Saturday, April 28, 2012

Special properties make skin water resistant

Whenever we swim or take a bath, our bodies do not get soaked with water, sinking us to the bottom. Even though skin gets wet and wrinkled because of the water, it is largely kept out of our bodies. Scientists have finally discovered how that works, and it is attributed to special properties of fat, functioning as water repellents. Working out the mechanism enables us to improve drug delivery across the skin barrier.

Lipid bilayer
In biological structures such as cells, fat plays an important role. Because of their structure, individual lipid molecules form an excellent barrier to repel water, and keep the cellular contents separated from what lies outside. Lipids have two sides: a 'fatty' water-repelling part, and a part that attracts water. Two lipid molecules can connect with each other using the fatty part, which leaves the hydrophilic (water-attracting) part protruding on the outside. The resulting lipid bilayer is impenetrable for water and therefore forms a solid barrier for cells. And the same goes for skin, albeit a bit different.
Basic structure of a lipid bilayer. Hydrophobic parts find each other while the hydrophilic parts come in contact with the watery surroundings. Because of the structure, water cannot cross the bilayer, thereby sealing the structure.
Skin layer
Lipid bilayers in the skin are a bit different, scientists from the Swedish Karolinska Institute discovered. Instead of the hydrophobic parts being on the inside, the skin has them protrude outward, basically reversing the structure. According to the researchers, skin consists of alternating stacks of lipid bilayers, making it impossible to penetrate by water, except for carefully carved openings in the skin called pores. Because of this structure, it is impossible to soak up water in the parts of the skin that lie between the lipid bilayers, as would happen with a conventional fatty barrier. Stacking the molecules the other way around results in a tightly packed structure where no water can exist between the different layers.

Not only is it impossible for water to make it across or in between the barriers, but the same goes for drugs. Discovering the lipid bilayer structure in skin gives rise to studies focusing on how to bypass the barrier and get drugs into our system by skin treatment. Choosing the skin as entry point for drugs makes it easier to give localised treatment, which is why in some cases it is preferred above other ways of administering drugs. Next to that, the scientists also claim their study can help create artificial skin, for example to help burn victims. 

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