## 3 Corrosion Properties
The main challenge for Mg and its alloys is to control the rate of degradation, which is caused when it encounters body fluids due to the influence of different factors, such as pH, alloying elements, concentration, and types of ions. This means that magnesium implant materials require sufficient mechanical strength and integrity during their time in the human body. Different studies have revealed that these factors can be controlled by modifying the surface and polymeric coatings. The research literature has shown that there are different types of biopolymers, among which the natural ones stand out due to their biomimetic nature, biocompatibility, and cell proliferation because they provide barriers to limit direct contact between the surface of the Mg and the aqueous biological environment. Medical applications of Mg and Mg alloy coatings are challenging, and achieving a uniform coating and an effective degradation rate is difficult. In many cases, a pretreatment on the Mg surface is required to achieve better adhesion and corrosion resistance. Different surface  
Figure 1: Degradation process for biodegradable Mg implant. Figure 2: A schematic diagram illustrating (**a**) the implantation site and (**b**) magnesium alloy’s changes over time at 0.6- and 12-months post-implantation. modification methods were reviewed to improve the corrosion resistance of magnesium or its alloys. Thus far, many techniques have been developed for the protection of the substrate; however, not all of them are used since some are toxic or repress biocompatibility. The most commonly used technique in natural biopolymers is chemical conversion because it provides excellent adherence, attributed to the formation of chemical bonds with the substrate. A candidate for biomedical implants must satisfy several requirements: it must offer mechanical support, degrade at a reasonable rate to be replaced by the new bone, favor cell adhesion, proliferation, and cellular differentiation, prevent infection, and exert a positive osteogenic effect. The latter makes corrosion prevention for Mg alloys very attractive, with the release of osteoinductive factors and growth factors to speed up the healing process. Figure 3 shows the mechanism for biodegradable implants. Indicators such as pH change, hydrogen evolution, Mg\({}^{2+}\) release, changes in mechanical strength, or morphological changes are essential in measuring the corrosion behavior of the material. However, mechanical strength changes have not been widely investigated. There are very few investigations of natural coatings on Mg with in vivo assessments, which are necessary for future studies. In order to evaluate the potential of these materials in clinical applications, it is necessary to obtain more substantial evidence of optimal performance, qualitative research, and development, together with the collaboration of clinicians to obtain materials for specific uses. Natural coatings are promising because they protect against corrosion, can be functionalized, improve osseointegration, and the body can metabolize the subproducts of the degradation as drug release. There are many efforts to diminish corrosion, and the progress is promising. However, more studies with other natural polymers, such as fibrin or stearic acid, which are more frequently studied with other metals, are necessary. Furthermore, more studies on drug delivery and the release of osteoinductive factors and growth factors are required. Undesired degradation of certain implants could be dangerous when placed in the human body if the ions being released are toxic; they could cause discoloration of the implant or the adjacent tissue [40; 41]. Furthermore, unwanted corrosion may compromise the mechanical properties of the implant. Types of unwanted corrosive behavior in implants in  
Figure 3: The mechanism for biodegradable implants. clude galvanic, pitting, crevice, and fatigue corrosion. In one such example from a fractured stainless-steel implant inside a patient's thigh, [PERSON] et al.