FIG. 3.

(A, B) Human mesenchymal stem cells (hMSCs) encapsulated in a photopolymerized hydrolytically biodegradable PEG hydrogel and cultured in osteogenic medium. After encapsulation and when limited degradation has occurred, hMSCs adopt a spherical morphology (A). With sufficient degradation, hMSCs are able to migrate and form cell–cell junctions and adopt a more osteogenic-like phenotype (B). Reproduced with permission from Cushing et al.⁵³ (C, D) Engineered cartilage after 2 (C) and 6 (D) weeks in vitro culture (glycosaminoglycans stained red). Chondrocytes were encapsulated in a biodegradable PEG-co-PVA hydrogel exhibiting bimodal degradation. Reprinted with permission from Martens et al.⁵⁶ (E, F) Fibroblasts encapsulated in an enzymatically degradable PEG hydrogel. When crosslinks are degraded, fluorescence is emitted at the degradation site enabling spatial visualization of the degrading gel. After 7 days postencapsulation, cell-mediated degradation was observed only in the direction of the extended process (E); however, when treated with an MMP inhibitor, no cell-mediated degradation was observed (F). Reproduced with permission from Lee et al.⁶⁴ Color images available online at www.liebertpub.com/ten.