Dextran dex

L-Lactide and D-lactide were obtained from Musashino Chemical Laboratory, Ltd. (Tokyo, Japan). PEG (number-averaged molecular weight (M_n) = 4600) and monomethoxy-PEG (M_n = 1000) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Carbonyl diimidazole (CDI), tin-2-ethylhexanoate, and dextran (Dex) (M_n = 150,000) were obtained from Fujifilm Wako Pure Chemical Co. (Osaka, Japan). All other chemicals were of reagent grade and were used without further purification.

An aqueous two-phase system consisting of a chain-structured flexible polymer, polyethylene glycol (PEG) (Mw 7300–9300 Da, Fuji Film Wako Pure Chemical Industries, Osaka, Japan), and a branched stiff polymer, Dextran (DEX) (Mw 180,000–210,000 Da, Fuji Film Wako Pure Chemical Industries, Osaka, Japan) was adopted. Based on the results obtained in our recent systematic study, here we used the composition PEG:DEX = 5 wt%:5 wt%, which corresponds to a phase-separated state near the binodal line of the phase-separation, and micro w/w droplets of tens to hundreds μm rich in DEX emerged in the outer solution of rich in PEG^{29 (link),32 (link)}. For visualization of the DEX-rich phase with fluorescence microscopy, fluorescein isothiocyanate bound DEX (FITC-DEX, average Mw 250,000 Da, Ex: 488 nm, Em: 520 nm, Sigma-Aldrich, St. Louis, MO, USA) was used. For the experiment in the presence of living cells, 0.9% NaCl solution (Fuji Film Wako Pure Chemical Industries, Osaka, Japan) was used. For the other experiments, purified water (Milli-Q, 18.2 MΩ cm) was used.