Going down to micron scale mobile robots, the grand challenge is the limitation on scaling down onboard actuators and power sources. Two alternative approaches are proposed to solve this challenge. First, biological cells, e.g. bacteria, attached to the surface of a microrobot are used as onboard microactuators and microsensors using the chemical energy. Bacteria-propelled randomly swimming microrobots are steered using chemical and pH gradients in the environment and remote magnetic fields. As the second approach, external actuation of untethered magnetic microrobots using remote magnetic fields in enclosed spaces is demonstrated. New magnetic microrobot locomotion principles based on rotational stick-slip and rolling dynamics are proposed. Novel magnetic composite materials are used to address and control teams of microrobots. Such untethered microrobot teams are demonstrated to control microfluidic flow locally, trap live cells and transport them, and manipulate microgels with embedded cells with or without contact inside microfluidic channels for tissue engineering applications.