Ga-based liquid metal (LM), particularly gallium-based alloy, uniquely combines metallic conductivity with fluidic flexibility, offering attractive opportunities for biomedical technologies that are difficult to achieve with conventional solid-state metals. This review firstly summarizes the expanding applications of LM in microfluidics, flexible electronics, biosensing, drug delivery, and thermal therapy, highlighting the functional advantages arising from their fluidity, deformability, and electrical conductivity. However, the limitations that hinder broader biomedical implementation remain: though the native gallium oxide layer can stabilize LM structures, it also introduces challenges in oxidation control, wettability, interfacial adhesion, conductivity, and long-term reliability. Against this background, surface engineering is presented as a central strategy for addressing these limitations. We systematically review surface modification approaches based on small molecules, polymers, biological coatings, and related interfacial strategies for improving stability, biocompatibility, and functionality. We further discuss fabrication approaches for integrating surface engineered LM into wearable platforms, including 3D printing and hydrogel-based architectures. Finally, persistent challenges involving surface tension, adhesion, nanoparticle aggregation, conductivity loss, electrochemical corrosion, mechanical mismatch, biocompatibility, and sterilization are critically evaluated together with corresponding solutions. This application-surface engineering framework provides a roadmap for designing multifunctional, surface engineered LM-based systems, while outlining future directions for translating these materials from laboratory studies to clinical and practical biomedical applications.