Natural hollow clay nanotubes and their applications as polymer nanocomposites in tissue engineering
Li Wen Wong, Calvin Bok Sun Goh, Pooria Pasbakhsh, Joash Ban Lee Tan
Abstract
Tissue engineering has garnered considerable attention within the broader field of regenerative medicine that utilizes naturally-occurring nanomaterials as fillers in polymeric scaffolds and as carriers for sustained, targeted drug delivery. These nanomaterials act as functional constructs for the recovery of defective tissues and organs, which may aid in overcoming the current challenges of donor organ shortage. The present article looks into the properties of naturally-occurring nanomaterials, including halloysite nanotubes (Hal), imogolite, and chrysotile, and their potential to improve both the mechanical and biological aspects of polymeric scaffolds in tissue engineering applications. While Hal is natively comprised of hydrous aluminosilicate (primarily in the form of hollow tubes), imogolites are comprised of silanol tetrahedrons and Al–OH octahedrons with typically narrower and shorter dimensions than Hal. Even so, both Hal and imogolites have been found to be highly biocompatible and with negligible cytotoxicities. Conversely, the extensively fibrous and smaller dimensions of chrysotile (compared to Hal and imogolites) have been associated with bioaccumulation and asbestosis, limiting chrysotile applications. Nevertheless, the electrostatically-charged lumens of these nanomaterials enable the encapsulation and sustained release of active agents into the surrounding tissues. Furthermore, the large surface areas and high aspect ratio of both Hal and imogolites greatly enhance the crosslinking and load-bearing capacities of composite polymeric scaffolds; while also providing accessible sites that facilitate cellular attachment and proliferation. This review contributes towards a better understanding of natural nanotube utilization in tissue engineering by highlighting their potential applications to polymer nanocomposites.