Understanding how soaps and detergents work could soon lead to better methods of carrying medicinal drugs around the body and enabling them to reach the brain more easily.
At the Institute of Physics Condensed Matter and Materials Physics Conference in Bristol Wednesday, theoretical physicist Dr. Gerhard Goldbeck-Wood from Molecular Simulations Limited in Cambridge describes how he is investigating the suitability of using tiny polymer cages -– which behave just like soap molecules -– as carriers for drugs that act on the brain.
There are many different ways in which drugs can be transported around the body. One way is for the drug to be contained within a coating that initially protects it so it can be carried through the bloodstream, but then breaks down after a certain time, allowing the drug to be delivered.
Drugs which act directly on the brain, however, such as antidepressants, need a somewhat more complex version of this carrier system. Not only must they dissolve in the oily surroundings in the brain while passing readily through blood, they must also be able to pass the blood-brain barrier.
The blood-brain barrier prevents circulating blood from coming into contact with the fluid surrounding our brains. It is semi-permeable, which means it blocks the path of large objects such as red blood cells, but will allow smaller objects to pass through it. Many of the drug carriers typically used are too large to pass this barrier, but the new polymer cages are only a few molecules big, and pass through happily.
These polymer cages work in a similar way to soaps. Soaps are made from molecules that have one end which likes water (hydrophilic), and another end that likes fat (hydrophobic). Dirt is "fatty" and so any muck on our clothes or bodies is attracted to the fat-liking end of soap molecules and gets stuck there. Because the other ends of soap molecules are attracted to water, rinsing gets rid of soap -- which takes the stuck-on dirt with it.
In the spherical polymer cages, the water-liking ends of the molecules are on the outside, allowing them to pass quite happily through the water-like bloodstream. Meanwhile all the fat-liking ends, which are also attracted to drugs, are on the inside, protecting the drug they surround.
Dr. Goldbeck-Wood started the research at the Materials Science and Metallurgy Department at Cambridge University. A collaboration between the department in Cambridge and Molecular Simulations Limited in Cambridge enabled him to view the cages under a powerful electron microscope. This has revealed that once the drug is inside them, the tiny cages change size and lose their initial spherical shape.
By applying computer-based simulations first used in materials science to understand polymer detergents, Dr. Goldbeck-Wood is now starting to be able to simulate such behavior and determine how well the drug is contained and whether it will influence either how or how quickly the drug is released.
The researchers hope that as well as providing the information needed to improve the polymer cages enough to become a viable new drug delivery system, these experiments and simulations can eventually be used to help design the most effective carriers for different types of drugs.
Institute of Physics
[Contact: Dr. Goldbeck-Wood,