TSUKUBA, JAPAN: Nanoparticles are particles that are smaller than 100 nanometers. They are classically attained from metals and on account of their small size, they have unique properties that make them useful for biomedical applications. However, without treatment to make their surfaces biologically slow, their effectiveness is severely limited.
University of Tokyo scientists led by Kazuhiko Ishihara have found the use of MPC polymers to alter the surfaces of nanoparticles.
In an article published in the journal Science and Technology of Advanced Materials, they studied current ways in which polymeric nanoparticles can be utilised to transport a sort of small nanoparticles called quantum dots into cells.
MPC polymers are huge molecules made from chains of 2-methacryloyloxyethyl phosphorylcholine (MPC). Bioactive nanoparticles whose surfaces have been altered with them can be utilised as anti-tumor compounds, gene carriers, contrast agents that improve MRI images, and protein detectors.
These polymers mimic cellular membranes and allow the delivery of bioactive molecules that are normally not very soluble in water or that might produce unwanted biological side effects. When researchers join MPC polymers to the surface of inorganic nanoparticles, they can make substances that are easily delivered into the blood or other tissue.
Ishihara's team has recently used this process with quantum dots to produce nanoparticles that can outperform traditional organic fluorescent dyes in biomedical imaging. Using a simple solvent evaporation technique, they were able to fabricate polymer nanoparticles that contained a core of quantum dots enmeshed in the nanoparticle polymer PLA (poly L-lactic acid), which was then surrounded by a layer of an MPC-polymer derivative called PMBN.
This grouping produced particles that maintained the same levels of fluorescence in a solution after being stored for more than six months at 4 degrees Celsius, and that functioned in environments of varying acidity. While traditional organic dyes lose their fluorescence with repeated illumination, the polymer quantum dot nanoparticles did not.
To be useful, nanoparticles need to be transported into cells. To achieve this, the team tested the performance of several molecules by fixing them onto the surface of the PMBN/PLA/quantum dot particles. The study showed that when the cell-penetrating peptide called R8 - an octapeptide made from eight arginine amino acids - was attached to the nanoparticles, they were taken up by cells within 4 hours and had no toxic or inflammatory effect on the cells even after three days.
Advance testing demonstrated that cells with the polymer quantum dot particles multiplied normally and that the nanoparticles spread evenly into each daughter cell upon division. Unlike organic fluorescent dyes, this did not weaken the fluorescence signal even after 30 hours of proliferation.
"This was the first report viewing the long-term retention of nanoparticles in cells. Preparation of bioactive nanoparticles with MPC polymers can be used to fabricate in-cell nanodevices whose interaction with cells can be completely controlled," noted Ishihara.
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