Mc1000 ion sputter coater

As described above, rBMSCs coated microspheres were obtained and then wash three times with 4°C prechilled PBS for 5 min each. After aspirating PBS, add 2.5% isopropanol at 4°C for 2 h. Wash three times at 4°C pre-chilled PBS for 5 min each. The microspheres were dehydrated with alcohol gradient (20 mins each in 50, 60, 70, 80, 90% and 30 mins in 100%). Finally, critical point drying was performed. The Hitachi MC1000 Ion Sputter Coater was used to spray gold on the surface of the material for 120 s. Scanning electron microscopy (SEM) images were captured in the field-emission mode using a FEI Quanta 450FEG (USA) at an acceleration voltage of 5 kV.

Before imaging, scaffold samples (~ 5 mm × 5 mm × 2 mm) were cut and placed onto a metallic stub by a double-sided carbon tape and coated with platinum using a Hitachi MC1000 Ion Sputter Coater for about 60 s. The morphology of 3D porous PU scaffold was observed by a Hitachi UHR FE-SEM SU8010 (Tokyo, Japan) at an acceleration voltage of 3 kV.