Fabrication of the DOAMS

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Three-dimensional (3D) DOAMS molds (master) with or without imperfection were designed in SolidWorks (Dassault Systèmes, Vèlizy-Villacoublay, France) and then printed with gray resin on a Form2 3D printer (Formlabs, Somerville, USA) or MicroFine green resin (Protolabs, Maple Plain, USA). A SYLGARD 184 (Dow Inc., Midland, USA) PDMS mold (negative) was fabricated from the master mold by mixing two-part resin systems containing vinyl groups (part A) and hydrosiloxane groups (part B), and the material was cast around the master. After cross-linked network formation, the flexible elastomeric molds were carefully removed. Carbopol 971P NF (Lubrizol, Wickliffe, USA) polymer was dissolved in dimethylformamide under sonication (100 kHz) with a concentration of 25 mg/ml. FITC (5%) was added to the Carbopol solution as an indicator. After weighing and balancing the molds, 200ul of Carbopol solution was added, followed by 10 min of vacuum (600 mmHg) treatment. After centrifugation (2000 rpm for 10 min; Eppendorf AG 22331 Hamburg, Germany), the molds were placed in a desiccator for another 10-min treatment and then placed in a vacuum chamber for 24 hours at 45°C. The casting process was repeated between one and five times. Subsequently, 50 mg of PCL (45 kDa; CAPA 6400, Perstorp) was introduced to the mold, followed by heating to 120°C; the mold was then placed in a vacuum for 3 hours. After cooling to room temperature, the MN arrays were carefully peeled off from the PDMS mold and maintained at room temperature for further applications.