Magnetically Actuated Biohybrid Microswimmers for Precise Photothermal Muscle Contraction.

Various strategies have been designed for myotube contraction and skeletal muscle stimulation in recent years, aiming in the field of skeletal muscle tissue engineering and bionics. However, most of the current approaches lack controllability and adaptability for precise stimulation, especially at the microlevel. Herein, wireless and precise activation of muscle by using magnetic biohybrid microswimmers in combination with near-infrared (NIR) laser irradiation is successfully demonstrated. Biohybrid microswimmers are fabricated by dip-coating superparamagnetic Fe₃O₄ nanoparticles onto the <i>chlorella</i> microalgae, thus endowing robust navigation in various biological media due to magnetic actuation. Under the guidance of a rotating magnetic field, the engineered microswimmer can achieve precise motion toward a single C2C12-derived myotube. Upon NIR irradiation, the photothermal effect from the incorporated Fe₃O₄ nanoparticles results in local temperature increments of approximately 5 °C in the targeted myotube, which could efficiently trigger the contraction of myotube. The mechanism underlying this phenomenon is a Ca²⁺-independent case involving direct actin-myosin interactions. <i>In vivo</i> muscle fiber contraction and histological test further demonstrate the effectiveness and biosafety of our design. The as-developed biohybrid microswimmer-based strategy is possible to provide a renovation for tissue engineering and bionics.