Different factors influence the development‎ and control of ageing. It is well known that progressive telomere shorting is one of the molecular mechanisms underlying ageing. The shelterin complex consists of six telomere-specific proteins which are involved in the protection of chromosome ends. More particularly, this vital complex protects the telomeres from degradation, prevents from activation of unwanted repair systems, regulates the activity of telomerase, and has a crucial role in cellular senescent and ageing-related pathologies. This review explores the organization and function of telomeric DNA along with the mechanism of telomeres during ageing, followed by a discussion of the critical role of shelterin components and their changes during ageing.

The main mechanisms by which nanoparticles influence the bone microniche to direct osteogenesis. Nanoparticles modulate immune responses, induce osteogenic and angiogenic differentiation while suppressing osteoclast activity and differentiation.

Innate immune cells play a crucial role in bone development and repair. Macrophages are the main effector cells in immune responses to implants and are indispensable for bone healing success. The heterogeneity and plasticity of macrophages make them a prime target for immune system modulation to enhance bone repair and regeneration. It is believed that the polarization of macrophage phenotype towards the anti-inflammatory M2, rather than the inflammatory M1 phenotype, promotes osteogenesis. Tissue-engineered bioimplants are potentially capable of producing signals to modulate macrophage polarization. Therefore, development of smart immunomodulatory bioimplants via manipulation of their properties seem a promising strategy for tuning immune responses to optimize bone repair without any unwanted inflammatory reactions. The purpose of the present review is to summarize the currently available studies performed on the effects of macrophage polarization, especially towards M2 phenotype, both in bone repair and in bioimplant-stimulated osteogenesis. Moreover, this literature highlights the need to focus future studies on the development of smart immunomodulatory implants capable of switching macrophage polarization-enhancing bone implant-host tissue integration.