Nanoparticles — particles only nanometers or billionths of a meter wide — are widely investigated as vehicles to help deliver drugs into patients. Now scientists find the shape of these nanoparticles influences how well they enter cells, with disk-shaped nanoparticles doing better than rod-shaped ones. These findings, detailed in the Proceedings of the National Academy of Sciences, could help researchers design better nanoparticle-based therapies.
Past research suggested the size, material compositions and surface electric charge of nanoparticles affected how cells took up nanoparticles, but less was known about the effects of shape.
“In nature, pathogens come in very diverse shapes, and it makes you think if there are evolutionary advantages to that, which led us to think whether we might experiment with nanoparticles based on their shapes,” says biomedical engineer Krishnendu Roy, now at the Georgia Institute of Technology.
To find out, Roy and his colleagues at the University of Texas at Austin fabricated disk- and rod-shaped nanoparticles of a variety of widths and heights. These were all tagged with fluorescent molecules that helped the scientists keep track of them.
In experiments with a variety of human and mouse cells grown in the lab, the researchers found disk-shaped nanoparticles were better taken up than rod-shaped nanoparticles of similar volume. Larger nano-disks and nano-rods were also better taken up than smaller counterparts, unlike past results with nano-spheres.
“This work analyzes the really fundamental properties of cell-nanoparticle interactions, but also has very practical implications when it comes to drug delivery for cancer therapies and other therapeutics,” Roy says. “This opens up a tremendous amount of potential for, say, better targeting a tumor or an organ with certain shapes.”
It remains uncertain why nano-disks did better than nano-rods in these experiments. “One of the major factors we calculate might be responsible is the difference in energy required for cell membranes to wrap around disks versus rods,” Roy says.
Intriguingly, while the epithelial and immune cells the researchers investigated preferred larger disks, endothelial cells preferred intermediate-sized ones.
“We don’t claim the phenomenon of nano-disks being taken up better by cells than nano-rods is a universal one — the results might differ depending on what cells you use, or what conditions the cells are under, or what materials the nanoparticles are made of,” Roy says. “You don’t want to draw too broad a conclusion from our findings.” Future research will also need to see if the effects observed in cultured cells will apply to cells in living animals.