Sylgard 184b

Reduced glutathione (GSH), gelatin (from porcine skin), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), and kojic acid (KA) was purchased from Sigma-Aldrich (St. Louis, MO, USA), sodium hyaluronate (100 k, HA) was purchased from SNVIA (Busan, Korea). Chondroitin sulfate (CS) was purchased from Wako Chemicals (Osaka, Japan). α-Melanocyte stimulating hormone (α-MSH) was purchased from TOCRIS (Bristol, UK), and apoptosis detection kit using FITC (fluorescein isothiocyanate)-labeled annexin V was purchased from BD Biosciences (Bedford, MA, USA). A liquid prepolymer (Sylgard 184A) and a curing agent (Sylgard 184B) for the polydimethylsiloxane (PDMS) molding were purchased from Dow Corning (Midland, MI, USA). All chemicals were used without further purification. Porcine skin (hair removed) was procured from a local butcher shop and kept at −20 °C until it was used in experiments.

The master mold was treated with a vaporized silane coupling agent (Sigma Aldrich, Trichloro-1H, 1H, 2H, 2H-Perfluorooctyl-silane) to form a surface self-assembled monolayer (SAM) for 10 min at 140 °C to improve the demolding. The h-PDMS solution was prepared by mixing 1.7 g of vinylmethyl copolymers (Gelest, VDT-731), 9 μL of platinum-catalyst (Gelest, SIP6831.2), 0.05 g of the modulator (Sigma Aldrich, 2,4,6,8-Tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane), 1 g of toluene, and 0.5 g of siloxane-based silane reducing agent (Gelest, HMS-301). The h-PDMS was spin-coated on the master mold at 2000 rpm for 60 s, and then baked at 80 °C for 2 h. A degassed mixture 10:1 weight ratio of a PDMS (Dow corning, Sylgard 184 A) and curing agent (Dow corning, Sylgard 184 B) was poured on the h-PDMS layer then baked at 80 °C for 3 h. The soft mold was demolded carefully from the master mold, then treated identically to a self-assembled monolayer (SAM) as reported above.

For preparing the lower substrate, PDMS resin is prepared by mixing the base (Sylgard 184 A, Dow Corning Corp., Midland, Michigan, USA) and a curing agent (Sylgard 184 B, Dow Corning Corp., Midland, Michigan, USA) at a weight ratio of 10:1. Then, the PDMS resin is poured onto a glass substrate (S9213, Matsunami, Osaka, Japan), followed by spin coating (ACE-200, DongAh Trade Corp., Seoul, Korea) at 2500 rpm for 60 s. The resultant sample is then cured at 70 °C for more than 1 h. For the patterning process, the PDMS layer was pyrolyzed by CW laser (Sprout-G-5 W, Lighthouse Photonics, San Jose, CA, USA) irradiating power of 0.3 W to 2.4 W focused by the objective lens (M Plan APO 2X, Mitutoyo, Kawasaki, Japan). Lower substrate and upper glass substrate with three holes were attached using oxygen plasma treatment (CUTE-3MPR/D, Femto Science Inc., Yongin, Korea). Finally, inlet and outlet tubes (AWG-11G, Banseok Precision Ind., Seoul, Korea) were inserted into the hole and sealed with silicon bond (3140 RTV, Dow Corning Corp., Midland, Michigan, USA).

The master mold was coated by liquid-phase SAM to improve mold release in a solution mixture of a 1000:1 volume ratio of hexane and (heptadecafluoro-1,1,2,2-tetra-hydodecyl)trichlorosilane (H5060.1, JSI silicone) for 10 min. h-PDMS solution was prepared by mixing 3.4 g of vinylmethyl copolymers (VDT-731, Gelest), 18 μL of platinum-catalyst (SIP6831.2, Gelest), 0.1 g of modulator (2,4,6,8-Tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, Sigma-aldrich), 2 g of toluene and 1 g of siloxane-based silane reducing agent (HMS-301, Gelest). The h-PDMS was spin-coated on the master mold at 3000 rpm for 50 s, then baked at 70 °C for 2 h. A degassed mixture of a 10:1 weight ratio of PDMS (Sylgard 184 A, Dow corning) and its curing agent (Sylgard 184 B, Dow corning) was poured on the h-PDMS layer, then baked at 100 °C for 2 h. The soft-mold was released from the master mold, then coated with vapor-phase SAM by a typical vaporizing process using (tridecafluoro-1,1,2,2-tetrahydrooctyl)trichlorosilane (SIT8174.0, Gelest) for 30 min at 5 Torr followed by DI water for 10 min at 10 Torr. The 3 μL of NPC was dropped on a glass substrate, then it was covered by the soft-mold. UV light was illuminated for 5 min at 2 bar to harden the NPC (Nanosis 820, NND). The soft-mold was released to complete the replication process.

Bagasse was acquired from a farmland in Guangxi province. Sudan IV and petroleum ether were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). PDMS prepolymer (Sylgard 184A) and curing agent (Sylgard 184B) were produced by Dow Corning Corp. (Midland, MI, USA). Potassium hydroxide (KOH), xylene, carbon tetrachloride, dichloromethane, ethanol, isopropyl alcohol, methanol, hexane and sodium chloride (NaCl) were offered by Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Gasoline was provided by China National Petroleum Corp. (Beijing, China). DE was purchased from Shijiazhuang Huabang Mineral Products Co., Ltd. (Shijiazhuang, China).

To obtain polydimethylsiloxane (PDMS) samples with different thicknesses, the weights of Sylgard-184A and Sylgard-184B (Dow Corning, Auburn, MI, USA) were set to a ratio of 10:1. We then placed the mixture into a vacuum to remove air bubbles. The three different weights (150, 900 and 2000 mg) of mixture were then poured onto the mold, and were well-distributed using the rotator shaker (30 rpm) for 10 min at room temperature. After curing at 80 °C for 24 h, the samples were demolded and the thickness was measured using a micrometer screw gauge (Mitutoyo, Japan).