Scientists Built a Flexible Brain Probe That Can Interact With Multiple Regions at Once

A new generation of ultra-thin brain implant may give scientists a far more precise way to study neural circuits and, eventually, help treat conditions such as epilepsy. The experimental device, developed by an international research team, can simultaneously deliver light and drugs while recording electrical activity deep inside the brain.

The system, called the microfluidic Axialtrode, or mAxialtrode, is a long, flexible electrode containing microscopic channels along its length. It is designed to both record and influence brain activity at multiple depths through a single, minimally invasive implant. The work was recently detailed in the journal Advanced Science.

How the new implant is built

The mAxialtrode begins as a relatively thick polymer rod that is heated and drawn into a needle-thin fiber. At its center is a light-guiding channel capable of carrying laser light for optogenetic experiments, in which genetically modified nerve cells are activated or silenced using specific wavelengths.

Around this optical core, researchers integrated eight microscopic channels capable of carrying fluids or ultra-fine metal wires. These channels allow the same implant to deliver drugs to selected brain layers while simultaneously recording electrical activity from nearby neurons with high temporal precision.

The completed fiber measures less than 0.5 millimeters in diameter and is considerably more flexible than conventional silicon-based probes. This softness is intended to reduce the mechanical mismatch with delicate brain tissue, potentially helping limit scarring and inflammation when an implant remains in place for extended periods.

Why flexibility and length matter

Most current brain implants rely on rigid materials such as silicon, which can irritate surrounding tissue and trigger immune responses. In contrast, the mAxialtrode’s plastic-like optical fibers are designed to move more naturally with the brain’s subtle movements inside the skull.

The device also features a specially angled tip intended to minimize tissue damage during insertion. Rather than pushing through tissue with a blunt edge, its sharpened, asymmetric design is meant to move more gently through different brain layers, leaving a narrower track and potentially improving long-term stability.

Crucially, the implant is designed as an “axial” tool, interacting with multiple points along its length rather than solely at its tip. This allows researchers to access several brain regions or layers along a single vertical trajectory and observe how signals propagate through networks involved in processes such as memory, decision-making and seizure activity.

Limitations of existing optical fibers

Standard optical fibers used in neuroscience are generally flat-ended strands of glass or plastic that emit light only from their distal tip. Although widely used in optogenetics to activate targeted populations of neurons, they typically limit experiments to a single stimulation site at a time.

This one-point approach can be restrictive because many brain functions depend on coordinated activity across layered structures such as the cortex and deeper regions including the hippocampus. Researchers may therefore need to insert multiple fibers or electrodes to study these circuits, increasing surgical complexity and tissue disruption.

By combining optical delivery, fluid injection and multi-site electrical recording within one slender probe, the mAxialtrode aims to reduce the number of separate devices that need to be inserted. In principle, this could simplify experiments and enable more sophisticated approaches to mapping how information travels through the brain.

Results from live animal testing

To test the concept, the international research team evaluated the implant in live mice. The fiber was inserted into the animals’ brains and connected to external light sources, micro-pumps and electrophysiology equipment, allowing researchers to simultaneously stimulate and monitor cortical and deeper structures.

Experiments showed that the device could deliver both blue and red light, enabling researchers to control different optogenetic tools while recording electrical signals from regions including the cerebral cortex and hippocampus. The recordings captured how neurons responded to light-driven activation, providing a detailed view of network dynamics.

The microscopic fluid channels were also used to inject separate substances at different depths spaced nearly 3 millimeters apart. This demonstrated that researchers could potentially deliver drugs or neuromodulators precisely where needed while monitoring the immediate electrophysiological effects in surrounding tissue.

Despite the complexity of the experimental setup, the single lightweight fiber was well tolerated by the mice, which were able to move freely without obvious distress. The researchers note that this behavioral tolerance represents an important step toward future long-term experiments involving freely moving animals.

Potential impact on epilepsy and beyond

The project brought together expertise from Denmark’s Technical University, or DTU, the University of Copenhagen, University College London and other partners, including specialists in epilepsy and neural circuit analysis. Their goal is eventually to move the technology from an experimental research platform toward a tool with potential clinical relevance.

In epilepsy, seizures often arise when abnormal electrical activity spreads through interconnected brain networks. A device capable of monitoring electrical patterns, delivering anti-seizure drugs and applying targeted light or electrical stimulation in the same region could potentially offer a way to interrupt seizures more precisely than current approaches.

Beyond epilepsy, the implant could support research into memory formation, decision-making, sleep and neuropsychiatric disorders, where communication between cortical layers and deeper structures is critical. Researchers envision experiments that follow how information propagates through neural circuits in real time while specific points within those networks are simultaneously modulated.

Long road to clinical use

Despite its potential, the scientists emphasize that the mAxialtrode remains far from routine clinical use. Any implant intended for patients would need extensive biocompatibility testing, long-term safety studies and rigorous regulatory review before being introduced into hospitals.

Engineers must also refine manufacturing methods so the fibers can be produced consistently at scale and integrated with reliable connectors, pumps and stimulation hardware suitable for human use. How durable the device remains inside a living brain over months or years is another unanswered question that future studies will need to address.

The research team is now pursuing patent protection for the underlying technology and exploring partnerships intended to accelerate its development. If further studies in larger animals prove successful, early-phase clinical trials involving carefully selected patient groups could follow later this decade.

Although significant scientific and regulatory challenges remain, the mAxialtrode reflects a broader trend in neurotechnology toward multifunctional, minimally invasive systems that can both record and influence brain activity. Such tools could eventually reshape how researchers — and potentially clinicians — investigate complex neurological diseases.