Tuesday, September 14, 2010

Human Skin

Today’s post will be focused on carnal desires (yet still be safe for work). I’m talking about the great desire for artificial skin.

Human skin performs an wide range of tasks: keeping our insides in and the outside out [1], providing us with our senses of touch, heat and cold, providing a base for hair attachment and the list goes on.

Anybody who has ever developed products that interact with skin has always run into one big problem: no artificial equivalent exists. Researchers have been working on developing such a construction, but in all cases they are usually trying to recreate only one or two of the properties of skin. To totally duplicate skin via artificial constructs would be a nightmarish task.

Since an artificial skin doesn’t exist, the only alternative is to use human subjects. This is particularly true when developing pressure-sensitive adhesives. Human skin is a low-surface energy substrate, but you quickly find out that other low-surface energy materials such as polypropylene and polyethylene do not are not a good mimic for skin when testing adhesion (such as in a peel test). The reasons are manifold :
  • skin is more than a stiff surface; it is compliant and deforms under the stress from the adhesive when being removed. All that deformation is recorded implicitly in the peel test data.
  • The condition of human skin varies from person to person, and within each person from body part to body part. Changes also occur over time such as when sweating.
  • Hair coverage is variable and can greatly interfere with adhesion.[2]
In two different employment positions I have volunteered [3] to be subjected to adhesives of my own construct. Usually the back is used for the test surface as it is a large, relatively uniform and relatively flat – so important to maintaining a constant peel angle. While the test generally were fine, there were times that I “gave the skin off my own back” to the project. (Is that the sign of a committed employee or someone who should be committed?)

[1] Clearly there are exceptions to even this simple desire such as when we sweat or absorb drugs and chemicals transdermally
[2] Having a hairy chest may be great for attracting the ladies, but it is the last thing you want when suffering a heart attack and the medics can't get a good EKG reading because the electrodes won't stick to you skin through all the hair.
[3] And this certainly does not mean that I was "volunteered". The Nuremburg Code which was developed after World War II closely regulates human experimentation to ensure that all subjects are voluntary and give informed consent. This clearly prevents managers from going around and asking for volunteers.

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