A Soft Microrobot for Single-Cell Transport, Spheroid Assembly, and Dual-Mode Drug Screening.

Physiologically relevant 3D cellular in vitro systems have enabled disease modeling and drug screening, yet these approaches remain hindered by stochastic self-assembly, structural heterogeneity, and limited diffusion. While hydrogel scaffolds, 3D bioprinting, and microfluidic platforms have improved spatial organization and environmental control in such systems, these approaches often lack real-time adaptability. This work introduces a soft and untethered hydrogel microrobot enabling targeted single-cell delivery, spheroid self-assembly, photothermal actuation, and sensing. The microrobot is composed of an alginate hydrogel network carrying gold nanorods for plasmonic heating and Rhodamine B for real-time temperature sensing. Microfluidic encapsulation is used to fabricate uniform spherical microrobots. Microrobot locomotion is achieved through thermophoretic convection, allowing precise manipulation within 3D workspaces in an externally controlled manner. The microrobots facilitate single-cell pick-up and spheroid formation through carefully designed surface coatings. The microrobots simultaneously function as localized heaters, modulating the cell microenvironment via photothermal actuation, and as sensors, providing real-time feedback on local changes in temperature. Combining photothermal stimulation with chemotherapeutic testing reduces the invasive behavior of fibrosarcoma cells in proof-of-concept studies, demonstrating the system's capability to function as a drug screening tool.