New drug-delivery systems have remained a challenge for pharmaceutical scientists due to the use of expensive polymers and the low loading capacity of prepared nanoparticles. There is pressure to develop formulations that contain not only cheaper materials but also have controlled-release properties. Halloysite nanotubes (HNTs) are a naturally occurring clay mineral similar to kaolin, possessing a special particle shape in the form of an ultramicroscopic multilayered hollow cylinder. Its uses encompass a wide range in anticancer therapy, sustained- and controlled-release drug-delivery systems, cosmetics, delivery of proteins, vaccines and genes. These advantages are due to its biocompatibility, significant mechanical strength and natural availability. The surfaces of the tubules can be modified by coating different polymers for application in the drug-delivery system. This review is focused on the various aspects of HNTs such as structure, properties, loading methods, applications and characterizations.
