Engineering Nature: Human Skin
This week’s blog will be the final continuation in the current series examining biomimicry and the engineering advances that have resulted from its study. We will examine the extremely unique properties of human skin and its incredible ability to heal itself. The skin is a complex organ in the human body. It must be extremely flexible so that it does not crack during the scores of joint movements in a given day. Skin must also be sensitive so that it can respond to stimuli, such as touch and pressure, which are then transmitted in electrical impulses, so therefore skin must also conduct electricity. However, most crucial, if the skin is to survive the heavy demand of a daily routine it must be able to repair itself. While it may seem to be a relatively simple process due to how often we have seen a cut scab itself over, the process is complicated and difficult to reproduce in a synthetic material. By examining the properties that allow skin to heal itself, many researchers and engineers have been attempting to recreate these traits and apply them to synthetic materials in order to create products that never require service or repair.
The skin is often overlooked for the incredible job it does keeping us protected. Almost regardless of how much skin is damaged it has the ability to regrow and repair itself. Once the body limits the blood loss at a cut site, proteins in the blood, such as fibrin, work with the platelets to form a scab over the wound which will protect the compromised area while it regrows. The blood is brought to the site through capillaries which gradually shrink as they elongate, increasing the pressure. This pressure forces more blood into the area and thus more fibrin that can create a stronger scab. After a scab is formed the skin slowly grows back in a woven pattern until the gap is covered. If the cut goes deeper than the epidermis, into the dermis, a cicatrisation begins as your body attempts to create fibrous scar tissue from the granular tissue.i This granular tissue can have up to 100% of the strength of normal skin. At this time the strength of granular tissue cannot be replicated.
In one approach to recreating the self-healing process of skin, micro-capsules containing a healing agent were embedded into a plastic or carbon material. When the material cracks or is damaged the microcapsules are cracked open and the healing agent fills the crack and hardens. However there are many limits to this method that make it far less than ideal, such as the amount of material that can be stored in the microcapsule as well as the quality of adhesion between the healing substance and the initial surface. In a more recent approach engineers have used fluid dynamic simulations and finite approaches to create plastics that are impregnated with a fine network of channels. Each of these channels is less than 100 millionths of a meter in diameter.ii These micro-vascular networks penetrate the material, similar to the human’s circulation system, and supply the healing agent in various areas and at varying pressures. The healing agent will be released wherever a crack appears and can be resupplied from a channel similar in form to a main vein. iii When engineers replicated pulses, similar to a heartbeat, the healing agent was supplied to the crack in waves and created the strongest adhesion. Currently the attempt is to use this technology in plane wings, which experience small cracks that can lead to failure and must be replaced often.
While technology has given us many improvements on the human form, the original is in some cases superior. However, if the study of human skin can improve to allow for artificial materials to have the same properties, vast improvement in machine and product maintenance may be possible.
i Oswald, Rachel Discovery Fit & Health “How Your Skin Works” 2012
iiBattison, Leila BBC News “Self-healing Materials Take Cue from Nature” WWW Document (http://www.bbc.co.uk/news/science-environment-15096393) September 29, 2012
iii Relevant Progression “Biomimicry: Self-Healing Materials” October 3, 2011