# Nanomaterials in Bone Regeneration
## 4 Nanoparticles
### Carbon Nanoparticles
A cryogenic method was used to prepare CS/MW-CNTs/nHAp scaffolds suitable for bone tissue substitution, thus creating a 3D porous scaffold with nHAp clusters on its surface. In combination with MSCs, this type of scaffold showed better biocompatibility, very good mechanical properties, and an increase in apatite level was noted [190]. Further studies showed the appropriate use of CNTs to strengthen bone grafts composed of collagen/HAp nanocomposite. This study demonstrated the possibility of using CNTs instead of collagen, as both the biological and mechanical properties of nanomaterial were improved. It is still necessary to verify whether this replacement will not have a negative impact on bone remodeling and its healing [191]. An unusual but interesting solution, both in terms of biological and mechanical properties, is the combination of CNTs with a polymeric material, such as PCL, PLA, or poly (lactic-co-glycolic) acid (PLGA). Conductive biomaterials enable very good signal transmission from an external source to the seeded cells. Osteoblasts are one of the cells whose properties improved due to an electrical signal [192]. The addition of CNTs to PLA significantly improved the mechanical and surface properties of this polymer, thereby increasing osteoblast adhesion and proliferation. Scaffolds composed of PLA/MW-CNTs with uniformly dispersed nHAp in the nanomaterial showed a high degree of osteoblast differentiation [193]. The incorporation of CNTs into PLGA by electrospinning created a suitable nanocomposite for MSCs to grow. Better adhesion, proliferation, and differentiation in osteoblasts were observed in these cells, and ALP production was significantly higher compared to the control sample. If a third component (nHAp) was added, this nanocomposite deposited a relatively high amount of HAp crystals during mineralization [194]. Other nanomaterials created by combining CNTs with different synthetic polymers, such as polyurethane, polymethacrylate, polypropylene, HA, etc., also showed significantly higher adhesion, proliferation, ALP levels, and mineralization [180]. Graphene, another structural modification of carbon, is also used in biomedicine. Graphene films, which are incorporated into polymers in very small concentrations, significantly improve their physical properties. Graphene in the form of a 3D foam was used for culturing and differentiating human MSCs. The results showed not only promoted cell proliferation in the scaffolds but accelerated differentiation into bone cells [195]. Graphene oxide (GO) structurally forms a kind of thin foils, which have relatively high stiffness and can therefore be used as a suitable horizontal system for cell culture. A scaffold was formed by uniformly dispersing a very small amount of GO slices (0.5 wt%) in the ultrahigh molecular weight PE matrix. Due to the presence of GO, the mechanical properties were significantly improved, as the biocompatibility of PE to osteoblasts was retained [196]. Scaffolds with a very low graphene content, which serves as a reinforcement for nanofibrous polymers, appear to be promising materials in hard tissue substitutions. The results of rheological tests show that the use of the electrospinning preparation of scaffolds allows the GO to be evenly dispersed in the polymer solution and significantly increases the mechanical properties of the polymers despite the very low graphene loading [197]. An interesting and very unusual finding was made by scientists who cultured human osteoblasts on graphene sheets in the presence or absence of FBS. Indeed, it was found that the presence or absence of serum proteins did not affect the initial interaction of cells with graphene, unlike other materials [198]. The GO/graphene-HAp hybrid composite in SBF solution showed significantly increasing HAp formation and higher osteoblast viability [199].