Relationships between printability and rheology of inks for personalized nutrition

This study explores the relationship between printability and rheology of 3D food printing inks developed for personalized nutrition. We have developed a wide variety of inks differing in macronutrient composition, with formulations either carbohydrate-rich, protein-rich, or fiber-rich. We have experimentally characterized their rheology and printability. Rheological measurements, obtained via strain sweeps, were analyzed by a descriptive model capturing the elastic modulus, $tan\left(\delta \right)$ , the yield stress, the critical strain, and the strain-thinning index. Printability was assessed through the required printing force, and the printing accuracy via top-view image analysis. The yield stress showed a strong correlation with the printing force. Moderate correlations were found between printing accuracy yield stress, $tan\left(\delta \right)$ , and strain-thinning exponent. We attribute the moderate correlations to inhomogeneity of the inks imparted by their imperfect mixing and hydration. These issues merit further investigation in the context of 3D food printing. However, interestingly, the yield stress correlated with the strain-thinning exponent, suggesting that higher yield stress inks require stronger strain/shear thinning to be printable. The correlations of printing accuracy with $tan\left(\delta \right)$ , and strain-thinning exponents align with findings from previous studies. Together with results of earlier studies, a printability window could be constructed, holding for a wide range of food ink formulations. This is an important step towards developing inks for personalized nutrition.