Dopamine da

All reagents used in experiments were of analytical grade. Graphite powder was purchased from Alfa Aesar (Shanghai, China). Nickel sulfate hexahydrate, iron sulfate heptahydrate, hydrazine hydrate (80 wt%), and glucose were procured from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Ascorbic acid (AA), uric acid (UA), and dopamine (DA) were purchased from Acros (Shanghai, China). Deionized water (18.2 MΩ·cm) was used in all experiments.

50% AR AgiSyn 003 (DSM-AGI, Nederland) was placed into Tris-(hydroxymethyl) aminomethane (Tris, Sigma-Aldrich, MO, USA) buffer (10 mM, pH 8.5) with 0.1–3 mg/mL dopamine (DA, Acros Organics, NJ, USA) and 1.2 mg/ml of ammonium persulfate (Sigma-Aldrich, St. Louis, MO, USA) added next. The AR-based composites were mixed using the ultrasonic oscillator for 5 min, after which the composites turned dark brown after mixing. The hybrid materials were then heated at 180 °C and stirred to dehydrate the mixtures. Various amounts of 1.5% 2,4,6-trimethylbenzoyl-diphenyl-phosphineoxide (TPO, Ciba Specialty Chemicals Inc., Basel, Switzerland) photo-initiators, 0.1% 2-Hydroxy-4-methoxybenzophenone-5-sulfonic acid (HMBS, Tokyo Chemical Industry, Tokyo, Japan) and 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO, Acros Organics, Morris Plains, NJ, USA) were dissolved in 2-Hydroxylethyl methacrylate (HEMA, Sigma-Aldrich and then added to the AR-based composites, mixed at 80 °C to form the 40–80% AR-contained resin for 3D printing.