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Revision as of 04:47, 17 October 2016


Stanford-Brown 2016

The Problem

The high energy content of ionizing radiation in space poses a severe threat to life, technology, and synthetic materials alike in an extraterrestrial context. Energized subatomic particles generated from nuclear events carry over large distances in space, and are capable of tearing through organic materials and altering molecular bonds. On Earth, the vast majority of space radiation is deflected by the magnetosphere. Much of the radiation that passes through Earth’s magnetic field is then filtered out by the atmosphere, allowing only UV, visible light, and some infrared wavelengths to reach the surface. Extended UV exposure can disrupt the molecular interactions within thin membranes, creating micropores that decrease the material’s structural integrity and impermeability.
Balloons flown in Earth’s stratosphere are offered limited UV protection due to thinning of the atmosphere with increasing altitude. Chief Scientist of World View Enterprises Alan Stern stated that the materials used in his near-space exploration vessels cannot be reused due to the radiation damage they sustain during flight. Representatives of other major ballooning projects such as Google X’s Project Loon and the Stanford Space Initiative’s Balloon team expressed to members of our team that radiation exposure was the most significant factor in limiting the lifespans of their balloons.
On Earth, the main source of concern for radiation damage is ultraviolet radiation (UVR). These wavelengths are between 290 and 400 nm when they hit the Earth’s surface, and do more damage the shorter they get. UV wavelengths between 320 and 400 nm are called UV-A, and are the culprits behind sunburns and cataract formation. UV-A radiation creates indirect DNA damage through the generation of reactive oxygen species (ROS), forming strand breaks in DNA and DNA-protein crosslinks. [2] Shorter wavelengths from 290 to 320 nm are called UV-B wavelengths. UV-B is absorbed directly into DNA and causes damage to DNA at the molecular level. [3] Excessive UV-B exposure can induce significant DNA mutation and cell death, and our bioballoon will be exposed to dangerous amounts of radiation due to its high elevation during flight. Ideally, our balloon coating would have included an interweaving of zinc oxide, a white pigment that excels at blocking and reflecting UV-A and UV-B rays. [4] Zinc oxide is used in many commercial sunscreens, as a solution with as low as 25% zinc oxide content results in protection of at least SPF 20. [5] However, we wanted to produce our UV protector entirely biologically rather than attempting to incorporate an inorganic compound into our membrane. As such, we decided to focus on creating a method of UV protection for our balloon that utilises a melanin coating attached to the balloon’s outer membrane.

References
1. How to Protect Astronauts from Space Radiation on Mars. (2016). NASA. Retrieved 9 October 2016, from http://www.nasa.gov/feature/goddard/real-martians-how-to-protect-astronauts-from-space-radiation-on-mars
2. Brenner, M. & Hearing, V. (2007). The Protective Role of Melanin Against UV Damage in Human Skin†. Photochemistry And Photobiology, 84(3), 539-549. http://dx.doi.org/10.1111/j.1751-1097.2007.00226.x
3. Ultraviolet Radiation: How It Affects Life on Earth : Feature Articles. (2016). Earthobservatory.nasa.gov. Retrieved 9 July 2016, from http://earthobservatory.nasa.gov/Features/UVB/
4. Soni, R. & Toetia, M. (2016). Impact of Zinc Oxide on the UV Absorbance and Mechanical Properties of UV cured films. Presentation, Department of Chemistry, C.C.S. University of Meerut.
5. ZINC OXIDE | ZnO - PubChem. (2016). Pubchem.ncbi.nlm.nih.gov. Retrieved 9 July 2016, from https://pubchem.ncbi.nlm.nih.gov/compound/zinc_oxide#section=Therapeutic-Uses

Our Solution

To install radiation resistance in all of our biomembranes, the team investigated the absorptive properties of melanin and designed a novel binding mechanism to incorporate the pigment directly into materials.
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Melanin-based protection

Melanin Production

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Binding Agent

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Melanin-based protection

Melanin is the primary source of naturally-occurring UV protection for human skin. Darker skin pigmentation resulting from melanin production functions as a UV absorbent, and melanin when used as a sunscreen has been shown to absorb between 50-75% of UVR. [1] Two main types of melanin exist: eumelanin and pheomelanin, with eumelanin being darker and browner in colour and more effective at photoprotection. After significant UV-A absorbance, melanin tends to produce ROS and create single-strand DNA breaks, with pheomelanin being significantly more susceptible to photodegradation than eumelanin. Thus, brown eumelanin was chosen as a good candidate for our balloon’s UV protection.

References
1. Brenner, M. & Hearing, V. (2007). The Protective Role of Melanin Against UV Damage in Human Skin†. Photochemistry And Photobiology, 84(3), 539-549. http://dx.doi.org/10.1111/j.1751-1097.2007.00226.x
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