Abstract: In a vessel, such as a flexible bag, a fluid is received and agitated using an internal fluid-agitating element driven by an external motive device and supported by a bearing, such as a roller bearing. The bearing may comprise a thrust bearing having at least one race fabricated of polyvinylidene fluoride and a plurality of associated rollers, preferably comprising a ceramic material, such as silicon nitride. Experiments show beneficial results in terms of particle generation when this particular combination of materials is used in the context of agitating fluids, and benefits as well when different materials are used to form the rollers.