Cell Frequently Asked Questions

Which cartridge do I choose?

Choosing the correct cartridge to grow your cells can be confusing if you do not have experience with hollow fibers. Which cartridge you choose depends on what products/applications you are working with. If you are collecting secreted antibodies or proteins, the cellulosic will work great since these cartridges tend to have a low MWCO which captures most products from the cells. The MWCO of cellulosic is usually 30 kD or lower. If you are growing cells for isolation for which you will need a large quantity, any of the cartridges will work. The cellulosics are good since they have a large surface area, whereas the polysulfone/polypropylene work well since they have a larger pore which allows free movement of all proteins and cell effluence across the membrane. For shear stress studies, we recommend the polypropylene since they have a large fiber inner diameter.

What kind of cells can I grow with CellMax^®?

Any cell that you can grow in culture flasks can grow in the CellMax system, which makes it so unique and useful. Even feeder layers can be grown in the cartridge since these types of cells can be harvested using the standard harvesting techniques. However, the CellMax is not normally used if you want to see the cell morphology due to the cylindrical shape of the cartridge.

My immortal mammalian cells are dying! Why?

Cells are very sensitive and a slight change in the microenvironment can have catastrophic effects. Changing media formulations can cause cells to go into shock, where they look like they are dead but are not. Microbial or fungal contamination can kill cells, but usually this is pretty obvious when it happens. Media that is too acidic can be harmful to your culture, and since cells produce acid as a byproduct of respiration, they create their own toxic environment. It is important to keep cells in fresh media with less than 2 mg/ml of lactic acid concentration. Sometimes, cells just die. If the cell line is immortal, it can have a random mutation that just kills the cells after a time. In any case. it is always best to keep several seed vials ready in case your cells do die.

What is shear stress and why is it important?

All cells have a limit to the amount of physical stress, also known as "shear stress", that they can withstand before their cellular envelope ruptures . There are many ways to impart shear stress on a cell, such as sonic vibration, agitation, sparging, pumping, etc. In hollow fiber tangential flow filtration, there are three factors that contribute to shear stress (¥) according to the provided equation: the fiber inner diameter (D), the quantity of fibers (N) and the fluid flow rate (Q). When processing whole cells, care must be taken not to exceed the known shear stress limit for that given cell line. The best way to avoid shearing the cells is by maintaining a flow rate that keeps the shear stress below the limit:

What effect does pore size have on my cell culture?

Pore size determines what molecules pass across the membrane into or out of the cell chamber. A large pore size (0.5 µm) allows most molecules to diffuse across the membrane. This is beneficial if you are performing an experiment in which no molecular species are collected. The large pore size also ensures that no growth factors are excluded.

A small pore size (50 kD and lower) is used when you want to collect a secreted product from a cell line. Antibodies and most proteins are larger than 50 kD and will not pass out of the cell chamber, therefore can be harvested manually when the culture is ready. Sometimes, the 50 kD cut-off can prevent necessary growth factors diffusing from the media. This is usually encountered with added factors that do not occur in standard media. The growth factors can be added directly into the cell chamber if this is the case.