Controllable degradation of medical magnesium by electrodeposited composite films of mussel adhesive protein (Mefp-1) and chitosan

A CO-releasing coating based on carboxymethyl chitosan-functionalized graphene oxide for improving the anticorrosion and biocompatibility of magnesium alloy stent materials

Due to its biofunctions similar to NO, the CO gas signaling molecule has gradually shown great potential in cardiovascular biomaterials for regulating the in vivo performances after the implantation and has received increasing attention. To construct a bioactive surface with CO-releasing properties on the surface of magnesium-based alloy to augment the anticorrosion and biocompatibility, graphene oxide (GO) was firstly modified using carboxymethyl chitosan (CS), and then CO-releasing molecules (CORM401) were introduced to synthesize a novel biocompatible nanomaterial (GOCS-CO) that can release CO in the physiological environments. The GOCS-CO was further immobilized on the magnesium alloy surface modified by polydopamine coating with Zn2+ (PDA/Zn) to create a bioactive surface capable of releasing CO in the physiological environment. The outcomes showed that the CO-releasing coating can not only significantly enhance the anticorrosion and abate the corrosion degradation rate of the magnesium alloy in a simulated physiological environment, but also endow it with good hydrophilicity and a certain ability to adsorb albumin selectively. Owing to the significant enhancement of anticorrosion and hydrophilicity, coupled with the bioactivity of GOCS, the modified sample not only showed excellent ability to prevent platelet adhesion and activation and reduce hemolysis rate but also can promote endothelial cell (EC) adhesion, proliferation as well as the expression of nitric oxide (NO) and vascular endothelial growth factor (VEGF). In the case of CO release, the hemocompatibility and EC growth behaviors were further significantly improved, suggesting that CO molecules released from the surface can significantly improve the hemocompatibility and EC growth. Consequently, the present study provides a novel surface modification method that can simultaneously augment the anticorrosion and biocompatibility of magnesium-based alloys, which will strongly promote the research and application of CO-releasing bioactive coatings for surface functionalization of cardiovascular biomaterials and devices.

Synthesis of Star 6-Arm Polyethylene Glycol-Heparin Copolymer to Construct Anticorrosive and Biocompatible Coating on Magnesium Alloy Surface

Magnesium alloy has become a research hotspot of the degradable vascular stent materials due to its biodegradability and excellent mechanical properties. However, its rapid degradation rate after implantation and the limited biocompatibility restrict its application in clinic. Constructing a multifunctional bioactive polymer coating on the magnesium alloys represents one of the popular and effective approaches to simultaneously improve the corrosion resistance and biocompatibility. In the present study, the copolymer of 6-arm polyethylene glycol and heparin (PEG-Hep) was successfully synthesized and then immobilized on the surface of chitosan (Chi)-modified magnesium alloy surface through electrostatic interaction to improve the corrosion resistance and biocompatibility. The results of attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy showed that a dense and compact coating was created on the magnesium alloy surface. The coating displayed excellent hydrophilicity. At the same time, the as-prepared coating can significantly not only improve the corrosion potential, reduce the corrosion current and the pH changes of the immersion solution, but also keep a relatively intact surface morphology after immersing in simulated body fluid solution for 14 days, demonstrating that the coating can significantly improve the corrosion resistance of the magnesium alloy. Moreover, the magnesium alloy with PEG-Hep coating exhibited excellent hemocompatibility according to the results of the hemolysis rate and platelet adhesion and activation. In addition, the modified magnesium alloy had a good ability to promote the endothelial cell adhesion and proliferation. Therefore, the PEG-Hep multifunctional coating can be applied in the surface modification of the biodegradable magnesium alloy stent to simultaneously improve the corrosion resistance and biocompatibility.

The effect of enzymes on the in vitro degradation behavior of Mg alloy wires in simulated gastric fluid and intestinal fluid

With an upsurge of biodegradable metal implants, the research and application of Mg alloys in the gastrointestinal environment of the digestive tract have been of great interest. Digestive enzymes, mainly pepsin in the stomach and pancreatin in the small intestine, are widespread in the gastrointestinal tract, but their effect on the degradation of Mg alloys has not been well understood. In this study, we investigated the impacts of pepsin and pancreatin on the degradation of Mg-2Zn alloy wires. The results showed that the pepsin and pancreatin had completely different even the opposite effects on the degradation of Mg, although they both affected the degradation product layer. The degradation rate of Mg wire declined with the addition of pepsin in simulated gastric fluid (SGF) but rose with the addition of pancreatin in simulated intestinal fluid (SIF). The opposite trends in degradation rate also resulted in completely different degradation morphologies in wires surface, where the pitting corrosion in SGF was inhibited because of the physical barrier effect of pepsin adsorption. In contrast, the adsorption of pancreatin affected the integrity of magnesium hydrogen phosphate film, causing a relatively uneven degraded surface. These results may help us to understand the role of different digestive enzymes in the degradation of magnesium and facilitate the development and clinical application of magnesium alloy implanted devices for the digestive tract.

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The pepsin in SGF and pancreatin in SIF have opposite effects on the degradation rate of Mg.

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Both enzymes can adsorb on the surface of Mg wire and affect the formation of the degradation layer.

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The physical barrier effect of pepsin adsorption retarded the pitting corrosion and corrosion rate in SGF.

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Adsorbed pancreatin affected the integrity of the products layer in SIF, resulting in an accelerated corrosion rate.

A platform for functionalization of cellulose, chitin/chitosan, alginate with polydopamine: A review on fundamentals and technical applications

Nature provides concepts and materials with interesting functionalities to be implemented in innovative and sustainable materials. In this review, it is illustrated how the combination of biological macromolecules, i.e. polydopamine and polysaccharides (cellulose, chitin/chitosan, alginate), enables to create functional materials with controlled properties. The mussel-adhesive properties rely on the secretion of proteins having 3,4-dihydroxyphenylalanine amino acid with catechol groups. Fundamental understanding on the biological functionality and interaction mechanisms of dopamine in the mussel foot plaque is presented in parallel with the development of synthetic analogues through extraction or chemical polymer synthesis. Subsequently, modification of cellulose, chitin/chitosan or alginate and their nanoscale structures with polydopamine is discussed for various technical applications, including bio- and nanocomposites, films, filtration or medical membranes, adhesives, aerogels, or hydrogels. The presence of polydopamine stretches far beyond surface adhesive properties, as it can be used as an intermediate to provide additional performance of hydrophobicity, self-healing, antimicrobial, photocatalytic, sensoric, adsorption, biocompatibility, conductivity, coloring or mechanical properties. The dopamine-based 'green' chemistry can be extended towards generalized catechol chemistry for modification of polysaccharides with tannic acid, caffeic acid or laccase-mediated catechol functionalization. Therefore, the modification of polysaccharides with polydopamine or catechol analogues provides a general platform for sustainable material functionalization.

Electrophoretic deposition of polymers and proteins for biomedical applications

This review is focused on new electrophoretic deposition (EPD) mechanisms for deposition biomacromolecules, such as biopolymers, proteins and enzymes. Among the rich literature sources of EPD of biopolymers, proteins and enzymes for biomedical applications we selected papers describing new fundamental deposition mechanisms. Such deposition mechanisms are of critical importance for further development of EPD method and its emerging biomedical applications. Our goal is to emphasize innovative ideas which have enriched colloid and interface science of EPD during recent years. We describe various mechanisms of cathodic and anodic EPD of charged biopolymers. Special attention is focused on in-situ chemical modification of biopolymers and crosslinking techniques. Recent innovations in the development of natural and biocompatible charged surfactants and film forming agents are outlined. Among the important advances in this area are the applications of bile acids and salts for EPD of neutral polymers. Such innovations allowed for the successful EPD of various electrically neutral functional polymers for biomedical applications. Particularly important are biosurfactant-polymer interactions, which facilitate dissolution, dispersion, charging, electrophoretic transport and deposit formation. Recent advances in EPD mechanisms addressed the problem of EPD of proteins and enzymes related to their charge reversal at the electrode surface. Conceptually new methods are described, which are based on the use of biopolymer complexes with metal ions, proteins, enzymes and other biomolecules. This review describes new developments in co-deposition of biomacromolecules and future trends in the development of new EPD mechanisms and strategies for biomedical applications.

Electrodeposited Biocoatings, Their Properties and Fabrication Technologies: A Review

Coatings deposited under an electric field are applied for the surface modification of biomaterials. This review is aimed to characterize the state-of-art in this area with an emphasis on the advantages and disadvantages of used methods, process determinants, and properties of coatings. Over 170 articles, published mainly during the last ten years, were chosen, and reviewed as the most representative. The most recent developments of metallic, ceramic, polymer, and composite electrodeposited coatings are described focusing on their microstructure and properties. The direct cathodic electrodeposition, pulse cathodic deposition, electrophoretic deposition, plasma electrochemical oxidation in electrolytes rich in phosphates and calcium ions, electro-spark, and electro-discharge methods are characterized. The effects of electrolyte composition, potential and current, pH, and temperature are discussed. The review demonstrates that the most popular are direct and pulse cathodic electrodeposition and electrophoretic deposition. The research is mainly aimed to introduce new coatings rather than to investigate the effects of process parameters on the properties of deposits. So far tests aim to enhance bioactivity, mechanical strength and adhesion, antibacterial efficiency, and to a lesser extent the corrosion resistance.

Mg-Zn-Ca Alloys for Hemostasis Clips for Vessel Ligation: In Vitro and In Vivo Studies of Their Degradation and Response

To control the degradation rate of magnesium (Mg) alloys, chitosan (CHI) and L-glutamic acid (LGA) were used as coatings on Mg-Zn-Ca alloys via dip coating. In this study, either two or seven CHI/LGA layers were applied as a coating on Mg-2.8Zn-0.8Ca alloy (ZX31) and Mg-2.8Zn-0.8Ca hemostasis clips (ZX31 clips). The morphologies, compositions, and surface roughness of the specimens were characterized via scanning electron microscopy, Fourier transform infrared spectroscopy, and surface measurement devices. The degradation rates and behavior of the specimens were evaluated by immersing them in simulated body fluids and by applying these ZX31 clips on rabbits’ uterine tubes for five weeks. The specimen with seven layers (ZX31(CHI/LGA)₇) exhibited improved corrosion behavior when compared with ZX31 or ZX31(CHI/LGA)₂, with a reduced degradation rate of the Mg alloy in a simulated body environment. In vivo experiments showed that ZX31 clips exhibited good biocompatibilities in each group but could not maintain the clamping function for five weeks. The weight loss of ZX31(CHI/LGA)₇ was significantly lower than that of the other groups. Consequently, it was verified that CHI can be used as a protective layer on a magnesium alloy surface via in vitro and in vivo experiments.

Fabrication of chitosan/heparinized graphene oxide multilayer coating to improve corrosion resistance and biocompatibility of magnesium alloys

Due to its good biodegradability and mechanical properties, magnesium alloys are considered as the ideal candidate for the cardiovascular stents. However, the rapid degradation in human physiological environment and the poor biocompatibility seriously limit its application for biomaterials. In the present study, a chitosan/heparinized graphene oxide (Chi/HGO) multilayer coating was constructed on the AZ31B magnesium alloy surface using layer-by-layer (LBL) method to improve the corrosion resistance and biocompatibility. The results of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectrum (RAMAN), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) showed that a dense and compact Chi/HGO multilayer coating was fabricated on the magnesium alloy surface. The results of potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), pH value changes and magnesium ion release suggested that the multilayer coating can significantly enhance the corrosion resistance of the magnesium alloy. Moreover, the Chi/HGO multilayer coating could not only significantly reduce the hemolysis rate and platelet adhesion, but also promote the adhesion and proliferation of endothelial cells. Therefore, the Chi/HGO multilayer coating can simultaneously improve the corrosion resistance and biocompatibility of the magnesium alloys.