Building towards a standardised approach to biocorrosion studies: a review of factors influencing Mg corrosion in vitro pertinent to in vivo corrosion

Abstract

The factors that influence magnesium (Mg) corrosion in vitro are systematically evaluated from a review of the relevant literature. We analysed the influence of the following factors on Mg biocorrosion in vitro: (i) inorganic ions, including both anions and cations, (ii) organic components such as proteins, amino acids and vitamins, and (iii) experimental parameters such as temperature, pH, buffer system and flow rate. Considerations and recommendations towards a standardised approach to in vitro biocorrosion testing are given. Several potential simulated body fluids are recommended. Implementing a standardised approach to experimental parameters has the potential to significantly reduce variability between in vitro biocorrosion tests, and to help build towards a methodology that accurately and consistently mimics in vivo corrosion. However, there are also knowledge gaps with regard to how best to characterise the in vivo environment and corrosion mechanism. The assumption that blood plasma is the correct bodily fluid upon which to base in vitro methodologies is examined, and factors that influence the corrosion mechanism in vivo, such as specimen encapsulation, bear consideration for further studies.

Updates on the research and development of absorbable metals for biomedical applications

“…In the in vivo environment, corrosion is influenced by the complex body fluid content (water, organic compounds, dissolved oxygen, anions, cations, amino acids, proteins, plasma, etc.) and the reciprocal interaction with the tissue response (Johnston et al 2018 ). As the metal implantation causes injury, the body responses to it by decreasing the pH value around the implantation site (i.e., 5.3–5.6), and this in turn may accelerate corrosion process of the implant and reduce the local oxygen concentration (Paramitha et al 2017 ).…”

“…As the metal implantation causes injury, the body responses to it by decreasing the pH value around the implantation site (i.e., 5.3–5.6), and this in turn may accelerate corrosion process of the implant and reduce the local oxygen concentration (Paramitha et al 2017 ). In their comprehensive review about factors influencing in vitro corrosion of magnesium and its pertinence to in vivo corrosion, Johnston et al ( 2018 ) urged the inclusion of factors such as (i) proteins, (ii) amino acids, (iii) vitamins, and (iv) tissue encapsulation. At this point, there is a lack of knowledge on the best method to characterize the in vivo environment and corrosion mechanism and to correlate the results with the processing technique and properties of the metals.…”

“…At this point, there is a lack of knowledge on the best method to characterize the in vivo environment and corrosion mechanism and to correlate the results with the processing technique and properties of the metals. In addition, the correlation between the results of in vitro and in vivo corrosion experiments is still barely established (Zheng et al 2014 ; Sanchez et al 2015 ; Johnston et al 2018 ).…”

Degradation and Biocompatibility of AZ31 Magnesium Alloy Implants In Vitro and In Vivo: A Micro-Computed Tomography Study in Rats

“…The correlation between in vitro and in vivo corrosion rates is unclear [41][42][43]. Although there was a correlation between the in vivo and in vitro degradation rates, the corrosion rate of the Mg implant differed markedly, depending on the site, due to the influence of the in vivo environment.…”

“…Johnston et al reported that large variations in in vitro corrosion rates hamper in vitro and in vivo comparisons [43]. Therefore, reproducible and standardized methods are needed to enable more accurate assessment of corrosion rates in vitro [16].…”