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The technology harnesses the brain’s own blood chemistry to assemble soft, light-controlled electrodes around neurons. A single shot transforms the mice’s brains into a biomanufacturing machine. Blood proteins churn the injected chemicals into a soft, flexible electrode mesh that seamlessly wraps around delicate neurons. Pulses of light aimed at the mesh quiet hyperactive cells. All the while, the mice go about their merry ways, with no inkling they’ve been turned into cyborgs. This science fiction-like invention is the brainchild of Purdue University scientists seeking to reimagine brain implants. These devices, often composed of rigid microelectrode chips, have already changed lives. They can collect electrical signals from the brain or spinal cord and translate these signals into speech or movement—returning lost abilities to people with paralysis or diseases of the brain. Implants can also jolt brain activity and pull people out of severe depression. Yet most implants require extensive surgery and risk damaging the brain’s delicate tissue. The new technology would avoid these downsides by building electrodes directly at the target. “Our work points to a future where doctors could ‘grow’ soft, wire-free electronic interfaces inside the brain using the patient’s own blood, then gently dial brain activity up or down from outside the head using harmless near-infrared light,” study author Krishna Jayant said in a press release. Probes Galore The brain produces every one of our sensations, movements, emotions, and decisions. Scientists have long sought to decode and manipulate its activity with a range of hardware. Some devices use electrodes to monitor single neurons in a lab dish. Others are physically inserted into brain regions that encode cognition and emotion. Some designs sit atop the brain, without puncturing its delicate tissue, and capture dynamic brain waves like a wide-lens camera. But brain tissue is soft and squishy; microelectrodes are not. The mismatch often leads to scarring, signal loss, and shortened device lifetimes. Replacing broken or infected implants is surgically complex and can further damage the brain. Some experts have even raised ethical concerns about long-term care. A recent explosion of soft, biocompatible materials suggests alternatives are possible, and we’ve seen a wave of creative new probes. In one example, a silk-like mesh drapes over the brain’s surface, and a related version maps electrical activity in brain organoids. Another device is smaller than a cell and, after injection, hitches a ride on immune cells into the brain. These systems can record and alter brain activity. But prebuilt implants often require surgery and struggle to integrate with their hosts without damaging surrounding tissue. So, why not grow an electrode directly inside the brain? “The ability to synthesize [conductive] materials on demand at a target site could overcome the limitations of conventional synthetic implants,” wrote M.R. Antognazza and G. Lanzani at the Italian Institute of Technology, who were not involved in the study. Under Construction Our cells are natural manufacturers, constantly assembling things like proteins, genetic messengers, and membranes. Cells rely on two essential ingredients to construct the complex structures of life: Biological building blocks and catalysts to bind them together. Synthetic materials work the same way. Monomers link like Lego blocks to form polymers with the help of a catalyst. The discovery of electrically conductive polymers, meanwhile, has galvanized efforts to grow living bioelectronics directly inside the body. In a previous study, researchers genetically engineered cells to produce a protein catalyst that helps assemble conductive structures on the surfaces of living neurons. Another approach used hydrogen peroxide—a common first-aid staple—to compile monomers into reliable electrodes that monitor nerves in leeches. These quirky early successes showcased the promise of brain-built electronics, but hit hard limits. The chemistry often relied on catalysts toxic to neurons. Even when successfully formed, the electrodes mostly just listened. Changing brain activity required additional physical cables. The Purdue team rewrote the recipe. They designed a monomer, called BDF, that with the help of hemoglobin—a protein in red blood cells—becomes a soft, flexible, and electrically conductive mesh surrounding neurons at the site of injection. The willowy electrode hugs the brain’s anatomy and moves with it, minimizing physical damage. It’s responsive to near-infrared light and can translate light pulses from outside the skull into electrical signals that alter brain activity. “Our key idea was to let the body’s own chemistry do the hard work,” said study author Sanket Samal. The appeoach worked in several tests. Injecting BDF into store-bought beef and lamb steaks produced the electrode mesh within a day at human body temperature. In zebrafish embryos, a