While the earlier research in drug delivery has been focused on development of drugs, present methodologies target development of the delivery device itself (1–3). Implantable drug delivery devices offer various advantages such as maintenance of therapeutic blood levels, improved patient compliance, and improved safety (4). Nanorobots capable of treatment, prophylaxis, and diagnosis represent the next generation of drug delivery devices (5,6). Carbon nanotubes have been developed to seek and destroy tumor cells (7). Recently, Martin et al. tailored the width of microfabricated nanochannels to solute size to control diffusion kinetics of macromolecules (8).
In this study, a nanoporous metal surface has been characterized for purpose of drug delivery. Drug loading into nanopores can be achieved using solutions, colloidal solutions, or polymer–drug systems. Early reports in literature have suggested use of lithography techniques for fabrication of nanostructures (9,10). Silicon wafers are coated with a combination of gold and silver. Gold is selected as a suitable surface material because it has been extensively used in development of novel nanodiagnostic tools due to its mechanical stability and biocompatibility (11–13). In photolithography, a photomask is used to transfer the pattern onto the wafer and a layer of photosensitive polymer (photo-resist) is applied using spin coating technique. The wafers are then exposed to ultraviolet light. The mask protects the portion of the wafer it covers, whereas the uncovered part gets etched by light. Silver, which is used as a sacrificial material, is precipitated out leaving, nanopores behind.
In the present study, standard metric techniques, namely scanning electron microscope (SEM) and atomic force microscope, were used for characterization of the nanopores. The dimensions of the nanopores were estimated, and the measurements were used to determine the total volume of pores available for drug loading. For purpose of estimation, a bare metal stent was used as a reference. Hence, the volume of nanopores if they were built on a stent surface was calculated.
In this study, nanopores were loaded using methyl orange, pH indicator (14). Poly (2-octyl cyanoacrylate) was used as a the polymer matrix because of its strong adhesive properties, biocompatibility, and as a drug carrier (15–17). It is also approved by FDA and is being currently used as a tissue adhesive (18). The role of the polymer here is to act as a sealing film formation to limit the rapid release of methyl orange from the nanopores.