Magnetite‐Loaded Polymeric Micelles as Ultrasensitive Magnetic‐Resonance Probes

Abstract

These nanoconstructs are composed of amphiphilic block copolymers with distinct hydrophobic and hydrophilic segments that can self-assemble into supramolecular core±shell structures (usually 10 to 100 nm) in aqueous solution. The hydrophobic micelle core provides an ideal carrier compartment for hydrophobic agents, and the shell consists of a protective corona that stabilizes the nanoparticles. Many hydrophobic drugs such as paclitaxel and doxorubicin have been successfully loaded inside the micelle core to improve drug solubility and pharmacokinetics. [2,3,6,7] In addition to therapeutic applications, polymeric micelles have also received increasing attention in diagnostic imaging applications. When incorporated into micelles, different types of contrast agents have achieved longer blood half-life, improved biocompatibility, and better contrast.[1]In this communication, we report the development of superparamagnetic polymeric micelles as a new class of magnetic resonance imaging (MRI) probes with remarkably high spin± spin (T 2 ) relaxivity and sensitivity. Superparamagnetic iron oxide (SPIO) nanoparticles such as magnetite (FeO´Fe 2 O 3 ) are known to have a strong effect on T 2 . Better detection sensitivity and slower kidney clearance of SPIO nanoparticles make them advantageous over Gd-based small molecular contrast agents. Currently, most T 2 contrast agents are composed of hydrophilic magnetite nanoparticles dispersed in a dextran matrix. [8,9] In contrast, our micelle design consists of a cluster of hydrophobic magnetite particles encapsulated inside the hydrophobic core of polymeric micelle whose surface is stabilized by a poly(ethylene glycol) (PEG) shell. This unique core±shell composite design has allowed us to achieve an ultrasensitive MRI detection limit of 5.2 lg mL ±1 (~5 nM), a sensitivity that promises to expand the ªtool boxº of MR probes for molecular imaging and image-visible drug-delivery applications.We used an amphiphilic diblock copolymer of poly(e-caprolactone)-b-poly(ethylene glycol) (PCL-b-PEG) for the micelle formation (Fig. 1). This copolymer was synthesized by a ringopening polymerization of e-caprolactone using monomethoxy-terminated PEG (5 kDa; 1 Da .

Clusters of Superparamagnetic Iron Oxide Nanoparticles Encapsulated in a Hydrogel: A Particle Architecture Generating a Synergistic Enhancement of the T2 Relaxation

“…The high relaxivities of these clusters, ranging between 245 and 410 mM À1 s À1 , can be attributed to their structure: densely packed nanoparticles have high magnetizations. 7,17 Similar to what has been reported using single SPIONs, the relaxivities of ARTICLE the clusters are also found to increase with increasing diameter. 6 However, the clusters show a poorly defined dependence of relaxivity on the diameter, which can be ascribed to the difficulties obtaining accurate sizes as well as the differences in the size distribution of each batch of particles.…”

Development of transparent, conducting composites by surface infiltration of nanotubes into commercial polymer films

“…This may be due to the partial in-plane alignment of the tubes in the surface layer. It is well known that alignment effects can act to increase percolation thresholds for rod-like fillers [23,24]. The measured value of percolation exponent of s=1.8 is very close to the universal 3-dimensional value of s 3D =2.0 [19].…”

Octapod iron oxide nanoparticles as high-performance T2 contrast agents for magnetic resonance imaging

“…Notably, the octapod iron oxide nanoparticles exhibited stronger T 2 contrast effects than spherical iron oxide nanoparticles, suggesting that the octapod iron oxide nanoparticles may serve as highly sensitive T 2 contrast agents. Our results demonstrate that structurally increasing the effective radii of iron oxide through morphology control is an attractive alternative to existing strategies, such as metal doping and particle clustering 18,[37][38][39] to increase the T 2 relaxivity of iron oxide nanoparticles.…”