Since iron oxide particles are mainly intended for medical use (for example, for use as contrast agents in tumor therapy) and are directly injected into the body, the doses administered must not cause toxicity.

 

SPION: iron oxide core and hygroscopic shell. © Kunzman et al., 2011.SPION: iron oxide core and hygroscopic shell. © Kunzman et al., 2011.The SPION currently used are made up of two components: A core of iron oxide and a shell of a hygroscopic polymer The shell prevents the nanoparticles from agglomeration, reduces their toxicity, and controls their behaviour and distribution in the body. SPION particles with dextran shells have already been studied intensively and have been admitted for clinical applications by the US Food and Drug Administration (FDA).

 

Intravenously injected SPION are mainly taken up by macrophages. In these cells, the polymer coating is degraded and is then excreted via the urine or the stool. The iron contained in the SPION is built into the body’s iron stores. The low toxicity of SPION is not surprising considering that natural iron concentrations in the body may be as high as approximately 4000 mg/adult person while no more than 50 – 200 mg/person are administered during medical treatment.

SPION that are provided with a special polymer shell (polyethylene glycol – PEG) are taken up less readily by the macrophages. The retention time of SPION in the body is prolonged through such modification, and the probability of reaching the desired target (for example, the tumor) is increased.

 

 

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