Figure 5.

Biocompatibility and photothermal stimulation of HEK 293 cells using TACSI microrobots. a) Cell viability over 72 h for control without GNRs or microrobots, encapsulated GNRs@Alg at 10 mg ml⁻¹, and TACSI microrobots with 10 mg ml⁻¹ GNRs@Alg loading is presented (n = 1000). b) Exemplary fluorescence images of TACSI microrobots with cells in culture. Red signal indicates microrobots while green signal shows cells. Scale bar: 50 µm. c) Schematic representation of a photothermal biostimulation event and d) corresponding experiment. Microrobot is guided onto cells in (1) and (2), and actuated via laser light following sedimentation (3). Thermal cell stimulation triggers a drastic increase in intracellular calcium signal is detected (4). Scale bar: 30 µm. e) Change in normalized intracellular calcium intensity of a single cell stimulated with a single microrobot at different laser power densities. Laser duration: 1 s. f) Cell response to different photothermal heat doses against Gd³⁺ treated control (n = 20). Temperatures correspond to 2, 4, 6 µW µm⁻² in order. g) Fluorescent image of a single HEK 293 cell during three different laser power actuations. White outline indicates the position of the microrobot. Scale bar: 20 µm.