The use of zerovalent iron (Fe-0)-coated plates, which act both as a source of catalyst and as a reducing agent during surface-initiated atom transfer radical polymerization (SI-ATRP), enables the controlled growth of a wide range of polymer brushes under ambient conditions utilizing either organic or aqueous reaction media. Thanks to its cytocompatibility, Fe-0 SI-ATRP can be applied within cell cultures, providing a tool that can broadly and dynamically modify the substrate's affinity toward cells, without influencing their viability. Upon systematically assessing the application of Fe-based catalytic systems in the controlled grafting of polymers, Fe-0 SI-ATRP emerges as an extremely versatile technique that could be applied to tune the physicochemical properties of a cell's microenvironments on biomaterials or within tissue engineering constructs.