Hydrogels based on poly(ethylene glycol) diacrylate (PEGDA) have been engineered for a variety of biomedical applications including drug delivery, cell delivery, and tissue engineering. The miniaturization of these materials to nanoscale and microscale particles has been a subject of intense activity, and promises to extend their range of applicability. In general, however, these efforts have been frustrated by the inhibition of chain growth polymerization by oxygen, an effect that is exacerbated as target length scales are reduced. Here, we report a method that exploits the undesirable oxygen-inhibited photopolymerization to produce size-controlled PEGDA hydrogel particles. The role of initial solution composition in determining the relative particle to droplet size ratio is reported, and is found to contribute through its influence on the polymerization rate, as well as the diffusivity of oxygen. Facile control of photopolymerization kinetics via UV light intensity and/or exposure time, allowed PEGDA particles to be produced with dimensions independent of the parent spherical droplets formed by conventional microfluidic emulsification. (C) 2017 Elsevier Inc. All rights reserved.