The emergence of novel techniques in biology and material science, coupled with greater understandings of cell-material interactions, have given rise to the creation of living materials and bioarchitectures imbued with engineered living behaviors. These multidimensional materials and constructs capable of performing programmable and time-or stimuli-dependent activities, namely 4D behaviors, may do so as a result of material features alone, or as a product of incorporated biological or cellular agents. This review discusses fabrication strategies employed in the development of 4D living materials and examples of their 4D activities driven by cellular events or processes. The fabrication strategies investigated throughout are focused on those that facilitate the responsive, functional transformation of the 3D structure with the time that extends beyond changes driven solely by material features, and enable an increase in the cell-dependent functional capacity of the construct. Living materials comprised of cells and their own products, as well as both cells and added non-living materials are investigated. Further, the authors analyze how material complexities and biological complexities have thus far been interfaced to allow for intricate living behaviors, and discuss the design considerations and challenges encountered in developing living materials. Finally, the future directions of living materials are outlined.

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