*3.1. Bone Regeneration*

A perfect bone and cartilage repair scaffold materials should neither suppress the activity of normal cells nor induce toxicity during and after implantation [469]. Figure 23 illustrates the basic cycle of tissue regeneration using nanobiomaterials or derived scaffolds [255].

**Figure 23.** Basic principle procedures for tissue engineering. (Adapted with permission from ©2019 American Chemical Society [255]).

The various synthetic nanostructured matrices are able to stimulate cell differentiation with a focus on preserving the structural features, composition, and biology of natural bone tissue [470]. The main constituents used so far in this regard are nano-hydroxyapatite [471], anodized titanium [472], collagen [473], and silver-incorporated calcium silicate. Nanobiomaterials (1–100 nm) generated from polymers, metals, ceramics, and composites act as effective constituents for hard tissue and play a significant role in osteointegration on nanostructured surfaces [474].

Alumina has been widely used for the fabrication of knee and hip joint prosthesis with low wear rates [475]. Bioactive glasses were used as a prosthesis for the restoration of the ossicular chain of the middle ear and oral implant to preserve the alveolar ridge from bone resorption [476,477]. Different metal oxides such as ZnO, Fe2O3, TiO2, and Al2O3, and polymers such as PLA, PGA, and their copolymers were used with bioactive glass systems for hard tissue engineering applications [478,479].
