The most common materials of hollow fiber membrane include polysulfone, polyethersulfone, polyvinylidene fluoride, polypropylene, cellulose acetate, etc. It adopts tangential flow filtration method and features high filtration accuracy, high filling density, low filtration pressure, and easy to clean. It is widely used in industries such as biopharmaceuticals, sewage treatment, seawater desalination, and new energy. In the biopharmaceutical process, hollow fiber filters are widely used in the research and production of antibodies, vaccines, cells, and gene therapy due to its highly retention ability of bacteria and viruses, and protein and not easily to blocked.
The core of the perfusion process that distinguishes it from traditional feeding processes is the cell retention. Due to its high retention efficiency and not easy to clog, and high cell culture density, hollow fibers has become the preferred cell retention method of perfusion process in current antibody industry, compared with centrifugation, gravity sedimentation, ultrasonic interception, and rotary filtration .
According to different production purposes and the characteristics of expression products, perfusion is usually divided into several forms: N-1 Perfusion, Intensified Fed batch, Concentrated Fed batch, and Continuous Perfusion.
N-1 fusion, as part of process strengthening, has been widely used in the seed train process of antibody upstream production. Biopharmaceutical companies adopt this method mainly because it can reduce process cycles, achieve high-density inoculation, and reduce hardware investment. It can achieve a cell density of 108 cells/ml or above in 6-9 days, and this cultivation mode generally uses 0.2 μm/0.45 μm hollow fibers.
From SBL homepage
The Intensified Fed batch mode is an enhanced feed batch process aimed at achieving the accumulation of highly expression products in a short period of time, usually with a culture time of no more than one month. Compared to traditional processes, this method features rapid expansion of cell density to over 108cells/ml in a short period of time. The 0.2/0.45 μm hollow fiber is used for high-speed perfusion to achieve the retention of high-density cells and the harvest of target products.
This process has a relatively mature use. For example, WuXi Biologics and Jinsrui Boomerang Biological respectively use their respective continuous production process platforms with ATF interception devices to achieve a high-yield record of over 86g/L high expression within 30 days and an average daily output of over 3g/L .
Compared with the Fed-batch culture process, the concentrated Fed-batch culture process can obtain higher cells and product concentration. ATF or TFF is an appointed device for the retention of cells and target proteins, and 50kDa hollow fiber is highly recommended.
The culture time is about 2-3 weeks, and the cell density can reach 100-200 million cells/ml. The concentrated Fed-batch process provides an excellent choice for the pharmaceutical industry. It is reported that the concentrated Fed-batch process can be used to culture CHO cell, and the product expression can reach 17g/L. (Source: Refine Technology, LLC)
Continuous Perfusion is a long-term perfusion culture mode, usually with a cell culture time of 1-3 months or even longer. Compared to the Fed-batch process, it features high cell density and high product expression, which can achieve the needs of continuous production and harvest. There are reports that for the production of dual or multi antibodies, the perfusion process can significantly reduce the levels of polymers, acidic charge isomers, and HCP. The continuous perfusion process usually uses 0.2 μm/0.45 μm hollow fibers.
Hollow fiber bioreactors
Hollow fiber bioreactors have various advantages compared to traditional reactors. Hollow fibers can form porous filtration supports that are easy for cells to adhere to, and nutrient transport is from bottom to top. Cells can easily pile up with each other, forming a layer with multiple layers of cells (as shown in the figure below), which is most similar to the cell growth mode in vivo.
The hollow fiber system is suitable for monoclonal antibody production, recombinant protein production, virus amplification, lymphocyte culture, in vitro toxicology research, and stem cell culture. It has the advantages of simple installation and can meet the demand for higher titers using a smaller volume. It is a new choice for laboratory research and large-scale cell culture.
SEM of cell culture by in hollow fiber bioreactor (From C3 Homepage)
Cobetter hollow fiber filters are available in MWCO of 100 kDa/300 kDa/500 kDa and 750 kDa, used for the concentration of cells, bacteria and viruses.
 Michael A. MacDonald, Matthias Nöbel etc. Perfusion culture of Chinese Hamster Ovary cells for bioprocessing applications. Critical Reviews in Biotechnology. DOI: 10.1080/07388551.2021.1998821
 Zhou, Hang | Fang, Mingyue | Zheng, Xiang | Zhou, Weichang. (2021). "Biotechnology and Bioengineering" Improving an intensified and integrated continuous bioprocess platform for biologics manufacturing.118(9) - 3618～3623.