Non-eroding drug-releasing implants with ordered nanoporous and nanotubular structures: concepts for controlling drug release

To address the limitations of systemic drug delivery, localized drug delivery systems (LDDS) based on nano-engineered drug-releasing implants are recognized as a promising alternative. Nanoporous anodic alumina (NAA) and nanotubular titania (TNT) fabricated by a simple, self-ordering electrochemical process, with regard to their outstanding properties, have emerged as one of the most reliable contenders for these applications. This review highlights the development of new LDDS based on NAA and TNT, focusing on a series of strategies for controlling their drug release characteristics that are based on: modification of their nanopore/nanotube structures, altering internal chemical functionalities, controlling pore openings by biopolymer coatings and using polymeric micelles as drug nano-carriers loaded within the implants. Several new strategies on externally triggered stimuli-responsive drug release for LDDS are also reviewed, and their significance toward the development of advanced smart implants for localized therapy is discussed. Finally, the review is summarized with conclusions and future prospects in this research field.