A pilot study of a novel biodegradable magnesium alloy airway stent in a rabbit model

Development of implantable electrode based on bioresorbable Mg alloy for tissue welding application

An implantable electrode based on bioresorbable Mg-Nd-Zn-Zr alloy was developed for next-generation radiofrequency (RF) tissue welding application, aiming to reduce thermal damage and enhance anastomotic strength. The Mg alloy electrode was designed with different structural features of cylindrical surface (CS) and continuous long ring (LR) in the welding area, and the electrothermal simulations were studied by finite element analysis (FEA). Meanwhile, the temperature variation during tissue welding was monitored and the anastomotic strength of welded tissue was assessed by measuring the avulsion force and burst pressure. FEA results showed that the mean temperature in the welding area and the proportion of necrotic tissue were significantly reduced when applying an alternating current of 110 V for 10 s to the LR electrode. In the experiment of tissue welding ex vivo, the maximum and mean temperatures of tissues welded by the LR electrode were also significantly reduced and the anastomotic strength of welded tissue could be obviously improved. Overall, an ideal welding temperature and anastomotic strength which meet the clinical requirement can be obtained after applying the LR electrode, suggesting that Mg-Nd-Zn-Zr alloy with optimal structure design shows great potential to develop implantable electrode for next-generation RF tissue welding application.

Effects of shape and structure of a new 3D-printed personalized bioresorbable tracheal stent on fit and biocompatibility in a rabbit model

To date, several types of airway stents are available to treat central airway obstructions. However, the ideal stent that can overcome anatomical, mechanical and microbiological issues is still awaited. In addition, therapeutic effect and self-elimination of these stents are desirable properties, which pose an additional challenge for development and manufacturing. We aimed to create a prototype bioresorbable tracheal stent with acceptable clinical tolerance, fit and biocompatibility, that could be tested in a rabbit model and in the future be further optimized to enable drug-elution and ensure local therapeutic effect. Twenty-one New Zealand White Rabbits received five different types of bioresorbable tracheal stents, 3D-printed from poly(D,L-lactide-co-ε-caprolactone) metacrylates. Various configurations were tested for their functionality and improved until the best performing prototype could undergo detailed in vivo assessment, regarding clinical tolerance, migration and biocompatibility. Previously tested types of 3D printed stents in our preliminary study required improvement due to several problems, mainly related to breakage, unreliable stability and/or migration within the trachea. Abandoned or refined pre-prototypes were not analyzed in a comparative way. The final best performing prototype stent (GSP2 (Group Stent Prototype 2), n = 8) allowed a transoral application mode and showed good clinical tolerance, minimal migration and acceptable biocompatibility. The good performance of stent type GSP2 was attributed to the helix-shaped surface structure, which was therefore regarded as a key-feature. This prototype stent offers the possibility for further research in a large animal model to confirm the promising data and assess other properties such as bioresorption.

Effect of unsoluble corrosion products of WE43 alloys in vitro on macrophages

Magnesium alloys have been used to manufacture biodegradable implants, bone graft substitutes, and cardiovascular stents. WE43 was the most widely used magnesium alloy. The degradation process begins when the magnesium alloy stent is implanted in the body and comes into contact with body fluid. The degradation products include hydrogen, Mg2+ , local alkaline environment, and unsoluble products. A large number of studies focused on Mg2+ and pH in vitro, and in vivo of magnesium alloys, but few studies on unsoluble corrosion products (UCPs). In this study, UCPs of WE43 alloy were prepared by immersion in vitro, and their effects on macrophages were investigated. The results showed that the unsoluble corrosion products were Mg24Y5, Mg12YNd, and MgCO3 ·3H2 O, which were dose-dependent on the apoptosis and necrosis of macrophages. After phagocytosis of UCPs, macrophages mainly metabolize in lysosome, and autophagy also participates in the metabolism of UCPs. It also decreases mitochondrial membrane potential and increases lysosomes, endoplasmic reticulum stress, and P2X7 receptor activation. These will increase reactive oxygen species (ROS) in cells, activating NLRP3 inflammatory corpuscles, activating the downstream pro-IL18 and pro-IL1β, and converting it to IL-18, and IL-1β. However, its pro-inflammatory effect is far lower than that of the classical Lipopolysaccharide (LPS) pro-inflammatory pathway. This work has increased our understanding of magnesium alloy metabolism and provides new ideas for the clinical application of magnesium alloys.

Research on the Current Application Status of Magnesium Metal Stents in Human Luminal Cavities

The human body comprises various tubular structures that have essential functions in different bodily systems. These structures are responsible for transporting food, liquids, waste, and other substances throughout the body. However, factors such as inflammation, tumors, stones, infections, or the accumulation of substances can lead to the narrowing or blockage of these tubular structures, which can impair the normal function of the corresponding organs or tissues. To address luminal obstructions, stenting is a commonly used treatment. However, to minimize complications associated with the long-term implantation of permanent stents, there is an increasing demand for biodegradable stents (BDS). Magnesium (Mg) metal is an exceptional choice for creating BDS due to its degradability, good mechanical properties, and biocompatibility. Currently, the Magmaris® coronary stents and UNITY-BTM biliary stent have obtained Conformité Européene (CE) certification. Moreover, there are several other types of stents undergoing research and development as well as clinical trials. In this review, we discuss the required degradation cycle and the specific properties (anti-inflammatory effect, antibacterial effect, etc.) of BDS in different lumen areas based on the biocompatibility and degradability of currently available magnesium-based scaffolds. We also offer potential insights into the future development of BDS.

Biomechanical analysis of tracheal stent during cough reflex

Tracheal stenting is a common method which is widely used to cure different tracheal disorders including airways stenosis, chronic coughs, and accidents. In this study, we aimed to analyze the reaction of the trachea wall to exhale in three phases of light, moderate, and vigorous activities at air flows of 15 L/min (light), 26 L/min (medium), and 30 L/min (vigorous). Fluid structure interaction (FSI) was used for the numerical analysis using computed tomography (CT) images. The flow was assumed incompressible and turbulent. The stent is silicone with a Young’s modulus equal to 1 MPa, Poisson’s ratio 0.28, and density of 2330 kg/m3. The stent length was 60 mm and fix support boundary condition was applied for all inputs and outputs. Numerical simulation was performed using ANSYS software. The induced stresses, strains, wall deformation, flow pressure, and the flow velocity were obtained. The results showed that the stent prevented the local deformation of the wall of trachea and it reduced the induced strain in the position. But the stenting could lead to stress concentration. Finally, the stent prevented the damage to the trachea muscles during coughs in row.

Systems, Properties, Surface Modification and Applications of Biodegradable Magnesium-Based Alloys: A Review

In recent years, biodegradable magnesium (Mg) alloys have attracted the attention of many researchers due to their mechanical properties, excellent biocompatibility and unique biodegradability. Many Mg alloy implants have been successfully applied in clinical medicine, and they are considered to be promising biological materials. In this article, we review the latest research progress in biodegradable Mg alloys, including research on high-performance Mg alloys, bioactive coatings and actual or potential clinical applications of Mg alloys. Finally, we review the research and development direction of biodegradable Mg alloys. This article has a guiding significance for future development and application of high-performance biodegradable Mg alloys, promoting the future advancement of the magnesium alloy research field, especially in biomedicine.

A narrative review of new research progress regarding the use of airway stents in benign airway stenosis

INTRODUCTION

Benign airway stenosis is a severe disease that can result in death with improper treatment. Clinicians must know about airway stents to choose the best one in their daily practice.

AREAS COVERED

PubMed, Embase, and other electronic databases and websites were searched to identify relevant randomized controlled trials and meta-analyses. This review summarizes different types of airway stents and analyzes their advantages and disadvantages.

EXPERT OPINION

Increasing attention has been given to the indications and prognosis of benign airway stenosis treated with different airway stents. With more investigations and data, better alternatives to silicone stents could be developed in the future.

Histological and structural effects of biodegradable polydioxanone stents in the rabbit trachea

OBJECTIVES

The aim of this study was to evaluate the potential biologic effects caused by successive placement of biodegradable polydioxanone (PDO) stents in the rabbit trachea. PDO stents could eventually induce a fibroproliferative reaction in the submucosa that could be beneficial in the treatment of malacia due to an increase in its consistency without impairing the tracheal lumen.

METHODS

Sixteen adult NZ rabbits were distributed into 3 groups with different survival times according to the number of stents placed: One stent (14 weeks), 2 stents (28 w.), and 3 stents (42 w.). Stent insertion was performed endoscopically in the cervical trachea of the animal. Histopathological studies included Masson's trichrome staining for submucosal fibrosis and Safranin O to assess structural integrity of cartilage. Potential inflammatory changes were analysed by means of immunohistochemistry determining the number of CD45 positive cells.

RESULTS

Stent placement was successful in every case. Histological studies did not show a statistically significant increase in tracheal wall collagen area and cartilage structure was not modified in those rabbits with one or more PDO stents inserted compared to non-stented tracheal sections. Furthermore, no statistically significant changes in the number of CD45+ cells were observed in stented tracheal segments compared to normal tracheal tissues.

CONCLUSIONS

According to our data, successive PDO stenting caused mild inflammatory changes in the tracheal wall, no increase in the collagen matrix, and the cartilaginous support was not modified during a long follow-up period (up to 42 weeks). These findings suggest that they may be safe and show good biocompatibility in the long-term.

Biodegradable Zn-2Ag-0.04Mg Alloy for Bone Regeneration In Vivo

To evaluate the bone regeneration capacity of Zn-2Ag-0.04Mg alloy scaffold in vivo. Zn, Zn-2Ag and Zn-2Ag-0.04Mg scaffolds were implanted in the femur of New Zealand rabbits, and the degradation of the scaffolds and the regeneration of the bone were observed at 6th week and 6th month. Two-dimensional and three-dimensional micro-CT results showed the new bone in Zn-2Ag-0.04Mg alloy scaffold group was significant more than Zn scaffold group, the bone volume in Zn-2Ag-0.04Mg was higher. Moreover, the osteogenic index in the Zn-2Ag-0.04Mg alloy scaffold group was also higher than Zn scaffold group. At 6th month, the scaffold of Zn-2Ag-0.04Mg was smaller than Zn group or Zn-2Ag group. HE staining of the liver, kidney, and heart did not detect any abnormalities, confirmed the biosafety of the Zn-2Ag-0.04Mg alloy scaffold. The Zn-Ag-0.04Mg alloy scaffold exhibits good biocompatibility and bone regeneration ability in vivo.

State of the Science in Tracheal Stents: A Scoping Review

OBJECTIVE

Recent material science advancements are driving tracheal stent innovation. We sought to assess the state of the science regarding materials and preclinical/clinical outcomes for tracheal stents in adults with benign tracheal disease.

METHODS

A comprehensive literature search in April 2021 identified 556 articles related to tracheal stents. One-hundred and twenty-eight full-text articles were reviewed and 58 were included in the final analysis. Datapoints examined were stent materials, clinical applications and outcomes, and preclinical findings, including emerging technologies.

RESULTS

In the 58 included studies, stent materials were metals (n = 28), polymers (n = 19), coated stents (n = 19), and drug-eluting (n = 5). Metals included nitinol, steel, magnesium alloys, and elgiloy. Studies utilized 10 different polymers, the most popular included polydioxanone, poly-l-lactic acid, poly(d,l-lactide-co-glycolide), and polycaprolactone. Coated stents employed a metal or polymer framework and were coated with polyurethane, silicone, polytetrafluoroethylene, or polyester, with some polymer coatings designed specifically for drug elution. Drug-eluting stents utilized mitomycin C, arsenic trioxide, paclitaxel, rapamycin, and doxycycline. Of the 58 studies, 18 were human and 40 were animal studies (leporine = 21, canine = 9, swine = 4, rat = 3, ovine/feline/murine = 1). Noted complications included granulation tissue and/or stenosis, stent migration, death, infection, and fragmentation.

CONCLUSION

An increasing diversity of materials and coatings are employed for tracheal stents, growing more pronounced over the past decade. Though most studies are still preclinical, awareness of tracheal stent developments is important in contextualizing novel stent concepts and clinical trials. Laryngoscope, 2021.

Biodegradable JDBM coating stent has potential to be used in the treatment of benign biliary strictures

In our previous study, to find out the optimal alloy suitable for biliary surgery, magnesium alloy Jiao Da Bio-magnesium (denoted as JDBM) alloy, Zn-3Cu alloys, and their respective coating (MgF₂-PDLLA) products were produced for our research. We found that JDBM seems to be a potential material for clinical biliary stent application due to its uniform degradation and good compatibility. In order to apply the JDBM alloy to treat benign bile duct stricture, our group prepared the bare JDBM and its coating product into finished stents by mesh weaving carving technology and conducted the mechanical property tests, degradation tests and biocompatibility tests. During the mechanical property tests, we found the bare JDBM stent was more suitable than titanium alloy stent when applies to the bile duct, and the coating of the JDBM coating stent has no effect on its mechanical properties. Our in vitro and in vivo experiments revealed that the degradation rate of the JDBM coating stent is lower than that of the JDBM stent, and both stents were biosafe. Thus, there is promise for JDBM coating stents for the treatment of benign biliary strictures.

In-vivo efficacy of biodegradable ultrahigh ductility Mg-Li-Zn alloy tracheal stents for pediatric airway obstruction

Pediatric laryngotracheal stenosis is a complex congenital or acquired airway injury that may manifest into a potentially life-threatening airway emergency condition. Depending on the severity of obstruction, treatment often requires a combination of endoscopic techniques, open surgical repair, intraluminal stenting, or tracheostomy. A balloon expandable biodegradable airway stent maintaining patency while safely degrading over time may address the complications and morbidity issues of existing treatments providing a less invasive and more effective management technique. Previous studies have focused on implementation of degradable polymeric scaffolds associated with potentially life-threatening pitfalls. The feasibility of an ultra-high ductility magnesium-alloy based biodegradable airway stents was demonstrated for the first time. The stents were highly corrosion resistant under in vitro flow environments, while safely degrading in vivo without affecting growth of the rabbit airway. The metallic matrix and degradation products were well tolerated by the airway tissue without exhibiting any noticeable local or systemic toxicity.

Mechanical performance and biocompatibility assessment of Zn-0.05wt%Mg-(0.5, 1 wt%) Ag alloys

Zn alloys are emerging as promising degradable biomedical materials due to their tailorable mechanical properties and moderate biodegradable rate, compared with conventional biodegradable metallic materials. Ag, as an effective antibacterial and reinforcing element, was incorporated into Zn-0.05Mg alloys. In the present work, the effects of the Ag addition on mechanical, cytotoxic, hemolytic, pyrogenic, histological behaviors of the animal were investigated. The compressive yielding strength is enhanced from 198 MPa for Zn-0.05Mg alloy up to 224 and 234 MPa for Zn-0.05Mg-0.5Ag and Zn-0.05Mg-1Ag alloys, respectively. When the compressive strain was 65%, the strength of the Zn-0.05Mg-1.0Ag alloy reached 833 MPa, which was much higher than that of 721 MPa for Zn-0.05Mg alloy. The relative growth rate (RGR) for the extracts of Zn-0.05Mg-1Ag alloy with the concentrations of 10, 50, and 100% after 5 days incubation reaches 98.5, 95.2, and 94.2%, which are higher than those in extracts of Zn-0.05Mg-0.5Ag alloy (98.2, 93.9, 92.1%). The hemolysis rate of the Zn-0.05Mg alloys with 0.5 and 1 wt% Ag is 2.46 and 2.28%, respectively. The variations of body weight and temperature, postinjection symptoms, pathological morphologies of the visceral organs demonstrate that the alloys are nontoxic according to the toxicity rating standards. Zn-0.05wt%Mg-(0.5, 1 wt%) Ag alloys are experimentally safe materials and promising for the future application as biodegradable medical devices.

Traditional and bionic dynamic hip screw fixation for the treatment of intertrochanteric fracture: a finite element analysis

PURPOSE

The dynamic hip screw (DHS) is widely used for fixing intertrochanteric femur fractures. A porous bionic DHS was developed recently to avoid the stress concentration and risk of post-operative complications associated with titanium alloy DHSs. The purpose of this study was to compare the effects of traditional titanium alloy, bionic titanium alloy, and bionic magnesium alloy DHS fixation for treatment of intertrochanteric fractures using finite element analysis.

METHODS

A three-dimensional model of the proximal femur was established by human computed tomography images. An intertrochanteric fracture was created on the model, which was fixed using traditional and porous bionic DHS, respectively. The von Mises stress, maximum principal stress, and minimum principal stress were calculated to evaluate the effect of bone ingrowth on stress distribution of the proximal femur after fixation.

RESULTS

Stress concentration of the bionic DHS model was lower compared with traditional DHS fixation models. The von Mises stress, maximum principal stress, and minimum principal stress distributions of bionic magnesium alloy DHS models improved, along with simulation of the bone healing process and magnesium alloy degeneration, assumed to biodegrade completely 12 months post-operatively. The distribution of maximum principal stress in the secondary tension zone of the bionic DHS model was close to the intact bone. In the minimum principal stress, the region of minimum stress value less than - 10 MPa was significantly improved compared with traditional DHS models.

CONCLUSION

The bionic magnesium alloy DHS implant can improve the stress distribution of fractured bone close to that of intact bone while reducing the risk of post-operative complications associated with traditional internal fixations.