Cardiac tissue engineering enables the generation of artificial tissues for advanced drug testing and disease modelling as well as for cardiac repair. Most commonly, such tissues are generated by manually dispensing cell-matrix-suspensions into specifically designed molds. While good functionality and advanced maturation can be achieved, the native tissue architecture and hierarchy is often not replicated. 3D bioprinting is a promising strategy to improve tissue functionality by generating hierarchic structures and complex geometries. This technology has previously been used to generate models of heart, however, these models either show limited functionality or require support structures to generate stable constructs.

Here, we describe an approach which enables direct 3D-bioprinting of hiPSC-derived cardiomyocytes in a collagen-based bioink. Cardiomyocytes derived from hiPSC were suspended in a bioink comprised of rat collagen-I and hyaluronic acid. A commercial extrusion bioprinter was used to extrude the bioink into a support bath of gelatin/gum arabic microparticles. The bioprinter was modified to allow for cooling of the bioink and extend the time window for printing. After bioink gelation, support bath was removed and constructs were cultured free-floating for up to 30 days. Synchronous contractions of printed cardiac rings (5 x 5 x 1 mm) were observed as early as 3 days after generation and were responsive to pharmacological stimulation.

This approach enables direct 3D-bioprinting of stable functional cardiac tissues without the need for additional support structures. In addition, it allows for the generation of multi-layered constructs using distinct bioinks.