Visual H₂ sensor for monitoring biodegradation of magnesium implants in vivo

A visual sensor for H₂ was used to transdermally monitor H₂ that originated from biodegrading magnesium (Mg) alloys implanted subcutaneously in mice. The visual sensor consisted of a thin film of H₂-sensitive material (MoO₃ and Pd catalyst) coated on a flexible plastic sheet that was pressed against the mouse skin directly above the implant. Although the H₂ levels permeating through the skin during the degradation process were very low, the sensor changed color to give a three dimensional (3D) visualization of H₂ permeation. The correlation between the visual sensor response and measurements made with an electrochemical H₂ microsensor on several magnesium alloys demonstrates that the visual sensor has the capability to monitor in real-time the dissolution rate of implants in vivo. This detection method is noninvasive, easy to implement, effective and potentially low cost compared to electrochemical detection.

Biodegradable Mg implants offer advantages over permanent implants such as stainless steel that are used for broken bone repair. Mg alloys gradually dissolve, avoiding the need for removal by a later surgery if complications arise. Here we report a visual H₂ sensor that can be used in the research laboratory to monitor the corrosion process in vivo during animal testing of different Mg alloys. The sensor consists of a plastic sheet with a thin coating that changes color in the presence of H₂ gas. The sensor is easily used by taping it on the skin over the Mg implant. The color change gives a map of the H₂ level permeating from the degrading Mg through the skin above it. This low cost, simple method of monitoring the dissolution of biodegradable implants would greatly facilitate the development of the biodegradable materials, especially in animal studies where in vivo biodegradation is tested.