MAGICOAT -Controlling the degradation of MAGnesium alloys for biomedical applications using Innovative smart COATings

Summary:

Magnesium and corresponding alloys (Mg) are widely considered as prospective materials for a wide range of structural applications due to its excellent mechanical properties including light weight, high strength/weight ratio and stiffness/weight ratio. The main challenge associated with the use of Mg is the control of its high propensity for oxidation (2.34 V vs. SHE), being the most active metal in the galvanic series. The protection of Mg against corrosion has been inestigated worldwide for vehicle applications, including studies of CICECOUA [1, 2], to keep metal alloys protected from the surroundings and increase service life of structures.

More recently, Mg alloys have also been considered for application as implants in the human body due to its excellent mechanical properties and biocompatibility. These differ much from permanent titanium and stainless steel implants because the aim in using Mg is to favour the absorption of the implant. Nevertheless, current technologies are not yet capable of overcoming the significant high reactivity of Mg alloys, as they are extremely susceptible to uncontrollable and highly localized corrosion, often accompanied by hydrogen formation which brings serious complications if used within the human body.

The main goal of MAGICOAT is to develop smart coating systems capable of controlling the level of degradation of Mg alloys, finding a compromise between the performance of materials and its biocompatibility, which will be assessed at all stages of the project.

The coating system to be developed consists of two layers: an inorganic layer consisting of conversion films of layered double hydroxides (LDHs) and a polymeric layer impregnated with polymeric capsules loaded with relevant active species (Fig.1).

The technology of conversion films based on LDHs has been successfully developed for aeronautical applications in the group of UA with several papers published, a patent filed [number WO2013156541A1] and an FCT project carried out in collaboration with EADS/AIRBUS (Germany) [PTDC/CTMMAT/1515/2012]. In MAGICOAT, the knowledge of these systems will be used as basis for development of LDH films in Mg, giving particular attention to the structural features which may be relevant from a biological perspective: (i) intercalation of biocompatible corrosion inhibitors to delay the onset of corrosion of Mg by release triggered by anionexchange and (ii) interfacial modification of the LDH films with adhesive promoting molecules to increase the compatibility with subsequent polymeric layer. The second layer will be based upon the use of polymeric matrices available for biomedical applications, loaded with different polymeric capsules for controlled release of active species (e.g. corrosion inhibitors, antiinflammatory drugs, lubricant molecules).

In the past decade the group of UA has developed a new generation of active corrosion protection coatings consisting of polymer and inorganic coatings with nanocontainers (capsules and ionexchange clays) loaded with corrosion inhibitors, pH sensing species or healing agents for protection of metal alloys for vehicle applications [38]. This experience will be used in this project, constituting a totally innovative strategy in the biomedical area, focusing on the following objectives:

– Investigation of corrosion mechanism in Mg alloys.
– Selection of biocompatible corrosion inhibitors, antiinflammatory drugs and lubricant molecules.
– Synthesis, growth and characterization of LDH conversion films with intercalated active species for controlled release, upon stimuli by chemical triggers.
– Synthesis and characterization of micro/nanocapsules, for controlled release of encapsulated active species by mechanical action, for incorporation in polymeric coating matrices.
– Development, characterization and optimization of multilayer coatings with enhanced properties (biodegradability, biocompatibility and increased corrosion resistance).

To achieve the proposed goal, MAGICOAT will be implemented by a consortium led by the group of Dr. Tedim from CICECOUA, with recognized expertise on corrosion investigation and development of nanostructured materials for anticorrosion coatings [38], in collaboration with HZG (Germany) and ISPUP. The group of HZG led by Dr. Scharnagl has strong experience on the development of novel light alloys for biomedical applications [9] and the group of ISPUP, led by Dr. Fraga, will be involved in the assessment of biocompatibility of the developed materials [10].

The expected results of MAGICOAT will be the development of a class of biocompatible responsive coatings for bioabsorbale Mg implants. Furthermore, the international nature of the consortium will contribute for an effective dissemination of results to biomedical enterprises. Ultimately, MAGICOAT will become a landmark in the field of coating technology for biomedical applications.