The conversion of waste obtained from agricultural processes into biocompatible materials (biomaterials) used in medical surgery is a strategy that will add more value in waste utilization. This strategy has successfully turned the rather untransformed wastes into high value products. Eggshell is an agricultural waste largely considered as useless and is discarded mostly because it contributes to pollution. This waste has potential for producing hydroxyapatite, a major component found in bone and teeth. Hydroxyapatite is an excellent material used in bone repair and tissue regeneration. The use of eggshell to generate hydroxyapatite will reduce the pollution effect of the waste and the subsequent conversion of the waste into a highly valuable product. In this paper, we reviewed the utilization of this agricultural waste (eggshell) in producing hydroxyapatite. The process of transforming eggshell into hydroxyapatite and nanohydroxyapatite is an environmentally friendly process. Eggshell based hydroxyapatite and nanohydroxyapatite stand as good chance of reducing the cost of treatment in bone repair or replacement with little impact on the environment.

Antioxidative compounds play a vital role to inhibit the oxidation of oxidizable products and influences the body defense system against Reactive Oxygen Species (ROS), which are harmful byproducts engendered during normal aerobic cellular respiration. ROS are specialized class of highly reactive molecules that originates during oxygen metabolism, whereas extensive evidences indicate the involvement of ROS in the development of degenerative diseases in humans. Despite the fact that synthetic antioxidants such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are threat to human's health; they are widely employed as chemical preservatives to avert potential deterioration of food products. Several toxicological findings reveal that natural antioxidants are capable of providing protection against free radical-related diseases, cancer and other cardiovascular infections. In cognizance with these facts, natural antioxidant attracts a great deal of research interest; therefore, this review provides a comprehensive and an up-to-date overview of the three most essential natural plant antioxidants; their antioxidative properties, methods of analysis and evaluation. These Polyphenols comprise: Phenolic acid, an essential polyphenol that are broadly dispersed in plants to exert positive influence on oxidative stress; Flavonoid, an ubiquitous antioxidant that functions in free radical scavenging, metal ion chelation and enzymes inhibition to suppress the synthesis of free radicals; and Tannic acid, a water soluble anti-nutrient that acts to precipitate alkaloids & proteins, reduce mineral & vitamin utilization and restrict the activities of digestive enzymes. In conclusion, a variety of plant species were characterized to indicate in vitro antioxidative properties.

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