Halloysite clay nanotubes for controlled delivery of chemically active agents

In this work we explored the capabilities of halloysite nanotubes as capsules for encapsulation and controlled delivery of the chemically and biologically active substances. Halloysite is a two-layered aluminosilicate which has a predominantly hollow tubular structure in the submicron range and is chemically similar to kaolinite [1, 2]. In the first section of this work, we analyzed the structure of the halloysite nanotubes as well as its capability to encapsulate and deliver biologically and chemically active agents, similarities and differences between release characteristics of different agents and how these differences relate with their chemical structure. Models were used to describe the release characteristics of the active agents. Study of the interaction between loaded agents and halloysite nanotubes provides better understanding of the release characteristics of the loaded agents and how halloysite can be implemented for technological and medical applications. The second part of the work deals with self-healing coatings produced on the basis of halloysite nanotubes loaded with corrosion inhibitors. Self-healing coatings are one of the effective methods to protect metals from corrosion and deterioration. The difference between self-healing coatings and the usual coatings is the ability of the first to recover after the formation of the damages due to external or internal stresses. High efficiency of the self- healing coatings produced by halloysite nanotubes were demonstrated on 110 Copper alloys and 2024 aluminum alloys. Controlled delivery of the corrosion inhibitors with additional encapsulation of the halloysite nanotubes by synthesizing stoppers at tube endings was also demonstrated. Additional encapsulation of the halloysite nanotubes may be necessary when slow release of the loaded agents is required or rapid convection of the liquid in the surrounding environment takes place (since this may cause rapid release of the loaded agents without additional encapsulation). The third part of this work deals with pharmaceutical applications of the halloysite nanotubes. Toxicity analysis was performed by using MCF-7 and HeLa cells since this is the main issue to be considered before using halloysite for any technological and medical applications. Halloysite nanotubes were readily taken up by the cells and cells survived for a reasonably long time after uptake indicating the biocompatible nature of the halloysite nanotubes. The possibility to encapsulate glycerol, a skin moisturizing agent, was also demonstrated for pharmaceutical applications. It was shown that halloysite has a huge capability for encapsulating a wide range of pharmaceuticals and effectively deliver over a long time range which may increase the quality of pharmaceutical products