Described is a method of expanding human progenitor calls by suspension culturing under non-static conditions. Said folding top comprises at least one folding canopy and a rod mechanism for unfolding and folding the canopy. At a position between the adjustable pulleys assembly and string holding assembly there is a shaft rotatably connected to the base for supporting a plurality of adjustable cams for applying tension to the strings when rotated, said shaft having a handle at one of its ends. The body is square or rectangular in shape to easily fit between the interior and exterior walls within the cavity.