A stretchy and flexible battery pouch filled with strategically placed holes is more breathable than cotton. That could make it an ideal power source for wearable sports or fitness devices built directly into clothing.

“This is especially useful for athletes or individuals who wear electronics for extended periods – smart clothing for fitness tracking, medical monitoring devices and similar applications that demand both comfort and reliable performance,” says at Yale University.

To design the new battery, Xu and his colleagues created a pattern of long, rectangular holes in a pouch cell battery – a type of lithium battery that resembles a flat bundle with a limited degree of bendability. Simulations showed how the array of rectangular holes enabled the battery to be stretched or folded 180 degrees without tearing, compared with alternative hole patterns involving squares or circles.

“One challenge was maintaining enough active material to keep the battery’s energy density high – too many or too large holes would reduce the energy storage capacity,” says Xu. “We had to balance mechanical stretchability with electrical performance.”

When stretched by 10 per cent or even folded up, the holey battery design could still resist physical stress and continue to power LED light bulbs – with the stretching and folding experiments each performed 100 times. Testing in a temperature and humidity chamber also showed that the battery was twice as breathable as cotton.

As a practical demonstration of the possible uses, the researchers wove the battery into a lab coat and tested its performance while the wearer ran around exercising. Its holes enabled the battery to quickly dissipate heat so it would not feel painful or trap sweat on the wearer’s skin.

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The battery still needs more wear-and-tear testing, so the researchers plan to test its performance in commercial health monitoring devices and sports gear.

They are also investigating how to best scale up production – automated manufacturing must be able to provide consistent hole placement and sealing to avoid leaks or short circuits in the battery pouch.

Flexible and wear-resistant strands of conductive fibre have been used to make smart clothes with embedded computers and sensors, such as hats that can sense traffic light changes.

Previous efforts to create fibres with a hardwearing coating and a conductive core have run into problems. Materials cooling and contracting at different rates during manufacture or being twisted or washed once in a final product often cause tiny stress cracks, stopping a smart device from working.

Now, at Nanyang Technological University, Singapore, and his colleagues have made conductive materials that cool and contract in a similar way to the aluminosilicate glass used in smartphone screens, so that stress cracks don’t appear. The material borrows techniques for making fibre-optic cable, and Wei says the process is both cheap and “industry ready”.

The technique involves placing a semiconductor wire made of silicon or germanium into molten glass at temperatures of about 1000°C and pulling it into fine strands. The glass is later etched away with hydrofluoric acid and replaced with a polymer coating, which allows for a more flexible material. The fibres can stretch for up to 10 kilometres.

Small amounts of this fibre are then woven into a fabric using standard weaving machines and normal cotton. Wei says cotton is needed to make the clothes comfortable because the new material alone feels like “fishing line” against the skin.

The researchers have used the fibre to make several prototype items that also include electronic sensors and chips that communicate via the conductive material, such as a hat that senses when traffic lights change colourĚýand passes the information to a smartphone app, a jumper that can receive and decode images transmitted by light pulses rather than radio waves, and a watch strap that measures its wearer’s heart rate.

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In tests over six months in which the clothes were worn, washed and dried repeatedly, the fibres held up and continued to conduct electricity.

There is still a weakness, however: the link between the flexible material and the rigid circuit boards that hold computer chips and other components tends to fail after a few months, causing the smart features to stop working.

“The only part that always leads to the failure of the test is the connection between the fibre and the outer circuit,” says Wei. “To find a stable way to make the connection, that’s the challenge now.”

Temporary tattoos made using graphene can continuously monitor blood pressure for days. The approach is very different from standard blood pressure cuffs, which haven’t changed much since they were first invented around a hundred years ago.

“The graphene tattoo is weightless, it is invisible. You put it on and you forget about it,” says at the University of Texas at Austin.

Akinwande and his colleagues created the tattoo, which consists of 12 nearly invisible graphene strips placed in two rows along the two main forearm arteries. The outermost strips of each row send small electrical signals deep into the arm and the inner strips can then detect the response and how it changes, which can be converted into a measure of blood flow.

The tattoos can continuously measure blood pressure with “Grade A” accuracy as defined by – the highest possible accuracy level for a medical device.

The team tested the tattoos on six people and found they worked well during hours of desktop work and walking. They even worked when participants performed push-ups or plunged their arms into a bucket of ice-cold water for a minute. The tattoos also worked at night without disturbing anyone’s sleep.

Currently, much of the hardware needed to record and analyse the data from the tattoo has to sit nearby and is connected by a wire. But in the future, the team might explore using wireless connections. Another possibility would be to use contacts between the graphene tattoos and a smartwatch worn on top of them, says Akinwande.

Having a device that can measure blood pressure even when the wearer is on the move or sleeping could prove useful in delivering a more reliable, baseline measurement. “We want to move towards measuring the blood pressure continuously and what I call passively, meaning that you don’t even know when your blood pressure is being measured,” says team member at Texas A&M University.

By comparison, a standard blood pressure monitor that makes a one-time measurement at the doctor’s office or at home can be inaccurate for many reasons, including factors such as stress or dehydration. Some people even experience temporary spikes in blood pressure when they see a doctor, says Jafari. Standard monitors also usually require people to sit instead of standing or moving around.

Other researchers have been investigating (PPG) as a light-based method of measuring blood pressure. Popular wearables such as have been testing this approach, but factors such as skin colour and the layer of fat underneath the skin can throw off PPG measurements.

Having demonstrated the graphene tattoos’ potential with healthy volunteers, the researchers next want to test them in people who have high blood pressure.