Controlling the biodegradation rate of magnesium-based implants through surface nanocrystallization induced by cryogenic machining

Magnesium alloys are emerging as a new class of biodegradable implant materials for internal bone fixation. They provide good temporary fixation and do not need to be removed after healing occurs, providing the relief to the patients and reducing the healthcare costs. However, premature failure of these implants often occurs due to the high biodegradation rate caused by low corrosion resistance of magnesium alloys in physiological environments. To control biodegradation/corrosion of magnesium alloys, grain refinement on the surface was achieved through machining-induced severe plastic deformation. Liquid nitrogen was used during machining to suppress grain growth. White layers, which consist of nanocrystallized grain structures, are reported herein for the first time in magnesium alloys. By controlling the machining conditions, white layers with various thicknesses were fabricated. In vitro corrosion tests proved that different machining conditions can significantly change the biodegradation rate of magnesium alloys.