Tunable microfluidic device fabricated by femtosecond structured light for particle and cell manipulation.

Smart devices made of stimuli-responsive (SR) hydrogel can realize accurate shape control with high repeatability attributed to their fast swelling and shrinking upon the change of external stimuli. Integrating these devices into microfluidic chips and utilizing their controllable deformation capability are highly promising approaches to enrich the functions of microfluidic devices and reduce their external apparatuses. Herein we propose and demonstrate a tunable microfluidic device (TMFD) by integrating a pH-sensitive hydrogel microring array into a microchannel. Instantaneous and reversible deformation of the microrings can be finished in less than 200 ms. The array gaps of the microrings are reversibly switched to realize the capture or release of microobjects. In addition, a femtosecond laser holographic processing method is firstly used to pattern and integrate the pH-sensitive hydrogel microrings into a microchannel, and the pH-responsive properties of the hydrogel affected by laser processing dosages are theoretically and experimentally investigated. With this method, the height, diameter (6-16 μm), swelling ratio (35-65%), and diameter change (2-5 μm) can be precisely controlled. As a proof of concept, the filtering of polystyrene particles with multiple sizes and complete trapping of PS particles and cells are demonstrated by these TMFDs. The developed TMFD can be easily integrated by the femtosecond laser holographic processing method, and operates robustly without the need for external precision apparatuses, which hold great promise in the applications of microobject manipulation and biomedical analysis.