Effect of Mucin and Bicarbonate Ion on Corrosion Behavior of AZ31 Magnesium Alloy for Airway Stents

Simulated biological fluids - a systematic review of their biological relevance and use in relation to inhalation toxicology of particles and fibres

The use of simulated biological fluids (SBFs) is a promising in vitro technique to better understand the release mechanisms and possible in vivo behaviour of materials, including fibres, metal-containing particles and nanomaterials. Applications of SBFs in dissolution tests allow a measure of material biopersistence or, conversely, bioaccessibility that in turn can provide a useful inference of a materials biodistribution, its acute and long-term toxicity, as well as its pathogenicity. Given the wide range of SBFs reported in the literature, a review was conducted, with a focus on fluids used to replicate environments that may be encountered upon material inhalation, including extracellular and intracellular compartments. The review aims to identify when a fluid design can replicate realistic biological conditions, demonstrate operation validation, and/or provide robustness and reproducibility. The studies examined highlight simulated lung fluids (SLFs) that have been shown to suitably replicate physiological conditions, and identify specific components that play a pivotal role in dissolution mechanisms and biological activity; including organic molecules, redox-active species and chelating agents. Material dissolution was not always driven by pH, and likewise not only driven by SLF composition; specific materials and formulations correspond to specific dissolution mechanisms. It is recommended that SLF developments focus on biological predictivity and if not practical, on better biological mimicry, as such an approach ensures results are more likely to reflect in vivo behaviour regardless of the material under investigation.

Exploring the interplay of mucin with biologically-relevant amorphous magnesium-calcium phosphate nanoparticles

HYPOTHESIS

It has been recently shown that, in our organism, the secretions of Ca²⁺, Mg²⁺ and phosphate ions lead to the precipitation of amorphous magnesium-calcium phosphate nanoparticles (AMCPs) in the small intestine, where the glycoprotein mucin is one of the most abundant proteins, being the main component of the mucus hydrogel layer covering gut epithelium. Since AMCPs precipitate in vivo in a mucin-rich environment, we aim at studying the effect of this glycoprotein on the formation and features of endogenous-like AMCPs.

EXPERIMENTS

AMCPs were synthesized from aqueous solution in the presence of different concentrations of mucin, and the obtained particles were characterised in terms of crystallinity, composition and morphology. Solid State NMR investigation was also performed in order to assess the interplay between mucin and AMCPs at a sub-nanometric level.

FINDING

Results show that AMCPs form in the presence of mucin and the glycoprotein is efficiently incorporated in the amorphous particles. NMR indicates the existence of interactions between AMCPs and mucin, revealing how AMCPs in mucin-hybrid nanoparticles affect the features of both proteic and oligosaccharidic portions of the glycoprotein. Considering that the primary function of mucin is the protection of the intestine from pathogens, we speculate that the nature of the interaction between AMCPs and mucin described in the present work might be relevant to the immune system, suggesting a novel type of scenario which could be investigated by combining physico-chemical and biomedical approaches.

Effect of Protein and Mechanical Strain on the Corrosion Resistance and Cytotoxicity of the Orthodontic Composite Arch Wire

In this study, the effects of the exposure to different types of salivary proteins (fibrinogen, IgG, and mucin) and application of an in vitro bending strain on the laser welding orthodontic composite arch wire (CAW) were investigated, and the resultant corrosion behavior and cytotoxicity were studied in vitro. The purpose was to determine the mechanisms by which protein exposure and bending loads contribute to the corrosion of the CAW either alone or in combination by mimicking the clinical application. The results showed that the application of a mechanical strain significantly decreased the corrosion resistance of the CAW and increased the release of toxic corrosion products. The addition of the proteins inhibited the corrosion of the CAW, but the mechanical loads counteracted this effect. Mucin enhanced the corrosion resistance of the CAW. The effects of the proteins or strain, either alone or in combination, should be considered in the application of medical materials of heterogenetic alloys.

Additive manufacturing of magnesium alloys

Magnesium alloys are a promising new class of degradable biomaterials that have a similar stiffness to bone, which minimizes the harmful effects of stress shielding. Use of biodegradable magnesium implants eliminates the need for a second surgery for repair or removal. There is a growing interest to capitalize on additive manufacturing's unique design capabilities to advance the frontiers of medicine. However, magnesium alloys are difficult to 3D print due to the high chemical reactivity that poses a combustion risk. Furthermore, the low vaporization temperature of magnesium and common biocompatible alloying elements further increases the difficulty to print fully dense structures that balance strength and corrosion requirements. The purpose of this study is to survey current techniques to 3D print magnesium constructs and provide guidance on best additive practices for these alloys.

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A review of additive manufacturing of magnesium alloys for biomedical applications.

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Examined challenges associated with vaporization and porosity.

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Surveyed multiple AM processes and the role of process parameters on print quality and performance.

In vitro degradation and biocompatibility evaluation of typical biodegradable metals (Mg/Zn/Fe) for the application of tracheobronchial stenosis

Tracheobronchial obstruction in children due to benign stenosis or tracheobronchomalacia still remains a challenging matter of concern. Currently, there is 10%-20% complication rate in clinical treatment. The non-biodegradable property of silicone stents and nickel-titanium memory alloy stents take the primary responsibility for drawbacks including stimulating local granulation tissue proliferation, displacement, and stent-related infections. Permanent tracheobronchial stent will be a persistent foreign object for a long time, causing excessive secretion of tracheal mucosa, ulceration and even perforation, which is particularly unsuitable for young children with persistent tracheal growth. In this study, the degradation and biocompatibility performance of three typical biodegradable metals were investigated as potential tracheobronchial stent materials. The results exhibited that these materials showed different degradation behaviors in the simulating respiratory fluid environment compared with SBF. Except for pure iron group, high purity magnesium and zinc showed favorable cell adhesion and proliferation in three culture methodologies (direct culture, indirect culture and extraction culture). The proper corrosion rate and good biocompatibility indicated that high purity magnesium and zinc may be good candidates as tracheobronchial stent materials.

Manufacturing of Mg-Ti Couples at Different Heat Treatment Temperatures and Their Corrosion Behavior in Chloride Solutions

In this study, rods of magnesium alloy and titanium alloy were cut to have similar height of about 5mm and size of 10 mm × 10 mm to fabricate three Mg-Ti couples. The Mg-Ti couple was heat treated at 540 °C, 570 °C, and 600 °C. The corrosion of these couples have been investigated and compared with AZ31 alloy. Potentiodynamic polarization and electrochemical impedance spectroscopy measurements were employed to study the corrosion behavior after 1.0 h and 48 h exposure to 3.5% NaCl solutions. The morphology of surfaces was examined by scanning electron microscopy (SEM) and the profile analysis was collected using an energy dispersive X-ray (EDX) analyzer after 5 days immersion in the chloride solutions. It is found that coupling Mg with Ti reduces the corrosion of AZ31 alloy, which further decreased with the increase of the temperature of treatment. Prolonging the time of exposure from 1.0 h to 48 h remarkably decreased the corrosion of the couples as well.

3D-Printed PCL/PLA Composite Stents: Towards a New Solution to Cardiovascular Problems

Biodegradable stents (BRS) offer enormous potential but first they must meet five specific requirements: (i) their manufacturing process must be precise; (ii) degradation should have minimal toxicity; (iii) the rate of degradation should match the recovery rate of vascular tissue; (iv) ideally, they should induce rapid endothelialization to restore the functions of vascular tissue, but at the same time reduce the risk of restenosis; and (v) their mechanical behavior should comply with medical requirements, namely, the flexibility required to facilitate placement but also sufficient radial rigidity to support the vessel. Although the first three requirements have been comprehensively studied, the last two have been overlooked. One possible way of addressing these issues would be to fabricate composite stents using materials that have different mechanical, biological, or medical properties, for instance, Polylactide Acid (PLA) or Polycaprolactone (PCL). However, fashioning such stents using the traditional stent manufacturing process known as laser cutting would be impossible. Our work, therefore, aims to produce PCL/PLA composite stents using a novel 3D tubular printer based on Fused Deposition Modelling (FDM). The cell geometry (shape and area) and the materials (PCL and PLA) of the stents were analyzed and correlated with 3T3 cell proliferation, degradation rates, dynamic mechanical and radial expansion tests to determine the best parameters for a stent that will satisfy the five strict BRS requirements. Results proved that the 3D-printing process was highly suitable for producing composite stents (approximately 85⁻95% accuracy). Both PCL and PLA demonstrated their biocompatibility with PCL stents presenting an average cell proliferation of 12.46% and PLA 8.28% after only 3 days. Furthermore, the PCL/PLA composite stents demonstrated their potential in degradation, dynamic mechanical and expansion tests. Moreover, and regardless of the order of the layers, the composite stents showed (virtually) medium levels of degradation rates and mechanical modulus. Radially, they exhibited the virtues of PCL in the expansion step (elasticity) and those of PLA in the recoil step (rigidity). Results have clearly demonstrated that composite PCL/PLA stents are a highly promising solution to fulfilling the rigorous BRS requirements.

The Role of Oral Cavity Biofilm on Metallic Biomaterial Surface Destruction-Corrosion and Friction Aspects

Metallic biomaterials in the oral cavity are exposed to many factors such as saliva, bacterial microflora, food, temperature fluctuations, and mechanical forces. Extreme conditions present in the oral cavity affect biomaterial exploitation and significantly reduce its biofunctionality, limiting the time of exploitation stability. We mainly refer to friction, corrosion, and biocorrosion processes. Saliva plays an important role and is responsible for lubrication and biofilm formation as a transporter of nutrients for microorganisms. The presence of metallic elements in the oral cavity may lead to the formation of electro-galvanic cells and, as a result, may induce corrosion. Transitional microorganisms such as sulfate-reducing bacteria may also be present among the metabolic microflora in the oral cavity, which can induce biological corrosion. Microorganisms that form a biofilm locally change the conditions on the surface of biomaterials and contribute to the intensification of the biocorrosion processes. These processes may enhance allergy to metals, inflammation, or cancer development. On the other hand, the presence of saliva and biofilm may significantly reduce friction and wear on enamel as well as on biomaterials. This work summarizes data on the influence of saliva and oral biofilms on the destruction of metallic biomaterials.

The effect of mucin, fibrinogen and IgG on the corrosion behaviour of Ni-Ti alloy and stainless steel

In this study, Ni-Ti alloy and stainless steal were exposed to artificial saliva containing fibrinogen, IgG or mucin, and the resultant corrosion behavior was studied. The purpose was to determine the mechanisms by which different types of protein contribute to corrosion. The effect of different proteins on the electrochemical resistance of Ni-Ti and SS was tested by potentiodynamic polarization, and the repair capacity of passivation film was tested by cyclic polarization measurements. The dissolved corrosion products were determined by ICP-OES, and the surface was analyzed by SEM and AFM. The results showed fibrinogen, IgG or mucin could have different influences on the susceptibility to corrosion of the same alloy. Adding protein lead to the decrease of corrosion resistance of SS, whereas protein could slow down the corrosion process of Ni-Ti. For Ni-Ti, adding mucin could enhance the corrosion stability and repair capacity of passivation film. The susceptibility to pitting corrosion of Ni-Ti and stainless steal in fibrinogen AS is not as high as mucin and IgG AS. There are different patterns of deposition formation on the metal surface by different types of protein, which is associated with their effects on the corrosion process of the alloys.

Flow-induced corrosion of absorbable magnesium alloy: In-situ and real-time electrochemical study

An in-situ and real-time electrochemical study in a vascular bioreactor was designed to analyze corrosion mechanism of magnesium alloy (MgZnCa) under mimetic hydrodynamic conditions. Effect of hydrodynamics on corrosion kinetics, types, rates and products was analyzed. Flow-induced shear stress (FISS) accelerated mass and electron transfer, leading to an increase in uniform and localized corrosions. FISS increased the thickness of uniform corrosion layer, but filiform corrosion decreased this layer resistance at high FISS conditions. FISS also increased the removal rate of localized corrosion products. Impedance-estimated and linear polarization-measured polarization resistances provided a consistent correlation to corrosion rate calculated by computed tomography.