Superparamagnetic iron oxide nanoparticles
Swiss researchers have discovered a method that allows for the controlled release of an active agent on the basis of a magnetic nanovehicle. The research was conducted as part of the National Research Program “Smart Materials,” a cooperation between the Swiss National Science Foundation and the Commission for Technology and Innovation. The specific work was conducted by researchers at ETH Lausanne, the Adolphe Merkle Institute, and the University Hospital of Geneva in Switzerland.The researchers demonstrated the feasibility of using a nanovehicle to transport drugs and release them in a controlled manner as explained in a Jan. 24, 2013 press release from the Swiss National Science Foundation. The nanocontainer used was a liposome with a diameter of 100 to 200 nm. The membrane of the vesicle was composed of phospholipids and the inside of the vesicle offered room for the drug. Superparamagnetic iron oxide nanoparticles (SPIONs) were integrated into the liposome membrane; the SPIONs become magnetic in the presence of an external magnetic field. Once they are in the field, the SPIONs heat up. The heat makes the membrane permeable, and the drug is released. The SPIONs also are a contrast agent in magnetic resonance imaging (MRI). A simple MRI shows the location of the SPION and allows for the release of the drug once it has reached the targeted spot (1, 2).
In their study, the researchers noted that liposomes have been characterized by cryogenic electron microscopy (CryoTEM) as well as in combination with nanoparticles in SPIONs incorporated inside the liposomal membrane. CryoTEM maintains the native state of the liposomes. The quick freezing of the sample immobilizes particles and liposomes exactly at their position in the suspension, which allows localization information to be extracted from the images. The researchers reported on the analysis of cryoTEM images of liposome-particle hybrids, including the estimation of the contrast transfer function (CTF) and electron dose as well as the correct positioning of the sample holder and tomography for accurate localization (1, 2).
Another challenge was to reach a temperature sufficiently high to open up the liposomes, according to the release. This problem was addressed by increasing the size of the SPION from 6 to 15 nm. The membrane of the vesicles had a thickness of only 4-5 nm. The researchers regrouped the SPION in one part of the membrane, which made the MRI detection easier. Before starting in-vivo tests, the researchers plan to study the integration of SPION into the liposome membrane in greater detail, according to the release.