Fig. 8. Selective drug delivery by lumen-capped halloysite nanotubes (HNTs) (A) TEM image of HNTs without end-capping; (B) TEM image of brilliant green loaded HNTs; (C) SEM image of HNTs with open lumen; (D) SEM image of HNTs with dextrin capped on the lumen end.¹³⁷.