3.2. Permeation of denaturant via microchannels
Using the value of P determined in as described in Section 3.1, a microchannel with channel height d = 500 μm, width W = 5 mm, total length Z = 40 cm was designed and fabricated. A 5 M GdnHCl solution was fed from the feed channel inlet, pure water was fed from the permeation channel inlet, and the GdnHCl concentrations at the feed and permeation channel outlets were measured (Fig. 5). By changing the flow rate of the feed side, the residence time, τ , in the channel was changed to be 10 minutes (in a time range of 0–50 minutes), 20 minutes (in a time range of 50–150 min), or 30 minutes (in a time range of 150–300 minutes). After switching the flow rate, the GdnHCl concentrations converged to a constant value for both the feed and permeate sides for each residence time. The expected GdnHCl concentration at the feed outlet, c fZ, calculated using eq. (3) is as shown in Table 1. The results shown in Fig. 5 are almost identical to the values calculated using eq. (3), and confirmed that the microchannel functioned as designed. The GdnHCl concentration required for model protein refolding was 0.5 mol/L or less. The concentration was attained at a residence time of 20 minutes at the feed outlet. It therefore appears that the refolding process can be carried out in only 20 minutes.