A team of researchers from China and Japan has developed a ultra-flexible brain implant electrode array. 

It overcomes a major hurdle in brain-computer interfaces (BCIs): the physical mismatch between stiff metal electrodes and soft brain tissue, which typically leads to chronic inflammation and signal degradation.

The development comes from Tsinghua University’s Shenzhen International Graduate School, the University of Tokyo and the Chinese Academy of Sciences’ Shenzhen-Hong Kong Institute of Brain Science.

Researchers tested the flexible brain implant in animal trials. Interestingly, it achieved long-term signal clarity and safe, stable functionality over an 18-month period.

Soft brain implant

Neuroscientists pursuing the dream of a highly functional brain-computer interface often face the issue of the fleshy wall. The human brain is naturally soft. The advanced electrode arrays implanted in the brain to read thoughts or restore movement are made of rigid metals like platinum.

When you put something hard against something soft inside a moving body, friction wins. Over time, the brain jiggles, the metal rubs, and chronic inflammation forms a wall of protective scar tissue. Signals degrade, and the implant goes blind.

The new development is based on an all-organic, ultra-flexible implant material called Chip (conductive hydrogel with interfacial percolation). 

In the past, trying to use hydrogels, which are water-swollen polymer networks, for brain implants was difficult. These materials are biocompatible but have some issues, such as poor electrical conductivity and a tendency to swell like sponges when in contact with bodily fluids. Swelling distorts the microscopic grid of electrode channels, ruining any hope of micro-engineering. 

The researchers defeated both problems with a manufacturing hack.

To begin with, the hydrogel was pre-anchored to a rigid, ultrathin parylene substrate to fully lock its shape. Then, it was carved using high-precision photolithography while it was completely dry.

The result is a 128-channel array that is a mere 9 micrometers thick — far thinner than a strand of human hair. Moreover, microscopic channels were packed tightly to achieve a data density 10 times higher than any previous hydrogel implant.

As per the study paper, it has an electrical conductivity of 2,512 S/cm, letting it catch the faintest whispers of cellular thought. 

Tested on rabbits

To see if the material could survive the wet environment of a living body, the team implanted the arrays into rabbits. 

For over 550 days, the freely moving animals broadcast crystal-clear neural activity. Even after 18 months, the signal-to-noise ratio remained at 94 percent of its day-one clarity. When the researchers examined the brain tissue using histological staining, they found almost no inflammation, no angry immune response, and no thick scar tissue.

“The resulting all-organic ECoG array conforms to the cortical surface, minimizing foreign body response and providing exceptional signal quality, with the longest record up to 550 d[ays],” the team noted in the study paper. 

The South China Morning Post (SCMP) reported that it demonstrated exceptional durability and safety by tolerating 1,000 cycles of 30 percent tensile strain. It is the absolute maximum deformation real brain tissue can withstand. 

Throughout this intense stress testing, the material maintained stable electrical performance, showing less than a 4 percent variation in its conductivity.

BCIs are advancing rapidly, but their long-term survival inside the body has always been the weak point. Invasive brain implants should ideally last a lifetime rather than just a few years. This new class of organic hydrogel could eventually solve the gap between machine and mind, offering a durable solution for the long term.

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