Liquid metal-based biomaterials and flexible devices for injectable and implantable healthcare

Injectable and implantable biomaterials and biomedical devices are crucial for disease diagnosis, monitoring, and treatment, enabling minimally invasive procedures, targeted therapies, and real-time monitoring capabilities. Liquid metals (LMs), known for their softness, fluidity, biocompatibility, and unique physicochemical properties, have emerged as promising materials for such applications. Through functionalization and engineering, LM-based biomaterials not only have been utilized in injectable drugs for cancer therapy, tumor recurrence suppression, and imaging, but also can be used for implantable physiological sensors and therapeutic devices. However, a systematic review of LM-based injectable and implantable biomaterials and devices for healthcare is still lacking. This review addresses this gap by providing a comprehensive analysis of LM-based biomaterials and devices for healthcare sensors, diagnostics, and therapeutics. First, the properties of LMs and their engineering strategies are outlined. Then, LM-based injectable and implantable biomaterials for drug delivery, cancer therapy, bioimaging, and their stimuli-responsive mechanisms, as well as implantable sensors for neural, cardiovascular, and gastrointestinal systems, are discussed. Finally, challenges in clinical translation and future research directions are proposed to advance LM-based biomedical technologies. STATEMENT OF SIGNIFICANCE: No existing review systematically overviews the engineering strategies, stimulus-responsive mechanisms, and biomedical applications specific to liquid metal-based injectable and implantable devices. This review addresses this gap by systematically analyzing LM-based biomaterials and devices, focusing on their applications in therapeutic biomaterials, soft therapeutic biodevices, and diagnostic sensors. We introduce the fundamental properties and advanced engineering strategies of LM biomaterials, analyze their roles in injectables with an emphasis on stimulus-responsive therapeutic mechanisms, and highlight their potential in soft biodevices for implantable applications such as soft electronics and neural interfaces. Key challenges hindering clinical translation are identified, and future directions are proposed, providing comprehensive insight for researchers and advancing the development of LM-based biomedical technologies.