Covalently Modified Halloysite Clay Nanotubes: Smart Nanomaterials for Drug Delivery Applications

Halloysite nanoclays (HNTs) are promising nanomaterials because of their versatile properties, such as hollow tubular morphology and tunable surface chemistry. HNTs are biocompatible, no toxic and abundantly available at low cost. Due to these characteristics HNTs are suitable for development of hybrid sustainable materials, which are perspective for polymeric matrices reinforcement, active food packaging and drug delivery. HNTs are quite polydisperse in size with a length of ca. 1 m, while the external diameter and the lumen range between 50-80 nm and 10-15 nm, respectively. Chemically, halloysite is composed of gibbsite octahedral sheet (Al-OH) groups on the inner surface and siloxane (Si−O−Si) groups on the external surface. This different chemistry allows the selective modification of HNTs surfaces. We performed several chemical functionalization of HNTs materials to confer properties valuable in specific applications. The introduction of chemical modification of both surfaces (inner lumen and outer surface) is a relevant strategy to tune the nanotube properties. Namely, chemical modification of HNT surfaces allows to obtain nanoarchitecture with targeted affinity through outer surface functionalization and drug cargo ability from the nanotube lumen.