4D–Printed Photothermally Actuated Soft Microgripper on an Optical Fiber Tip for Biomedical Applications

ABSTRACT In recent years, there has been growing demand for manipulating soft, microscale biological specimens such as cells and spheroids. Soft microgrippers have thus attracted significant interest for biomedical applications. In this study, we developed a photo–crosslinkable hydrogel based on temperature–responsive poly( N –isopropylacrylamide) (PNIPAAm) and used micro–stereolithography to fabricate a simple microgripper directly on the tip of an optical fiber. The hydrogel formulation was tuned to allow actuation at ambient cell culture temperature. To enable photothermal responsiveness, silver particles were embedded within the 3D–printed microgripper via a post–treatment photoreduction process using light irradiation. Based on multiphysics simulations, the microgripper geometry was designed to operate using only light emitted from the optical fiber tip. The structure was fabricated using a custom–built micro–stereolithography system, and photothermal actuation was demonstrated by irradiating a blue laser beam through the fiber. Finally, the microgripper successfully grasped and manipulated spheroids 200–250 µm in diameter at cell culture temperature, without causing noticeable cell damage. This 4D–printed, fiber–tip soft microgripper, actuated solely by light, eliminates the need for complex actuators at the end effector, offering a promising approach for building integrated biomanipulation platforms with multiple functional tools.