Mg Biodegradation Mechanism Deduced from the Local Surface Environment under Simulated Physiological Conditions

Area of Science:

• Biomaterials Science
• Corrosion Science
• Materials Engineering

Background:

• Magnesium (Mg)-based implants offer biodegradability but lack standardized use due to poorly understood degradation mechanisms.
• Interface pH is critical for controlling Mg degradation and the stability of surface degradation products.
• Dynamic in situ monitoring of interface pH is essential for understanding Mg alloy behavior in physiological environments.

Purpose of the Study:

• To investigate the in situ interface pH evolution on Mg-2Ag and E11 alloys.
• To determine the influence of calcium (Ca2+) on the pH buffering capacity at the Mg alloy/solution interface.
• To elucidate the role of degradation products in stabilizing the local pH environment.

Main Methods:

• In situ interface pH measurements during immersion of Mg-2Ag and E11 alloys.
• Dynamic flow conditions (1.5 mL min-1) using Hank's Balanced Salt Solution (HBSS).
• Comparison of experiments with and without physiological Ca2+ concentrations (2.5 × 10-3 M).

Main Results:

• The presence of Ca2+ promotes the precipitation/dissolution of amorphous calcium-phosphate (Ap-CaP) phases.
• These Ap-CaP phases act as an effective local pH buffering system at the Mg alloy surface.
• Interface pH was stabilized between 7.6 and 8.5, preventing excessive alkalinization.

Conclusions:

• Calcium ions play a crucial role in stabilizing Mg alloy degradation by forming a pH buffering layer.
• Understanding and controlling interface pH is key to optimizing Mg-based biomaterials for medical implants.
• The findings contribute to the standardization and wider application of biodegradable magnesium implants.