly got two original characteristics. It is parallelepiped in shape, and the agitator which looks more like a paddle or a beaver’s tail makes an elliptical movement rather than rotating around a vertical axis. It was therefore necessary to verify that, for the same energy output, the mixture in the reactor was as homogenous as that used in a cylindrical reactor whether the reactors are of the stainless steel or disposable variety. In other words, the objective was to verify that the fluid did not stagnate in any part of the reactor and that the quantity of energy deployed to agitate the fluid was at least equal to that necessary for traditional reactors. “Of course”, states Dominique Toye, “the company had already conducted trials with cell cultures and these showed promising results. As well as avoiding the disadvantage of cleaning traditional tanks, the Nucleo seemed to consume less electricity for the same performance. However, the company did not have the expertise to objectively demonstrate that the speed of liquid flow and the quality of the mixture were optimal”. In order to characterize the hydrodynamics involved, it was necessary to have a look in the interior.

Lasers applied to a study of velocimetry

In order to characterize the homogeneity of the liquid, the researchers used a velocimetry technique. “Velocity”, explains Dominique Toye, “is a movement divided by a time. To calculate the speed of the liquid in this bioreactor, we filled it with water and fine fluorescent particles which followed the flow. We needed a transparent liquid, and water presents the same flow properties (density, viscosity …) as the culture medium of the cells. Therefore there was no risk of bias. We placed two cameras in the direction of the tank in order to have a stereoscopic view which in turn enabled us to describe our observations in three dimensions. Then we used a laser to lit up a planar surface inside of the tank at very precise time intervals. With each pulsation of the laser, the fluorescent particles emitted light which made it possible for us to locate them and therefore to trace their movement. We were able to calculate the time and distance covered by the particles. We were able to calculate their speed and therefore that of the liquid. By repeating the experiment for different planes we were able to check the variation in speed according to the area of the tank and to see if the liquid had been equally distributed”. 

Liquid flow bioreactor

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