Enhanced in Vitro and in Vivo Performance of Mg-Zn-Y-Nd Alloy Achieved with APTES Pretreatment for Drug-Eluting Vascular Stent Application

Stent coating containing a charged silane coupling agent that regulates protein adsorption to confer antithrombotic and cell-adhesion properties

The evolution of endovascular therapies, particularly in the field of intracranial aneurysm treatment, has been truly remarkable and is characterized by the development of various stents. However, ischemic complications related to thrombosis or downstream emboli pose a challenge for the broader clinical application of such stents. Despite advancements in surface modification technologies, an ideal coating that fulfills all the desired requirements, including anti-thrombogenicity and swift endothelialization, has not been available. To address these issues, we investigated a new coating comprising 3-aminopropyltriethoxysilane (APTES) with both anti-thrombogenic and cell-adhesion properties. We assessed the anti-thrombogenic property of the coating using an in vitro blood loop model by evaluating the platelet count and the level of the thrombin-antithrombin (TAT) complex, and investigating thrombus formation on the surface using scanning electron microscopy (SEM). We then assessed endothelial cell adhesion on the metal surfaces. In vitro blood tests revealed that, compared to a bare stent, the coating significantly inhibited platelet reduction and thrombus formation; more human serum albumin spontaneously adhered to the coated surface to block thrombogenic activation in the blood. Cell adhesion tests also indicated a significant increase in the number of cells adhering to the APTES-coated surfaces compared to the numbers adhering to either the bare stent or the stent coated with an anti-fouling phospholipid polymer. Finally, we performed an in vivo safety test by implanting coated stents into the internal thoracic arteries and ascending pharyngeal arteries of minipigs, and subsequently assessing the health status and vessel patency of the arteries by angiography over the course of 1 week. We found that there were no adverse effects on the pigs and the vascular lumens of their vessels were well maintained in the group with APTES-coated stents. Therefore, our new coating exhibited both high anti-thrombogenicity and cell-adhesion properties, which fulfill the requirements of an implantable stent.

Challenges and Pitfalls of Research Designs Involving Magnesium-Based Biomaterials: An Overview

Magnesium-based biomaterials hold remarkable promise for various clinical applications, offering advantages such as reduced stress-shielding and enhanced bone strengthening and vascular remodeling compared to traditional materials. However, ensuring the quality of preclinical research is crucial for the development of these implants. To achieve implant success, an understanding of the cellular responses post-implantation, proper model selection, and good study design are crucial. There are several challenges to reaching a safe and effective translation of laboratory findings into clinical practice. The utilization of Mg-based biomedical devices eliminates the need for biomaterial removal surgery post-healing and mitigates adverse effects associated with permanent biomaterial implantation. However, the high corrosion rate of Mg-based implants poses challenges such as unexpected degradation, structural failure, hydrogen evolution, alkalization, and cytotoxicity. The biocompatibility and degradability of materials based on magnesium have been studied by many researchers in vitro; however, evaluations addressing the impact of the material in vivo still need to be improved. Several animal models, including rats, rabbits, dogs, and pigs, have been explored to assess the potential of magnesium-based materials. Moreover, strategies such as alloying and coating have been identified to enhance the degradation rate of magnesium-based materials in vivo to transform these challenges into opportunities. This review aims to explore the utilization of Mg implants across various biomedical applications within cellular (in vitro) and animal (in vivo) models.

Fucoidan/collagen composite coating on magnesium alloy for better corrosion resistance and pro-endothelialization potential

Magnesium alloy stents (MAS) have broad application prospects in the treatment of cardiovascular diseases. However, poor corrosion resistance and biocompatibility greatly limit the clinical application of MAS. In this work, the coating consisting of MgF2 layer, polydopamine layer, fucoidan and collagen IV was constructed on Mg-Zn-Y-Nd (ZE21B) alloy to improve its corrosion resistance and pro-endothelialization potential. The fucoidan and collagen IV in the coating could obviously enhance the hemocompatibility and pro-endothelialization potential respectively. Compared with bare ZE21B alloy, the fucoidan/collagen composite coating modified ZE21B alloy possessed lower corrosion current density and better corrosion resistance. Moreover, the modified ZE21B alloy exhibited relatively low hemolysis rate, fibrinogen adsorption and platelet adhesion in the blood experiments, suggesting the improved hemocompatibility. Furthermore, the modified ZE21B alloy favorably supported the adhesion and proliferation of vascular endothelial cells (ECs) and effectively regulated the phenotype of smooth muscle cells (SMCs), thus improving the pro-endothelialization potential of vascular stent materials. The fucoidan/collagen composite coating can significantly improve the corrosion resistance and pro-endothelialization potential of ZE21B alloy, showing great potential in the development of degradable MAS.

Development and Future Trends of Protective Strategies for Magnesium Alloy Vascular Stents

Magnesium alloy stents have been extensively studied in the field of biodegradable metal stents due to their exceptional biocompatibility, biodegradability and excellent biomechanical properties. Nevertheless, the specific in vivo service environment causes magnesium alloy stents to degrade rapidly and fail to provide sufficient support for a certain time. Compared to previous reviews, this paper focuses on presenting an overview of the development history, the key issues, mechanistic analysis, traditional protection strategies and new directions and protection strategies for magnesium alloy stents. Alloying, optimizing stent design and preparing coatings have improved the corrosion resistance of magnesium alloy stents. Based on the corrosion mechanism of magnesium alloy stents, as well as their deformation during use and environmental characteristics, we present some novel strategies aimed at reducing the degradation rate of magnesium alloys and enhancing the comprehensive performance of magnesium alloy stents. These strategies include adapting coatings for the deformation of the stents, preparing rapid endothelialization coatings to enhance the service environment of the stents, and constructing coatings with self-healing functions. It is hoped that this review can help readers understand the development of magnesium alloy cardiovascular stents and solve the problems related to magnesium alloy stents in clinical applications at the early implantation stage.

Magnesium-Based Temporary Implants: Potential, Current Status, Applications, and Challenges

Biomedical implants are important devices used for the repair or replacement of damaged or diseased tissues or organs. The success of implantation depends on various factors, such as mechanical properties, biocompatibility, and biodegradability of the materials used. Recently, magnesium (Mg)-based materials have emerged as a promising class of temporary implants due to their remarkable properties, such as strength, biocompatibility, biodegradability, and bioactivity. This review article aims to provide a comprehensive overview of current research works summarizing the above-mentioned properties of Mg-based materials for use as temporary implants. The key findings from in-vitro, in-vivo, and clinical trials are also discussed. Further, the potential applications of Mg-based implants and the applicable fabrication methods are also reviewed.

A "built-up" composite film with synergistic functionalities on Mg-2Zn-1Mn bioresorbable stents improves corrosion control effects and biocompatibility

Control of premature corrosion of magnesium (Mg) alloy bioresorbable stents (BRS) is frequently achieved by the addition of rare earth elements. However, limited long-term experience with these elements causes concerns for clinical application and alternative methods of corrosion control are sought after. Herein, we report a "built-up" composite film consisting of a bottom layer of MgF₂ conversion coating, a sandwich layer of a poly (1, 3-trimethylene carbonate) (PTMC) and 3-aminopropyl triethoxysilane (APTES) co-spray coating (PA) and on top a layer of poly (lactic-co-glycolic acid) (PLGA) ultrasonic spray coating to decorate the rare earth element-free Mg-2Zn-1Mn (ZM21) BRS for tailoring both corrosion resistance and biological functions. The developed "built-up" composite film shows synergistic functionalities, allowing the compression and expansion of the coated ZM21 BRS on an angioplasty balloon without cracking or peeling. Of special importance is that the synergistic corrosion control effects of the "built-up" composite film allow for maintaining the mechanical integrity of stents for up to 3 months, where complete biodegradation and no foreign matter residue were observed about half a year after implantation in rabbit iliac arteries. Moreover, the functionalized ZM21 BRS accomplished re-endothelialization within one month.

Surface Heparinization of a Magnesium-Based Alloy: A Comparison Study of Aminopropyltriethoxysilane (APTES) and Polyamidoamine (PAMAM) Dendrimers

Magnesium (Mg)-based alloys are biodegradable metallic biomaterials that show promise in minimizing the risks of permanent metallic implants. However, their clinical applications are restricted due to their rapid in vivo degradation and low surface hemocompatibilities. Surface modifications are critically important for controlling the corrosion rates of Mg-based alloys and improving their hemocompatibilities. In the present study, two heparinization methods were developed to simultaneously increase the corrosion resistance and hemocompatibility of the AZ31 Mg alloy. In the first method, the surface of the AZ31 alloy was modified by alkali-heat treatment and then aminolyzed by 3-amino propyltriethoxy silane (APTES), a self-assembly molecule, and heparin was grafted onto the aminolyzed surface. In the second method, before heparinization, polyamidoamine dendrimers (PAMAM4-4) were grafted onto the aminolyzed surface with APTES to increase the number of surface functional groups, and heparinization was subsequently performed. The presence of a peak with a wavelength of about 1560 cm^-1 in the FTIR spectrum for the sample modified with APTES and dendrimers indicated aminolysis of the surface. The results indicated that the corrosion resistance of the Mg alloy was significantly improved as a result of the formation of a passive layer following the alkali-heat treatment. The results obtained from a potentiodynamic polarization (PDP) test showed that the corrosion current in the uncoated sample decreased from 25 µA to 3.7 µA in the alkali-heat-treated sample. The corrosion current density was reduced by 14 and 50 times in samples treated with the self-assembly molecules, APTES and dendrimers, respectively. After heparinization, the clotting time for pristine Mg was greatly improved. Clotting time increased from 480 s for the pristine Mg sample to 630 s for the APTES- and heparin-modified samples and to 715 s for the PAMAM- and heparin-modified samples. Cell culture data showed a slight improvement in the cell-supporting behavior of the modified samples.

Topography Control of Micro-Nanosized Anatase Coating on Magnesium Alloy

Constructing surface topographies in the micro- or nanometer range is an effective way to improve the biocompatibility of biomaterials. For the present work, anatase coatings with controllable micro/nanoscale characteristics were successfully prepared on an MgZn alloy surface via solvothermal route, and their formation mechanisms are discussed. The features of the as-prepared coatings were characterized using a scanning electron microscope (SEM), a transmission electron microscope (TEM), an atomic force microscope (AFM), X-ray diffraction (XRD), and a contact angle goniometer. The corrosion behavior of the coatings was also evaluated by testing the open circuit potential (OCP) in SBF (Simulated Body Fluid). The results show that a gradual variation of the anatase coating morphologies was obtained through adjusting the solvothermal reaction conditions. With the increase of NH4F concentration in the solution, the cross-combined anatase nanosheets became more dispersed. The micro/nanostructured anatase coatings provide the MgZn alloy with good corrosion resistance, which increased with the density of anatase nanosheets in the coatings. In addition, the coatings exhibit the inhibition of platelet aggregation, and the micro/nano structures can also adsorb endothelial cells.

Current Status and Outlook of Temporary Implants (Magnesium/Zinc) in Cardiovascular Applications

Medical application materials must meet multiple requirements, and the designed material must mimic the structure, shape. and support the formation of the replacing tissue. Magnesium (Mg) and Zinc alloys (Zn), as a “smart” biodegradable material and as “the green engineering material in the 21st century”, have become an outstanding implant material due to their natural degradability, smart biocompatibility, and desirable mechanical properties. Magnesium and Zinc are recognized as the next generation of cardiovascular stents and bioresorbable scaffolds. At the same time, improving the properties and corrosion resistance of these alloys is an urgent challenge. particularly to promote the application of magnesium alloys. A relatively fast deterioration rate of magnesium-based materials generally results in premature mechanical integrity compromise and local hydrogen build-up, resulting in restricted applicability. This review article aims to give a comprehensive comparison between Zn-based alloys and Mg-based alloys, focusing primarily on degradation and biocompatibility for cardiovascular applications. The recent clinical trials using these biodegradable metals have also been addressed.

A biodegradable magnesium alloy vascular stent structure: Design, optimisation and evaluation

The existing biodegradable magnesium alloy stent (BMgS) structure is prone to problems, such as insufficient support capacity and early fracture at areas of concentrated stress. Herein, a stent structural design, which reduced the cross section of the traditional sin-wave stent by nearly 30% and introduces a regular arc structure in the middle of the support ring. The influence of the dual-parameter design of bending radius (r) and ring length (L) on plastic deformation, expansion and compression resistance performances are discussed. The non-dominated sorting genetic algorithm II (NSGA-II) was used to search for the optimal solution. It was found that the introduction of parameter r effectively improved the plastic deformation and expansion performance, and the reduction of L improved stent compression resistance. Finally, an optimized stent configuration was obtained. In vitro mechanical tests, including balloon inflation, radial strength and flexibility, verified the simulation results. The radial strength for the optimised stent increases by approximately 40% compared with that for the sinusoidal stent. Microarea X-ray diffraction result shows that the circumferential residual stress for the optimised stent decreases by half compared with that for the sinusoidal stent, thus effectively reducing the stress concentration phenomenon. STATEMENT OF SIGNIFICANCE: Despite current progress in BMgS research, the optimal design of the structure is limited. We present a new type of structurally designed stent. The performance of this stent was analysed by a finite element method and experimentally verified. The structural design positively influenced stent performance.

Composite Coating Prepared with Ferulic Acid to Improve the Corrosion Resistance and Blood Compatibility of Magnesium Alloy

Magnesium (Mg) alloy has been used for medical vascular stents because of its good biocompatibility and degradability, but its rapid degradation and poor blood compatibility limits its further application. In this study, ferulic acid (FA) was conjugated onto the polydopamine (PDA) deposited Mg-Zn-Y-Nd alloy to prepare a PDA/FA multi-functional coating with better corrosion resistance and blood compatibility. The results suggest that the PDA/FA coating possessed potential application for surface modification of a medical Mg alloy.

A surface-eroding poly(1,3-trimethylene carbonate) coating for magnesium based cardiovascular stents with stable drug release and improved corrosion resistance

Magnesium alloys with integration of degradability and good mechanical performance are desired for vascular stent application. Drug-eluting coatings may optimize the corrosion profiles of magnesium substrate and reduce the incidence of restenosis simultaneously. In this paper, poly (trimethylene carbonate) (PTMC) with different molecular weight (50,000 g/mol named as PTMC5 and 350,000 g/mol named as PTMC35) was applied as drug-eluting coatings on magnesium alloys. A conventional antiproliferative drug, paclitaxel (PTX), was incorporated in the PTMC coating. The adhesive strength, corrosion behavior, drug release and biocompatibility were investigated. Compared with the PLGA control group, PTMC coating was uniform and gradually degraded from surface to inside, which could provide long-term protection for the magnesium substrate. PTMC35 coated samples exhibited much slower corrosion rate 0.05 μA/cm2 in comparison with 0.11 μA/cm2 and 0.13 μA/cm2 for PLGA and PTMC5 coated counterparts. In addition, PTMC35 coating showed more stable and sustained drug release ability and effectively inhibited the proliferation of human umbilical vein vascular smooth muscle cells. Hemocompatibility test indicated that few platelets were adhered on PTMC5 and PTMC35 coatings. PTMC35 coating, exhibiting surface erosion behavior, stable drug release and good biocompatibility, could be a good candidate as a drug-eluting coating for magnesium-based stent.

Advances in coatings on magnesium alloys for cardiovascular stents - A review

Magnesium (Mg) and its alloys, as potential biodegradable materials, have drawn wide attention in the cardiovascular stent field because of their appropriate mechanical properties and biocompatibility. Nevertheless, the occurrence of thrombosis, inflammation, and restenosis of implanted Mg alloy stents caused by their poor corrosion resistance and insufficient endothelialization restrains their anticipated clinical applications. Numerous surface treatment tactics have mainly striven to modify the Mg alloy for inhibiting its degradation rate and enduing it with biological functionality. This review focuses on highlighting and summarizing the latest research progress in functionalized coatings on Mg alloys for cardiovascular stents over the last decade, regarding preparation strategies for metal oxide, metal hydroxide, inorganic nonmetallic, polymer, and their composite coatings; and the performance of these strategies in regulating degradation behavior and biofunction. Potential research direction is also concisely discussed to help guide biological functionalized strategies and inspire further innovations. It is hoped that this review can give assistance to the surface modification of cardiovascular Mg-based stents and promote future advancements in this emerging research field.

Sol-gel coating loaded with inhibitor on ZE21B Mg alloy for improving corrosion resistance and endothelialization aiming at potential cardiovascular application

To improve the service performance of vascular stents, we designed/selected a series of organic compounds from commercial drugs, natural plants, and marine life as the potential corrosion inhibitors for ZE21B alloy. Paeonol condensation tyrosine (PCTyr) Schiff base was found to be the most efficient inhibitor among them. The biocompatible, self-healing, anti-corrosive sol-gel coating loaded with corrosion inhibitor was fabricated on the Mg substrate through a convenient dip-coating tactic. The corrosion resistance, self-healing ability, cytotoxicity, and hemocompatibility of the coated sample were evaluated. These results suggested the potentiality of Schiff base inhibitor-loaded sol-gel coating for enhanced corrosion protection and desired biocompatibility of bioabsorbable cardiovascular implants.

PDLLA-Zn-nitrided Fe bioresorbable scaffold with 53-μm-thick metallic struts and tunable multistage biodegradation function

Balancing the biodegradability and mechanical integrity of a bioresorbable scaffold (BRS) with time after implantation to match the remodeling of the scaffolded blood vessel is important, but a key challenge in doing so remains. This study presents a novel intercalated structure of a metallic BRS by introducing a nanoscale Zn sacrificial layer between the nitrided Fe platform and the sirolimus-carrying poly(d,l-lactide) drug coating. The PDLLA-Zn-FeN BRS shows a multistage biodegradation behavior, maintaining mechanical integrity at the initial stage and exhibiting accelerated biodegradation at the subsequent stage in both rabbit abdominal aortas and human coronary arteries, where complete biodegradation was observed about 2 years after implantation. The presence of the nanoscale Zn sacrificial layer with an adjustable thickness also contributes to the tunable biodegradation of BRS and allows the reduction of the metallic strut thickness to 53 μm, with radial strength as strong as that of the current permanent drug-eluting stents.

Degradation behaviors and in-vivo biocompatibility of a rare earth- and aluminum-free magnesium-based stent

Biodegradable stents can provide scaffolding and anti-restenosis benefits in the short term and then gradually disappear over time to free the vessel, among which the Mg-based biodegradable metal stents have been prosperously developed. In the present study, a Mg-8.5Li (wt.%) alloy (RE- and Al-free) with high ductility (> 40%) was processed into mini-tubes, and further fabricated into finished stent through laser cutting and electropolishing. In-vitro degradation test was performed to evaluate the durability of this stent before and after balloon dilation. The influence of plastic deformation and residual stress (derived from the dilation process) on the degradation was checked with the assistance of finite element analysis. In addition, in-vivo degradation behaviors and biocompatibility of the stent were evaluated by performing implantation in iliac artery of minipigs. The balloon dilation process did not lead to deteriorated degradation, and this stent exhibited a decent degradation rate (0.15 mm/y) in vitro, but divergent result (> 0.6 mm/y) was found in vivo. The stent was almost completely degraded in 3 months, revealing an insufficient scaffolding time. Meanwhile, it did not induce possible thrombus, and it was tolerable by surrounding tissues in pigs. Besides, endothelial coverage in 1 month was achieved even under the severe degradation condition. In the end, the feasibility of this stent for treatment of benign vascular stenosis was generally discussed, and perspectives on future improvement of Mg-Li-based stents were proposed.

Properties of Titanium Oxide Coating on MgZn Alloy by Magnetron Sputtering for Stent Application

Constructing surface coatings is an effective way to improve the corrosion resistance and biocompatibility of magnesium alloy bioabsorbable implants. In this present work, a titanium oxide coating with a thickness of about 400 nm was successfully prepared on a MgZn alloy surface via a facile magnetron sputtering route. The surface features were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and the contact angle method. The corrosion behavior and biocompatibility were evaluated. The results indicated that the amorphous TiO2 coating with a flat and dense morphology was obtained by magnetron-sputtering a titanium oxide target. The corrosion current density decreased from 1050 (bare MgZn alloy) to 49 μA/cm2 (sample with TiO2 coating), suggesting a significant increase in corrosion resistance. In addition, the TiO2 coating showed good biocompatibilities, including significant reduced hemolysis and platelet adhesion, and increased endothelial cell viability and adhesion.

Endothelial progenitor cells as the target for cardiovascular disease prediction, personalized prevention, and treatments: progressing beyond the state-of-the-art

Stimulated by the leading mortalities of cardiovascular diseases (CVDs), various types of cardiovascular biomaterials have been widely investigated in the past few decades. Although great therapeutic effects can be achieved by bare metal stents (BMS) and drug-eluting stents (DES) within months or years, the long-term complications such as late thrombosis and restenosis have limited their further applications. It is well accepted that rapid endothelialization is a promising approach to eliminate these complications. Convincing evidence has shown that endothelial progenitor cells (EPCs) could be mobilized into the damaged vascular sites systemically and achieve endothelial repair in situ, which significantly contributes to the re-endothelialization process. Therefore, how to effectively capture EPCs via specific molecules immobilized on biomaterials is an important point to achieve rapid endothelialization. Further, in the context of predictive, preventive, personalized medicine (PPPM), the abnormal number alteration of EPCs in circulating blood and certain inflammation responses can also serve as important indicators for predicting and preventing early cardiovascular disease. In this contribution, we mainly focused on the following sections: the definition and classification of EPCs, the mechanisms of EPCs in treating CVDs, the potential diagnostic role of EPCs in predicting CVDs, as well as the main strategies for cardiovascular biomaterials to capture EPCs.

Surface Engineering of Cardiovascular Devices for Improved Hemocompatibility and Rapid Endothelialization

Cardiovascular devices have been widely applied in the clinical treatment of cardiovascular diseases. However, poor hemocompatibility and slow endothelialization on their surface still exist. Numerous surface engineering strategies have mainly sought to modify the device surface through physical, chemical, and biological approaches to improve surface hemocompatibility and endothelialization. The alteration of physical characteristics and pattern topographies brings some hopeful outcomes and plays a notable role in this respect. The chemical and biological approaches can provide potential signs of success in the endothelialization of vascular device surfaces. They usually involve therapeutic drugs, specific peptides, adhesive proteins, antibodies, growth factors and nitric oxide (NO) donors. The gene engineering can enhance the proliferation, growth, and migration of vascular cells, thus boosting the endothelialization. In this review, the surface engineering strategies are highlighted and summarized to improve hemocompatibility and rapid endothelialization on the cardiovascular devices. The potential outlook is also briefly discussed to help guide endothelialization strategies and inspire further innovations. It is hoped that this review can assist with the surface engineering of cardiovascular devices and promote future advancements in this emerging research field.

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.

A pure zinc membrane with degradability and osteogenesis promotion for guided bone regeneration: In vitro and in vivo studies

Selection of an appropriate membrane material for guided bone regeneration (GBR) is still ongoing among resorbable and nonresorbable membranes with different characteristics. The major problem with nonresorbable membranes is the inevitable secondary surgery, while resorbable polymer membranes have limitations in providing sufficient mechanical support during the bone repair period due to premature loss of mechanical strength. Pure magnesium foil has been evaluated to explore its feasibility as a resorbable GBR membrane. It exhibited better mechanical properties, whereas poor formability and fast degradation rate were noted. In light of this, pure zinc membrane was developed as a pilot research in this paper. We designed three types of pure zinc membranes: pure Zn without pores, pure Zn with 300 µm diameter and 1000 µm diameter pores, and pure titanium without pores as a control. The mechanical property, in vitro immersion tests, and MC3T3-E1 cell viability assays were tested. Moreover, in vivo behaviors of three type zinc membranes were evaluated by using a rat calvarial critical-sized bone defect model. The experimental results indicated that pure Zn membrane with 300 µm pores showed the most favorable osteogenic capability, comparable to that of titanium membrane without pores. Therefore, considering appropriate degradation rate, adequate mechanical maintenance, and profitable osteogenic capacity, metallic pure zinc is believed to be a promising candidate for barrier membranes in GBR therapy for bone regeneration, and its mechanical property can be enhanced with further alloying. STATEMENT OF SIGNIFICANCE: Metallic element zinc plays a pivotal role in the growth and mineralization of bone tissues. As a pilot research, three type of guided bone regeneration (GBR) membranes were developed in the present work: pure Zn without pores, pure Zn with 300 µm-diameter and 1000 µm-diameter pores respectively. The mechanical property, in vitro immersion tests and MC3T3-E1 cell viability assays were tested, with pure titanium without pores as a control, thereafter the in vivo performance were evaluated by using a rat calvarial critical-sized bone defect model. It indicated that pure Zn membrane with 300 µm pores showed the most favorable osteogenic capability, comparable to that of titanium membrane control, and is believed to be a promising material candidate as barrier membrane in GBR therapy for bone regeneration.

Fabrication and characterization of silk fibroin coating on APTES pretreated Mg-Zn-Ca alloy

To delay the degradation of magnesium alloys, silk fibroin as a natural organic polymer coating was fabricated on a 3-amino-propyltriethoxysilane (APTES) pretreated Mg-Zn-Ca alloy. APTES pretreatment coated the surface of magnesium alloys with amino groups, which can bond with functional groups in silk fibroin to form a compact coating/substrate interface. The influences of the APTES concentration and drying temperature on the coating adhesion and interface were investigated to explore the optimal parameters in the fabrication process. The nanoporous silk fibroin films completely covered the APTES pretreated Mg-Zn-Ca surface, which reached a thickness of ~7 μm. The chemical states for the coated Mg-Zn-Ca alloy were compared to those of the bare Mg-Zn-Ca alloy and the APTES pretreated Mg-Zn-Ca alloy to illustrate the coating mechanism. During in vitro degradation and electrochemical measurements in simulated body fluid (SBF), the samples with the silk fibroin coating showed remarkably improved corrosion resistance and a slower degradation rate compared to those of the bare samples, suggesting that the silk fibroin coating was an effective protection coating for the substrates and can delay the degradation of magnesium alloys. Moreover, a model for the in vitro degradation was proposed. In vitro cell experiments confirmed the excellent biocompatibility of silk fibroin coated Mg-Zn-Ca structure.

Metal-Based Nanostructures/PLGA Nanocomposites: Antimicrobial Activity, Cytotoxicity, and Their Biomedical Applications

Among the different synthetic polymers developed for biomedical applications, poly(lactic-co-glycolic acid) (PLGA) has attracted considerable attention because of its excellent biocompatibility and biodegradability. Nanocomposites based on PLGA and metal-based nanostructures (MNSs) have been employed extensively as an efficient strategy to improve the structural and functional properties of PLGA polymer. The MNSs have been used to impart new properties to PLGA, such as antimicrobial properties and labeling. In the present review, the different strategies available for the fabrication of MNS/PLGA nanocomposites and their applications in the biomedical field will be discussed, beginning with a description of the preparation routes, antimicrobial activity, and cytotoxicity concerns of MNS/PLGA nanocomposites. The biomedical applications of these nanocomposites, such as carriers and scaffolds in tissue regeneration and other therapies are subsequently reviewed. In addition, the potential advantages of using MNS/PLGA nanocomposites in treatment illnesses are analyzed based on in vitro and in vivo studies, to support the potential of these nanocomposites in future research in the biomedical field.

In vivo and in vitro evaluation of a biodegradable magnesium vascular stent designed by shape optimization strategy

The performance of biodegradable magnesium alloy stents (BMgS) requires special attention to non-uniform residual stress distribution and stress concentration, which can accelerate localized degradation after implantation. We now report on a novel concept in stent shape optimization using a finite element method (FEM) toolkit. A Mg-Nd-Zn-Zr alloy with uniform degradation behavior served as the basis of our BMgS. Comprehensive in vitro evaluations drove stent optimization, based on observed crimping and balloon inflation performance, measurement of radial strength, and stress condition validation via microarea-XRD. Moreover, a Rapamycin-eluting polymer coating was sprayed on the prototypical BMgS to improve the corrosion resistance and release anti-hyperplasia drugs. In vivo evaluation of the optimized coated BMgS was conducted in the iliac artery of New Zealand white rabbit with quantitative coronary angiography (QCA), optical coherence tomography (OCT) and micro-CT observation at 1, 3, 5-month follow-ups. Neither thrombus or early restenosis was observed, and the coated BMgS supported the vessel effectively prior to degradation and allowed for arterial healing thereafter. The proposed shape optimization framework based on FEM provides an novel concept in stent design and in-depth understanding of how deformation history affects the biomechanical performance of BMgS. Computational analysis tools can indeed promote the development of biodegradable magnesium stents.

A pH-sensitive self-healing coating for biodegradable magnesium implants

Self-healing coatings have attracted attention on surface modification of magnesium alloys, as it can recover the barrier ability of the coatings from corrosion attack. Nevertheless, previous works on this aspect are not suitable for biomedical magnesium alloys owing to the lack of biocompatibility. In this study, we fabricated a self-healing coating on biomedical Mg-1Ca alloy by compositing silk fibroin and K₃PO₄. PO₄^3- ions act as corrosion inhibitor, while K³⁺ ions help to regulate the secondary structures of silk fibroin. The scratch test, scanning vibrating electrode technique (SVET), and electrochemical impedance spectroscopy (EIS) provide comprehensive results, confirming the pH-sensitive self-healing capacity of the composite coating. Moreover, cells' (MC3T3-E1) multiple responses including spreading, adhesion, proliferation, and differentiation illustrate the preferable biocompatibility as well as the osteogenic activity of the coating. These primary findings might open new opportunities in the exploration of self-healing coatings on biomedical magnesium alloys. STATEMENT OF SIGNIFICANCE: Biomedical magnesium alloys surface modifications have been studied for years, which however the biomedical self-healing coatings were rarely involved. In this work, silk fibroin and phosphate (K₃PO₄) were composited to fabricate coating on biomedical magnesium alloys. The coating not only owned the self-healing ability with pH sensitivity, but also endowed the substrate preferable corrosion resistance as well as osteogenic activity. This work gives a new insight into surface modification for biomedical Mg alloys.

Ta ion implanted nanoridge-platform for enhanced vascular responses

Bare metal stents are commonly used in interventional cardiology; they provide successful treatment because of their excellent mechanical properties, expandability ratios, and flexibility. However, their insufficient vascular affinity can induce the development of neointimal hyperplasia following arterial injury and subsequent smooth muscle cell overgrowth in the lumen of a stented vessel. Nanoengineering of the bare metal stent surface is a valuable strategy for eliciting favorable vascular responses. In this study, we introduce a target-ion-induced plasma sputtering (TIPS) technique to fabricate a platform with a favorable endothelial environment. This technique enables the simple single-step production of a Ta-implanted nanoridged surface on a stent with a complex 3D geometry that shows a clear tendency to become oriented parallel to the direction of blood flow. Moreover, the nanoridges developed show good structural integrity and mechanical stability, resulting in apparently stable morphologies under high strain rates. In vitro cellular responses to the Co-Cr, such as endothelialization, platelet activation, and blood coagulation, are considerably altered after TIPS treatment; endothelium formation is rapid and surface thrombogenicity is low. An in vivo rabbit iliac artery model is used to confirm that the nanoridged surface facilitates rapid re-endothelialization and limits the formation of neointima compared to the bare stent. These results indicate that the Ta ion implanted nanoridge platform fabricated using the TIPS technique has immense potential as a solution for in-stent restenosis and ensuring the long-term patency of bare metal stents.

In Vitro and in Vivo Studies on Two-Step Alkali-Fluoride-Treated Mg-Zn-Y-Nd Alloy for Vascular Stent Application: Enhancement in Corrosion Resistance and Biocompatibility

Bioabsorbable magnesium alloys are becoming prominent materials for cardiovascular stents, as their desirable mechanical properties and favorable biosafety. However, the rapid corrosion of magnesium alloys under physiological conditions hinders their wider application as medical implant materials. Fluoride chemical conversion treatment is an effective and simple technique to improve the corrosion resistance for magnesium alloys. Despite previous literature reporting on fluoride chemical conversion treatment with hydrofluoric acid (HF) in different conditions, some defects are still present on the surface of the coating. In this study, we report on a two-step alkali-fluoride treatment of magnesium alloy by effectively removing the second phase in the substrate surface and form a dense and flawless magnesium fluoride (MgF₂) coating to endow the magnesium alloy greater corrosion resistance. The results showed that the serious pitting corrosion caused by galvanic corrosion could be effectively prevented after removing of the second phase of the surface. In vivo tests in a rat subcutaneous implantation model showed that two-step alkali-fluoride-treated MgZnYNd alloy (MgZnYNd-A-F) uniformly corroded with a low corrosion rate. No subcutaneous gas cavities or significant inflammatory cell infiltration were observed for MgZnYNd-A-F in in vivo tests. The two-step alkali-fluoride treatment can significantly improve the corrosion resistance and biocompatibility of magnesium alloy, which has great potential in the application of vascular stents because of its simplicity and effectiveness.

Silk fibroin film-coated MgZnCa alloy with enhanced in vitro and in vivo performance prepared using surface activation

Magnesium and its alloys have generated considerable interest as one of the most promising biodegradable metals for biomedical bone implants. However, the enormous challenges are to improve their rapid corrosion excessively as well as to endow them with biocompatibility and biosafety. Herein, we introduce a natural silk fibroin protein coating to control the corrosion resistance and enhance the biocompatibility of MgZnCa alloy. To obtain a robust and reliable coated structure, different surface-activation processes are employed to increase the available functional groups on MgZnCa surfaces before coating. Compared to oxygen plasma activation, our unique vacuum ultraviolet-ozone (VUV/O₃) activation method is effective in realizing uniform silk fibroin films as a protective barrier on MgZnCa alloy surfaces, and the nanoscratch test verified the superior adhesion strength of the silk fibroin-coated magnesium alloy structure. Long-term immersion results combined with electrochemical tests showed the preferable in vitro anticorrosion behavior and a low degradation rate of coated Mg alloy (1/8 times that of uncoated Mg alloy). Cell adhesion and cytotoxicity tests demonstrated that silk fibroin-coated MgZnCa presented improved biocompatibility with bone marrow mesenchymal stem cells. An animal study involving silk fibroin-coated MgZnCa implanted on one side of a rabbit spine for 180 days showed remarkably improved in vivo corrosion resistance, with 1/18 times the degradation rate of uncoated MgZnCa. These results not only comprehensively confirmed the validity of the VUV/O₃-activation method as a coating strategy but also implied the tremendous potential of the modified Mg alloy for application as a degradable biomedical implant material. STATEMENT OF SIGNIFICANCE: MgZnCa alloy is a promising material in clinical implantation. Silk fibroin (SF) is a natural organic material with biocompatibility and biodegradability. To date, the combination of SF and MgZnCa alloy has exhibited considerable prospects for orthopedic applications. The realization of a direct coating is an enormous challenge because strong chemical bonds cannot be easily formed between organic and inorganic materials. To solve this bottleneck, we proposed a unique vacuum ultraviolet-ozone (VUV/O₃) surface-activation method for the first time to modify the Mg alloy surface before SF coating, which significantly enhanced both in vitro and in vivo performance, such as superior biocompatibility and remarkably improved corrosion resistance of magnesium alloys (∼1/18 the in vivo degradation rate of uncoated MgZnCa).

Mechanism of Acceleration of Iron Corrosion by a Polylactide Coating

Strong and biodegradable materials are key to the development of next-generation medical devices for interventional treatment. Biodegradable polymers such as polylactide (PLA) have controllable degradation profiles, but their mechanical strength is much weaker than some metallic materials such as iron; on the other hand, tuning the corrosion rate of iron to a proper time range for biomedical applications has always been a challenge. Very recently, we have achieved a complete corrosion of iron stent in vivo within the clinically required time frame by combining a PLA coating, which provides a new biomaterial type for the next-generation biodegradable coronary stents termed as a metal-polymer composite stent. The underlying mechanism of accelerating iron corrosion by a PLA coating remains an open fundamental topic. Herein, we investigated the corrosion mechanism of an iron sheet under a PLA coating in the biomimetic in vitro condition. The Pourbaix diagram (potential vs pH) was calculated to present the thermodynamic driving force of iron corrosion in the biomimetic aqueous medium. Electrochemical methods were applied to track the dynamic corrosion process and inspect various potential cues influencing iron corrosion. The present work reveals that acceleration of iron corrosion by the PLA coating arises mainly from decreasing the local pH owing to PLA hydrolysis and from alleviating the deposition of the passivation layer by the polymer coating.

The degradation and transport mechanism of a Mg-Nd-Zn-Zr stent in rabbit common carotid artery: A 20-month study

Mg-based stent is a promising candidate of the next generation fully degradable vascular stents. The latest progress includes the CE approval of the Magmaris ® WE43 based drug eluting stent. However, so far, the long term (more than 1 year implantation) in vivo degradation and the physiological effects caused by the degradation products were still unclear. In this study, a 20 month observation was carried out after the bare Mg-Nd-Zn-Zr (abbr. JDBM) stent prototype was implanted into the common carotid artery of New Zealand white rabbit in order to evaluate its safety, efficacy and especially degradation behavior. The degradation of the main second phase Mg₁₂Nd was also studied. Results showed that the bare JDBM stent had good safety and efficacy with a complete re-endothelialization within 28 days. The JDBM stent struts were mostly replaced in situ by degradation products in 4 month. The important finding was that the volume and Ca concentration of the degradation products decreased in the long term, eliminating the clinicians' concern of possible vessel calcification. In addition, the alloying elements Mg and Zn in the stent could be safely metabolized as continuous enrichment in any of the main organs were not detected although Nd and Zr showed an abrupt increase in spleen and liver after 1 month implantation. Collectively, the long term in vivo results showed the rapid re-endothelialization of JDBM stent and the long term safety of the degradation products, indicating its great potential as the backbone of the fully degradable vascular stent.

STATEMENT OF SIGNIFICANCE

Mg-based stent is a promising candidate of the next generation fully degradable stents, especially after the recent market launch of one of its kind (Magmaris). However the fundamental question about the long term degradation and metabolic mechanism of Mg-based stent and its degradation products remain unanswered. We implanted our patented Mg-Nd-Zn-Zr bare stent into the common carotid artery of rabbits and conducted a 20 months observation. We found that the Ca containing degradation products could be further degraded in vivo. All the alloying elements showed no continuous enrichment in the main organs of rabbits. These findings eliminate the clinicians' concern of possible vessel calcification and element enrichment after the implantation of Mg alloy based stents to some extent.

A silk-based coating containing GREDVY peptide and heparin on Mg-Zn-Y-Nd alloy: improved corrosion resistance, hemocompatibility and endothelialization

Magnesium (Mg) alloys have been intensively investigated as potential absorbable coronary stent materials as their use avoids risks such as late inflammation and restenosis generated by permanent metallic implants. Besides that, clinical trials on coronary stents fabricated from Mg alloys have made great progress recently. However, the over-rapid corrosion rate, magnesium corrosion-induced thrombosis formation and delayed endothelium regeneration continue to be problematic for coronary artery stent therapy. In this study, silk fibroin blended with heparin and GREDVY (Gly-Arg-Glu-Asp-Val-Tyr) peptide was immobilized on a HF-pretreated MgZnYNd alloy surface via a polydopamine layer to improve its corrosion resistance, blood compatibility and endothelialization. Standard electrochemical measurements along with the long-term immersion results indicated that the functionalized MgZnYNd alloy had preferable anti-corrosion abilities compared with the bare MgZnYNd alloy. The modified surface exhibited outstanding hemocompatibility with reduced platelet adhesion, hemolysis rate and prolonged blood coagulation time. Human umbilical vein endothelial cell (HUVEC) and vascular smooth muscle cell (VSMC) co-culture results revealed more attached HUVECs on the functionalized samples than on the MgZnYNd alloy surfaces. The excellent corrosion retardation, hemocompatibility and re-endothelialization of the multi-functional coating indicate a promising method in the field of biodegradable magnesium-based implantable cardiovascular stents.

Strategy of Metal-Polymer Composite Stent To Accelerate Biodegradation of Iron-Based Biomaterials

The new principle and technique to tune biodegradation rates of biomaterials is one of the keys to the development of regenerative medicine and next-generation biomaterials. Biodegradable stents are new-generation medical devices applied in percutaneous coronary intervention, etc. Recently, both corrodible metals and degradable polymers have drawn much attention in biodegradable stents or scaffolds. It is, however, a dilemma to achieve good mechanical properties and appropriate degradation profiles. Herein, we put forward a metal-polymer composite strategy to achieve both. Iron stents exhibit excellent mechanical properties but low corrosion rate in vivo. We hypothesized that coating of biodegradable aliphatic polyester could accelerate iron corrosion due to the acidic degradation products, etc. To demonstrate the feasibility of this composite material technique, we first conducted in vitro experiments to affirm that iron sheet corroded faster when covered by polylactide (PLA) coating. Then, we fabricated three-dimensional metal-polymer stents (MPS) and implanted the novel stents in the abdominal aorta of New Zealand white rabbits, setting metal-based stents (MBS) as a control. A series of in vivo experiments were performed, including measurements of residual mass and radial strength of the stents, histological analysis, micro-computed tomography, and optical coherence tomography imaging at the implantation site. The results showed that MPS could totally corrode in some cases, whereas iron struts of MBS in all cases remained several months after implantation. Corrosion rates of MPS could be easily regulated by adjusting the composition of PLA coatings.

A DFT study of the adsorption of short peptides on Mg and Mg-based alloy surfaces

Adsorption of short peptides, including three dipeptides: Arg–Gly, Gly–Asp, Arg–Asp, and one tripeptide RGD, on the surfaces of Mg and Mg alloys (Mg–Zn, Mg–Y, and Mg–Nd), was studied using first-principles calculations based on density functional theory (DFT), considering van der Waals (vdW) correction.

Synthesis of aromatic-doped polycaprolactone with tunable degradation behavior

A novel aromatic-doped polycaprolactone (Aro-PCL) material was synthesized through a facile PCL aminolysis-condensation polymerization incorporating the aromatic moiety to PCL chain and assessed by focusing on the dynamic aggregation and crystalline microdomains associated with the in vitro degradation properties, mechanical performance and biocompatibility.

Arginine-leucine based poly (ester urea urethane) coating for Mg-Zn-Y-Nd alloy in cardiovascular stent applications

Selected from the family of self-designed biodegradable amino acid-based poly (ester urea urethane) (AA-PEUU) pseudo-protein biomaterials, arginine-leucine based poly (ester urea urethane)s (Arg-Leu-PEUUs) were used as protective and bio-functional coatings for bio-absorbable magnesium alloy MgZnYNd in cardiovascular stent applications. Comparing with poly (glycolide-co-lactide) (PLGA) coating, the Arg-Leu-PEUU coating had stronger bonding strength with the substrate; in vitro electrochemical and long-term immersion results verified a significantly better corrosion resistance. Acute blood contact tests proved a better hemocompatibility of Arg-Leu-PEUU coating. The immunofluorescent staining and cell proliferation test indicated that Arg-Leu-PEUU coating had a far better cytocompatibility. The Arg-Leu-PEUU coating stimulated human umbilical vein endothelial cells (HUVEC) to release reasonably increased amount of nitric oxide (NO), suggesting its potential in retarding thrombosis and restenosis. The superior corrosion resistance and biocompatibility as well as the indigenous NO production bio-functionality of the Arg-Leu-PEUU copolymer family indicate their capability to offer a far better protection of the magnesium-based implantable cardiovascular stent and bring their application closer to clinical reality.

In vitro and in vivo degradation of rapamycin-eluting Mg-Nd-Zn-Zr alloy stents in porcine coronary arteries

In this work, rapamycin-eluting poly (d, l-lactic acid) coating (PDLLA/RAPA) was prepared on biodegradable Mg-Nd-Zn-Zr alloy (JDBM) for both in vitro and in vivo investigation of the degradation behaviors of the magnesium alloy stent platform. Electrochemical tests and hydrogen evolution test demonstrated significant in vitro protection of the polymeric coating against magnesium degradation both in short and long term. The 3-month in vivo study on the RAPA-eluting JDBM stent implanted into porcine coronary arteries confirmed its favorable safety, and in the meanwhile revealed similar neointima proliferation compared to the second generation DES Firebird 2 with no occurrence of adverse complications. Moreover, Micro-CT examination combined with IVUS and OCT detection indicated a remarkably lower degradation rate and prolonged radial supporting duration of the drug-eluting JDBM stent as compared to the bare, attributable to the protection of the coating in vivo. Hence, rapamycin-eluting JDBM stents exhibit great potential for clinical application.

In situ incorporation of heparin/bivalirudin into a phytic acid coating on biodegradable magnesium with improved anticorrosion and biocompatible properties

Drugs were incorporated into a phytic acid coating on Mg by an in situ chemical route for corrosion control and biocompatibility.

A novel biodegradable and biologically functional arginine-based poly(ester urea urethane) coating for Mg–Zn–Y–Nd alloy: enhancement in corrosion resistance and biocompatibility

Novel biodegradable and functional Arg-PEUU coating materials for MgZnYNd alloy stents may make drugs like sirolimus or paclitaxel unnecessary.

Enhanced corrosion protection and biocompatibility of a PLGA–silane coating on AZ31 Mg alloy for orthopaedic applications

This paper reports a multi-step procedure to fabricate a novel corrosion resistant and biocompatible PLGA–silane coating on the magnesium (Mg) alloy AZ31.