Similarities and differences in coatings for magnesium-based stents and orthopaedic implants

Abstract

Magnesium (Mg)-based biodegradable materials are promising candidates for the new generation of implantable medical devices, particularly cardiovascular stents and orthopaedic implants. Mg-based cardiovascular stents represent the most innovative stent technology to date. However, these products still do not fully meet clinical requirements with regards to fast degradation rates, late restenosis, and thrombosis. Thus various surface coatings have been introduced to protect Mg-based stents from rapid corrosion and to improve biocompatibility. Similarly, different coatings have been used for orthopaedic implants, e.g., plates and pins for bone fracture fixation or as an interference screw for tendon-bone or ligament-bone insertion, to improve biocompatibility and corrosion resistance. Metal coatings, nanoporous inorganic coatings and permanent polymers have been proved to enhance corrosion resistance; however, inflammation and foreign body reactions have also been reported. By contrast, biodegradable polymers are more biocompatible in general and are favoured over permanent materials. Drugs are also loaded with biodegradable polymers to improve their performance. The key similarities and differences in coatings for Mg-based stents and orthopaedic implants are summarized.

Bioabsorbable zinc ion induced biphasic cellular responses in vascular smooth muscle cells

“…Among them, Mg-based alloys have been widely explored in stent applications because of their biodegradability, bioabsorbility, and low thrombogenicity1234. However, the main drawbacks of conventional Mg alloys are insufficient mechanical strength and rapid corrosion accompanied with hydrogen gas evolution, pH increase, and premature loss of mechanical integrity5.…”

Microstructural characterization, biocorrosion evaluation and mechanical properties of nanostructured ZnO and Si/ZnO coated Mg/HA/TiO2/MgO nanocomposites

“…Sustained drug release is essential in preventing an inflammation response and reducing late restenosis. It has been shown that porosity and size had effects on the drug release mechanisms of PLGA [52]. Nano porosities in coating layers facilitate the mechanical interlocking of the cells with the surface, thereby favouring osseointegration process.…”

Reduction in the Corrosion Rate of Magnesium and Magnesium Alloy Specimens and Implications for Plain Fully Bioresorbable Coronary Artery Stents: A Review

“…2) in the review by Ma et al [34], the subject is coatings for both Mg-based bioresorbable stents and orthopaedic implants and only a minimal reference to corrosion is made; and 3) the review by Uddin et al [35] focused on surface treatments for controlling the corrosion of Mg and Mg-based alloys for applications in orthopaedics and cardiovascular stenting; and 4) the review by Hornberger et al [36] is on coatings for biomedical applications and not on stents per se and the coverage on corrosion is short.…”