The adhesion of soft connective tissues (tendons, ligaments, and cartilages) on bones in many animals can maintain high toughness (∽800 J m−2) over millions of cycles of mechanical loads. Such fatigue-resistant adhesion has not been achieved between synthetic hydrogels and engineering materials, but is highly desirable for diverse applications such as artificial cartilages and tendons, robust antifouling coatings, and hydrogel robots. Inspired by the nanostructured interfaces between tendons/ligaments/cartilages and bones, we report that bonding ordered nanocrystalline domains of synthetic hydrogels on engineering materials can give a fatigue-resistant adhesion with an interfacial fatigue threshold of 800 J m−2, because the fatigue-crack propagation at the interface requires a higher energy to fracture the ordered nanostructures than amorphous polymer chains. Our method enables fatigue-resistant hydrogel coatings on diverse engineering materials with complex geometries. We further demonstrate that the fatigue-resistant hydrogel coatings exhibit low friction and low wear against natural cartilages.

In vivo bioprinting has recently emerged as a direct fabrication technique to create artificial tissues and medical devices on target sites within the body, enabling advanced clinical strategies. However, existing in vivo bioprinting methods are often limited to applications near the skin or require open surgery for printing on internal organs. Here, we report a ferromagnetic soft catheter robot (FSCR) system capable of in situ computer-controlled bioprinting in a minimally invasive manner based on magnetic actuation. The FSCR is designed by dispersing ferromagnetic particles in a fiber-reinforced polymer matrix. This design results in stable ink extrusion and allows for printing various materials with different rheological properties and functionalities. A superimposed magnetic field drives the FSCR to achieve digitally controlled printing with high accuracy. We demonstrate printing multiple patterns on planar surfaces, and considering the non-planar surface of natural organs, we then develop an in situ printing strategy for curved surfaces and demonstrate minimally invasive in vivo bioprinting of hydrogels in a rat model. Our catheter robot will permit intelligent and minimally invasive bio-fabrication.