A Review on the Optimal Design of Magnetic Nanoparticle-Based <i>T</i>₂ MRI Contrast Agents

• Main Author: Nina Kostevšek
• Format: Article
• Language: English
• Published: MDPI AG 2020-02-01
• Series: Magnetochemistry
• Subjects: nanoparticles; magnetic resonance imaging; liposomes; biomimetics
• Online Access: https://www.mdpi.com/2312-7481/6/1/11

Relaxivity <i>r</i>₂ and thus the contrast efficacy of superparamagnetic nanoparticles (NPs) can be enhanced via either NP&#8217;s magnetic properties or coating optimization. Numerous reports can be found about the investigation of the optimal iron oxide nanoparticles (IO NPs) size, shape, crystallinity and composition that yield high saturation magnetization (<i>m</i>_s) values and, consequently, high <i>r</i>₂ values. Although the use of an appropriate coating can boost up the NPs MRI contrast agent efficiency, this topic has been largely understudied. Therefore, in this review, the factors affording <i>r</i>₂ enhancement of spherical magnetic NPs are discussed. Based on the literature, the requirements for an optimal surface coating that may increase <i>r</i>₂ values and ensure stability and biocompatibility of NPs are listed. One of the best candidates that fulfil these requirements are liposomes with embedded magnetic NPs, so-called magneto-liposomes. The analysis of the literature elucidated the most appropriate phospholipid compositions for the relaxivity enhancement and for magneto-liposomes in vivo stability. Finally, the future directions in the development of NP-based contrast agents are given. For example, most of the synthetic NPs are recognized and eliminated as a foreign substance by the immune system. To overcome this issue, a design of a biomimetic, cell-membrane-based nanocarrier for contrast agents is proposed. Disguised with cell membranes, NPs or other active components can act as autogenous cells and thus ensure the inherent biocompatibility.