Microdevices having a preferential axis of magnetization and uses thereof

A method for manipulating a plurality of microdevices in an array of microchannels, which method comprises:

• a) providing a plurality of microdevices, each said microdevice comprising
• 1) a magnetizable substance;
• and
• 2) a photorecognizable coding pattern, wherein each said microdevice has a preferential axis of magnetization that is substantially aligned with the microdevice's major axis;
• b) providing a microchannel array comprising a plurality of microchannels, said microchannels are sufficiently wide to permit rotation of said microdevices within said microchannels but sufficiently narrow to prevent said microdevices from forming a chain when the major axis of said microdevices is substantially perpendicular to the major axis of said microchannels;
• and wherein the height of the microchannels and/or a constraint on the microdevices by a magnetic field does not allow the microdevices to stand up within the microchannels;
• c) introducing said plurality of microdevices into said plurality of microchannels;
• and
• d) rotating said microdevices within said microchannels by a magnetic force, whereby a combined effect of said magnetic force and said preferential axis of magnetization of said microdevices substantially separates said microdevices from each other.