Fiber-shaped neural probe with alterable elastic moduli for direct implantation and stable electronics-brain interfaces

Implantable neural probes face a dilemma. Rigid neural probes ease a direct implantation, but the brain tissue suffers from a vulnerable interface and strong neuroinflammatory response due to mechanical mismatch between the probe and the brain tissue. Flexible neural probes offer stable interfaces and eliminated neuroinflammatory responses but require auxiliary implantation. Here we have created a new kind of micro fiber-shaped neural probes with alterable elastic moduli before and after implantation. Carbon nanotube fiber and calcium crosslinked sodium alginate functioned as core electrode and sheath layer, respectively. The response of calcium crosslinked sodium alginate to water will alter the probe elastic moduli from ~10 GPa to ~10 kPa post implantation which is close to the elastic modulus of the brain tissue. The micro fiber probes were directly implanted into the mice brain without any assistant materials. After implantation, they became soft and offered dynamically adaptable interfaces with reduced inflammatory responses, benefiting long-term monitoring of neuron signals. A continuous 4-week monitoring of neuron signals had been achieved. The simplicity of the strategy makes it suitable for versatile neuron techniques in neuron recording and modulation.