**1. Introduction**

Bone is a part of vertebrate skeleton. It plays a multitude of important roles in the body like imparting structural support, protection of organs, acting as a site for production of blood cells, and also as repertoire of minerals. Bones comprise differentiated cell types, blood vessels, protein, minerals, and vitamins that facilitate their growth and repair system [1]. Bones have an inner and outer layer. The hard-outer layer of bone which is called "cortical bone" is usually tough and strong, whereas the inner spongy part is called "trabecular bone" and is lighter and less dense. Each of these parts comprises different cell types, nonmineral proteinaceous matrix (osteoid), and matrix-deposited inorganic minerals. Another important concept in bone biology and understanding its transformational changes is that of modeling and remodeling. The scenario where the sites of bone formation and resorption are different surfaces of the bone is called bone modeling. This is responsible for increased length and girth of long bone, leading to skeletal development and changes. Bone remodeling on the other hand is important for maintenance of bone mass in adults by replacement of old bone tissue with new ones [2]. Several factors which affect bone, muscles, and joints are responsible for causing diseases

like osteoarthritis (degenerative joint disease), rheumatoid arthritis (autoimmune disease), fibromyalgia (chronic condition of pain in bones, muscles, and tender areas with fatigue) and bone fractures. Aging plays an important role in manifestation of bone-related diseases along with other sub-factors like lifestyle, level of activity, family history, level of physical activity, drug usage, etc. However, in certain clinical situations, the natural bone repair may be too slow or inadequate; therefore, an alternative bone grafting strategy is required to address this problem.
