Corrosion of metallic biomaterials

ANDREA GOMEZ SANCHEZ; SILVIA CERÉ

Handbook of Biomaterials

John Wiley & Sons Inc

Año: 2023;

IntroductionIn the last 40 years? life expectancy increased more than 10 years and preserving an optimal quality of life is a challenge for science. The demand for high-performance implantable biomaterials in cardiology, vascular therapy, orthopaedic and dentistry has dramatically increased with the aim of replacing or improving the lost functionality [1]. Metallic materials have been used for more of 200 years as biomaterials, however, in the last years there has been a big concern to achieve specific goals (proper degradation or long lasting life in body fluid for cardiovascular and orthopaedic purposes, bioactivity for enhancing bone osseointegration, functionalization with drug carriers, among others), together with the main property required for the biocompatible metallic materials that is, adequate mechanical properties for the function they have to accomplish in service [2]. Since metallic materials are hosted in the body, and body environment is a corrosive media to most of the biocompatible metals, corrosion phenomena should be a concern, being a clinically important phenomenon [3]. The corrosion products are biologically active, and patients do exhibit symptoms relative to corrosion products from implants that must be minimized by proper and better materials selection that have to be tailored for the function they are applied for. Materials applied in regenerative medicine play a preponderant role to attend a multidisciplinary problem that concerns the intersection between medicine and materials science in favor of improving the quality of life.Research strategy Corrosion matters. Since corrosion is a surface phenomenon, the implant surface and its engineering play a key role in the performance in service of the implant, so many efforts are done in studying and further modifying the surface in order to improve corrosion resistance and/or enhance a pursue property as osseointegation, for example. All biocompatible metallic materials corrode in the body environment at some extent. There is a need of testing both permanent and degradable metallic materials in body fluids and do the intent of predicting implant performance in time. There are, however, major concerns when planning the assays. A rationalized testing plan should begin with in vitro testing, and once this stage is overcome, pass to the in vivo stage to contrast the implant performance in a more realistic media. There are many variables to take into account when in vitro testing is planned: electrolyte composition and its gas content, temperature, immersion time of the samples in the media, a battery of complementary assays simultaneously performed (e.g. electrochemical tests, analytical tests, surface tests). An additional problem that arises when facing a new study is that bibliography is scattered and difficult to compare since many of the above named variables can be interchanged and combined and also, different surface finish can be provided to the material, adding an extra variable that affects the corrosion response. The in vivo analysis also presents numerous variables in literature: animal model, place of implantation, implantation time, and another brunch of kind of analysis for the histology results, blood testing, mechanical properties and so on. The wide spectra of study and the enormous quantity of information that appears in bibliography can be overwhelming when a decision has to be taken to set an experimental design with the intention of emulate, in the best way possible, the service condition. ChallengesWhen studying corrosion of implantable metals, one of the main concerns is ?how long it is going to last?, whenever the implant is designed for a permanent or temporary device, that question remains. The prediction of implant life is not straight forward. Permanent devices do not corrode in a uniform way, so, Faraday law to predict corrosion rate is not adequate, hence it is crucial to know the predominant corrosion form, and to study the passive layer and its stability. Regarding temporary devices, although a big effort is placed in getting materials that uniformly corrode, still it is a non-achieved goal, and then the alarm regarding the calculus of the corrosion rate by Faraday law, is the same than for permanent implants. Another point to take into account when studying corrosion of implants in vitro is the immersion time of the devices, and the flowing conditions, trying to represent the most faithfully possible the life in service. In an attempt to have in a glance the number of possible ways to face the research, together with the many variables that can be settled to study the corrosion of implantable metals, we organized this chapter in different tables regarding the objective searched.The numerical values obtained from the different corrosion assays that are shown along the tables in this chapter, do not constitute a property, ?correct? or unique value but represent the behavior of the metal in a settled experimental condition, that is composed by many aspects. The change of any of them (electrolyte composition, surface finish, sample geometry, aeration condition, immersion time, among others) can lead to different numerical values, that may be as valid as the ones shown in this tables. The values shown and chosen in the tables were selected among many and very valuable research work, intended to pick up those which were accompanied with the clearest and complete information about the experimental set up. This chapter is organized in XX blocks, first presenting the type of corrosion mainly found in biomaterials, then the standards currently used to evaluate corrosion of metallic prosthesis, and potential materials, the simulated body fluid solutions most used in corrosion tests and the ?real? body fluids composition, the ions release of the main prosthesis metals, the surface composition of metallic biomaterials, the electrochemical parameters from polarization tests in biodegradable metals in vitro?.. The organization in tables has the intention of establishing a point of comparison among the results and to help to decide the starting point of a research test in an easier and more visual way.