A Visual Hydrogen Sensor Prototype for Monitoring Magnesium Implant Biodegradation.

Alternative metals such as magnesium (Mg) and its alloys have been recently developed for clinical applications such as temporary implants for bone and tissue repair due to their desirable mechanical properties and ability to biodegrade harmlessly by releasing Mg, OH, and H as biodegradation products. The current methods for monitoring Mg-alloy biodegradation are either invasive and/or costly, complex, or require large equipment and specially trained personnel, thus making real-time and point-of-care monitoring of Mg-alloy implants problematic. Therefore, innovative methods are critically needed. The objective of this research was to develop a novel, thin, and wearable visual H sensor prototype for noninvasive monitoring of Mg-implant biodegradation in medical research and clinical settings with a fast response time. In this work, we successfully demonstrate such a prototype composed of resazurin and catalytic bimetallic gold-palladium nanoparticles (Au-Pd NPs) incorporated into a thin agarose/alginate hydrogel matrix that rapidly changes color from blue to pink upon exposure to various levels of H at a constant flow rate. The irreversible redox reactions occurring in the sensor involve H, in the presence of Au-Pd NPs, converting resazurin to resorufin. To quantify the sensor color changes, ImageJ software was used to analyze photographs of the sensor taken with a smartphone during H exposure. The sensor concentration range was from pure H down to limits of detection of 6 and 8 μM H (defined via two methods). This range is adequate for the intended application of noninvasively monitoring Mg-alloy implant biodegradation in animals for medical research and patients in clinical settings.