title: Studying the effect of particle size and coating type on the blood kinetics of superparamagnetic iron oxide nanoparticles.
abstract: OBJECTIVE
  Magnetic resonance imaging (MRI), one of the most powerful imaging techniques available, usually requires the use of an on-demand designed contrast agent to fully exploit its potential. The blood kinetics of the contrast agent represent an important factor that needs to be considered depending on the objective of the medical examination. For particulate contrast agents, such as superparamagnetic iron oxide nanoparticles (SPIOs), the key parameters are particle size and characteristics of the coating material. In this study we analyzed the effect of these two properties independently and systematically on the magnetic behavior and blood half-life of SPIOs.
  
  
  METHODS
  Eleven different SPIOs were synthesized for this study. In the first set (a), seven carboxydextran (CDX)-coated SPIOs of different sizes (19-86 nm) were obtained by fractionating a broadly size-distributed CDX-SPIO. The second set (b) contained three SPIOs of identical size (50 nm) that were stabilized with different coating materials, polyacrylic acid (PAA), poly-ethylene glycol, and starch. Furthermore, small PAA-SPIOs (20 nm) were synthesized to gain a global insight into the effects of particle size vs coating characteristics. Saturation magnetization and proton relaxivity were determined to represent the magnetic and imaging properties. The blood half-life was analyzed in rats using MRI, time-domain nuclear magnetic resonance, and inductively coupled plasma optical emission spectrometry.
  
  
  RESULTS
  By changing the particle size without modifying any other parameters, the relaxivity r(2) increased with increasing mean particle diameter. However, the blood half-life was shorter for larger particles. The effect of the coating material on magnetic properties was less pronounced, but it had a strong influence on blood kinetics depending on the ionic character of the coating material.
  
  
  CONCLUSIONS
  In this report we systematically demonstrated that both particle size and coating material influence blood kinetics and magnetic properties of SPIO independently. These data provide key information for the selection of a contrast agent for a defined application and are additionally valuable for other nano areas, such as hyperthermia, drug delivery, and nanotoxicology.
authors.affiliation: MR and CT Contrast Media Research, Bayer Pharma AG, Berlin, Germany.
authors.forename: Farnoosh
authors.initials: F
authors.lastname: Roohi
authors.forename: Jessica
authors.initials: J
authors.lastname: Lohrke
authors.forename: Andreas
authors.initials: A
authors.lastname: Ide
authors.forename: Gunnar
authors.initials: G
authors.lastname: Schütz
authors.forename: Katrin
authors.initials: K
authors.lastname: Dassler
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D000818:Animals; D002460:Cell Line; D003287:Contrast Media / Q000737:chemistry* / Q000493:pharmacokinetics*; D006207:Half-Life; D007501:Iron / Q000097:blood* / Q000737:chemistry* / Q000493:pharmacokinetics; D008279:Magnetic Resonance Imaging; D058185:Magnetite Nanoparticles / Q000737:chemistry*; D008297:Male; D051379:Mice; D010087:Oxides / Q000097:blood* / Q000737:chemistry* / Q000493:pharmacokinetics; D010316:Particle Size; D011092:Polyethylene Glycols / Q000737:chemistry; D051381:Rats; D017208:Rats, Wistar; D013213:Starch / Q000737:chemistry; D013329:Structure-Activity Relationship; D013499:Surface Properties
chemical_list: D000180:Acrylic Resins; D003287:Contrast Media; D058185:Magnetite Nanoparticles; D010087:Oxides; C094094:carboxydextran-coated magnetic iron oxide particles; D011092:Polyethylene Glycols; C006903:carbopol 940; D013213:Starch; D007501:Iron