Cell contractile forces drive spatiotemporal morphogenesis in 4D bioprinted living constructs

Current 4D materials typically rely on external stimuli such as heat or light to accomplish changes in shape, limiting the biocompatibility of these materials. Here, a composite bioink consisting of oxidized and methacrylated alginate (OMA), methacrylated gelatin (GelMA), and gelatin microspheres is developed to accomplish freestanding 4D bioprinting of cell-laden structures driven by an internal stimulus: cell contractile forces (CCFs). 4D changes in shape are directed by forming bilayer constructs consisting of one cell-free and one cell-laden layer. Human mesenchymal stem cells (hMSCs) are encapsulated to demonstrate the ability to simultaneously induce changes in shape and chondrogenic/osteogenic differentiation. Finally, the capability of patterning each layer of the printed constructs to obtain complex geometric changes—including bending around two separate, non-parallel axes—is exhibited. Bioprinting of such 4D constructs mediated by CCFs empowers the formation of more complex constructs, contributing to a greater degree of in vitro biomimicry of biological 4D phenomena.