Hybrid diacrylate resin-gelatin methacryloyl composite with bone-to-brain stiffness range.

Biointerfacing techniques for connecting implants to living tissues are advancing, but matching stiffness at hard-soft interfaces, such as between tendon and bone, remains challenging. This is critical for improving biomechanical tissue models, repairing trauma, and integrating soft robotic technologies like artificial muscles. Here we introduce a 3D-printable, biocompatible composite combining a hydrogel (gelatin methacryloyl) with a hybrid resin of diacrylates and epoxide. By adjusting the mixture ratio, the material's elastic modulus spans a wide physiological range, from 15 kPa (soft brain tissue) to 1.4 GPa (similar to bone), covering six orders of magnitude. Mechanical tests confirm this tunability, and cytocompatibility tests show high cell viability, proliferation, and metabolic activity. The approach offers a path to creating efficient gradient stiffness interfaces, potentially leading to more accurate tissue phantoms and devices for human body repair and augmentation, especially where continuous hard-to-soft transitions are essential.