Metal 3D-printed fiber-optic-embedded smart interbody fusion cage with force self-sensing

Condition monitoring is crucial for assessing the therapeutic efficacy of implanted medical devices. This study presents an innovative endophytic optical fiber smart interbody fusion cage that integrates Fiber Bragg Grating (FBG) and Fabry-Perot (F-P) microcavity technologies to enable real-time, high-precision load monitoring during interbody fusion and evaluation of bone fusion status. The sensor employs metal additive manufacturing for integrated packaging, with optical fibers embedded in situ during the fabrication of the Interbody fusion device. Prior to embedding, the optical fibers were metalized to prevent damage during the process. Dynamic testing results indicate that the designed sensor exhibits a maximum full-scale error of 2.50%, demonstrating reliable performance in dynamic force measurement. Force-temperature coupling experiments show a maximum full-scale force error of 3.64% and a maximum full-scale temperature error of 4.09%. Finally, a high-temperature sterilization test involving repeated heating to 180 °C and cooling cycles provides preliminary evidence of sensor compatibility with preoperative sterilization conditions. Moreover, only minor spectral changes are observed, and the second force dynamic test conducted post-sterilization presents a maximum full-scale error of 2.80%, validating sensor robustness under these extreme conditions.