Do you have a protocol to share for re-using ultracentrifuge tubes, and have you verified that it results in contaminant-free tubes? My lab uses ultracentrifugation to isolate viruses and various extracellular vesicles, but disposing insert tubes can be rather expensive. We've considered re-use, but have some reservations: 1) resuspension of pellets is rarely 100% complete, and we can't have carryover material; 2) any substances used for cleaning would also have to be removed completely; 3) physical damage to the tubes (e.g., scratching) would make 1) and 2) more difficult.