A rubber duck that was stuck to a seaside rock for more than a year has proved the strength of a new sticky material. The adhesive could be used in deep-sea robots and repair work, or as surgical glue for medical procedures.

鈥淲e developed a super-adhesive hydrogel that works extremely well even underwater 鈥� something very few materials can achieve,鈥� says at Shenzhen University in China. Hydrogels are stretchy and soft materials.

Fan, then at Hokkaido University in Japan, and his colleagues analysed 24,000 sticky protein sequences from many different organisms to identify the stickiest combinations of amino acids, the building blocks of proteins. They used that information to create 180 different types of adhesive hydrogel. Then, they trained artificial intelligence models on the hydrogels鈥� material properties to predict even better recipes for super-sticky materials.

This process let the team develop a new class of versatile and sticky hydrogel. The material bonds to surfaces even when it has been unstuck and restuck multiple times or immersed in seawater, says Fan. It exceeded 1 megapascal of adhesion strength underwater 鈥� about 10 times stronger than most soft, sticky materials under the same conditions.

The research 鈥渄emonstrates a paradigm shift in the way we can design high-performance soft materials鈥�, says at Syracuse University in New York state. He praised the team for identifying stickiness patterns in natural proteins and capturing them in the new material.

The most whimsical demonstration of the hydrogel鈥檚 sticky strength involved keeping that yellow rubber duck attached to the wave-soaked rock by the shore. In a more practical experiment, the hydrogel instantly sealed a leaking water pipe. This suggests it could help repair underwater structures or make flexible electronics and robotics water-resistant.

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The material was also biocompatible, which the researchers proved by implanting it under the skin of mice. This could make it useful for biomedical applications, such as affixing implants or working as surgical glue.

The hydrogel鈥檚 stickiness is remarkable, says Qin, but he notes that the material must be relatively thick to perform well. He hopes to see it tested outside ideal experimental conditions, especially in real-world situations with rough, contaminated or moving surfaces.

The researchers have submitted a patent for the new material through Hokkaido University, where most of them work.

A harder form of diamond that has eluded scientists for decades can now be synthesised in the laboratory, and could be used to make extremely tough cutting and drilling tools.

Diamonds as we know them have a cubic arrangement of atoms in their crystalline structure. But for at least 60 years, we have been aware of another form 鈥� hexagonal diamond 鈥� that is much tougher, thanks to its crystals having no uniform shear lines along which breaks can propagate.

Natural hexagonal diamond occurs in meteorites, where it is known by the mineral name lonsdaleite, but only in mixtures with cubic diamond. Previous attempts to synthesise hexagonal diamonds have yielded only tiny traces that are similarly impure.

Now, at the Center for High Pressure Science and Technology Advanced Research in Beijing and his colleagues have succeeded in creating a relatively large sample of hexagonal diamond that is 1 millimetre in diameter and 70 micrometres thick, with purity close to 100 per cent.

While normal diamond has been synthesised for some time, the researchers explored a range of pressures and temperatures to find a sweet spot in which hexagonal diamonds were produced. This ended up being 1400掳C at 20鈥塯igapascals 鈥� 200,000 times the atmospheric pressure on Earth.

Such a material has never been made before, so it will need to be thoroughly studied to determine its properties, says Mao. 鈥淚t鈥檚 incredibly valuable,鈥� he says. 鈥淏ut once we know how to make it, anyone can produce it. So then the important thing is to get a patent and find a way to make it less expensive.鈥�

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Hexagonal diamonds are predicted to be about 60 per cent harder than regular diamonds based on their structure. Cubic diamond has a hardness of around 115 gigapascals when measured in a Vickers hardness test. The hexagonal diamond created by Mao and his team measures 120 gigapascals, but they believe they can improve this significantly as they develop their technique further.

If hexagonal diamond can be synthesised with sufficient thicknesses, it could be used to make harder and more resilient tools for a range of uses in industry, such as drilling for geothermal energy, says at the University of Cambridge. 鈥淥bviously, the deeper you go, the hotter it gets, [and] it could enable them to go deeper underground.鈥�

Batteries enhanced with a polymer material that releases fire-suppressing chemicals at high temperatures are significantly less likely to explode into flames. This technique could boost the safety of battery-reliant machines, like electric cars and medical devices.

鈥淥ur approach enhances safety within mainstream liquid lithium batteries,鈥� says at the Institute of Chemistry, Chinese Academy of Sciences. 鈥淚t鈥檚 like popping open a safety valve 鈥� these chemicals smother flammable gases before they can explode, helping prevent fires.鈥�

Zhang and her colleagues created and tested the flame-retardant polymer material in a prototype lithium metal battery. Such batteries are currently in limited use, but next-generation versions are candidates to replace the batteries in electric cars and portable electronic devices. That is because lithium metal can store 10 times as much energy as popular lithium-ion batteries by using pure lithium, rather than graphite, in the negative electrode.

The researchers exposed the prototype battery and a standard lithium metal battery to gradually hotter temperatures, starting from 50掳C. When external temperatures rose above 100掳C, both batteries experienced overheating 鈥� but the prototype鈥檚 special polymer material began breaking down automatically, releasing chemicals that act like 鈥渕icroscopic fire extinguishers鈥�, says Zhang.

Beyond 120掳C, the standard battery without safety features overheated to 1000掳C within 13 minutes and burst into flames. But under the same conditions, the prototype battery鈥檚 peak temperature only reached 220掳C, without any resulting fire or explosion.

This 鈥渋nnovative material science approach鈥� can reduce the risk of battery fires or overheating, not only in lithium metal batteries but also in certain lithium-ion batteries and lithium-sulphur batteries, says at the SLAC National Accelerator Laboratory in California. It could lead to safer batteries, in particular for electric vehicles or even electric aircraft, he says.

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The fire-suppressing technology would integrate well into existing battery manufacturing as a 鈥渘ear-term safety upgrade, while the industry pursues long-term solutions鈥� involving alternative battery designs and chemistries, says Zhang. Still, injecting the polymer material into batteries would require some retuning of manufacturing processes, she says.