Ecoflex 00 50

GO was purchased from Hengqiu Tech., Inc. Hexane was purchased from Anachemia Canada, Inc. Polylactic acid (PLA) was purchased from XYZ printing. Ecoflex 00-50 was purchased from Smooth-On, Inc. 184 silicone elastomer kit was purchased from SYLGARD. DOPA was purchased from Sigma-Aldrich. PVDF was purchased from Tullagreen, Carrigtwohill, Co. Cork IRELAND. Tris-HCl and DMF were purchased from Sigma-Aldrich. Acetone was purchased from Thermo Scientific (USA). PVP was purchased from Shanghai Aladdin Bio-Chem Technology Co., LTD. Silver epoxy kit H20E was purchased from Epoxy Technology, Inc. The live/dead cell staining kit was purchased from Shanghai Bioscience Technology Co. Ltd. The primary antibodies of α-actinin, CX43 and vWF were purchased from Abcam (Britain). α-SMA antibodies was purchased from Bosterbio (USA). Alexa Fluor 568 donkey anti-rabbit IgG (H&L) and Alexa Fluor 488 donkey anti-mouse IgG (H&L) were acquired from Life Technologies (USA). Masson’s Trichrome Stain Kit was purchased from Beijing Solarbio Science & Technology CO., LTD.

The strain sensor was fabricated using the following procedure (Figure 1a): 20 g Ecoflex rubber (mass ratio A:B = 1:1, Ecoflex00-50, SMOOTH-ON) was poured onto an acrylic mold (length × width × thickness: 40 mm × 20 mm × 5 mm) that had been previously cleaned with acetone, ethanol, and deionized water. After the rubber was cured (1 h at 70°C), the electrode areas were masked on the cured rubber using polyimide (PI) tape. The viscous graphene solution was coated on the exposed rubber, overlapping the PI tape. The PI film was then removed from the Ecoflex rubber, leaving viscous graphene solution on the rubber surface. Copper wires were attached to the ends of the viscous graphene solution with silver paste. Then another layer of liquid Ecoflex was cast over the viscous graphene solution area and the bottom Ecoflex rubber. Finally, the complete part was cured at 70 °C for 2 h.

Overall, the flow chamber is a cassette-like insert as shown in Figure 1. It consists of a milled acrylic body and an aluminum lid that can hold a 38 × 76 mm² glass slide of 1 mm thickness on which cells are cultured in a regular incubator before it is placed in the flow chamber. A specifically designed, cast silicone O-ring made of Ecoflex 00-50 (Smooth-On, Macungie, PA, USA) seals the flow channel. The locking mechanism is a single pin that can be removed and inserted by hand. Figure 5 provides a detailed view of the chamber and its individual parts. For the tests reported herein, a rectangular channel of 0.3 × 20 mm² cross-section was used. With the insertable glass-slide forming the bottom and the acrylic cassette the top, this corresponds to a parallel flow chamber setup. The level of shear stress τ [Pa] acting on the cells can be approximated as
where Q is the flow-rate [m³/s], μ is the dynamic viscosity [Pa s], and w [m] and h [m] are channel width and height, respectively (Levitan et al., 2000 (link)). The tests reported herein were run with flow rates between 5 ml/min and 20 ml/min, resulting in shear stresses between 0.25 Pa and 1 Pa. These numbers were further validated by computational fluid dynamics (CFD) analyses (see section Flow and WSS Analysis).

The soft helical template was generated by fixing a straight TPU filament onto a metal cone and heating the filament with a heat gun (200 °C) to reach the various diameter helical soft template. Then, this soft helical template was first fixed to a mould, and the elastomer precursor (Ecoflex 0050, Smooth-on) was poured into the mould. After the precursor was cured, the microchannel was generated by pulling the template out. Next, a syringe injected the liquid metal (−19 °C, Dingguan Metal Technology Co.) into the microchannel. Finally, both ends of the microchannel were sealed by the silicone precursor.