**Technical Design**

A dilution-filtration system is developed as shown in Fig.16 (Hemofilter: Plasmflo TM AP-05H/L, ASAHI; Pumps: 400F/M1, Watson-Marlow; silicone tubing: 985-75, Pall). For removing CPAs, thawed cell suspension is first transferred into the special blood bag (made by an infusion bag). Then, the suspension is driven by the blood pump to flow circularly among the bag, the mixer and the hemofilter. While going through the mixer, the suspension is quickly diluted by diluent, and the dilution ratio can be controlled to prevent lysis. In the hemofilter, extracellular solution containing CPA is partly ultrafiltrated while cells keep inside. Along with the circulation goes on, CPAs in cell suspension can be removed continuously. The whole process is conducted automatically in a closed system, and thus it is hopeful for this method to reduce human labor as well as the risk of contamination significantly.

Fig. 16. Principle of the dilution-filtration system. Cell suspension is diluted and ultrafiltrated during circulating in the system, and then the CPAs inside can be continuously removed.
