Progress in scaffold-free bioprinting for cardiovascular medicine

Biofabrication of tissue analogues is aspiring to become a disruptive technology capable to solve standing biomedical problems, from generation of improved tissue models for drug testing to alleviation of the shortage of organs for transplantation. Arguably, the most powerful tool of this revolution is bioprinting, understood as the assembling of cells with biomaterials in three-dimensional structures. It is less appreciated, however, that bioprinting is not a uniform methodology, but comprises a variety of approaches. These can be broadly classified in two categories, based on the use or not of supporting biomaterials (known as "scaffolds," usually printable hydrogels also called "bioinks"). Importantly, several limitations of scaffold-dependent bioprinting can be avoided by the "scaffold-free" methods. In this overview, we comparatively present these approaches and highlight the rapidly evolving scaffold-free bioprinting, as applied to cardiovascular tissue engineering.