(a) Schematic of micro/nano-patterning in 3D hydrogels using focused laser (single-photon or two-photon). Using different photo-chemical designs of crosslinkers, one could achieve reversible biochemical patterning, mechanical modulation and multiplex immobilization of biochemical cues (see text for detailed description).[135,206,207] (b) Fluorescent confocal micrograph of 3D micro-patterns of SHH (green) and CNTF (red) within an agarose hydrogel.[207] Reproduced with permission from [207]. Copyright 2011, Nature Publishing Group. (c) Fluorescent confocal micrograph of micro-patterned 3D helices of fluorescently labeled peptides, of which one (red) was reversibly removed after UV exposure.[135] Reproduced with permission from [135]. Copyright 2012, Wiley-VCH (Germany).