The magnetic field of the Nd FeB magnet cylinder . (A) The system of coordinates and flux-density plot of the NdFeB magnet cylinder. O denotes the center point of the surface of the magnet pole. r and z denote the horizontal and vertical distance from the O point, respectively. (B) The distribution of the magnetic flux density. (C) The distribution of the magnetic flux gradient. (D) The magnetic attraction force on MagMSCs in the r direction (Fr) when z is 1 mm. B, Magnetic flux density; (); Magnetic field gradient in the r direction; Fr, magnetic attraction force on MagMSCs.