Droplet microfluidic technology is applied for the high-throughput synthesis via Michael-type addition of reactive, micrometer-sized poly(ethylene glycol) (PEG) hydrogels ("microgels") with precisely controlled dimension and physicochemical properties. A versatile chemical scheme is used to modify the reactive PEG microgels with tethered biomolecules to tune their bioactive properties for the bioreactor culture and manipulation of various (stem) cell types.