A perspective on the physical, mechanical and biological specifications of bioinks and the development of functional tissues in 3D bioprinting

Bioinks are the basic building blocks for the fabrication of 3D bioprinted constructs. These bioinks play key roles in structural support, adhesion, and differentiation of incorporated cells. Due to diversity of tissue types found in the body, and the need to recapitulate many of the structural and functional characteristics of a target tissue, there are many potential bioinks, but relatively few at the moment possess optimal properties. Bioinks may be classified on the basis on their ultimate role in a 3D bioprinted construct such as imparting biological functionality, serving as sacrificial material, or supporting and providing rigidity to complex constructs. Physical, mechanical and biological characteristics must all be taken into account in the design and composition of bioinks. The incorporation of guidance cues such as topography, growth factors, and morphogens is necessary to control cell fate. These 3D bioprinted constructs should be integrated into bioreactor systems, to support tissue development. Finally, the methodologies to non-destructively monitor both deposited bioinks and construct maturation are necessary for the successful development of a functional tissue.