Formic acid

Human hair was collected from local barber shops. PCL (Mn 45,000), urea (CH₄N₂O), sodium dodecyl sulfate (SDS), and 2-mercaptoethanol were purchased from Sigma-Aldrich (St. Louis, MO, USA). Sodium hydroxide and formic acid were purchased from Samchun Chemicals (Seoul, Korea).

PCL (average molecular weight (Mw), 45,000 Da; Sigma-Aldrich, St. Louis, MO, USA) was used for 3D printing, while PCL (average Mw 80,000 Da; Sigma-Aldrich, St. Louis, MO, USA) was used for electrospinning. Formic acid (FA, 99.0%; Samchun Pure Chemical Co., Ltd., Seoul, Korea) was used as a solvent. Ethanol (99.9%, Ducsan Pure Chemicals Co., Ltd., Kyunggi, Korea) was diluted to 70% and used to sterilize the scaffold.

First, 0.75 g of AT-CNT and 1.50 g of 5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphine cobalt(II) (CoTMPP, 98%, Porphyrin Systems) were mixed in an agate mortar for 15 min. The mixture was heated at 400 °C under 1 L min⁻¹ N₂ flow for 3 h (ramping rate: ca. 2.1 °C min⁻¹). The heat-treated powder and 3.75 mL of tetraethyl orthosilicate (TEOS, 98%, Aldrich) were mixed in the mortar for 5 min. The same volume of formic acid (99.5%, Samchun Chemical) was added to the mixture to initiate TEOS polymerisation. The mixture was dried at 60 °C for 3 h. The dried solid was ground to fine powder and a part (0.60 g) was pyrolyzed at 900 °C under 1 L min⁻¹ N₂ flow for 3 h (ramping rate: ca. 2.1 °C min⁻¹). To etch the silica and acid-soluble Co-species, the pyrolyzed powders were added to an acid solution of 4 M HF + 2 M HCl (diluted from 50 wt% HF (JT Baker) and 36 wt% HCl) with a similar volume of ethanol (94.5%, Samchun Chemical) and stirred at RT for 30 min. The suspension was filtered and washed with ethanol and DI water. Acid leaching was repeated once more in the same manner. Finally, the product was dried at 60 °C and collected. Then, the Co–N/CNT-based cathode was prepared by drop-casting catalyst ink on both sides of a carbon paper (0.2 mg cm⁻²).

The reference standard of VD, VA, and trans-cinnamaldehyde (IS) was purchased from Sigma-Aldrich (St. Louis, MO, USA). Formic acid (99.0%) was obtained from Samchun Pure Chemical (Pyeongtaek, Korea). An Elga Purelab Option Q purification system was used in preparation of ultrapure distilled water (DW). All the other reagents were of analytical grade and obtained from Sigma-Aldrich (St. Louis, MO, USA).

Formic acid was acquired from Samchun (Pyeongtaek, Republic of Korea). All HPLC-grade solvents and fetal bovine serum (FBS) were obtained from Thermo Fisher Scientific (Waltham, MA, USA). Minimum Essential Medium, Alpha Modification (α-MEM), was purchased from Hyclone (Logan, UT, USA). AS-MX phosphate, fast red violet LB salt, and naphthol were procured from Sigma-Aldrich (St. Louis, MO, USA). Antibodies targeting c-Fos and NFATc1 were purchased from Santa Cruz Biotechnology (Santa Cruz, CA, USA). Antibodies targeting TRAF6, c-Src, CAII and HRP-conjugated secondary antibodies (anti-rabbit IgG and anti-mouse IgG) were purchased from Cell Signaling Technology (Danvers, MA, USA). TaqMan Universal Master Mix II and TaqMan probes for the target genes, including c-Fos, NFATc1, Prdm1, Irf8, MafB, Ctsk, Itgβ3, Mmp9, and 18S rRNA, were obtained from Applied Biosystems (Foster City, CA, USA). TSN standard was purchased from ChemFace (Wuhan, China).