Washington University in St. Louis scientists have developed a smart gold nanocage covered with a polymer which can act as an effective drug delivery system.
The nanocage is filled with a medicinal substance, such as a chemotherapy drug or bactericide. Designed in Younan Xia's lab, the cage releases carefully titrated amounts of a drug only near the tissue that is the drug's intended target, thus maximizing the drug's beneficial effects while minimizing its side effects.
It's actually the absorption component that the scientists exploit to open and close the nanocages.
The polymer, poly(N-isopropylacrylamide), and its derivatives has what's called a critical temperature and when it reaches this temperature it undergoes a transformation called a phase change.
If the temperature is lower than the critical temperature, the polymer chains are water-loving and stand out from the cage like brushes. The brushes seal the cage's pores and prevent its cargo from leaking out.
On the other hand, if the temperature is above the critical temperature, the polymer chains shun water, shrink together and collapse. As they shrink, the pores of the cage open, and its contents flood out.
"It's a bit counter-intuitive. Typically when you go to higher temperature, a molecule will expand, but this one does the opposite," Nature quoted Xia as saying.
Like everything else about this system, the polymer is tunable and the scientists can control its critical temperature by altering its composition.
For medical applications, they tune the critical temperature to one right above body temperature (37 degrees Celsius) but well below 42 degrees Celsius (107 degree Fahrenheit), the temperature at which heat would begin to kill cells.
The researchers loaded capsules with doxorubicin, a common chemotherapy drug and, triggered the drug's release with a laser, which killed breast cancer cells growing in wells on a plastic plate.
And finally, they loaded the capsules with an enzyme that snips open the cell walls of bacteria and used them to kill a bacterium that is a normal part of the flora of our mouths and throats.
The study was published in the journal Nature Materials.