MIT engineers have created a synthetic, sticky hydrogel that is over 90 percent water. The hydrogel - a transparent, rubber-like material - can adhere to surfaces like glass, silicon, ceramics, aluminum, and titanium with a toughness comparable to the bond between tendon and cartilage on bone. In experiments to demonstrate its robustness, the researchers applied a small square of their hydrogel between two plates of glass, from which they then suspended a 55-pound weight. They also glued the hydrogel to a silicon wafer, which they then smashed with a hammer. While the silicon shattered, its pieces remained stuck in place. This durability makes the hydrogel an ideal candidate for protective coatings on underwater surfaces such as boats and submarines. Since the hydrogel is biocompatible, it could also be suitable for a range of health-related applications, such as biomedical coatings for catheters and sensors implanted in the body.