Preliminary study on modelling, fabrication by photo-chemical etching and in vivo testing of biodegradable magnesium AZ31 stents

Novel coatings for the continuous repair of human bone defects

Bone defects are the second most common tissue grafts after blood. However, bone grafts face several problems, such as bone scaffolds, which have low bioactivity and are prone to corrosion. Much of the current research on bone scaffolds is focused on the mechanical aspects such as structure and strength. Surface modification of the bone scaffold is carried out in terms of the mechanical structure or structural design of the bone scaffold with reference to a bionic structure. However, with the development of mechanical designs, materials science, and medicine, many studies have reported that promoting bone growth by modifying the structure of the scaffold or coating is not possible. Therefore, the application of a bioactive coating to the surface of the bone scaffold is particularly important to generate a synergistic effect between the structure and active coating. In this article, we present several perspectives to improve the bioactivity of bone scaffolds, including corrosion resistance, loading of bioactive coatings or drugs on bone scaffolds, improved adhesion to the surface of the bone scaffolds, immune response modulation, and drawing on bionic structures during manufacturing.

Dual-Mode Flexible Sensor Based on PVDF/MXene Nanosheet/Reduced Graphene Oxide Composites for Electronic Skin

MXene materials have the metallic conductivity of transition metal carbides. Among them, Ti₃C₂T_X with an accordion structure has great application prospects in the field of wearable devices. However, flexible wearable electronic devices face the problem of single function in practical application. Therefore, it is particularly important to study a flexible sensor with multiple functions for electronic skin. In this work, the near-field electrohydrodynamic printing (NFEP) method was proposed to prepare the composite thin film with a micro/nanofiber structure on the flexible substrate using a solution of poly(vinylidene fluoride)/MXene nanosheet/reduced graphene oxide (PMR) nanocomposites as the printing solution. A dual-mode flexible sensor for electronic skin based on the PMR nanocomposite thin film was fabricated. The flexible sensor had the detection capability of the piezoresistive mode and the piezoelectric mode. In the piezoresistive mode, the sensitivity was 29.27 kPa^-1 and the response/recovery time was 36/55 ms. In the piezoelectric mode, the sensitivity was 8.84 kPa^-1 and the response time was 18.2 ms. Under the synergy of the dual modes, functions that cannot be achieved by a single mode sensor can be accomplished. In the process of detecting the pressure or deformation of the object, more information is obtained, which broadens the application range of the flexible sensor. The experimental results show that the dual-mode flexible sensor has great potential in human motion monitoring and wearable electronic device applications.

Multi-Objective Optimization of Bioresorbable Magnesium Alloy Stent by Kriging Surrogate Model

PURPOSE

The study proposed a multi-objective optimization method based on Kriging surrogate model and finite element analysis to mitigate the redial recoil and foreshortening ratio of bioresorbable magnesium alloy stent, and investigate the impact of strut thickness on stent expansion behavior.

METHODS

Finite element analysis have been carried out to compare the expansion behavior of stents with various strut thickness. Latin hypercube sampling (LHS) was adopted to generate train sample points in the design space, and the Kriging surrogate model was constructed between strut parameters and stent behavior. The genetic algorithm (GA) was employed to find the optimal solution in the global design space.

RESULTS

Stents with thinner struts experience lower stress but suffer from severe radial recoil and foreshortening effects. The radial recoil is decreased by 66%, and foreshortening ratio is reduced by 60% for the optimized stent with U-bend width 90.7 [Formula: see text] and link width 77.9 [Formula: see text]. The errors between Kriging surrogate model and finite element simulation are 6% and 9% for the radial recoil and foreshortening ratio.

CONCLUSION

Stent expansion behavior are highly dependent on design parameters, i.e. thickness, U-bend and link strut width. The purposed Multi-objective optimization approach based on Kriging surrogate model and finite element analysis is efficient in stent design optimization problem.

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.

Biodegradability and Cytocompatibility of 3D-Printed Mg-Ti Interpenetrating Phase Composites

Orthopedic hybrid implants combining both titanium (Ti) and magnesium (Mg) have gained wide attraction nowadays. However, it still remains a huge challenge in the fabrication of Mg-Ti composites because of the different temperatures of Ti melting point and pure Mg volatilization point. In this study, we successfully fabricated a new Mg-Ti composite with bi-continuous interpenetrating phase architecture by infiltrating Mg melt into Ti scaffolds, which were prepared by 3D printing and subsequent acid treatment. We attempted to understand the 7-day degradation process of the Mg-Ti composite and examine the different Mg2+ concentration composite impacts on the MC3T3-E1 cells, including toxicity, morphology, apoptosis, and osteogenic activity. CCK-8 results indicated cytotoxicity and absence of the Mg-Ti composite during 7-day degradation. Moreover, the composite significantly improved the morphology, reduced the apoptosis rate, and enhanced the osteogenic activity of MC3T3-E1 cells. The favorable impacts might be attributed to the appropriate Mg2+ concentration of the extracts. The results on varying Mg2+ concentration tests indicated that Mg2+ showed no cell adverse effect under 10-mM concentration. The 8-mM group exhibited the best cell morphology, minimum apoptosis rate, and maximum osteogenic activity. This work may open a new perspective on the development and biomedical applications for Mg-Ti composites.

Fluorescent In Situ 3D Visualization of Dynamic Corrosion Processes of Magnesium Alloys

Magnesium (Mg) alloys as implant materials with excellent biodegradation ability have promising clinical applications for tissue repair and restoration. Although the corrosion processes of Mg alloys in biophysiological media are closely related with their biodegradation ability, only limited methods have been developed for characterization of their corrosion processes, including electrochemical analysis, weight loss measurement, and hydrogen evolution analysis. Moreover, these methods suffer from drawbacks of poor spatiotemporal resolution, static observation, and tedious operation. To tackle these challenges, we herein developed a fluorescent probe PSPA for in situ 3D monitoring of the dynamic corrosion processes of Mg alloys on the basis of its selective turn-on detection ability toward magnesium hydroxide [Mg(OH)₂], which is the main corrosion product of Mg alloys in biophysiological media. As far as we know, this is the first example of a fluorescent probe for the monitoring of corrosion processes of Mg alloys in biophysiological media. We believe this fluorescence analysis method with easy operation and high spatiotemporal resolution advantages will contribute greatly to the clinical applications of Mg alloy implants.

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.

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

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

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Key factors in designing BM brain stents were discussed.

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

A multi-dimensional non-uniform corrosion model for bioabsorbable metallic vascular stents

Bioabsorbable metallic vascular stents (BMVSs) are an innovative technological advancement in the medical engineering field of vascular implants. BMVSs have great potential to revolutionize vascular intervention, but the lack of understanding of the construction material's natural corrosion within the body inhibits the use in clinical medicine. In this study, a corrosion function concept for in vivo implants was created to develop a multi-dimensional, non-uniform corrosion model with a larger goal of simulating the mechanical integrity of BMVSs. This proposed corrosion model simulates the corrosion rate and its effects on magnesium (Mg) alloy AZ31 based on continuum damage mechanics. The model was calibrated using three degradation experiments on Mg alloy specimens. These experiments focused on multi-dimensional corrosion, mass loss rate, and mechanical integrity during the corrosion process. Lastly, to verify the applicability of the proposed model, the resulting corrosion behaviors and mechanical characteristics of the BMVSs were implemented into a finite element framework to produce an overarching simulation of the BMVS's degradation in vivo. The results of the experiments and simulations revealed a proportional link between the corrosion of BMVSs and the number of exposed surfaces. A non-linear decline in mechanical integrity with increasing mass loss was also discovered through experimentation and modeling. Furthermore, the model and simulation can provide some details about changes in morphology and mechanics during BMVS corrosion. This work gives new insights into accurately modeling for BMVS degradation and can be used to optimize product development of BMVSs. STATEMENT OF SIGNIFICANCE: Bioabsorbable metallic vascular stents (BMVSs) are an innovative technological advancement in the medical engineering field of vascular implants. Despite BMVSs have great potential to revolutionize vascular intervention, the lack of understanding of the construction material's natural corrosion within the body inhibits their use in clinical medicine. In this study, a novel multi-dimensional non-uniform corrosion model was proposed to unveil the mechanisms during the in vivo degradation of bioabsorbable metallic implants, which can accurately capture the overlooked changes in morphology and mechanics during BMVS corrosion. This work provides a technical solution to enhance the modeling accuracy in BMVS degradation and can be further used to optimize the design of BMVSs in the future.