*2.1. Materials*

All cell culture materials and reagents (including MTX, chlorpromazine and filipin) were purchased from Sigma Aldrich, St. Louis, MO, USA. Cell culture dishes, pipettes and other disposable plastics were purchased from Mid Sci, St. Louis, MO, USA. The *MTT* and XTT Cell Viability Assay Kit was obtained from Biotium, New York, NY, USA. The Annexin V-FITC Apoptosis Kit was purchased from Enzo Life Sciences, Inc. (New York, NY, USA) and DiOC18(7) from ThermoFisher Scientific (Waltham, MA, USA). All three-cell lines used colon cancer (CT26WT), and osteosarcoma (K7M2-WT) and a pre-osteoblast cell line (MC3T3-E1) were purchased from ATCC (Manassas, VA, USA).

#### *2.2. Production of Shortened HNTs*

Commercial-grade HNTs (10 g, Sigma Aldrich, St. Louis, MO, USA) were immersed in 50 mL PBS for 24 h and ultra-sonicated for 30 min using a sonicator (Qsonica, Newtown, CT, USA) at 70% power. The solution was allowed to set for 30 min, HNTs were then ultra-sonicated for another 30 min. Then, the mixture was transferred to 50 mL centrifuge tube and centrifuged at 100× *g* for 10 min. The pelleted deposits were collected and dried at 60 ◦C for 2 days. See Figure 1 for details regarding this procedure.

**Figure 1.** The process of reducing the length of halloysite nanotubes (HNTs). Between each step, the composites were washed and filtered using methanol, sodium chloride, a sodium bicarbonate solution, and distilled water (DI).
