Preparation of TiH1.924 nanodots by liquid-phase exfoliation for enhanced sonodynamic cancer therapy

Abstract

Metal hydrides have been rarely used in biomedicine. Herein, we fabricate titanium hydride (TiH_1.924) nanodots from its powder form via the liquid-phase exfoliation, and apply these metal hydride nanodots for effective cancer treatment. The liquid-phase exfoliation is an effective method to synthesize these metal hydride nanomaterials, and its efficiency is determined by the matching of surface energy between the solvent and the metal hydrides. The obtained TiH_1.924 nanodots can produce reactive oxygen species (ROS) under ultrasound, presenting a highly efficient sono-sensitizing effect. Meanwhile, TiH_1.924 nanodots with strong near-infrared (NIR) absorbance can serve as a robust photothermal agent. By using the mild photothermal effect to enhance intra-tumoral blood flow and improve tumor oxygenation, a remarkable synergistic therapeutic effect is achieved in the combined photothermal-sonodynamic therapy. Importantly, most of these TiH_1.924 nanodots can be cleared out from the body. This work presents the promises of functional metal hydride nanomaterials for biomedical applications.

Fig. 1. The preparation and application of TiH_1.924 nanodot.

Schematic illustration to show the preparation of TiH_1.924 nanodots by liquid-phase exfoliation and their applications for combined photothermal-sonodynamic cancer therapy.

Fig. 2. Preparation and characterization of TiH_1.924 nanodots.

a Schematic illustration to show light-phase exfoliation to prepare TiH_1.924 nanodots. b A photograph of commercial TiH_1.924 powder, the TEM images and corresponding photographs of exfoliated dispersions using various solvents (H₂O, glycerol, dimethyl sulfoxide/N-methyl pyrrolidone (DMSO/NMP) DMSO/NMP, DMSO, polyethylene glycol 200 (PEG 200), NMP, N,N-dimethylformamide (DMF)/NMP, pyridine, DMF, acetonitrile, tetrahydrofuran (THF), ethanol, and acetone) for TiH_1.924 exfoliation. c The surface energies of various solvents used to exfoliate TiH_1.924. d A photograph of exfoliated TiH_1.924 nanodots in NMP. Inset is the particle-size distribution (PSD) of TiH_1.924 nanodots determined by the TEM image (n = 100 nanodots examined over TEM images). e High-resolution TEM (HRTEM) image of TiH_1.924 nanodots. f XRD spectra of TiH_1.924 nanodots. g XPS spectra to show Ti 2p peaks for the TiH_1.924 nanodots sample. h TEM images and PSD of ZrH₂ nanodots, CaH₂ nanodots, and HfH_1.983 nanoparticles exfoliated in NMP (n = 100 nanomaterials examined over TEM images). A representative image of three biological replicates from each group is shown in b, e.

Fig. 3. Sonodynamic and photothermal performance of TiH_1.924 nanodots.

a Schematic illustration of sonodynamic and photothermal properties of TiH_1.924 nanodots. b Time-dependent oxidation of DPBF indicating ROS generation by US-activated TiH_1.924 nanodots. c Comparison of DPBF oxidation by TiH_1.924 nanodots, untreated TiH_1.924, and commercial TiO₂ under US irradiation for 5 min. d ESR spectra demonstrating ROS (¹O₂) generation for TiH_1.924 and TiO₂ under US irradiation for 1 min. e, f Normalized absorption spectra (e) and optical bandgaps (f) of TiH_1.924 nanodots and TiO₂. g Schematic illustration of the activation mechanism of TiH_1.924 and TiO₂ under US irradiation. h UV-vis-NIR absorbance spectra at different concentrations of TiH_1.924 nanodots (4, 8, 16, 32, 64, and 128 µg mL⁻¹). The inset is the photograph of TiH_1.924 nanodots with different concentrations. i Concentration-dependent photothermal heating curves of TiH_1.924 nanodots (0, 0.02, 0.04, 0.08, 0.16, and 0.32 mg mL⁻¹). j The photothermal profile after laser exposure to reach a steady temperature and then to cool down by turning the laser off. k Heating/cooling profiles for five repeated ON-OFF cycles of laser irradiations.

Fig. 4. In vitro mild PTT-enhanced SDT via TiH_1.924-PVP.

a Schematic illustration of TiH_1.924-PVP for mild PTT-enhanced sonodynamic therapy. b Relative viabilities of 4T1 cells after incubation with various concentrations of TiH_1.924-PVP for 12 h and 24 h (n = 6 biologically independent samples). c Relative viabilities of 4T1 cells after different treatments, including control, TiH_1.924-PVP, NIR, US, NIR/US, TiH_1.924-PVP/NIR, TiH_1.924-PVP/US, and TiH_1.924-PVP/NIR/US (n = 6 biologically independent samples). d Confocal images of 4T1 cells stained with calcein AM (green, live cells) and propidium iodide (red, dead cells) after different treatments. e Confocal images of 4T1 cells stained with DCFH-DA after various treatments. The nuclei and intracellular ROS were stained by DAPI (blue) and DCFH-DA (green), respectively. TiH_1.924-PVP: 50 µg mL⁻¹, NIR laser: 1064 nm, 0.8 W cm⁻², 10 min, T < 42 °C; US irradiation: 40 kHz, 3 W cm⁻², 1 min per cycle, 5 cycles. Data are presented as mean values ± SD. Statistical significance was calculated with two-tailed Student’s t test (c). A representative image of three biological replicates from each group is shown in d, e.

Fig. 5. In vivo tumor accumulation and mild PTT-defeated tumor hypoxia via TiH_1.924-PVP.

a In vivo PA imaging of 4T1 tumor-bearing mice after intravenously injected with TiH_1.924-PVP. b Time-dependent tumor PA signals at 900 nm based on PA imaging data in a (n = 3 biologically independent mice). c Biodistribution of TiH_1.924-PVP in mice (n = 3 biologically independent mice). d, e IR thermal images (d) and temperature change curves (e) of 4T1 tumors under the 1064-nm laser irradiation, for untreated mice and TiH_1.924-PVP injected mice (irradiated at 8 h p.i.). f Representative immunofluorescence images of tumor slices after hypoxia staining. The nuclei, blood vessels, and hypoxia areas were stained by DAPI (blue), anti-CD31 antibody (red), and antipimonidazole antibody (green), respectively. TiH_1.924-PVP: 20 mg kg⁻¹; NIR laser: 1064 nm, 0.8 W cm⁻², 20 min. A representative image of three biological replicates from each group is shown in f. Data are presented as mean values ± SD.

Fig. 6. In vivo mild PTT-enhanced SDT via TiH_1.924-PVP.

a Schematic illustration to show the combination of PTT and SDT with TiH_1.924-PVP nanodots. b, c Average tumor growth curves (b) and individual tumor growth curves (c) on mice after different treatments, including control, TiH_1.924-PVP, NIR/US, TiH_1.924-PVP/NIR, TiH_1.924-PVP/US, and TiH_1.924-PVP/NIR/US (n = 5 biologically independent mice). d Micrograph of DCFH-DA stained tumor slices collected for mice receiving different treatments. e H&E stained tumor slices collected from different treatment groups. f Survival curves of mice after various treatments. g Biodistribution of TiH_1.924-PVP post i.v. injection in mice on different days (n = 3 biologically independent mice). h The detected Ti mass in urine and feces at different time points post i.v. injection of TiH_1.924-PVP (n = 3 biologically independent mice). The Ti contents were measured by ICP-OES. TiH_1.924-PVP: 20 mg kg⁻¹; NIR laser: 1064 nm, 0.8 W cm⁻², 20 min, T < 45 °C; US irradiation: 40 kHz, 3 W cm⁻², 1 min per cycle, 20 cycles. A representative image of three biological replicates from each group is shown in d, e. Data are presented as mean values ± SD. Statistical significance was calculated with two-tailed Student’s t test (b) and Logrank test (two-sided) for trend (f).