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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.

Halloysite nanotubes (Hal) with unique nanosized tubular structures are promising nanoclay for potential applications as reinforcement fillers, anticorrosion coatings, as well as drug carriers, and adsorbents. Thus far, previous studies on acid treatment of Hal have focused only on Hal from a single source under various conditions of acid strength, temperature, and treatment duration. This study is the first to characterize and compare the effects of acid treatment on three types of Hal (Dragonite (DG), HalloPure (HP), and Camel Lake (CLA)) originated from different geological deposits, and the results considered in terms of their suitability for various applications. Analyses revealed porous tubular structure with an increased lumen diameter of up to 78% and improved surface area from 54 m2 g−1 to 160 m2 g−1 on acid-treated CLA (acid-CLA). By comparison, lumen diameters were reported to increase by only 46% and 52% for acid-DG and acid-HP, respectively. Despite that, crystallinity of acid-DG showed the most reduction, from 64.5% to 59.4%, with a high recorded surface area of 229 m2 g−1, whereas crystallinity of acid-HP showed the least reduction from 62.5% to 61.1% with a surface area of 121 m2 g−1. Therefore, the obtained results support the hypothesis that various Hal can be affected differently by acid treatment, and not all types of Hal are suitable for acid treatment, especially for those intended for use as reinforcement materials.