The skin is the largest organ in the human body. Skin is made up of two layers, the epidermis and the dermis. The epidermis is the outer layer of skin that keeps vital fluids in and harmful bacteria out of the body. The dermis is the inner layer of skin that contains blood vessels, nerves, hair follicles, oil, and sweat glands. Severe damage to large areas of skin exposes the human organism to dehydration and infections that can result in death.
Traditional ways of dealing with large losses of skin have been to use skin grafts or from a different person/cadaver. The former approach has the disadvantage that there may not be enough skin available, while the latter suffers from the possibility of rejection or infection. Until the late twentieth century, skin grafts were constructed from the patient's own skin. This became a problem when skin was too far damaged or when too much of the organ was ruined.
Synthetic skin was invented by John F. Burke, chief of Trauma Services in Massachusetts General Hospital. He was assisted by Ioannis V. Yannas, a chemistry professor at Massachusetts Institute of Technology, Cambridge, Massachusetts. In the 1970s, they created a polymer with collagen fibers and sugar molecules. A small porous was formed. When the porous was placed on the wound, skin cells around it seemed to encourage a faster healing process. This allowed the healing process to continue at a much faster rate. They also created a skin from shark cartilage and cowhide. When this skin dried and was sterilized, it could be made into a thin membrane in which materials could pass through like with the original dermis. Silicon was then added to create a protective top layer to represent the epidermis. This added layer protected the new dermis as well as the inner fluids of the body. The synthetic dermis allowed blood vessels to grow, but couldn’t produce hair follicles or sweat glands.
In the late 1970s, medical researchers began experimenting with sheets of artificial skin that could be permanently grafted onto patients who have no other options. Two Boston surgeons discovered a successful new artificial skin design in 1981 that is known as Integra. Instead of replicating the function of healthy skin, Integra “tricks” real skin cells into growing a new dermis, which would replace the damaged dermis.
Research is continually being done on artificial skin. Typically, a collagen scaffold is used (the protein that underlies the structure of skin), which can be additionally seeded with patient's own cells, or with foreskin from newborns that has been removed during circumcision.The edges of the scaffold meet with the healthy skin, allowing the new skin to heal quicker. Artificial skin can be used to save patients who have lost more than 50% of their own skin to burns, skin disorders, or certain forms of cancer. Additional technologies, such as an autologous spray-on skin produced by Avita Medical, are being tested in efforts to accelerate healing and minimize scarring.
The Fraunhofer Institute for Interfacial Engineering and Biotechnology is working towards a fully automated process for producing artificial skin. Their goal is a simple two-layer skin without blood vessels that can be used to study how skin interacts with consumer products, such as creams and medicines. They hope to eventually produce more complex skin that can be used in transplants.
Hanna Wendt, and a team of her colleagues in the Department of Plastic, Hand and Reconstructive Surgery at Medical School Hannover Germany, have found a method for creating artificial skin using spider silk. Before this, however, artificial skin was grown using materials like collagen. These materials did not seem strong enough. Instead, Wendt and her team turned to spider silk, which is known to be 5 times stronger than Kevlar. The silk is harvested by “milking” the silk glands of golden orb web spiders. The silk was spooled as it was harvested, and then it was woven into a rectangular steel frame. The steel frame was 0.7 mm thick and the resulting weave was easy-to-handle, as well as easy to sterilize. Human skin cells were added to the meshwork silk and were found to flourish under an environment providing nutrients, warmth and air. However at this time, using spider silk to grow artificial skin in mass quantities is not practical because of the tedious process of harvesting spider silk.
Australian researchers are currently searching for a new, innovative way to produce artificial skin. This would produce artificial skin quicker, and in a more efficient way. The skin produced would only be 1 millimeter thick and would only be used to rebuild the epidermis. They can also make the skin 1.5 millimeters thick, which would allow the dermis to repair itself if needed. This would require bone marrow from a donation or from the patient's body. The bone marrow would be used as a “seed," and would be placed in the grafts to mimic the dermis. This has been tested on animals and has been proven to work with animal skin. Professor Maitz said, “In Australia, someone with a full-thickness burn to up to 80 per cent of their body surface area has every prospect of surviving the injury…However their quality of life remains questionable as we're unable, at present, to replace the burned skin with normal skin…We're committed to ensuring the pain of survival is worth it, by developing a living skin equivalent.”
Another form of “artificial skin” has been created out of flexible semiconductor materials that can sense touch for those with prosthetic limbs. The artificial skin is anticipated to augment robotics in conducting rudimentary jobs that would be considered delicate and require sensitive “touch”. Scientists found that by applying a layer of rubber with two parallel electrodes that stored electrical charges inside of the artificial skin, tiny amounts of pressure could be detected. When pressure is exerted, the electrical charge in the rubber is changed and the change is detected by the electrodes. However, the film is so small that when pressure is applied to the skin, the molecules have nowhere to move and become entangled. The molecules also fail to return to their original shape when the pressure is removed.
Artificial Microfluidic Skin for In Vitro Perspiration Simulation and Testing
An artificial skin has also been recently demonstrated at the University of Cincinnati for in-vitro sweat simulation and testing, capable of skin-like texture, wetting, sweat pore-density, and sweat rates. The sweat simulator employs a simple bi-layer membrane design to resolve all drawbacks associated with use of commercial membranes. A bottom 0.2 µm track etched polycarbonate membrane layer provides flow-rate control by creating a pressure drop and therefore a constant sweat flow. A top photo-curable layer provides skin-like features such as sweat pore density, hydrophobicity, and wetting hysteresis. Key capabilities of this sweat simulator include: constant ‘sweat’ rate density without bubble-point variation even down to ~1 L/hr/m2; replication of the 2 pores/mm2 pore-density and the ~50 µm texture of human skin; simple gravity-fed flow control; low-cost and disposable construction.
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