Extended Data Fig. 1: Preparation of the samples.

a. Fabrication process of steel pillar arrays with U-shaped grooves. The arrays are fabricated using a precision milling process. The tip of the milling cutter is a ball nose with a diameter of 300 µm. The spindle rotational and translational speeds, and depth-of-cut are 60,000 r/min, 150 mm/min and 40 µm, respectively. The desired depth of 400 µm is reached after ten successive cuts (step 1) after which the sample is rotated by 90°, and ten new cuts are performed. The SEM image is a side-view of the pillars with their U-shaped grooves. b. SEM images of the fibrous membranes treated at various temperatures. Images are obtained with a FEI Quanta 450 FEG microscope after membranes were inserted into a tube furnace (GSL-1500X) at the target temperature and calcinated for 1 h in air. c. Fibrous membranes are embedded into pillar arrays at the desired depth using a pre-designed 3D mold. After removing the mold, the obtained STA is consolidated by a sintering step performed at 800 °C for typically 5 min. d. SEM image of the pillars without U-shaped grooves. This material is made for achieving the sample B. It is fabricated using 2-flute end mill with a diameter of 300 µm. During micro-milling, the spindle rotational and translational speeds are 60,000 r/min and 150 mm/min, and the depth-of-cut is 30 µm.