Carbon nanotubes (CNTs) have been used in various fields as composites with other substances or alone to develop highly functional materials. CNTs hold great interest with respect to biomaterials, particularly those to be positioned in contact with bone such as prostheses for arthroplasty, plates or screws for fracture fixation, drug delivery systems, and scaffolding for bone regeneration. Accordingly, bone-tissue compatibility of CNTs and CNT influence on bone formation are important issues, but the effects of CNTs on bone have not been delineated. Here, it is found that multi-walled CNTs adjoining bone induce little local inflammatory reaction, show high bone-tissue compatibility, permit bone repair, become integrated into new bone, and accelerate bone formation stimulated by recombinant human bone morphogenetic protein-2 (rhBMP-2). This study provides an initial investigational basis for CNTs in biomaterials that are used adjacent to bone, including uses to promote bone regeneration. These findings should encourage development of clinical treatment modalities involving CNTs.

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There is increasing interest in the unique biological and medical properties of carbon nanotubes (CNTs), and it is expected that biomaterials incorporating CNTs will be developed for clinical use. There has been a great deal of progress in improving the various properties of CNTs for use in biomaterials and for promotion of tissue regeneration as scaffold materials. The effects of CNTs on cells and tissues are extremely important for their use in biomaterials. This tutorial review clarifies the current state of knowledge in the interdisciplinary field of CNT-based nanobiotechnology to determine whether CNTs may be useful in biomaterials. Future perspectives in this rapidly developing field will also be discussed.

Carbon fibers are state-of-the-art materials with properties that include being light weight, high strength, and chemically stable, and are applied in various fields including aeronautical science and space science. Investigation of applications of carbon fibers to biomaterials was started 30 or more years ago, and various products have been developed. Because the latest technological progress has realized nano-level control of carbon fibers, applications to biomaterials have also progressed to the age of nano-size. Carbon fibers with diameters in the nano-scale (carbon nanofibers) dramatically improve the functions of conventional biomaterials and make the development of new composite materials possible. Carbon nanofibers also open possibilities for new applications in regenerative medicine and cancer treatment. The first three-dimensional constructions with carbon nanofibers have been realized, and it has been found that the materials could be used as excellent scaffolding for bone tissue regeneration. In this critical review, we summarize the history of carbon fiber application to the biomaterials and describe future perspectives in the new age of nano-level control of carbon fibers (122 references).

Since attention has been paid to the use of multiwalled carbon nanotubes (MWCNTs) as biomaterials in contact with bone, it is critical to understand the reaction of bone cells to MWCNTs. We show that MWCNTs inhibit osteoclastic bone resorption in vivo and that MWCNTs inhibit osteoclastic differentiation and suppressed a transcription factor essential for osteoclastogenesis in vitro. These results suggest that MWCNTs have beneficial effects on bones when they are used as biomaterials.

Inorganic polyphosphates [Poly(P)] are often distributed in osteoblasts. We undertook the present study to verify the hypothesis that Poly(P) stimulates osteoblasts and facilitates bone formation. The osteoblast-like cell line MC 3T3-E1 was cultured with Poly(P), and gene expression and potential mineralization were evaluated by reverse-transcription polymerase chain-reaction. Alkaline phosphatase activity, von Kossa staining, and resorption pit formation analyses were also determined. The potential role of Poly(P) in bone formation was assessed in a rat alveolar bone regeneration model. Poly(P) induced osteopontin, osteocalcin, collagen 1alpha, and osteoprotegerin expression and increased alkaline phosphatase activity in MC 3T3-E1 cells. Dentin slice pit formation decreased with mouse osteoblast and bone marrow macrophage co-cultivation in the presence of Poly(P). Promotion of alveolar bone regeneration was observed locally in Poly(P)-treated rats. These findings suggest that Poly(P) plays a role in osteoblastic differentiation, activation, and bone mineralization. Thus, local poly(P) delivery may have a therapeutic benefit in periodontal disease.

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Carbon nanotubes (CNTs) possess exceptional mechanical, thermal, and electrical properties, facilitating their use as reinforcements or additives in various materials to improve the properties of the materials. Furthermore, chemically modified CNTs can introduce novel functionalities. In the medical field, biomaterials are expected to be developed using CNTs for clinical use. Biomaterials often are placed adjacent to bone. The use of CNTs is anticipated in these biomaterials applied to bone mainly to improve their overall mechanical properties, for applications such as high-strength arthroplasty prostheses or fixation plates and screws that will not fail. In addition, CNTs are expected to be used as local drug delivery systems (DDS) and/or scaffolds to promote and guide bone tissue regeneration. However, studies examining the use of CNTs as biomaterials still are in the preliminary stages. In particular, the influence of CNTs on osteoblastic cells or bone tissue is extremely important for the use of CNTs in biomaterials placed in contact with bone, and some studies have explored this. This review paper clarifies the current state of knowledge in the context of the relationship between CNTs and bone to determine whether CNTs might perform in biomaterials in contact with bone, or as a DDS and/or scaffolding for bone regeneration.