Figure 2.

Overview—evolving strategies for controlling shape in bioprinting. A) To enhance chemical crosslinking strategies mainly step growth reactions and the transition from ultraviolet to visible light crosslinking have been applied more frequently. Also, technological advances like in situ photo-crosslinking can improve shape fidelity and broaden the spectrum of applicable materials based on chemical crosslinking strategies. B) In terms of physical interactions, weak bonds, like host–guest interactions and β-sheets, are applied to adjust the rheological properties of the materials. C) Rheological tuning is leading toward a two-step crosslinking utilizing a first step of crosslinking to enable printing with high shape fidelity and a second step to ensure long-term stability enabling to adjust the viscosity of the material to a level that is needed for the different fabrication steps. D) Further technological advances, like coaxial bioprinting and the application of microfluidic approaches in bioprinting, help broadening the spectrum of materials that can be applied for bioprinting. E) Also, printing into support baths is a promising strategy to enable fabrication of more sophisticated structures with less stringent demands on viscoelastic properties of bioinks.