Cell separation is the first step at recovering the protein product (cells) from the culture. The timing for termination of the Cell Culture is crucial and predetermined based on the quality and quantity of the product accumulated in the bioreactors. The first step in mammalian separation is usually centrifugation: a technique used for the separation of cells from culture through rapid spinning and sedimentation. The technique of centrifugation is based on the principle of density difference between particles to be separated and the medium. Centrifugation is mostly used for separating solid particles from liquid phase (fluid/particle separation).
Microbial harvest is similar to mammalian however a lysing step must occur prior to centrifugation to free the protein contained within the bacteria.
The next step is a filtration one to remove the large debris through depth filtration. Prior to centrifugation and depth filtration steps, the product is cloudy. These two steps increase the transparency of the mixture and therefore often known as Clarification steps. At this point, cells and large debris have been separated from the mixture.Depth filtration uses single use plastic pods that have no reusable wetted parts. These depth filter pods are held in a vice-like holder because the plastic housings themselves do not have the required pressure capacity. Depth filtration is an adequate alternative to centrifugation.
Sterile grade membrane filtration is often the next step during harvest to remove smaller particles and microbial contamination. Sterile grade filtration is usually rated as 0.22µm or smaller and leaves the product translucent in appearance and ready for downstream bioprocess steps.
Product transfer assemblies to transfer media, cells etc