Magnesium exhibits a promising applicability biodegradable implant material.Biodegradable implants allow musculoskeletal healing while safely degrading in the physiological environment to finally give place to the completely restored tissue. This technology spares injured patients to multiple surgical interventions and harmful side effects than can arise from conventional implant materials such as Ti-based alloys and stainless steel. Mainstream biodegradable materials, like PGA and PLA, can display unsatisfactory mechanical strength and acidic degradation products. Statistics tell us that metallic implants are removed 19 to 54% of the time depending on the fracture type. Implant removal has been considered as the biggest drawback by 91% of the patients in a recent study conducted in the UK, with 80% of the enquired patients showing willingness to participate in clinical trials for comparison between bio-resorbable implants and permanent ones. Economically, biodegradable implants can be more cost-effective up to seven hundred dollars less per implant. Hence, the socioeconomic demand for bio-resorbable prosthetic devices is undeniable and asks for improved solutions that can satisfy the necessities of all involved parts, from patients to health authorities. Magnesium is the lightest engineering metal with high strength-to-weight ratio, it abundantly present in bone and an essential element in body metabolism, making it biocompatible. Its mechanical properties like the elastic modulus and the compressive yield strength are close to those of bone. Although the initial use of Mg-based implants can be dated back to 1878, its use for bioapplications was abandoned in the mid-20th century, due to the fast corrosion rate in chloride containing media, which is the case of the human body. Magnesium suffers mainly from localized corrosion with side propagating pitting, with homogeneous corrosion being hardly relevant. Because Mg is anodic to any other engineering metal, macro and micro galvanic coupling between the metal and other metal impurities and secondary phases are key aspects in controlling the degradation rate. An additional complication is hydrogen evolution deriving from the cathodic partial reactions, which can cause toxic effects for the body tissue and induce local embrittlement. Pitting and hydrogen embrittlement are two of the most propelling forms of causing premature implant failure due to stress corrosion cracking. It is also an essential element in body metabolism. Today, the biodegradability of Mg and Mg-alloys is a hot topic motivating the development of corrosion controlling strategies in order to validate the applicability of these materials for artificial orthopedic load bearing structures such as pins, plates, screws, etc.
During the MAGPLANT project, localized electrochemical techniques like micro-ISE (Ion-Selective Electrodes), SVET (Scanning Vibrating Electrode Technique) and microamperometry have been used to investigate Mg corrosion processes in various corrosion environments including the magnesium/cellular interface.
