The droplets can navigate mazes with the same efficiency

Jan 15, 2010 09:46 GMT  ·  By
Mineral oil drops always selected the shortest way out of a maze. Their movements were based on the acidity gradient of the solution they were navigating
   Mineral oil drops always selected the shortest way out of a maze. Their movements were based on the acidity gradient of the solution they were navigating

Lab rats could soon see themselves out of work, a science team at the Northwestern University says. The group managed to devise a new method of making oil drops navigate a maze, with the same efficiency that the rodents showed at performing this task. The innovation could be used for studies ranging from fighting cancer to making traffic flow more fluid, and eliminating road congestion. In fact, the researchers say, almost all problems featuring mazes could be taken on using oil rather than rats, ScienceNow reports.

NU physical chemist Bartosz Grzybowski has been the leader of the new research effort, which has actually sought to develop a new cure for cancer. The team was looking at ways of eliminating the blockage that all current cancer therapies faced, namely the intricate, maze-like system of blood vessels in the human body. At this point, all cancer drugs rely on either nanoparticles or liposomes to deliver vaccine molecules to tumors directly. But both classes of materials tend to get lost inside the labyrinth of blood vessels at some point. The new work may offer a foundation to how to counteract this effect, and make these particles and molecules able to find their respective targets.

For the new experiment, the group constructed a number of silicon mazes, each about 6.5 square centimeters in size. They filled them with an alkaline solution of potassium hydroxide, and placed small droplets of mineral oil or dichloromethane (an organic solvent) at the “entry.” At the other end, the scientists placed a “reward,” in the form of a piece of agarose gel soaked in hydrochloric acid. “We wanted to give [the droplets] a bit of a challenge and see if they could do more than just go in a straight line,” the team leader explained. All the drops were loaded with some weak acids and red dye, so that the group could follow their paths easily.

The molecules at the entry to the maze are propelled forward when the acid from the reward leaks into the potassium hydroxide solution. A gradient is created, which increases the surface tension on the side of the droplet facing towards the maze. The surface tension on the other side, which is facing towards the entry, decreases, so the molecule moves forward. “We can call them chemo-rats,” Grzybowski said of the droplets, which always managed to find the shortest way out of the maze. They simply followed the difference of acidity in the solution's gradient, towards the place where it had the highest value. This was the exit, or the place where the reward was placed.