All the lipid compounds, 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC), 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-(lissamine rhodamine B sulfonyl) (Rhod-DPPE), cholesterol, and 1,2-dioleoyl-sn-glycero-3-phospho-l-serine (DOPS), were purchased from Avanti. (Ethylene glycol) ethyl ether diacrylate (PEGDA) with a molecular weight of 700 g/mol was obtained from Sigma–Aldrich. A cationic monomer, N-[(3-dimethylamino)propyl]-2-methacrylamide (DMAPMA), was purchased from TCI. Acrylic Cytarabine (AAc) was purchased from Wako Pure Chemicals. 2-Hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure2959) was obtained from Dow Chemicals. Bis[N,N-bis(carboxymethyl)aminomethyl]fluorescein (calcein) was obtained from Dojindo. All the chemicals were used without any further purification.
2.2. Micropatterned substrate
The substrate was prepared according to previous reports  and . Briefly, microwells with diameters of 1, 2, 4, or 8 mm were fabricated on a large intestine Si substrate covered with a 120-nm-thick thermal oxide layer using a conventional photolithographic and dry etching technique. An overhang shape was formed at the microwell apertures by the selective wet etching of the Si under the SiO2 layer with a KOH solution. Finally, the substrate was treated with Piranha solution for 1 min to make the inside surface of the microwell hydrophilic.