Deep-Penetrating Mechano-Optics: Autonomous NIR signaling for Bio-Implant surveillance

The development of near-infrared (NIR) mechanoluminescent materials that operate autonomously without external excitation is crucial for deep-tissue biomechanical sensing but remains challenging due to the scarcity of efficient, long-wavelength emitting systems. Herein, we report a highly efficient, self-recoverable NIR-I mechanoluminescent material based on Cr 3+ -doped MgNb 2 O 6 . Through strategic Li + co-doping for charge compensation, we achieved a 2.75-fold enhancement in mechanoluminescent intensity. The optimized phosphor exhibits broadband emission centered at 880 nm, representing one of the longest wavelengths reported for Cr 3+ -activated mechanoluminescent systems. This deep-penetrating NIR-I emission enables detectable mechano-optical signaling through up to 10 mm of biological tissue. Leveraging this capability, we design a proof-of-concept application as a smart, mechano-responsive liner for in situ monitoring of implant kinematics and positioning accuracy in total knee arthroplasty. This work not only introduces a high-performance NIR-I mechanoluminescent material but also opens new avenues for real-time, non-invasive surveillance of bio-implants and deep-tissue biomechanics.