Hydrogels and scaffolds designed for a 3D follicle culture. (a–b) PEG-based hydrogels with a difunctional peptide as the cross-linker for an ovarian follicle culture. (b) i-iii Morphology of ovarian follicles cultured in PEG hydrogel within 10 days. Scale bars: 100 mm. Reproduced with permission [92]. 2011, Biomaterials. (c–f) 3D-printed microporous gelatin scaffolds seeded with follicles. (c) Schematic of the thermoreversible properties of gelatin. (d) Photographs of a five-layered 3D-printed scaffold. Scale bar: 250 mm. (e) Follicles were seeded in a 60° scaffold, and confocal fluorescence images (f) of follicles cultured for 2 days. Scale bars: 100 mm. Reproduced with permission [30]. Copyright 2017, Nature Communication. (g) Schematic of the ovarian constructs. The ovarian constructs were fabricated using a cross-linked alginate layer and poly-l-ornithine (PLO) layer encapsulated with granulosa and theca cells to replicate the key structure of ovarian follicles. (h) Different cells and granulosa cells were labeled with CellTracker Green, and theca cells were labeled with CellTracker orange within the constructs. Reproduced with permission [34]. Copyright 2012, Reproductive Biology and Endocrinology.