Applications of Carbon Nanotubes in Bone Regenerative Medicine

Abstract

Scaffolds are essential for bone regeneration due to their ability to maintain a sustained release of growth factors and to provide a place where cells that form new bone can enter and proliferate. In recent years, scaffolds made of various materials have been developed and evaluated. Functionally effective scaffolds require excellent cell affinity, chemical properties, mechanical properties, and safety. Carbon nanotubes (CNTs) are fibrous nanoparticles with a nano-size diameter and have excellent strength and chemical stability. In the industrial field, they are used as fillers to improve the performance of materials. Because of their excellent physicochemical properties, CNTs are studied for their promising clinical applications as biomaterials. In this review article, we focused on the results of our research on CNT scaffolds for bone regeneration, introduced the promising properties of scaffolds for bone regeneration, and described the potential of CNT scaffolds.

Keywords: bone defects; bone regeneration; carbon nanotubes; scaffolds.

Figure 1

Scaffolds for bone regeneration include biodegradable and nonbiodegradable scaffolds, as well as composite scaffolds comprised of a combination of each material. PCL (polycaprolactone), BCs (bioresorbable ceramics), BG (bioactive glass), PLLA (poly-l-lactic) acid, PEEK (polyetheretherketone).

Figure 2

(a) Scanning electron microscope (SEM) image of a carbon nanotube porous block (CNTp). Scale bar, 100 μm. (b) SEM image of CNTp. Scale bar, 10 μm. (c) When a scaffold composed of interconnected porous hydroxyapatite ceramics (IP-CHAs) was immersed in a bovine serum albumin (BSA) solution, more protein was adsorbed to CNTp and the protein concentration in the solution was reduced. Image is modified from a study by Tanaka et al. [51].

Figure 3

(a) SEM image of multi-walled carbon nanotubes (MWCNT)-coated collagen scaffold, (b) SEM image of the internal pores of MWCNT-coated sponge. Fibers can be observed on the surface of MWCNTs. Reproduced with permission from [87] Elsevier, 2011. (c) SEM image of collagen/MWCNT composite scaffold. MWCNT aggregates were confirmed within the collagen fiber (white arrows). Reproduced with permission from [88] Elsevier, 2016.

Figure 4

Survival curve of rasH2 mouse with intravenous administration of MWCNTs. The experiment was performed with n = 15 in each group. Even in the group without MWCNT administration, no significant difference was found between the vehicle group and the mortality rate. Image is modified from a study by Sobajima et al. [94].

Figure 5

(a) The microcomputed tomography (μCT) image of ectopic bone formed at three weeks after subcutaneous implantation of scaffold with recombinant human bone morphogenetic protein-2 (rhBMP-2) in a mouse model. Ectopic bone formation comparable to that of the MWCNT block was found in the polyethylene terephthalate (PET)-reinforced collagen scaffold. Image is modified from a study by Tanaka et al. [74]. (b) In a mouse calvarial defect model, critical size bone defects were repaired with new bone in both the IP-CHA and CNTp groups. Image is modified from a study by Tanaka et al. [51].

Figure 6

Characteristics of CNT scaffolds. The material properties of CNTs are suitable for bone regeneration scaffolds due to their biocompatibility, structure, mechanical properties, and ability to provide sustained release.