n methylpyrrolidone triethylcitrate and other liquid esters of natural products previous to this study little published work is available that evaluates the use of a magnetic embolic agent for endovascular drug delivery or the treatment of cerebral avms or aneurysms alksne and fingerhut bulletin of the los angeles neurological societies 30 153 155 1965 and alksne and smith supra developed the idea of the use of a magnetic agent to improve the thrombosis of aneurysms the first work used carbonyl iron powder suspended in human serum albumin that was held in place by an external magnet attached to the skull however clotting took five days some magnetic pieces fragmented off and the patient needed to return to the operating room to remove the magnet in a subsequent study the material used was the same carbonyl iron powder but instead suspended in a liquid methyl methacrylate monomer that is polymerized from catalysis by methyl methacrylate n butyl methacrylate polymer alksne and smith 1977 the embolic becomes a non fragmenting solid in 30 60 minutes the use of magnetically guided particles and devices are seen in many applications such as the aforementioned magnetic embolic agents intravascular catheter guidance frei et al medical research engineering 5 4 11 18 1966 and targeted drug delivery gupta and hung international journal of pharmaceutics 59 57 67 1990 frequently these types of microparticles are made from iron oxide fe 3 o 4 also known as magnetite although the chemical formula for magnetite is fe 3 o 4 it is often written as feo u00b7 fe 2 o.