*2.3. Fabrication of Nanofiber Scaffold*

In this study, 8 wt% polycaprolactone (PCL) solution was prepared by dissolving PCL with an average molecular weight (Mw) of 70,000–90,000 (PCL, Sigma-Aldrich, St.Louis, MO, USA) in 99.5% chloroform (Samchun Pure Chemical Co., Seoul, Republic of Korea). The mixture was then homogenized with a magnetic stirrer for 12 h at room temperature.

The electrospinning setup consisted of a high-voltage power supply, syringe pump, nozzle spinneret with an inner diameter of 210 μm, and a grounded solid drum collector, which rotated at a speed of about 30 rpm. The nozzle spinneret tip-to-collector distance was maintained at 100.0 mm. The electrical potential between the nozzle spinneret and the drum collector was 10.0 kV. The flow rate of the PCL solution was controlled by a syringe pump at 0.1 mL/h. The thickness uniformity of the nanofibers was improved by providing the nozzle spinneret with a traveling motion speed of 1 mm/s along the drum axis direction. The nanofibers were electrospun until they reached a thickness of 100 μm (actually, 113.7 ± 2.7 μm), which was measured using an ultra-precision micrometer (Mitutoyo) with a constant compression of 0.5 *N*. During electrospinning, the temperature and relative humidity were maintained at 19–20 ◦C and 50−55%, respectively. The electrospun nanofibers were provided with 5 min of heat treatment at 60 ◦C using a dry oven to improve nanofiber interconnectivity. The nanofibers were then cut into the same size of the chamber (12 × 12 mm) with a scalpel and carefully placed into the microfluidic chamber using a tweezer. The morphology of the electrospun nanofibers was observed by scanning electron microscopy (SEM; Hitachi, Tokyo, Japan). The porosity

of the nanofibers was measured using a mercury porosimeter (Micromeritics Instrument Co., Norcross, GA, USA). The filling pressure of mercury was 1.23 psi, and the equilibrium time was 10 s.
