I am trying to generate sphere formed MDA MB 231 cells using Mammocult media from Stem Cells. After 7 days of culture in ultra low adherent plate, the formed tumorsphere.

When i tried to filter the media to get spheres which are over 70micrometer, all the cells adhered with the membrane. Then i took the whole media containg sphere from wells of low adherent plate and centrifuge them but found literally no cell pellet or the pellet is loosely adhered at the bottom and disappeared after washing.

How to overcome this ? How to get the cell pellet from primary sphere culture for subculture or further experiment?