Exogenous Physical Irradiation on Titania Semiconductors: Materials Chemistry and Tumor‐Specific Nanomedicine

Abstract

Titania semiconductors can be activated by external physical triggers to produce electrons (e−) and holes (h+) pairs from the energy‐band structure and subsequently induce the generation of reactive oxygen species for killing cancer cells, but the traditional ultraviolet light with potential phototoxicity and low‐tissue‐penetrating depth as the irradiation source significantly hinders the further in vivo broad biomedical applications. Here, the very‐recent development of novel exogenous physical irradiation of titania semiconductors for tumor‐specific therapies based on their unique physiochemical properties, including near infrared (NIR)‐triggered photothermal hyperthermia and photodynamic therapy, X‐ray/Cerenkov radiation‐activated deep‐seated photodynamic therapy, ultrasound‐triggered sonodynamic therapy, and the intriguing synergistic therapeutic paradigms by combined exogenous physical irradiations are in focus. Most of these promising therapeutic modalities are based on the semiconductor nature of titania nanoplatforms, together with their defect modulation for photothermal hyperthermia. The biocompatibility and biosafety of these titania semiconductors are also highlighted for guaranteeing their further clinical translation. Challenges and future developments of titania‐based therapeutic nanoplatforms and the corresponding developed therapeutic modalities for potential clinical translation of tumor‐specific therapy are also discussed and outlooked.

Remotely Activated Nanoparticles for Anticancer Therapy

“…9c regarding the ROS generation of HeLa cells W/O UV stimulation and W/O lipid-coated ZnO NPs (ZnO-DOPC NPs), it was highlighted that only in the presence of ZnO-DOPC NPs and UV light there was ROS production, responsible of the observed cell death reported with the MTT assay [130]. Titania, another semiconductor material characterized by a band gap energy comparable to zinc oxide, possesses almost the same light-responsive properties, and additionally, it is associated with a very low toxicity [19,125]. Several examples of titania NPs have been thus proposed for PDT [19,131,132].…”

“…In the last years, several researchers have proposed a new anticancer therapeutic approach based on the conjugation of two different components, i.e., an external physical stimulation and a NP, which can be remotely activated by the stimulation. Both the stimulation and the NP themselves are administered individually at a harmless dose, however when administered simultaneously, their synergy results in the cancer cell death, also limiting the negative outcomes for the surrounding tissues [16][17][18][19]. Several physical stimulations have been employed so far for this purpose, such as radiations [17], radiofrequencies [20], microwaves [21], light [22], and mechanical waves [16].…”

Two-dimensional nanomaterials: fascinating materials in biomedical field

“…As to TiO 2 , it has significantly different properties but a similar structure to MnO 2 . As a semiconductor, TiO 2 possesses good optical absorption at UV region to generate 1 O 2 , making it possible to act as PDT agent [121]. Much effort has been devoted to developing TiO 2 -based nanocomposite for inhibiting electron-hole pair recombination and expanding the light response to visible region.…”

Energy‐converting biomaterials for cancer therapy: Category, efficiency, and biosafety

“…Importantly, Cu 2‐x S‐enabled synergistic therapy could efficiently eliminate tumor cells. Comparatively, metal (Fe, Ni, Co, and Cu) phosphide‐based photo‐converted H‐ECBs have been successfully synthesized for hyperthermia recently by Zhang, Yan, and Chen (2018). For instance, Liu, Wu, et al (2019) constructed biocompatible ferrous phosphide biomaterials (FP) for imaging‐guided synergetic CDT/photo hyperthermia.…”