Tuning the Young’s modulus of gelatin methacryloyl hydrogels with masked stereolithography bioprinting

The mechanical properties of the extracellular matrix (ECM) are critical regulators of cell behavior. Native tissues span a broad mechanical spectrum, ranging from soft brain tissue to stiff bone and often exhibit a spatial heterogeneity in stiffness. To replicate these complex microenvironments in vitro , biomaterials must offer not only tunable stiffness but also spatial control over mechanical properties within three-dimensional (3D) constructs. Gelatin methacryloyl (GelMA) hydrogels are widely used in biofabrication. Due to their photopolymerizability, their stiffness can be modulated by altering the material composition and exposure to light. However, so far no bioprinting platform has integrated these tuning parameters to fabricate complex 3D constructs with spatially controlled mechanical properties. In this study, we demonstrate the use of a masked stereolithography bioprinter (mSLAb) to systematically tune the Young's modulus (YM) of 3D printed GelMA hydrogel constructs. Systematic variations in YM are achieved by adjusting the material composition. Furthermore, the mSLAb allows for tuning of the YM during the printing process by varying the light exposure and intensity, enabling the creation of YM gradients within the 3D construct. The mSLAb thus allows for generating a predefined 3D structure which mechanical properties can be modified during the printing process. With this approach, we achieved a stiffness range, spanning from roughly 1 kPa to over 200 kPa. These results establish mSLAb as a powerful platform for engineering mechanically customizable and structurally complex hydrogel constructs, with cell-instructive YM gradients with high spatial precision. • Young's modulus (YM) of GelMA is tuned using a masked stereolithography bioprinter (mSLAb). • Material composition and energy density are factors for tuning the YM using mSLAb. • mSLAb enables printing of complex 3D structures with spatially tuned stiffness.