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Waves and electromagnetic radiation
Published in Andrew Norton, Dynamic Fields and Waves, 2019
Most of the ultraviolet radiation (radiation with wavelengths from about lOnm to 400 nm) found on Earth originates in the Sun. UV radiation is readily absorbed by objects such as the human body and interacts with body chemicals. This is responsible for tanning — an effect that can be reproduced using UV-emitting fluorescent tubes (Figure 2.49a). In small doses, this can be harmless or even beneficial; for example, UV radiation is responsible for production of vitamin D by the body. A deficiency of vitamin D causes the condition known as rickets, in which the bones of growing children are malformed and fail to harden. In fact, the earliest life forms on this planet may have started because of the ability of UV radiation from the Sun to facilitate reactions between ammonia, methane, carbon dioxide and water. (These reactions form amino acids, the basic building blocks of proteins, which are, in turn, the essential ingredients of all life forms.) However, exposure to shorter-wavelength UV waves can be dangerous, leading to melanoma (skin cancer; see Figure 2.49b) and to eye cataracts.
Vitamin D-conjugated gold nanoparticles as functional carriers to enhancing osteogenic differentiation
Published in Science and Technology of Advanced Materials, 2019
Haram Nah, Donghyun Lee, Min Heo, Jae Seo Lee, Sang Jin Lee, Dong Nyoung Heo, Jeongmin Seong, Ho-Nam Lim, Yeon-Hee Lee, Ho-Jin Moon, Yu-Shik Hwang, Il Keun Kwon
Besides traumas, the most common contributing factors to bone fractures originate from structural exacerbation of bones and their low bone mineral density. Vitamin D is a well-known essential nutrient to the human body that is obtainable from supplements, diet, and sun exposure [5]. Synthesis of vitamin D occurs after exposure to sunlight through the liver or the kidney or it is obtained from the diet. The active vitamin D metabolite, 1α, 25-dihydroxyvitamin D3 (1,25(OH)2D3), assumes a vital function in skeletal homeostasis by regulating intestinal absorption of calcium and phosphate [6,7]. In addition, the active form of vitamin D plays a role in inhibition of osteoclastogenesis [8]. On the other hand, deficiency of vitamin D contributes to rickets in children and osteomalacia in adults [9]. Song et al. [10] investigated the osteogenic differentiation of human recombinant bone morphogenetic protein-2 (BMP-2) and vitamin D on adipose stem cells. Piek et al. [11] reported that vitamin D strongly improves the expression of genes on human mesenchymal stem cells as an enhancer of BMP-2-induced osteogenesis. However, adequate intake of vitamin D is not easy for modern people who are customarily indoors. Therefore, many researchers have attempted delivery of vitamin D through nanoparticles [12].