The effect of tensile and fluid shear stress on the in vitro degradation of magnesium alloy for stent applications

Endowing biodegradable Zinc implants with dual-function of antibacterial ability and osteogenic activity by micro-addition of Mg and Ag (≤ 0.1 wt.%)

Infection remains the devastating complications associated with surgical fixation of bones fractured during trauma. In this study, we report a low-alloyed Zn-Mg-Ag that simultaneously has optimized strength degeneration profiles during degradation, outstanding antibacterial efficacy and osteogenic activity. Our results showed that Zn-0.05Mg-0.1Ag alloy had favorable mechanical properties (UTS: 247.8 ± 1.6 MPa, Elong.: 35 ± 2.2 %) and presented a better hold of mechanical integrity than pure Zn during 28 days corrosion, 2.6 % vs. 18.7 % reduction. After one-year of natural aging, the alloy still preserved an elongation of 24.07 ± 3.84 %. As verified by microbial cultures, Zn-0.05Mg-0.1Ag alloy demonstrated high antibacterial performance against Gram-positive and Gram-negative strains, as well as antibiotic-resistant strains (MRSA) in vitro and in vivo due to the synergistic antibacterial actions of Zn²⁺ and Ag⁺. Meanwhile, Zn-Mg-Ag alloy also exhibited enhanced viability, osteogenic differentiation, and gene expressions of osteoblasts in vitro, as well as promoted osteogenic activity than pure Zn in the femoral condyle defect repair model. The co-releasing of Zn, Mg and Ag ions did not induce toxic side effects. Collectively, low alloyed Zn-0.05Mg-0.1Ag indicated long-lasting mechanical integrity during degradation, and presented the ability to synergistically inhibit bacteria and promote osteogenesis, possessing tremendous potential in treating implant-associated infections. STATEMENT OF SIGNIFICANCE: Infection after fracture fixation (IAFF) remains the most common and serious side effects of orthopedic surgery. Additionally, widespread antibiotic use contributes to the development of multi-drug resistant bacteria such as methicillin-resistant staphylococcus aureus (MRSA), which exacerbates IAFF treatment and prevention. IAFF treatment and prevention remain clinically challenging, so implants with dual antibacterial and osteogenic functions are in high demand. The antibacterial efficacy and osteogenic activity of low-alloyed Zn-Mg-Ag (≤0.1 wt.% Mg, Ag) alloys were investigated in vitro and in vivo. The results showed that micro addition of Mg and Ag could significantly improve osseointegration function, mechanical properties, and antibacterial performance. These quantification findings shed new light on the development and understanding of dual functional Zn-based orthopedic implants.

The Flow-Induced Degradation and Vascular Cellular Response Study of Magnesium-Based Materials

Magnesium (Mg)-based materials are considered as potential materials for biodegradable vascular stents, and some Mg-based stents have obtained regulatory approval. However, the development and application of Mg-based stents are still restricted by the rapid degradation rate of Mg and its alloys. In order to screen out the desirable Mg-based materials for stents, the degradation behavior still needs further systematic study, especially the degradation behavior under the action of near-physiological fluid. Currently, the commonly used Mg-based vascular stent materials include pure Mg, AZ31, and WE43. In this study, we systematically evaluated their corrosion behaviors in a dynamic environment and studied the effect of their degradation products on the behavior of vascular cells. The results revealed that the corrosion rate of different Mg-based materials was related to the composition of the elements. The dynamic environment accelerated the corrosion of Mg-based materials. All the same, AZ31 still shows good corrosion resistance. The effect of corrosive products on vascular cells was beneficial to re-endothelialization and inhibition of smooth muscle cell proliferation at the implantation site of vascular stent materials.

Current status and outlook of biodegradable metals in neuroscience and their potential applications as cerebral vascular stent materials

Over the past two decades, biodegradable metals (BMs) have emerged as promising materials to fabricate temporary biomedical devices, with the purpose of avoiding potential side effects of permanent implants. In this review, we first surveyed the current status of BMs in neuroscience, and briefly summarized the representative stents for treating vascular stenosis. Then, inspired by the convincing clinical evidence on the in vivo safety of Mg alloys as cardiovascular stents, we analyzed the possibility of producing biodegradable cerebrovascular Mg alloy stents for treating ischemic stroke. For these novel applications, some key factors should also be considered in designing BM brain stents, including the anatomic features of the cerebral vasculature, hemodynamic influences, neuro-cytocompatibility and selection of alloying elements. This work may provide insights into the future design and fabrication of BM neurological devices, especially for brain stents.

•

The current status of the application of biodegradable metals (BM) in neuroscience was presented.

•

We analyzed the possibility of producing biodegradable cerebrovascular Mg alloy stents for ischemic stroke treatment.

•

Key factors in designing BM brain stents were discussed.

•

This work may provide insights into the future design and fabrication of BM neurological devices, especially for brain stents.

Development of a micro-scale method to assess the effect of corrosion on the mechanical properties of a biodegradable Fe-316L stent material

The application of biodegradable materials to stent design has the potential to transform coronary artery disease treatment. It is critical that biodegradable stents have sustained strength during degradation and vessel healing to prevent re-occlusion. Proper assessment of the impact of corrosion on the mechanical behaviour of potential biomaterials is important. Investigations within literature frequently implement simplified testing conditions to understand this behaviour and fail to consider size effects associated with strut thickness, or the increase in corrosion due to blood flow, both of which can impact material properties. A protocol was developed that utilizes micro-scale specimens, in conjunction with dynamic degradation, to assess the effect of corrosion on the mechanical properties of a novel Fe-316L material. Dynamic degradation led to increased specimen corrosion, resulting in a greater reduction in strength after 48 h of degradation in comparison to samples statically corroded. It was found that thicker micro-tensile samples (h > 200 μm) had a greater loss of strength in comparison to its thinner counterpart (h < 200 μm), due to increased corrosion of the thicker samples (203 MPa versus 260 MPa after 48 h, p = 0.0017). This investigation emphasizes the necessity of implementing physiologically relevant testing conditions, including dynamic corrosion and stent strut thickness, when evaluating potential biomaterials for biodegradable stent application.

Effect of strain on degradation behaviors of WE43, Fe and Zn wires

The biodegradable metallic devices undergo stress/strain-induced corrosion when they are used for load-bearing applications. The stress/strain induced-corrosion behavior causes differences in corrosion rate, corrosion morphology, strain distribution and mechanical performance of the devices. One representative example is the biodegradable stent. Biodegradable stents undergo complex inhomogeneous deformation that can cause dramatic non-uniform stent degradation, resulting in stress concentration and stents failure. The degradation of biodegradable devices requires special attention to the mutual effect between the applied strain and degradation. The quantitative relationship between strain and corrosion of the sample alloys (WE43, Fe and Zn), selected from three typical biodegradable metals, is firstly investigated and compared in this study. The in vitro degradation and the strength retention of WE43, Fe and Zn wires were investigated under different elastic and plastic strain levels ranging from 0.1% to 30%. The results indicated that the applied strain could bring down the corrosion potential, increase corrosion current and accelerate the degradation of three biodegradable metals. Specifically, remarkable enhanced localized corrosion was observed for plastic strained WE43 compared with those with elastic strains. This localized corrosion morphology significantly accelerated the strength decline at first, while the differences diminished with longer immersion period. Fe and Zn exhibited increased degradation with plastic strain applications than those under elastic strains. However, the degradation was not further increased with the increasing magnitude of plastic strains. Moreover, the bended wires were subcutaneously implanted in the dorsal aspect of the rats and the effect of bending deformation on in vitro and in vivo degradation of three metallic wires were also compared. The U-bended WE43 wires suffered more severe in vitro degradation at the stress concentrated region. Surprisingly, the early fracture of the undeformed regions was observed in the in vivo test. In conclusion, the corrosion rate, corrosion morphology and mechanical properties of WE43, Fe and Zn was sensitive to magnitude of the applied strains. The quantification results provided new insights into understanding the strain-dependent corrosion of three biodegradable metals both in vitro and in vivo. STATEMENT OF SIGNIFICANCE: Biodegradable implants are subjected to various mechanical environment during the deployment and subsequent physiological activity. It is necessary to have a clear understanding of the effects of the applied stress on degradation. This study addresses the quantitative effects of applied strain/stress on the in vitro and in vivo degradation of three typical biodegradable metals (Mg, Fe and Zn). These quantification results provide new insights into understanding the strain-induced corrosion of three metals.

Conjugating heparin, Arg–Glu–Asp–Val peptide, and anti-CD34 to the silanic Mg–Zn–Y–Nd alloy for better endothelialization

Magnesium alloy is generally accepted as a potential cardiovascular stent material due to its good mechanical properties, biocompatibility, and biodegradability, and has become one of the research hotspots in this field. However, too fast degradation rate and delayed surface endothelialization have been the bottleneck of further application of magnesium alloy stent. In this study, we selected Mg–Zn–Y–Nd, a kind of biodegradable magnesium alloy for cardiovascular stent, and passivated its surface by alkali heat treatment and silane treatment to improve the corrosion resistance, subsequently conjugated Arg–Glu–Asp–Val (REDV) peptide and anti-CD34 to promote endothelial cells adhesion and capture endothelial progenitor cells respectively, further improving surface endothelialization. In addition, the heparin was also immobilized to the Mg–Zn–Y–Nd surface for the consideration of anti-coagulation and anti-inflammation. Systematic material characterization and biological evaluation show that we have successfully developed this composite surface on Mg–Zn–Y–Nd alloy, and achieved multiple functions such as corrosion resistance, promoting endothelialization, and inhibiting platelet/macrophage adhesion.

Biomechanical studies on biomaterial degradation and co-cultured cells: mechanisms, potential applications, challenges and prospects

This review provides a comprehensive overview of biomechanical studies on biomaterial degradation and co-cultured cells as well as valuable biomechanical ideas on how to design or optimize cell biomaterial co-culture system.