Titanium-based nanomaterials for cancer theranostics

The research of titanium-based nanomaterials (Ti-based NMs) has gradually expanded from the fields of photocatalysis, electronics, energy, and engineering to biomedicine in recent years. As a non-toxic transitional metal, Ti has been used to construct various nanomaterials with unparalleled structural, compositional, and physicochemical features combined with multitudinous alluring properties. These excellent and unique properties endow Ti-based NMs that have broad biomedical application potential. Ti-based NMs mainly include titanium oxides, titanium carbides, titanium nitrides, titanium sulfides, titanium hydrides, titanium-organic coordination compounds, and their nanocomposites. In this review, we mainly summarize the preparation, surface modification, and their recent progress of Ti-based NMs in cancer theranostics. The application of Ti-based NMs has gradually expanded from the simple drug delivery systems to versatile platforms for multiple therapies, including photothermal therapy (PTT), photodynamic therapy (PDT), and sonodynamic therapy (SDT), etc. To significantly improve the therapeutic efficiency of tumors and reduce the side effects compared with the single therapy, Ti-based NMs have been widely used in combination therapy. Moreover, the single/multi-modal imaging based on Ti-based NMs are also briefly introduced, as well as the strategies to enhance the diagnostic effectiveness. This review highlights the theranostic applications of Ti-based NMs with various composition, structure, and size. To promote the pre-clinical transformation of Ti-based NMs, the toxicity evaluation is also systematically discussed. In addition, the future challenge and perspective are briefly summarized.