**5. Drug delivery vehicle**

Nano titania holds a higher reputation among various nanodrug delivery materials due to its amenability to a vast array of surface functionalization for targeting tissues, easy forming composites with other metals, porous texture, and highly biocompatible nature [46]. Its excretion also occurs via a standard excretory route, i.e., the hepatourinary system. Nano titania has been reported to carry not only anticancer drugs but also other types of drugs, such as dexamethasone [47], DNA fragments [48], norfloxacin [49], ciprofloxacin [50], and aspirin [51], etc.

TiO2 nanowhiskers were employed in cancer therapeutics to deliver Temozolomide (TMZ) to Glioblastoma Multiforme (GBM) orthoptic models. These TiO2 nanowhiskers traversing the Blood-Brain Barrier (BBB) were accelerated by ultrasonication. Additionally, the ultrasound could also assist in releasing TMZ from TiO2 and generate ROS to induce apoptosis [52]. Likewise, Kim et al. have also reported ultrasounddriven doxorubicin delivery to cancer cells by TiO2 nanoparticles [53]. Among other anticancer drugs, 5 fluorouracil drug delivery to cancer cells by ZnO-doped TiO2 was performed by Faria et al. The ZnO doping could shift their absorption from UV (TiO2 only) to red (TiO2-ZnO), making it a perfect candidate for photodynamic therapy [54]. Liposome-covered TiO2 nanotubes have also delivered the 5 fluorouracil to HeLa cells [55]. Doxorubicin's successful loading on TiO2 nanotubes and efficient delivery to cancer cells is another example of TiO2 employment as a drug delivery vehicle. The drug release was lower pH dependent [56]. Similarly, paclitaxel delivery via Polyethylene Glycol (PEG) and folic acid surface decorated TiO2 nanoparticles was reported by Venkatasubbu et al. [57].

Not only in cancer theranostics but TiO2's role as a vehicle in other diseases, including rheumatoid arthritis, has also been explored. The porphyrin derivative, i.e., Tetra Sulphonatophenyl Porphyrin (TSPP), was loaded on TiO2 nanowhiskers by an adsorption process assisted by its porous nature [58–60]. The TiO2 could deliver the TSPP to inflamed tissue and release it upon photoactivation with 532 nm light.
