Stiffness‐Switchable Conductive Nanocomposites with Temperature‐Invariant Conductivity for Long‐Term Brain‐Computer Interfaces on Hair‐Covered Scalp

ABSTRACT Reliable neural recording on densely hair‐covered scalp remains challenging due to the incompatibility between efficient hair penetration, conformal skin contact, and low‐impedance electrical interfacing. Here, we report a claw‐shaped dry electrode that integrates thermoresponsive phase‐transition networks for reversible stiffness switching, with temperature‐invariant conductivity enabled by crystallization‐induced confinement, achieving comfortable, low‐impedance neural interfacing on densely hair‐covered scalps. The electrode comprises a bottlebrush polymer/multi‐walled carbon nanotubes (MWCNTs) composite, in which crystallizable alkyl side chains act as switching units, enabling rigid hair penetration at ambient conditions and compliant, adhesive scalp interfacing at skin temperature. Importantly, side‐chain crystallization imposes spatial confinement on MWCNTs, enabling efficient percolated networks with an ultralow percolation threshold (0.47 wt.%) and high electrical conductivity (1.8 S m ⁻¹ ). Meanwhile, strong MWCNTs‐polymer interfacial interactions provide multipoint anchoring that helps preserve conductive pathway continuity across phase transitions, achieving low electrode‐scalp impedance (∼38 kΩ) upon softening and conformal contact. Validated by steady‐state visual evoked potential measurements, this electrode enables high‐fidelity and frequency‐resolved neural signal acquisition and maintains stable operation for over 100 days, supporting a fully wearable brain‐computer interface with real‐time drone control.