Bioinspired Ultrasensitive and Stretchable MXene-based Strain Sensor via Nacre-Mimetic Microscale "Brick-and-Mortar" Architecture.

The development of wearable strain sensors with simultaneous large stretchability (strain >55%) and high sensitivity (gauge factor >100) remains a grand challenge to this day. Drawing on inspiration from nature, nacre has demonstrated outstanding mechanical properties, especially combining high strength and toughness, which is due in part to its delicate hierarchical layered architecture with rich interfacial interactions. Herein, we demonstrate that strain sensors based on this nacre-mimetic microscale "brick-and-mortar" architecture can simultaneously achieve ultrahigh sensitivity and large stretchability, while performing well in linearity, reliability, long-term durability, and monotonicity. The bioinspired sensor demonstrated a gauge factor >200 over a range of working strains up to 83%, and achieved a high gauge factor exceeding 8700 in the strain region of 76-83%. This successful combination of high sensitivity and large stretchability is attributed to 1) the microscale hierarchical architecture derived from the amalgamation of two-dimensional titanium carbide (MXene) Ti3C2Tx/one-dimensional silver nanowire "brick" and poly(dopamine)/Ni2+ "mortar" and 2) the synergistic toughing effects from interfacial interactions of hydrogen and coordination bonding, layer slippage, and molecular chain stretching. The synergistic behavior of the "brick" and "mortar" allows for controlled crack generation for high sensitivity, but can also dissipate considerable loading energy to promote stepwise propagation of cracks while stretching, guaranteeing the significant comprehensive sensing performance. Moreover, this bioinspired strain sensor is employed to monitor human activities under different motion states to demonstrate its feasibility for wearable, full-spectrum, human health and motion monitoring systems.