Fig. 2.

Illustration of (A) single-, (B) full-, and (C) micro-reactive inkjet printing approaches to fabricate alginate hydrogel. Reproduced with permission [95]. Copyright 2019, American Chemical Society. D) Schematic representation of the dual-material FRESH printing process and (E) the construct dimensions. F) Micrograph of the final printed model. G,I) Side and top view of the calcium imaging of the printed structure and H,J) their respective spontaneous and directional propagation calcium wave that indicates the transmission of the action potential across embedded cardiomyocytes. K,L) Calcium signal propagation observed after point stimulation. M) Transient calcium waves measured during spontaneous and induced (1–2 Hz) contractions. Reproduced with permission [96]. Copyright 2019, AAAS.