While human tissues are mostly soft, wet and bioactive; machines are commonly hard, dry and biologically inert. Bridging human-machine interfaces is of imminent importance in addressing grand societal challenges in healthcare, security, sustainability and joy of living; but extremely challenging, due to the fundamentally contradictory properties of human and machine. At MIT SAMs Lab, we use nanoengineered bioactive hydrogels to bridge human-machine interfaces. On one side, bioactive hydrogels with similar physiological properties as tissues can naturally integrate with human body, maintaining long-term biocompatibility and bioactivity. On the other side, the hydrogels embedded with electronic, optical and mechanical components can effectively interface with external machines for functions such as sensing and stimulation. In the talk, I will discuss our recent works on the design and fabrication of hydrogel-based biorobots and their biomedical applications. In particular, I will demonstrate two unconventional actuation mechanisms for hydrogel robots, hydraulic and magnetic actuations, to achieve high-speed, high-force and multifunctionalities. We will further discuss potential applications of hydrogel robots in biomedicine such as drug delivery, stimulation of various organs, and operations in gastrointestinal tract.