A U.S. Patent Application for a “Cell Retention Device and Method” was published by Boehringer Ingelheim on June 6th, 2019. The present invention relates to a cell retention device and method for use in a perfusion cell culture system where the cell retention device includes a hollow-fiber filter having an average pore size ranging from about 0.5 to about 20 .mu.m and having the ability to operate under perfusion cell culture conditions for up to 35 days without being clogged or losing its product sieving ability by more than 20%. Learn More