Figure 1.

Time trends for the number of articles found in the PubMed database (http://www.ncbi.nlm.nih.gov/pubmed/) (accessed 20 March 2014) by search using “carbon nanotubes” and “biomaterials” as keywords. Recent years have seen a rapidly increasing number of research articles on the application of CNTs to biomaterials; the number has been soaring since 2005, suggesting that the application of CNTs to biomaterials has become a highly competitive research field worldwide over the past few years. This graph indicates only a time course, and numerous articles on biological applications of CNTs do exist that cannot be captured with these two keywords.