Actually our bodies already have such "microrobots", they are called "actin" microfilaments. They can dynamically change from monomeric to polymeric form allowing cells to perform processes like phagocytosis (engulfing bad (pathogenic) material) and neurogenesis (axonal cone growth formation). Basically they help in changing/deforming shape of cells in response to signals from receptors on cell membrane. Human body is truly impressive in complexity and I think there is a lot we can learn from human physiology that we can apply in solving modern world engineering problems.