Fe28 ph meter

A DF-101S collector constant temperature magnetic stirrer (Zheng Great Wall Science Industry and Trade Co., Ltd., Zhengzhou, China) and a DHG-9146A electric heating constant temperature blast drying shaker (Shanghai Longyue Instrument Equipment Co., Ltd., Shanghai, China) were used for the synthesis of the materials. The SEM images for the characterization of material were obtained through a field-emission SEM (JSM-7600F, JEOL Ltd., Tokyo, Japan). The pH of solutions was measured through a FE 28 pH meter (Mettler-Toledo Instruments, Shanghai, China). A UV-5500 PC spectrophotometer (Shanghai Metash Instruments Co., Ltd., Shanghai, China) was used for the UV-Vis analysis. The tabletop low-speed centrifuge L420 and the ultrasonic cleaner used in this study were obtained from Hunan Xiang Yi Laboratory Instrument Development Co., Ltd. (Changsha, China) and Kunshan Jielimei Ultrasonic Instrument Co., Ltd. (Kunshan, China), respectively. The ultrapure water prepared through a water purification system (ATSelem 1820A, Antesheng Environmental Protection Equipment, Chongqing, China) was used for all experiments.

A quantity of 0.05 g of collagen fibers (self-produced from cattle skin using a standard procedure [27 (link)]) was immersed in 50 mL of a Cr(III) solution. The initial Cr(III) concentration was set to 5, 10, 20, 50, 100, 150, 200, 250, and 300 mg/L with solution pH values of 3.5, 4.0, and 4.5, respectively, adjusted by 0.05 mol/L NaHCO₃ or 0.05 mol/L HCl (FE28 pH meter, Mettler Toledo Instruments Co., Ltd., Columbus, OH, USA). The solution was shaken at 298, 308, and 318 K for 24 h (ZWY-2102C constant temperature oscillator, Shanghai Zhicheng Analytical Instruments Manufacturing Co., Ltd., Shanghai, China). The Cr(III) concentration in solution was detected using inductively coupled plasma atomic emission spectrometry (Optima 8000DV inductively coupled plasma emission spectrometer, PerkinElmer, Waltham, MA, USA). The equilibrium adsorption capacity q_e (mg/g) is calculated as
$$q_e=\frac{(C_0-C_e)V}{m}$$
where C₀ and C_e are the Cr(III) concentration in the solution before adsorption and at adsorption equilibrium, respectively, in mg/L; V is the volume of the Cr(III) solution, in L; and m is the mass of the collagen fiber, in g. All experiments were conducted in three parallel groups, and all reagents were of analytical grade, procured from Kelong Chemicals (Chengdu, China).

The in-vitro degradation of scaffolds was performed in 0.05 mol/L Tris-HCl buffer with the pH adjusted to 7.40 ± 0.05 via the addition of 1.0 mol/L HCl solution. The 10 mm × 10 mm × 2 mm scaffolds were weighed for initial mass (M_i) and added into the polypropylene centrifuge tubes filled with 10 mL of Tris-HCl. The centrifuge tubes were stored under 37 °C for up to 14 days, during which the immersion media was never refreshed. On Day 1 3, 7, 10, and 14, the scaffolds were taken out, blot dried with tissue paper and weighed for their moisture-containing mass (M_w). After weighing, the scaffolds were dried in an oven for 24 h under 65 °C to remove the moisture. The mass after drying (M_d) were then measured. The water uptake of scaffolds and the mass change of scaffolds after drying were calculated based on the equations reported elsewhere [38 (link)]:

In addition, the pH values of Tris-HCl immersing scaffolds at the abovementioned time points were characterized using the FE28 pH meter equipped with LE-460 electrode (Mettler-Toledo^®, Greifensee, Swiss). Five replicates of scaffolds and immersion media were tested for each type of scaffold material.

The capillary electrophoresis experiments were performed on an Agilent 7100 3D CE system (Agilent Technologies, Palo Alto, CA, USA) equipped with a diode array detector and Agilent ChemStation software. The bare fused-silica capillary (Yongnian Ruifeng Chromatographic Device Co., Ltd., Hebei, China) was 75 μm id and had a total length of 50 cm and an effective length of 41.8 cm. The water used for all the experiments was purified by water purification system (ATS-H20, Antesheng Environmental Protection Equipment Co., Ltd., Chongqing, China). Background electrolytes buffer and phenolic compound solutions were ultrasonicated in a KQ-100B ultrasonic cleaner (Kunshan Ultrasonic Instruments Co., Ltd., Kunshan, China). The pH of running buffer was measured by a FE28 pH meter (Mettler-Toledo Instruments, Shanghai, China).

HPLC analysis was performed on an Agilent 1260 Series liquid chromatograph system (Agilent Technologies, Palo Alto, California, CA, USA), which was equipped with a vacuum degasser, a binary pump, an autosampler and a diode array detector (DAD), controlled by Agilent Chem Station software. An Agilent ZORBAX SB-Aq column (250 mm × 4.6 mm i.d., 5 μm) along with a pre-column (ZORBAX SB-Aq guard column, 12.5 mm × 4.6 mm i.d., 5 μm) was employed for the separation. An isocratic elution of solvent A (0.1% formic acid water solution) and solvent B (acetonitrile) was applied for the separation: 0–8 min, 10% B. The flow rate was set at 0.6 mL/min, detection wavelength was set at 290 nm, the column temperature was kept at 30 °C and the injection volume for all samples was 5.0 μL. An FE28 pH meter (Mettler-Toledo Instruments, Shanghai, China) was used for measuring the pH of solutions. The temperature control process was carried out using a drying oven (DHG-9146A, Longyue Instrument Equipment Co., Shanghai, China). A magnetic stirrer (HJ-4, Jintan Baita Xinbao Experimental Instrument Factory, Changzhou, China) was used for preparing the PDA@HF. In addition, a gas bath thermostatic oscillator (SHZ-82, Jintan Chengxi Zhengrong Experimental Instrument Factory, Changzhou, China) was used for preparing the XOD@PDA@HF.

The total organic carbon (TOC) was measured on an Analytik Jena N/C 300 (Analytik Jena AG, Langewiesen, Germany) TOC analyzer. The pH values were measured via an FE28 pH meter (Mettler Toledo, Switzerland) equipped with a LE438 probe. The concentrations of dissolved oxygen were determined using a JPB-607A dissolved-oxygen analyzer (Xian Yima Optoelec Co., Ltd., Shaanxi, China).