Beilstein J. Nanotechnol. 2015, 6, 508–516. doi:10.3762/bjnano.6.53
The reliable production of carbon nanotubes and nanofibres is a relatively new development, and due to their unique structure, there has been much interest in filling their hollow interiors. In this review, we provide an overview of the most common approaches for filling these carbon nanostructures. We highlight that filled carbon nanostructures are an emerging material for biomedical applications.
The filling of TCNSs has shown much promise regarding the synthesis of nanowires, hydrogen storage, and drug delivery. Although most of the research has focussed on the development of the actual methods for filling, there are a number of biomedical applications of these fascinating materials that remain to be explored and developed. In this review, we aimed to provide an overview of the most common methods for filling of SWCNTs, MWCNTs and VGCNFs. Most of the reviewed literature relates to MWCNTs, as this material has been extensively studied. VGCNFs are an emerging material for filling applications, but not all VGCNFs are suitable. For example, the VGCNFs with a “deck of cards” morphology (i.e., a series of parallel graphene sheets stacked on top of each other) cannot be filled due to the lack of a hollow core . SWCNTs have significant promise, however, their high production cost has limited research in the past. As research into the efficient production of pristine SWCNTs has progressed, their cost has correspondingly rapidly decreased, which should lead to future SWCNT filling applications.
This article highlighted TCNSs as a suitable material for applications requiring filled nanostructures, as well as the unique strengths of both CNTs and CNFs. The remaining challenge is to prepare filled TCNS materials that achieve one or both of the following properties: (1) selective drug delivery using nanostructures, which is important for the development of nanosized needles or patches for the localised treatment of diseases; (2) autonomic healing of polymeric materials, such as tough hydrogels, which is important for load-bearing biomedical materials such as cartilage replacement. While there is much research into the filling of SWCNTs and MWCNTs, there is very limited research regarding the filling of VGCNFs, which have been demonstrated to be as efficient (if not more) for certain filling applications such as storage and self-assembly. However, a more reliable and thorough method to completely fill VGCNFs must be established, as current methods either result in partial filling, or can only fill with certain types of materials. In conclusion, it is clear that filled TCNSs offer great opportunities for a broad variety of applications, yet a number of challenges remain to be addressed.