Phenolphthalein

L. vannamei shrimp (Huazhong Agricultural University Agricultural Products Market, Wuhan, China), and high-oleic sunflower oil (Zhongliang Co., Ltd., Beijing, China).
Anhydrous ethyl ether, isopropyl alcohol, potassium hydroxide, chloroform, methanol, potassium thiocyanate, ferrous chloride, p-anisidine, hydrochloric acid, and glacial acetic acid were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Isooctane, 2,4-dinitrophenylhydrazine, and phenolphthalein were from Shanghai Macklin Biochemical Co., Ltd. (Shanghai, China). Deuterated chloroform (CDCl₃) was acquired from Cambridge Isotope Laboratories Inc. (Andover, MA, USA).

All chemicals were of analytical grade unless stated otherwise. Methanol and acetonitrile were purchase from CNW Technologies, Germany, ammonium acetate (SIGMA-ALDRICH, St. Louis, MO, USA), ammonium hydroxide (Fisher Chemical, Riverside, CA, USA), ddH₂O (Watsons, China). HCl (1 + 1 (v/v)), NaOH (200 g/L), glucose standard solution (2.5 g/L), methylene blue (10 g/L), phenolphthalein, CuSO₄ (0.05 g/mL), and NaOH (0.05 mol/L) were bought in Macklin (Shanghai, China). The dry yeast (Saccharomyces cerevisiae DV 10) was purchased from JATOU (Shanghai, China).

The mass ratio of the matrix and crosslinker in the PDMS prepolymer (Sylgard 184, Dow Corning, USA) was 10:1. The prepolymer was blended uniformly and poured over a four‐well plate (176 740, Thermo). PDMS prepolymer (0.2 g) was added per well, and the PDMS wells were cured at 80 °C for 2 h and processed by plasma for 30 W for 5 min. The PDMS surface was pretreated with 0.2 mg mL⁻¹ sulfo‐SANPAH and coated with 50 µg mL⁻¹ Collagen I for 10 h. Dialysis of Collagen I was added to the coated PDMS wells, and they were cured at 37 °C for 1 h. For collagen thickness measurements, phenolphthalein (P816041‐25 g, Macklin) was added to the dialysis fluid (PBS), adding color to Collagen I for easy identification. The collagen after dialysis was added to the wells coated with PDMS, and cured at 37 °C for 1 h. 12 cured samples were quickly cut from the middle by a sharp knife. The cross sections were imaged under the microscope. ImageJ was used for analyzing the collagen thickness.