Utilization of Carbon Nanotubes in Manufacturing of 3D Cartilage and Bone Scaffolds

Abstract

Cartilage and bone injuries are prevalent ailments, affecting the quality of life of injured patients. Current methods of treatment are often imperfect and pose the risk of complications in the long term. Therefore, tissue engineering is a rapidly developing branch of science, which aims at discovering effective ways of replacing or repairing damaged tissues with the use of scaffolds. However, both cartilage and bone owe their exceptional mechanical properties to their complex ultrastructure, which is very difficult to reproduce artificially. To address this issue, nanotechnology was employed. One of the most promising nanomaterials in this respect is carbon nanotubes, due to their exceptional physico-chemical properties, which are similar to collagens-the main component of the extracellular matrix of these tissues. This review covers the important aspects of 3D scaffold development and sums up the existing research tackling the challenges of scaffold design. Moreover, carbon nanotubes-reinforced bone and cartilage scaffolds manufactured using the 3D bioprinting technique will be discussed as a novel tool that could facilitate the achievement of more biomimetic structures.

Keywords: biomaterials; bioprinting; bone; carbon nanotubes; cartilage; scaffolds; tissue engineering.

Figure 1

Schematic, cross-sectional diagram of healthy articular cartilage: (a) cellular organization in the zones of articular cartilage; (b) collagen fiber architecture.

Figure 2

The hierarchical organization of cortical bone. On the first level, there are fibrils (~10 nm thick), composed of parallel aligned type I collagen strands, mineralized with evenly distributed hydroxyapatite crystals. Those fibrils are arranged in bundles, surrounded by extrafibrillar mineralized platelets. The bundles, arranged in the plywood-like structure form lamellae, where adjacent lamellae may have different orientation of bundles. The layers of concentrically aligned lamellae surrounding the Haversian canal forms a basic structural unit of bone—osteon (170–250 µm in diameter). Taken from [39].

Figure 3

Chondrocyte was grown on perpendicularly aligned, chemical vapor deposition (CVD) synthesized multi-walled carbon nanotubes (MWCNTs), low magnification (a) and high magnification (b). Cytoplasmic extensions are visible. Note the cell adhesion to the scaffold. Phyllopodia bend the nanotubes to their purposes.

Figure 4

Porosity is a crucial factor in designing a scaffold. If pores are too small (a) there is a limited diffusion of nutrients and metabolites, as well as cell infiltration into deeper layers of the scaffold. However, such spatial constraint places cells near each other and therefore promotes proliferation, until the space becomes exhausted. On the other hand, if the pores are bigger (b) the flow of nutrients and cell penetration is much more efficient. Due to the low surface area, cell interactions and adhesion are exacerbated, which leads to slower cell proliferation. The figure is a schematic representation of a porous scaffold and it is not drawn to scale.