Fig. 4: Photothermal properties, thermo-responsive drug delivery, and motion evaluation of nanorobots.

a Photothermal effect of UHHTNs in aqueous solution upon 980 nm laser irradiation under different power densities for 10 min. b TGA data obtained from the pristine UHHTNs (red) and UHHTNs containing PCM (blue). The 11.3% weight loss corresponds to the evaporation of PCM inside UHHTNs. c UV-vis-NIR spectra recorded from an aqueous suspension from free DOX (blue line), UHHTNs (red line) and UHHTNs loaded with PCM-DOX (green line). d Drug release profiles of DOX from the UHHTNs in DMEM with 10% serum under NIR light stimulation with different laser power densities. Inset: Schematic representation of the thermo-responsive drug delivery. Data are presented as mean ± s.d (n = 3 replicates). e Trajectories of PCM/nanorobots irradiated with different NIR power densities for 10 s (Supplementary Videos 1–5). f The average diffusion coefficient (D) values. Experimental data are mean ± s.d. of samples in a representative experiment (n = 10). g Steady-state temperature distribution of a PCM/nanorobot under NIR irradiation. h fluid velocity profile. i Schematic showing a mechanism of thermophoresis. When NIR light is locally absorbed on one side of a UHHTN, a local temperature gradient is formed across the UHHTN surface. This temperature gradient results in a corresponding osmotic pressure gradient which induces fluid flow at the UHHTN solvent interface. Source data for the figure are provided within the Source Data file.