A targeted rheological bioink development guideline and its systematic correlation with printing behavior

Bioprinting for tissue or disease models is a promising but complex process involving biofabrication, cell culture and a carrier material known as bioink. The native extracellular matrix (ECM), which forms the scaffold for cellsin vivo, consists of several components including collagen as a gelling agent to confer mechanical stiffness and provide a substrate for cell attachment. Bioprinting therefore needs an artificial ECM that fulfills the same functions as its natural counterpart during and after the printing process. The combination of bioink materials determines the immune response of the host, cell compatibility and adhesion. Here we evaluate multi-material blending with four pre-selected components using a design of experiments approach. Our exemplary designed hydrogel is highly reproducible for the development of artificial ECM and can be expanded to incorporate additional requirements. The bioink displays shear-thinning behavior and a high zero-shear viscosity, which is essential for the printing process. We assessed the printing behavior of our bioink over a wide range of the key process parameters for extrusion-based bioprinting (temperature, pressure, feed rate, and nozzle geometry). Several processing temperatures were linked by rheological measurements directly to the 3D printing process. The printing results were evaluated using a self-developed categoric strand screening process, varying the feed rate and pressure with a fixed nozzle. Accordingly, nozzles differing in size and shape were evaluated and the interactions between printing pressure and feed rate were characterized separately by applying a modified O-R-O test. We tested the short-term cultivation stability of our bioink to mimic the hypothermic and hyperthermic conditions of the human body. As result we present an expandable concept for bioink development and a highly reproducible and well-characterized procedure for printing with the newly developed hydrogel. We provide detailed insights into the relationship between printing parameters, rheological parameters and short-term cultivation stability.