## 2 Experimental Methods
### Characterization Methods  
The FTIR spectra were obtained by VERTEX80v Fourier transform infrared spectroscopy (Bruker, Karlsruhe, Germany). All spectra were recorded between 4000 cm\({}^{-1}\) and 400 cm\({}^{-1}\) with 64 scans and a resolution of 4 cm\({}^{-1}\). The data were prepared to fit the combination of a Lorentzian and Gaussian curve by Origin-Pro 8.5 (OriginLab, Northampton, MA, USA, 2012).  
Thermal behaviors were analyzed with a Diamond DSC (PerkinElmer, Waltham, MA, USA), such as the melting and transition temperatures, and crystallization behavior of the PCUs. Liquid N\({}_{2}\) was used to cool the DSC cell to obtain sub-ambient temperatures. All the samples were sealed in aluminum pans with sample weights ranging from 9 to 15 mg. The experiment was carried out under a constant nitrogen flow at a heating rate of 5 \({}^{\circ}\)C/min. After eliminating the thermal history,  
Figure 1: The chemical structures of the components in the polyurethane.  
the melting point and the glass transition temperature were taken from the second heating curve after a 2 min station behind the first heating.  
The mechanical behavior of the films was determined at room temperature after two weeks by a mechanical testing machine, a computer controlled hydraulic universal testing machine (M-30A, Shenzhen, China), using a crosshead speed of 50 mm\(\cdot\)min\({}^{-1}\). The tensile tests of the films were based on ASTM D882-12. At least six specimen determinations were conducted for each type of film to obtain the average value.  
The relative molecular mass of the pre-polymers and their distribution were determined by gel permeation chromatography (GPC) measurements, using an Alliance high performance liquid chromatography analyzer (Waters, Milford, MA, USA). Tetrahydrofuran was employed as the eluent at a flow rate of 1.000 mL/min at 30 \({}^{\circ}\)C. According to ASTM D6579-6, in order to determine the retention time data, number, and molecular weights, we calibrated the whole system with the monodisperse polystyrene distribution curve ranging from 2.98 to 706 kg/mol as the general calibration parameter.  
The phase-separated morphology observations were conducted on a flat mica substrate. Measurements were performed under ordinary conditions using a commercial atomic force microscope (Multimode 8 AFM, Bruker, Madison, WI, USA) equipped with Silicon TESP cantilevers in a non-contact (tapping) mode (Nanosensors PPP-NCH, spring constant 10-130 N). The data of the surface images were analyzed with NanoScope Analysis software (Bruker, Madison, WI, USA).  
The goniometer (OCA-35, Databynics, Stuttgart, Germany) was employed to measure the static contact angles of water droplets with the samples. Firstly, a piece of silicon wafer (nearly 1 \(\times\) 1 cm\({}^{2}\)) with the attached membrane was placed on the goniometer. Then, the liquid (ultrapure water, less than 1 \(\upmu\)L in volume) was dropped for testing. At least 3 measurements were taken for each surface on the air-exposed side at different locations. Finally, the average value was calculated using the in-built software.  
Animal experiments were approved by the Review Committee for the Use of Human or Animal Subjects of Wuhan University of Technology and conducted in accordance with the Declaration of Helsinki and with the Guide for Care and Use of Laboratory Animals as adopted and promulgated by the United National Institutes of Health. The normal L929 fibroblast cells and adult rabbit blood were used for the MTT assay and hemolytic tests, evaluating the cytotoxicity of the fabricated membranes through cellular viability and hemocompatibility tests. The experiments were carried out as previously reported [29; 30]. The cell morphology in different leaching liquor was observed through an Inversion fluorescence microscope (Olympus IX71, Tokyo, Japan), while cell viability was evaluated by a universal microplate spectrophotometer (Thermo Labsystems 1500-206, Waltham, MA, USA) with a 550 nm filter.