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Inefficient solid waste management of plastics and polymeric materials is one of the global challenges leading to environmental deterioration. This challenge has brought alarming concern to minimize volume of such wastes released into the environment. The concern proposes a solution to the existing problems to some extent by reuse, recycling, and efficient conversion of waste materials into alternative application. Chemical and thermo-mechanical conversion of plastic wastes into energy and their biodegradation were taken into account. Consequently, some newly employed recycling and conversion techniques of plastic wastes, and possible future alternatives with recommendations are reviewed in this article

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Hydroxyapatite (HAp) is the mineral phase of animal bones embedded in a collagen-containing organic matrix. It is a naturally optimized material for the physical support of the bones. Synthetic Hydroxyapatite based biomaterials, hence, find wide applications in orthopedics, dentistry, and tissue engineering due to their biocompatibility, bioactivity, osteoconductivity, and similar chemical composition to that of HAp present in animal bones. Different physicochemical synthetic methods and natural biogenic sources have been reported for the synthesis of nano-hydroxyapatite. However, particle size, aspect ratio, and the distribution of HAp in biomaterials have significant effects to use as bone substitutes and implants. This paper has summarized some synthetic methods of preparing nano-HAp from different biogenic approaches. Further, it focuses on some facile synthetic routes of preparing nano-HAp with controlled particle size with higher crystallinity and native bone architectures. This review article aims to correlate some simplistic and cost-effective biosynthetic approaches of nano-HAp, their size-dependent properties characterization, and biomedical applications.