Carbon nanotubes as functional excipients for nanomedicines: II. Drug delivery and biocompatibility issues

Carbon nanotubes (CNTs) have potential novel application in nanomedicine as biocompatible and supportive substrates, and as pharmaceutical excipients for creating versatile drug delivery systems. In the second part of this two-part review we focus on the application of CNTs as potential drug delivery systems via chemical functionalization of CNTs for exterior binding of therapeutic and biologically relevant molecules, and via encapsulation of these molecules within the inner cavities of CNTs. We review experimental results of CNT-mediated delivery of small molecules, DNA, proteins, and vaccines, and the potential of CNTs as matrices to support and stimulate neural growth. Last, we examine some toxicological and biocompatibility issues related to the use of CNTs as pharmaceutical excipients and discuss attributes that affect toxicity, such as structure (single-walled vs. multi-walled CNTs), length and aspect ratio, surface area, degree of aggregation, extent of oxidation, surface topology, bound functional group(s), and method of manufacturing.