Magnesium alloys and metal matrix composites (MMCs) are attractive materials for biomedical application. Magnesium has a module of elasticity that is close to that of human bones and it is biocompatible with the human body. Human body fluids make a corrosive environment to magnesium. In addition, different body parts are subjected to cyclic loading reaching a magnitude of about 80 MPa and an estimated total of 106 cycles per year. Therefore, understanding the fatigue behavior of magnesium alloys and magnesium metal matrix composites (MMCs) is an essential aspect especially when they are used as load bearing components. Magnesium has a hexagonal closed-packed (HCP) lattice structure with a c/a ratio of 1.623, and it does not have enough independent slip systems to sustain large plastic deformation. Therefore, magnesium deforms plastically by two different mechanisms: slipping and twinning. Twinning-detwinning deformation is manifested in the cyclic stress-strain response of wrought magnesium alloys when loaded along the working direction. A significant stress asymmetry is usually observed resulting in the devel-opment of high mean stress. Research on magnesium and its alloys is rapidly increasing. This chapter presents different aspects of fatigue, in general, and on magnesium in particular, including experimental method, damage models and fatigue life equation.
The name, magnesium (Mg), was derived from an ancient city in Greece called “Magnesia”where magnesium carbonate was first discovered. It was first isolated in its elemental form by English chemist Sir Humphry Davy in 1808 [1]. In the earth’s crust, magnesium is the sixth most abundant element and occurs in over 60 different minerals with at least 20% of Mg within them. Most commercially important of these minerals include dolomite, magnesite, brucite, and carnallite. Principally, magnesium is extracted from its minerals using a thermal reduction process [2]. Magnesium is also the third most abundant metal ion in seawater. Despite magnesium being only 0.13% of seawater, seawater remains an almost inexhaustible source for its extraction. Magnesium is extracted from seawater or brine using the electrolytic process of magnesium chloride [2]. Of the two extraction processes, the thermal reduction process is known to yield a higher purity of 99.99%, while the electrolysis process can achieve purity limited to 99.8%. Until the 1990s, the USA and Canada dominated the production of magnesium; however, the industrial revolution in China in the late 1990s turned the tables for magnesium production due to its lower operational (energy and labor) costs. It is estimated that 85% of the global magnesium production is currently done by China, and most of the remainder is produced by Russia, Turkey, Spain, Austria, etc. [3].
The metabolic syndrome is a cluster of metabolic risk factors that include obesity, hyperglycemia, dyslipidemia, and elevated blood pressure. This syndrome is of particular importance given its large prevalence in the general population worldwide and because it is a predisposing condition that increases the risk of cardiovascular disease and diabetes mellitus. The anti-atherogenic effects of the magnesium profile appear to involve the modification of several enzymes linked with lipid metabolism, inhibiting the activity of lecithin cholesterol acyl transferase and HMG-CoA reductase, and stimulating the activity of lipoprotein lipase. Magnesium is involved in more than 300 enzymatic reactions, including glycogen breakdown, fat oxidation, and ATP synthesis. In addition, disorders of intracellular magnesium homeostasis decrease tyrosine kinase activity at insulin receptors, increasing insulin resistance, and negatively influence glucose-stimulated insulin secretion, decreasing beta-cell function. Magnesium inhibits the effects of calcium from vascular smooth muscle sarcoplasmic reticulum by competing for a calcium receptor on a calcium-regulated efflux channel.
This chapter discusses potential applications of magnesium as adjunctive therapy in cutaneous conditions including pseudoxanthoma elasticum, psoriasis, hidradenitis suppurativa, cutaneous lupus erythematosus, mycosis fungoides, melanoma, acne vulgaris, melasma, Hailey–Hailey disease, and atopic dermatitis. Magnesium is a nutritionally essential element that is necessary for many physiologic processes in humans. It is a critical factor in bone mineralization, muscle contraction, nerve impulse transmission, and a necessary co-factor for over 300 enzymes. Magnesium has several dosage formulations pertaining to cutaneous treatment, including oral supplementation and topical variants. The dietary allowance of magnesium recommended by the Food and Drug Administration is up to 420 mg per day for adults. Fumaric acid esters (FAE) are another prospective oral supplementation of magnesium. Fumaderm is the only licensed FAE in Germany; it is comprised of dimethylfumarate and calcium, magnesium, and zinc salts of monoethyl hydrogen fumarate tablets.
The growing concerns regarding fuel consumption within the aerospace and transportation industries make the development of fuel-efficient systems a significant engineering challenge. Currently, materials are selected because of their abilities to satisfy engineering demands for good thermal conductivity, strength-to-weight ratio, and tensile strength. These properties make magnesium an excellent option for various industrial or biomedical applications, given that is the lightest structural metal available. The utilization of magnesium alloys, however, requires suitable welding and joining processes that minimizes microstructural changes while maintaining good joint/bond strength. Currently, magnesium are joined using; mechanical fastening, adhesive bonding, brazing, fusion welding processes or diffusion bonding process. Fusion welding is the conventional process used for joining similar metals. However, the application of any welding technique to join dissimilar metals presents additional difficulties, the principal one being; the reaction of the two metals at the joint interface can create intermetallic com pounds that may have unfavorable properties and metallurgical disruptions which dete-riorates the joint performance. This chapter investigates the welding and joining technologies that are currently used to join magnesium alloys with emphasis on the development of multi-material structures for applications in the biomedi cal industries. Multi-material structures often provide the most efficient design solution to engineering challenges.
Most studies that use magnesium oxide, or other poorly absorbed forms of magnesium, make no mention of the wide range of absorption characteristics of various magnesium formulations alluding to the lack of appreciation of this important variable. Studies that correlate magnesium levels with attention deficit disorder (ADD) and attention deficit hyperactivity disorder (ADHD) or use magnesium supplements to treat these disorders are poorly done and have multiple research design flaws, though there are notable exceptions. ADHD has multiple variants but is commonly thought to be exclusive to children; adult ADD and ADHD, though, may be among the most underdiagnosed psychiatric disorders and concomitant with the prediabetes and diabetes epidemic may be present in unprecedented numbers. Symptoms of adult ADD and ADHD can include "inattention, distractibility, restlessness, labile mood, quick temper, overactivity, disorganization, and impulsivity". Electroencephalograms are useful non-invasive measures of brain electrical activity that correlate with changes in cortical activity and function.
