The magnetic hydrodynamic instability of ferrofluid under an applied magnetic field is one of its important features.In this study,we generated uniform arrays of ferrofluid droplets by inducing the rupture of the interfacial continuity of the ferrofluid [1,2],and utilized these droplet arrays as magnetic dot arrays for magnetic cell patterning.Figure 1 shows the fabrication procedure of the cell culture substrate containing the magnetic dots.At the first step,a ferrofluid droplet was placed on a glass substrate,and then an out-of-plane magnetic field H was applied to induce the fission of the droplet.Once the self-assembled hexagonal droplet array was formed,we subsequently added a biocompatible UV curable agent (PEGDA) to cover the droplet array,followed by the solidification of the PEGDA by UV lighting (see the step 2).By this a solid platform containing ferrofluid droplets was created.Afterward we dried the ferrofluid droplets by air making the droplets became solid magnetic dots fixed within the solidified PEGDA; then we tore the magnetic dots embedded PEGDA from the glass to obtain the magnetic cell culture substrate (see the step 3).Figure 2(a) shows the hexagonally arranged magnetic dots.The diameter of the magnetic dots was 118.2±6.3 μm,and the distance between centers of each two adjacent dots was 204.9±8.6 μm; the small errors indicate the uniformity of the dot array.Figure 2(b) shows the patterned magnetically labeled RAW cells on a magnetic dot under an out-of-plane magnetic field,and Fig.2(c) is the fluorescent image of Fig.2(b).There are two major features of our method,one is this method allows us to control the droplet size and the number density of the droplet array by adjusting the applied magnetic field strength when inducing the magnetic hydrodynamic instability of the ferrofluid [2]; the other is the easy fabrication,there is no any mask is needed for the fabrication,means no photolithography process is involved,leading our method can be a potential candidate for relative applications.