Biopolymeric coatings for delivery of antibiotic and controlled degradation of bioresorbable Mg AZ31 alloys

Polymeric Coatings for Magnesium Alloys for Biodegradable Implant Application: A Review

Magnesium (Mg) alloys are a very attractive material of construction for biodegradable temporary implants. However, Mg alloys suffer unacceptably rapid corrosion rates in aqueous environments, including physiological fluid, that may cause premature mechanical failure of the implant. This necessitates a biodegradable surface barrier coating that should delay the corrosion of the implant until the fractured/damaged bone has healed. This review takes a brief account of the merits and demerits of various existing coating methodologies for the mitigation of Mg alloy corrosion. Since among the different coating approaches investigated, no single coating recipe seems to address the degradation control and functionality entirely, this review argues the need for polymer-based and biodegradable composite coatings.

Progress in bioactive surface coatings on biodegradable Mg alloys: A critical review towards clinical translation

Mg and its alloys evince strong candidature for biodegradable bone implants, cardiovascular stents, and wound closing devices. However, their rapid degradation rate causes premature implant failure, constraining clinical applications. Bio-functional surface coatings have emerged as the most competent strategy to fulfill the diverse clinical requirements, besides yielding effective corrosion resistance. This article reviews the progress of biodegradable and advanced surface coatings on Mg alloys investigated in recent years, aiming to build up a comprehensive knowledge framework of coating techniques, processing parameters, performance measures in terms of corrosion resistance, adhesion strength, and biocompatibility. Recently developed conversion and deposition type surface coatings are thoroughly discussed by reporting their essential therapeutic responses like osteogenesis, angiogenesis, cytocompatibility, hemocompatibility, anti-bacterial, and controlled drug release towards in-vitro and in-vivo study models. The challenges associated with metallic, ceramic and polymeric coatings along with merits and demerits of various coatings have been illustrated. The use of multilayered hybrid coating comprising a unique combination of organic and inorganic components has been emphasized with future perspectives to obtain diverse bio-functionalities in a facile single coating system for orthopedic implant applications.

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The challenges and current status of coatings are reviewed in light of clinical requirements.

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Multilayered hybrid coatings have been emphasized to obtain diverse bio-functionalities.

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The future developments and research directions on coatings for biodegradable implants are highlighted.

Simulating In Vitro the Bone Healing Potential of a Degradable and Tailored Multifunctional Mg-Based Alloy Platform

This work intended to elucidate, in an in vitro approach, the cellular and molecular mechanisms occurring during the bone healing process, upon implantation of a tailored degradable multifunctional Mg-based alloy. This was prepared by a conjoining anodization of the bare alloy (AZ31) followed by the deposition of a polymeric coating functionalized with hydroxyapatite. Human endothelial cells and osteoblastic and osteoclastic differentiating cells were exposed to the extracts from the multifunctional platform (having a low degradation rate), as well as the underlying anodized and original AZ31 alloy (with higher degradation rates). Extracts from the multifunctional coated alloy did not affect cellular behavior, although a small inductive effect was observed in the proliferation and gene expression of endothelial and osteoblastic cells. Extracts from the higher degradable anodized and original alloys induced the expression of some endothelial genes and, also, ALP and TRAP activities, further increasing the expression of some early differentiation osteoblastic and osteoclastic genes. The integration of these results in a translational approach suggests that, following the implantation of a tailored degradable Mg-based material, the absence of initial deleterious effects would favor the early stages of bone repair and, subsequently, the on-going degradation of the coating and the subjacent alloy would increase bone metabolism dynamics favoring a faster bone formation and remodeling process and enhancing bone healing.

Corrosion resistance and antibacterial properties of hydroxyapatite coating induced by gentamicin-loaded polymeric multilayers on magnesium alloys

As a result of their good biocompatibility, bioactivity, and mechanical properties, magnesium (Mg) alloys have received considerable attention as next generation biodegradable implants. Herein, in order to achieve a proper degradation rate and good antibacterial ability, we reported a novel hydroxyapatite coating induced by gentamicin (GS)-loaded polymeric multilayers for the surface treatment of the Mg alloy. The coating was characterized by X-ray diffraction, fourier transform infrared spectroscopy and scanning electron microscopy. The as-prepared hydroxyapatite coating showed the compact morphology and a well-crystallized apatite structure. This coating could improve the adhesion strength and reduce the corrosion rate of the substrate in simulated body fluid solution. Meanwhile, the drug release and antibacterial experiments demonstrated that the GS loaded specimen revealed a significant antimicrobial performance toward Staphylococcus aureus and had a prolonged release profile of GS, which would be helpful to the long-term bactericidal activity of the Mg implant. This coating showed acceptable biocompatibility via MTT assay and Live/dead staining. Thus, the multilayers-hydroxyapatite coated Mg alloy could improve the corrosion resistance and biocompatibility while delivering vital drugs to the site of implantation.