Short-term effects of biocorrodible iron stents in porcine coronary arteries

Absorbable implants in sport medicine and arthroscopic surgery: A narrative review of recent development

Over the past two decades, advances in arthroscopic and minimally invasive surgical techniques have led to significant growth in sports medicine surgery. Implants such as suture anchors, interference screws, and endo-buttons are commonly used in these procedures. However, traditional implants made of metal or inert materials are not absorbable, leading to complications that affect treatment outcomes. To address this issue, absorbable materials with excellent mechanical properties, good biocompatibility, and controlled degradation rates have been developed and applied in clinical practice. These materials include absorbable polymers, absorbable bioceramics, and absorbable metals. In this paper, we will provide a comprehensive summary of these absorbable materials from the perspective of clinicians, and discuss their clinical applications and related research in sport medicine.

Recent advances in Fe-based bioresorbable stents: Materials design and biosafety

Fe-based materials have received more and more interests in recent years as candidates to fabricate bioresorbable stents due to their appropriate mechanical properties and biocompatibility. However, the low degradation rate of Fe is a serious limitation for such application. To overcome this critical issue, many efforts have been devoted to accelerate the corrosion rate of Fe-based stents, through the structural and surface modification of Fe matrix. As stents are implantable devices, the released corrosion products (Fe2+ ions) in vessels may alter the metabolism, by generating reactive oxygen species (ROS), which might in turn impact the biosafety of Fe-based stents. These considerations emphasize the importance of combining knowledge in both materials and biological science for the development of efficient and safe Fe-based stents, although there are still only limited numbers of reviews regarding this interdisciplinary field. This review aims to provide a concise overview of the main strategies developed so far to design Fe-based stents with accelerated degradation, highlighting the fundamental mechanisms of corrosion and the methods to study them as well as the reported approaches to accelerate the corrosion rates. These approaches will be divided into four main sections, focusing on (i) increased active surface areas, (ii) tailored microstructures, (iii) creation of galvanic reactions (by alloying, ion implantation or surface coating of noble metals) and (iv) decreased local pH induced by degradable surface organic layers. Recent advances in the evaluation of the in vitro biocompatibility of the final materials and ongoing in vivo tests are also provided.

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.

Adaptation of Vascular Smooth Muscle Cell to Degradable Metal Stent Implantation

Iron-, magnesium-, or zinc-based metal vessel stents support vessel expansion at the period early after implantation and degrade away after vascular reconstruction, eliminating the side effects due to the long stay of stent implants in the body and the risks of restenosis and neoatherosclerosis. However, emerging evidence has indicated that their degradation alters the vascular microenvironment and induces adaptive responses of surrounding vessel cells, especially vascular smooth muscle cells (VSMCs). VSMCs are highly flexible cells that actively alter their phenotype in response to the stenting, similarly to what they do during all stages of atherosclerosis pathology, which significantly influences stent performance. This Review discusses how biodegradable metal stents modify vascular conditions and how VSMCs respond to various chemical, biological, and physical signals attributable to stent implantation. The focus is placed on the phenotypic adaptation of VSMCs and the clinical complications, which highlight the importance of VSMC transformation in future stent design.

FeMn and FeMnAg biodegradable alloys: An in vitro and in vivo investigation

Iron-based biodegradable metal bone graft substitutes are in their infancy but promise to fill bone defects that arise after incidents such as trauma and revision arthroplasty surgery. Before clinical use however, a better understanding of their in vivo biodegradability, potential cytotoxicity and biocompatibility is required. In addition, these implants must ideally be able to resist infection, a complication of any implant surgery. In this study there was significant in vitro cytotoxicity caused by pure Fe, FeMn, FeMn1Ag and FeMn5Ag on both human foetal osteoblast (hFOB) and mouse pre-osteoblast (MC3T3-E1) cell lines. In vivo experiments on the other hand showed no signs of ill-effect on GAERS rats with the implanted FeMn, FeMn1Ag and FeMn5Ag pins being removed largely uncorroded. All Fe-alloys showed anti-bacterial performance but most markedly so in the Ag-containing alloys, there is significant bacterial resistance in vitro.

Fe and C additions decrease the dissolution rate of silicon nitride coatings and are compatible with microglial viability in 3D collagen hydrogels

Silicon nitride (SiN) coatings may reduce unwanted release of metal ions from metallic implants. However, as SiN slowly dissolves in aqueous solutions, additives that reduce this dissolution rate would likely increase the lifetime and functionality of implants. Adding iron (Fe) and carbon (C) permits tuning of the SiN coatings' mechanical properties, but their effect on SiN dissolution rates, and their capacity to reduce metal ion release from metallic implant substrates, have yet to be investigated. Such coatings have recently been proposed for use in spinal implants; therefore, it is relevant to assess their impact on the viability of cells expected at the implant site, such as microglia, the resident macrophages of the central nervous system (CNS). To study the effects of Fe and C on the dissolution rate of SiN coatings, compositional gradients of Si, Fe and C in combination with N were generated by physical vapor deposition onto CoCrMo discs. Differences in composition did not affect the surface roughness or the release of Si, Fe or Co ions (the latter from the CoCrMo substrate). Adding Fe and C reduced ion release compared to a SiN reference coating, which was attributed to altered reactivity due to an increase in the fraction of stabilizing Si-C or Fe-C bonds. Extracts from the SiN coatings containing Fe and C were compatible with microglial viability in 2D cultures and 3D collagen hydrogels, to a similar degree as CoCrMo and SiN coated CoCrMo reference extracts. As Fe and C reduced the dissolution rate of SiN-coatings and did not compromise microglial viability, the capacity of these additives to extend the lifetime and functionality of SiN-coated metallic implants warrants further investigation.

Structure Optimization of a Fe-Mn-Pd Alloy by Equal-Channel Angular Pressing for Biomedical Use

In this work, a Fe-Mn-Pd alloy was produced by methods of equal channel angular pressing (ECAP) in order to obtain an alloy with a high rate of degradation for the development of biodegradable devices. Special efforts were made to the obtaining of an ultrafine-grained structure of alloys in a fully austenitic state at temperatures of 300 °C and 450 °C. Further investigation of its effect on the corrosion rate and mechanical properties was carried out. The formation of an austenitic structure with structural element sizes of 100-250 nm after deformation was confirmed by X-ray diffraction analysis. ECAP proved to be the reason for a significant increase in strength with maximum σ_UTS = 1669 MPa and σ_YS = 1577 MPa while maintaining satisfactory plasticity. The alloy degradation rate was investigated using the potentiodynamic polarization analysis. The corrosion rate of the alloy after ECAP (~1 mm/y) is higher than that of the coarse-grained state and significantly higher than that of annealed iron (~0.2 mm/y). ECAP in both modes did not impair the biocompatibility of the Fe-Mn-Pd alloy and the colonization of the sample surface by cells.

Long-term safety and absorption assessment of a novel bioresorbable nitrided iron scaffold in porcine coronary artery

This study aimed to investigate the long-term biocompatibility, safety, and degradation of the ultrathin nitrided iron bioresorbable scaffold (BRS) in vivo, encompassing the whole process of bioresorption in porcine coronary arteries. Fifty-two nitrided iron scaffolds (strut thickness of 70 μm) and 28 Vision Co–Cr stents were randomly implanted into coronary arteries of healthy mini-swine. The efficacy and safety of the nitrided iron scaffold were comparable with those of the Vision stentwithin 52 weeks after implantation. In addition, the long-term biocompatibility, safety, and bioresorption of the nitrided iron scaffold were evaluated by coronary angiography, optical coherence tomography, micro-computed tomography, scanning electron microscopy, energy dispersive spectrometry and histopathological evaluations at 4, 12, 26, 52 weeks and even at 7 years after implantation. In particular, a large number of struts were almost completely absorbed in situ at 7 years follow-up, which were first illustrated in this study. The lymphatic drainage pathway might serve as the potential clearance way of iron and its corrosion products.

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This study investigated the long-term safety and the total degradative process of nitrided iron scaffold in porcine coronary artery.

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The safety and biocompatibility of the nitrided iron scaffold were comparable to those of the Vision stent within 12 months after implantation.

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This ultrathin nitrided iron scaffold can be degraded and bioresorbed completely with long-term biocompatibility in porcine coronary artery.

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Interestingly, the lymphatic metabolic pathway might serve as the potential absorption route for iron and its corrosion products.

A Biodegradable Metal-Polymer Composite Stent Safe and Effective on Physiological and Serum-Containing Biomimetic Conditions

The new-generation coronary stents are expected to be biodegradable, and then the biocompatibility along with biodegradation becomes more challenging. It is a critical issue to choose appropriate biomimetic conditions to evaluate biocompatibility. Compared with other candidates for biodegradable stents, iron-based materials are of high mechanical strength, yet have raised more concerns about biodegradability and biocompatibility. Herein, a metal-polymer composite strategy is applied to accelerate the degradation of iron-based stents in vitro and in a porcine model. Furthermore, it is found that serum, the main environment of vascular stents, ensured the safety of iron corrosion through its antioxidants. This work highlights the importance of serum, particularly albumin, for an in vitro condition mimicking blood-related physiological condition, when reactive oxygen species, inflammatory response, and neointimal hyperplasia are concerned. The resultant metal-polymer composite stent is implanted into a patient in clinical research via interventional treatment, and the follow-up confirms its safety, efficacy, and appropriate biodegradability.

FeMn with Phases of a Degradable Ag Alloy for Residue-Free and Adapted Bioresorbability

The development of bioresorbable materials for temporary implantation enables progress in medical technology. Iron (Fe)-based degradable materials are biocompatible and exhibit good mechanical properties, but their degradation rate is low. Aside from alloying with Manganese (Mn), the creation of phases with high electrochemical potential such as silver (Ag) phases to cause the anodic dissolution of FeMn is promising. However, to enable residue-free dissolution, the Ag needs to be modified. This concern is addressed, as FeMn modified with a degradable Ag-Calcium-Lanthanum (AgCaLa) alloy is investigated. The electrochemical properties and the degradation behavior are determined via a static immersion test. The local differences in electrochemical potential increase the degradation rate (low pH values), and the formation of gaps around the Ag phases (neutral pH values) demonstrates the benefit of the strategy. Nevertheless, the formation of corrosion-inhibiting layers avoids an increased degradation rate under a neutral pH value. The complete bioresorption of the material is possible since the phases of the degradable AgCaLa alloy dissolve after the FeMn matrix. Cell viability tests reveal biocompatibility, and the antibacterial activity of the degradation supernatant is observed. Thus, FeMn modified with degradable AgCaLa phases is promising as a bioresorbable material if corrosion-inhibiting layers can be diminished.

Biodegradable Zn-Cu-Fe Alloy as a Promising Material for Craniomaxillofacial Implants: An in vitro Investigation into Degradation Behavior, Cytotoxicity, and Hemocompatibility

Zinc-based nanoparticles, nanoscale metal frameworks and metals have been considered as biocompatible materials for bone tissue engineering. Among them, zinc-based metals are recognized as promising biodegradable materials thanks to their moderate degradation rate ranging between magnesium and iron. Nonetheless, materials’ biodegradability and the related biological response depend on the specific implant site. The present study evaluated the biodegradability, cytocompatibility, and hemocompatibility of a hot-extruded zinc-copper-iron (Zn-Cu-Fe) alloy as a potential biomaterial for craniomaxillofacial implants. Firstly, the effect of fetal bovine serum (FBS) on in vitro degradation behavior was evaluated. Furthermore, an extract test was used to evaluate the cytotoxicity of the alloy. Also, the hemocompatibility evaluation was carried out by a modified Chandler-Loop model. The results showed decreased degradation rates of the Zn-Cu-Fe alloy after incorporating FBS into the medium. Also, the alloy exhibited acceptable toxicity towards RAW264.7, HUVEC, and MC3T3-E1 cells. Regarding hemocompatibility, the alloy did not significantly alter erythrocyte, platelet, and leukocyte counts, while the coagulation and complement systems were activated. This study demonstrated the predictable in vitro degradation behavior, acceptable cytotoxicity, and appropriate hemocompatibility of Zn-Cu-Fe alloy; therefore, it might be a candidate biomaterial for craniomaxillofacial implants.

Biodegradable Iron and Porous Iron: Mechanical Properties, Degradation Behaviour, Manufacturing Routes and Biomedical Applications

Biodegradable metals have been extensively studied due to their potential use as temporary biomedical devices, on non-load bearing applications. These types of implants are requested to function for the healing period, and should degrade after the tissue heals. A balance between mechanical properties requested at the initial stage of implantation and the degradation rate is required. The use of temporary biodegradable implants avoids a second surgery for the removal of the device, which brings high benefits to the patients and avoids high societal costs. Among the biodegradable metals, iron as a biodegradable metal has increased attention over the last few years, especially with the incorporation of additive manufacturing processes to obtain tailored geometries of porous structures, which give rise to higher corrosion rates. Withal by mimic natural bone hierarchical porosity, the mechanical properties of obtained structures tend to equalize that of human bone. This review article presents some of the most important works in the field of iron and porous iron. Fabrication techniques for porous iron are tackled, including conventional and new methods highlighting the unparalleled opportunities given by additive manufacturing. A comparison among the several methods is taken. The effects of the design and the alloying elements on the mechanical properties are also revised. Iron alloys with antibacterial properties are analyzed, as well as the biodegradation behavior and biocompatibility of iron. Although is necessary for further in vivo research, iron is presenting satisfactory results for upcoming biomedical applications, as orthopaedic temporary scaffolds and coronary stents.

Corrosion behavior and degradation mechanism of micro-extruded 3D printed ordered pore topological Fe scaffolds

The fabrication of ordered pore topological structures (OPTS) with an improved biodegradation profile offers unique attributes required for bone reconstruction. These attributes consisted of fully interconnected porous structure, bone-mimicking mechanical properties, and the possibility of fully regenerating bony defects. Most of the biomaterials based on magnesium were associated with the problem of too fast degradation rate. Here, the present aim was based on the fabrication of ordered pore topological Fe structures (OPTFS) using micro-extrusion-based 3D printing followed by pressureless microwave sintering. Two different kinds of pore features namely randomly distributed interconnected micropores and designed interconnected macropores were investigated. Static in vitro degradation results inferred that the H-2 mm pore size of hexagonal based ordered pore topological Fe structures (H-OPTFS) exhibited the highest degradation rate of 6.45 mg cm^-2  day^-1 on the 28th day. Electrochemical results revealed that the corrosion current density of the T-1 Fe sample with 44% porosity increased nearly by a multiple of three times as compared to dense Fe (from 16.79 to 44.63  μA cm - 2 ) _. Similarly, these results showed more significance in H-2 mm pores size (with highest 66% porosity) of H-OPTFS as compared to H-1.75 mm and H-1.5 mm pore size of H-OPTFS (≈2 times higher degradation rate than H-1.5 mm pore size). Moreover, the MG63 osteoblast cell line was adhered to and proliferated significantly throughout the surface and illustrated more than 80% cell viability of the prepared porous Fe scaffold. The analyzed results have shown the potential of fabricated OPTFS could be considered for biomedical applications.

Mechanical properties, in vitro and in vivo biocompatibility analysis of pure iron porous implant produced by metal injection molding: A new eco-friendly feedstock from natural rubber (Hevea brasiliensis)

Metal injection molding (MIM) has become an important manufacturing technology for biodegradable medical devices. As a biodegradable metal, pure iron is a promising biomaterial due to its mechanical properties and biocompatibility. In light of this, we performed the first study that manufactured and evaluated the in vitro and in vivo biocompatibility of samples of iron porous implants produced by MIM with a new eco-friendly feedstock from natural rubber (Hevea brasiliensis), a promisor binder that provides elastic property in the green parts. The iron samples were submitted to tests to determine density, microhardness, hardness, yield strength, and stretching. The biocompatibility of the samples was studied in vitro with adipose-derived mesenchymal stromal cells (ADSCs) and erythrocytes, and in vivo on a preclinical model with Wistar rats, testing the iron samples after subcutaneous implant. Results showed that the manufactured samples have adequate physical, and mechanical characteristics to biomedical devices and they are cytocompatible with ADSCs, hemocompatible and biocompatible with Wistars rats. Therefore, pure iron produced by MIM can be considered a promising material for biomedical applications.

Accelerated biodegradation of iron-based implants via tantalum-implanted surface nanostructures

In recent years, pure iron (Fe) has attracted significant attention as a promising biodegradable orthopedic implant material due to its excellent mechanical and biological properties. However, in physiological conditions, Fe has an extremely slow degradation rate with localized and irregular degradation, which is problematic for practical applications. In this study, we developed a novel combination of a nanostructured surface topography and galvanic reaction to achieve uniform and accelerated degradation of an Fe implant. The target-ion induced plasma sputtering (TIPS) technique was applied on the Fe implant to introduce biologically compatible and electrochemically noble tantalum (Ta) onto its surface and develop surface nano-galvanic couples. Electrochemical tests revealed that the uniformly distributed nano-galvanic corrosion cells of the TIPS-treated sample (nano Ta–Fe) led to relatively uniform and accelerated surface degradation compared to that of bare Fe. Furthermore, the mechanical properties of nano Ta–Fe remained almost constant during a long-term in vitro immersion test (~40 weeks). Biocompatibility was also assessed on surfaces of bare Fe and nano Ta–Fe using in vitro osteoblast responses through direct and indirect contact assays and an in vivo rabbit femur medullary cavity implantation model. The results revealed that nano Ta–Fe not only enhanced cell adhesion and spreading on its surface, but also exhibited no signs of cellular or tissue toxicity. These results demonstrate the immense potential of Ta-implanted surface nanostructures as an effective solution for the practical application of Fe-based orthopedic implants, ensuring long-term biosafety and clinical efficacy.

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The degradation rate of nanostructured Fe implants was accelerated by TIPS technique.

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Ta ions were accelerated strongly toward the Fe surface by TIPS process.

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Nano Ta–Fe showed long-term mechanical stability and accelerated degradation rate.

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Nanostructured Ta–Fe surface showed enhanced in vitro and in vivo cellular responses.

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Ta-implanted Fe is a promising material for biodegradable orthopedic implants.

Bioresorbable Metals for Biomedical Applications: From Mechanical Components to Electronic Devices

Bioresorbable metals and metal alloys are of growing interest for myriad uses in temporary biomedical implants. Examples range from structural elements as stents, screws, and scaffolds to electronic components as sensors, electrical stimulators, and programmable fluidics. The associated physical forms span mechanically machined bulk parts to lithographically patterned conductive traces, across a diversity of metals and alloys based on magnesium, zinc, iron, tungsten, and others. The result is a rich set of opportunities in healthcare materials science and engineering. This review article summarizes recent advances in this area, starting with an historical perspective followed by a discussion of materials options, considerations in biocompatibility, and device applications. Highlights are in system level bioresorbable electronic platforms that support functions as diagnostics and therapeutics in the context of specific, temporary clinical needs. A concluding section highlights challenges and emerging research directions.

Biodegradable Iron-Based Materials-What Was Done and What More Can Be Done?

Iron, while attracting less attention than magnesium and zinc, is still one of the best candidates for biodegradable metal stents thanks its biocompatibility, great elastic moduli and high strength. Due to the low corrosion rate, and thus slow biodegradation, iron stents have still not been put into use. While these problems have still not been fully resolved, many studies have been published that propose different approaches to the issues. This brief overview report summarises the latest developments in the field of biodegradable iron-based stents and presents some techniques that can accelerate their biocorrosion rate. Basic data related to iron metabolism and its biocompatibility, the mechanism of the corrosion process, as well as a critical look at the rate of degradation of iron-based systems obtained by several different methods are included. All this illustrates as the title says, what was done within the topic of biodegradable iron-based materials and what more can be done.

Recent advances and directions in the development of bioresorbable metallic cardiovascular stents: Insights from recent human and in vivo studies

Over the past two decades, significant advancements have been made regarding the material formulation, iterative design, and clinical translation of metallic bioresorbable stents. Currently, magnesium-based (Mg) stent devices have remained at the forefront of bioresorbable stent material development and use. Despite substantial advances, the process of developing novel absorbable stents and their clinical translation is time-consuming, expensive, and challenging. These challenges, coupled with the continuous refinement of alternative bioresorbable metallic bulk materials such as iron (Fe) and zinc (Zn), have intensified the search for an ideal absorbable metallic stent material. Here, we discuss the most recent pre-clinical and clinical evidence for the efficacy of bioresorbable metallic stents and material candidates. From this perspective, strategies to improve the clinical performance of bioresorbable metallic stents are considered and critically discussed, spanning material alloy development, surface manipulations, material processing techniques, and preclinical/biological testing considerations. STATEMENT OF SIGNIFICANCE: Recent efforts in using Mg, Fe, and Zn based materials for bioresorbable stents include elemental profile changes as well as surface modifications to improve each of the three classes of materials.  Although a variety of alloys for absorbable metallic stents have been developed, the ideal absorbable stent material has not yet been discovered. This review focuses on the state of the art for bioresorbable metallic stent development. It covers the three bulk materials used for degradable stents (Mg, Fe, and Zn), and discusses their advances from a translational perspective. Strategies to improve the clinical performance of bioresorbable metallic stents are considered and critically discussed, spanning material alloy development, surface manipulations, material processing techniques, and preclinical/biological testing considerations.

Antibacterial metals and alloys for potential biomedical implants

Metals and alloys, including stainless steel, titanium and its alloys, cobalt alloys, and other metals and alloys have been widely used clinically as implant materials, but implant-related infection or inflammation is still one of the main causes of implantation failure. The bacterial infection or inflammation that seriously threatens human health has already become a worldwide complaint. Antibacterial metals and alloys recently have attracted wide attention for their long-term stable antibacterial ability, good mechanical properties and good biocompatibility in vitro and in vivo. In this review, common antibacterial alloying elements, antibacterial standards and testing methods were introduced. Recent developments in the design and manufacturing of antibacterial metal alloys containing various antibacterial agents were described in detail, including antibacterial stainless steel, antibacterial titanium alloy, antibacterial zinc and alloy, antibacterial magnesium and alloy, antibacterial cobalt alloy, and other antibacterial metals and alloys. Researches on the antibacterial properties, mechanical properties, corrosion resistance and biocompatibility of antibacterial metals and alloys have been summarized in detail for the first time. It is hoped that this review could help researchers understand the development of antibacterial alloys in a timely manner, thereby could promote the development of antibacterial metal alloys and the clinical application.

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This paper focuses the recent development of several antibacterial metals and alloys as biomedical materials.

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The possible antibacterial mechanisms of antibacterial metals and alloys are summarized in this paper.

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This review discusses the feasibility of antibacterial metals and alloys as biomedical implants in the future.

Designing Better Cardiovascular Stent Materials - A Learning Curve

Cardiovascular stents are life-saving devices and one of the top 10 medical breakthroughs of the 21st century. Decades of research and clinical trials have taught us about the effects of material (metal or polymer), design (geometry, strut thickness, and the number of connectors), and drug-elution on vasculature mechanics, hemocompatibility, biocompatibility, and patient health. Recently developed novel bioresorbable stents are intended to overcome common issues of chronic inflammation, in-stent restenosis, and stent thrombosis associated with permanent stents, but there is still much to learn. Increased knowledge and advanced methods in material processing have led to new stent formulations aimed at improving the performance of their predecessors but often comes with potential tradeoffs. This review aims to discuss the advantages and disadvantages of stent material interactions with the host within five areas of contrasting characteristics, such as 1) metal or polymer, 2) bioresorbable or permanent, 3) drug elution or no drug elution, 4) bare or surface-modified, and 5) self-expanding or balloon-expanding perspectives, as they relate to pre-clinical and clinical outcomes and concludes with directions for future studies.

In Vivo Evaluation of Bioabsorbable Fe-35Mn-1Ag: First Reports on In Vivo Hydrogen Gas Evolution in Fe-Based Implants

This work investigates the influence of Ag (1 wt%) on the mechanical properties, in vitro and in vivo corrosion, and biocompatibility of Fe-35Mn. The microstructure of Fe-35Mn-1Ag possesses a uniform dispersion of discrete silver particles. Slight improvements in compressive properties are attributed to enhanced density and low porosity volume. Fe-35Mn-1Ag exhibits good in vitro and in vivo corrosion rate of Fe-35Mn due to an increase in microgalvanic corrosion. Gas pockets, which originate from an inflammatory response to the implants, are observed in the rats after 4 weeks implantation but are undetectable after 12 weeks. No chronic toxicity is observed with the Fe-35Mn-1Ag, suggesting acceptable in vivo biocompatibility. The high corrosion rate of the alloy triggers an increased level of nonadverse tissue inflammatory responses 4 weeks after implantation, which subsequently subsides at 12 weeks. The Fe-35Mn-1Ag displays properties that are suitable for orthopedic applications.

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

Magnesium metal (Mg) is a promising material for stent applications due to its biocompatibility and ability to be resorbed by the body. Manufacturing of stents by laser cutting has become an industry standard. Our alternative approach uses photo-chemical etching to transfer a pattern of the stent onto a Mg sheet. In this study, we present three stages of creating and validating a stent prototype, which includes design and simulation using finite element analysis (FEA), followed by fabrication based on AZ31 alloy and, finally, in vivo testing in peripheral arteries of domestic pigs. Due to the preliminary character of this study, only six stents were implanted in two domestic farm pigs weighing 25–28 kg and they were evaluated after 28 days, with an interim follow-up on day 14. The left and right superficial femoral, the left iliac, and the right renal artery were selected for this study. The diameters of the stented artery segments were evaluated at the time of implantation, on day 14 and then, finally, on day 28, by quantitative vessel analysis (QVA) using fluoroscopic imaging. Optical Coherence Tomography (OCT) imaging displayed some malposition, breaks, stacking, and protrusion into the lumen at the proximal, distal, and mid-sections of the stented arteries. The stents degraded with time, but simultaneously became embedded in the intima. After 28 days, the animals were euthanized, and explanted vessels were fixed for micro-CT imaging and histology studies. Micro-CT imaging revealed stent morphological and volumetric changes due to the in-body degradation. An in vivo corrosion rate of 0.75 mm/year was obtained by the CT evaluation. The histology suggested no-life threatening effects, although moderate injury, inflammation, and endothelialization scores were observed.

Drug-Eluting Stents and Balloons-Materials, Structure Designs, and Coating Techniques: A Review

Controlled drug delivery is a matter of interest to numerous scientists from various domains, as well as an essential issue for society as a whole. In the treatment of many diseases, it is crucial to control the dosing of a drug for a long time and thus maintain its optimal concentration in the tissue. Heart diseases are particularly important in this aspect. One such disease is an obstructive arterial disease affecting millions of people around the world. In recent years, stents and balloon catheters have reached a significant position in the treatment of this condition. Balloon catheters are also successfully used to manage tear ducts, paranasal sinuses, or salivary glands disorders. Modern technology is continually striving to improve the results of previous generations of stents and balloon catheters by refining their design, structure, and constituent materials. These advances result in the development of both successive models of drug-eluting stents (DES) and drug-eluting balloons (DEB). This paper presents milestones in the development of DES and DEB, which are a significant option in the treatment of coronary artery diseases. This report reviews the works related to achievements in construction designs and materials, as well as preparation technologies, of DES and DEB. Special attention was paid to the polymeric biodegradable materials used in the production of the above-mentioned devices. Information was also collected on the various methods of producing drug release coatings and their effectiveness in releasing the active substance.

In vivo biological safety evaluation of an iron-based bioresorbable drug-eluting stent

Bioresorbable stents (BRS) are investigated and designed to revascularize occluded arteries. The iron-based bioresorbable stent is a promising device in interventional therapies, although it's corrosion and bioresorption rate remain challenging. In this work, we introduced a novel nitrided iron coronary stent (IBS) with enhanced degradation rate compared with pure iron stent. To evaluate the biosafety of this device, a sub-chronic systemic toxicity study was conducted and a stainless steel stent (Supporter™) served as a control. Here, the bioresorbable stent was first evaluated in rat abdominal aortic implantation model. When subjected to exaggerated exposure dose, no clinical signs of toxicity or mortality were observed in either, the IBS group or the control group. Histopathological examinations showed the corrosion particles of iron were encapsulated by fibrocytes and engulfed by macrophages, indicating that the degradation of iron was in the early stage. Our results demonstrated that the nitrided iron stent did not induce systemic toxicity under the experimental conditions.

Microstructure, mechanical properties, degradation behavior, and biocompatibility of porous Fe-Mn alloys fabricated by sponge impregnation and sintering techniques

In this study, porous iron (Fe)-manganese (Mn) alloys with high porosity were successfully prepared by sponge impregnation and sintering (SIS). The compositions of the porous Fe-Mn alloys were strongly dependent on the sintering temperature, and the Mn content was ~44, 30, and 12 wt.% for alloys sintered at 1100, 1150, and 1200 °C, respectively. The porous Fe-Mn alloys exhibited a well-interconnected porous structure with ~85% porosity and average pore size ranging from 375 to 500 um. The porous Fe-44Mn and Fe-30Mn alloys were mainly composed of a γ-austenite phase, while the porous Fe-12Mn was composed of an α-ferrite phase. The yield strength and elastic modulus of the porous Fe-Mn alloys ranged from 6 to 10 MPa and from 0.12 to 0.37 GPa, respectively, similar to those of cancellous bone. The degradation rate of the porous Fe-Mn alloys decreased over time during immersion in simulated body fluid (SBF), and was 1.0 mm/year for Fe-44Mn, 0.81 mm/year for Fe-30Mn, 0.41 mm/year for Fe-12Mn, and 0.33 mm/year for pure Fe after 14 d SBF immersion. Moreover, the porous Fe-Mn alloys exhibited good biocompatibility with clearly enhanced cell proliferation after direct culturing of osteoblastic MC3T3-E1 cells for 7 d. Thus, these porous Fe-Mn alloys can be anticipated to be promising biodegradable implant materials. STATEMENT OF SIGNIFICANCE: This work reports on porous Fe-Mn alloys with high porosity, suitable mechanical properties and degradation rate, and good biocompatibility. The porous alloys prepared by sponge impregnation and sintering exhibited a well-interconnected porous structure with ~85% porosity and average pore size ranging from 375 to 500 um. The yield strength and elastic modulus of the porous alloys ranged from 6 to 10 MPa and from 0.12 to 0.37 GPa, respectively, similar to those of cancellous bone. The degradation rates in simulated body fluid (SBF) were ~1.0 mm/year for Fe-44Mn, 0.81 mm/year for Fe-30Mn, and 0.41 mm/year for Fe-12Mn, respectively. Moreover, the porous Fe-Mn alloys exhibited good biocompatibility with enhanced cell proliferation after direct culturing of osteoblastic MC3T3-E1 cells.

Highly Ductile Zn-2Fe-WC Nanocomposite as Biodegradable Material

Zinc (Zn) has been widely investigated as a biodegradable metal for orthopedic implants and vascular stents due to its ideal corrosion in vivo and biocompatibility. However, pure Zn lacks adequate mechanical properties for load-bearing applications. Alloying elements, such as iron (Fe), have been shown to improve the strength significantly, but at the cost of compromised ductility and corrosion rate. In this study, tungsten carbide (WC) nanoparticles were incorporated into the Zn-2Fe alloy system for strengthening, microstructure modification, and ductility enhancement. Thermally stable WC nanoparticles modified the intermetallic ζ-FeZn13 interface morphology from faceted to non-faceted. Consequently, WC nanoparticles simultaneously enhance mechanical strength and ductility while maintaining a reasonable corrosion rate. Overall, this novel Zn-Fe-WC nanocomposite could be used as biodegradable material for biomedical applications where pure Zn is inadequate.

Biological and mechanical characterization of biodegradable carbonyl iron powder/polycaprolactone composite material fabricated using three-dimensional printing for cardiovascular stent application

Biological and mechanical properties of biodegradable polymeric composite materials are strongly influenced by the choice of appropriate reinforcement in the polymer matrix. Non-compatibility of material in the vascular system could obstruct the way of the biological fluids. The concept of development of polymeric composite material for vascular implants is to provide enough support to the vessel and to restore the vessel in the natural state after degradation. In this research, the polycaprolactone composite materials (carbonyl iron powder/polycaprolactone) were developed by reinforcement of the 0%–2% of carbonyl iron powder using the solvent cast three-dimensional printing technique. The physicochemical properties of developed composites were characterized in conjunction with mechanical and biological properties. The mechanical characterizations were assessed by uniaxial tensile testing as well as flexibility testing. The results of mechanical testing assured that carbonyl iron powder/polycaprolactone composites have shown desirable properties for vascular implants. Besides the mechanical characterization, in vitro biological investigations of carbonyl iron powder/polycaprolactone were done for analyzing blood compatibility and cytocompatibility. The results revealed that the materials developed were biocompatible, less hemolytic, and having non-thrombogenic properties indicating the promising applications in the field of cardiovascular applications.

Evaluation of in vitro and in vivo biocompatibility of iron produced by powder metallurgy

Biodegradable metallic materials (BMMs) are expected to corrode gradually in vivo after providing the structural support to the tissue during its regeneration and healing processes. These characteristics make them promising candidates for use in stents. These endoprostheses are produced from metal alloys by casting and thermomechanical treatment. Since porous alloys and metals have less corrosion resistance than dense ones, the use of powder metallurgy becomes an option to produce them. Among the metals, iron has been proposed as a material in the manufacturing of stents because of its mechanical properties. However, even then it is unclear what toxicity threshold is safe to the body. Thus, the objective of this research was to verify the biocompatibility of sintered 99.95% and 99.5% pure iron by powder metallurgy in vitro with Adipose-derived mesenchymal stromal cells (ADSCs) and in vivo with a Wistar rat model. Herein, characterizations of iron powder samples produced by the powder metallurgy and the process parameters as compression pressure, atmosphere, sintering time and temperature were determined to evaluate the potential of production of biodegradable implants. The samples obtained from pure iron were submitted to tests of green and sintered density, porosity, microhardness, hardness and metallography. The biocompatibility study was performed by indirect and direct cell culture with iron. The effects of corrosion products of iron on morphology, viability, and proliferation of ADSCs were evaluated in vitro. Hemolysis assay was performed to verify the hemocompatibility of the samples. In vivo biocompatibility was evaluated after pure iron discs were implanted subcutaneously into the dorsal area of Wistar rats that were followed up to 6 months. The results presented in this paper validated the potential to produce biodegradable medical implants by powder metallurgy. Both iron samples were hemocompatible and biocompatible in vitro and in vivo, although the 99.95% iron had better performance in vitro than 99.5%.

Si-Fe-C-N Coatings for Biomedical Applications: A Combinatorial Approach

Ceramic coatings may prolong the lifetime of joint implants. Certain ions and wear debris may however lead to negative biological effects. SiN-based materials may substantially reduce these effects, but still need optimization for the application. In this study, a combinatorial deposition method enabled an efficient evaluation of a range of Si-Fe-C-N coating compositions on the same sample. The results revealed compositional gradients of Si (26.0-33.9 at.%), Fe (9.6-20.9 at.%), C (8.2-13.9 at.%) and N (39.7-47.2 at.%), and low oxygen contaminations (0.3-0.6 at.%). The mechanical properties varied with a hardness (H) ranging between 13.7-17.3 GPa and an indentation modulus (M) between 190-212 GPa. Both H and M correlated with the Si (H and M increased as Si increased) and Fe (H and M decreased as Fe increased) content. A slightly columnar morphology was observed in cross-sections, as well as a surface roughness in the nm range. A cell study revealed adhering pre-osteogenic MC3T3 cells, with a morphology similar to that of cells seeded on a tissue culture plastic control. The investigated coatings could be considered for further investigation due to the ability to tune their mechanical properties while maintaining a smooth surface, together with their promising in vitro cell response.

Bioresorbable Scaffolds: Current Technology and Future Perspectives

Metallic drug-eluting stents have led to significant improvements in clinical outcomes but are inherently limited by their caging of the vessel wall. Fully bioresorbable scaffolds (BRS) have emerged in an effort to overcome these limitations, allowing a "leave nothing behind" approach. Although theoretically appealing, the initial experience with BRS technology was limited by increased rates of scaffold thrombosis compared with contemporary stents. This review gives a broad outline of the current BRS technologies and outlines the refinements in BRS design, procedural approach, lesion selection, and post-procedural care that resulted from early BRS trials.

Recent Advances in Manufacturing Innovative Stents

Cardiovascular diseases are the most distributed cause of death worldwide. Stenting of arteries as a percutaneous transluminal angioplasty procedure became a promising minimally invasive therapy based on re-opening narrowed arteries by stent insertion. In order to improve and optimize this method, many research groups are focusing on designing new or improving existent stents. Since the beginning of the stent development in 1986, starting with bare-metal stents (BMS), these devices have been continuously enhanced by applying new materials, developing stent coatings based on inorganic and organic compounds including drugs, nanoparticles or biological components such as genes and cells, as well as adapting stent designs with different fabrication technologies. Drug eluting stents (DES) have been developed to overcome the main shortcomings of BMS or coated stents. Coatings are mainly applied to control biocompatibility, degradation rate, protein adsorption, and allow adequate endothelialization in order to ensure better clinical outcome of BMS, reducing restenosis and thrombosis. As coating materials (i) organic polymers: polyurethanes, poly(ε-caprolactone), styrene-b-isobutylene-b-styrene, polyhydroxybutyrates, poly(lactide-co-glycolide), and phosphoryl choline; (ii) biological components: vascular endothelial growth factor (VEGF) and anti-CD34 antibody and (iii) inorganic coatings: noble metals, wide class of oxides, nitrides, silicide and carbide, hydroxyapatite, diamond-like carbon, and others are used. DES were developed to reduce the tissue hyperplasia and in-stent restenosis utilizing antiproliferative substances like paclitaxel, limus (siro-, zotaro-, evero-, bio-, amphi-, tacro-limus), ABT-578, tyrphostin AGL-2043, genes, etc. The innovative solutions aim at overcoming the main limitations of the stent technology, such as in-stent restenosis and stent thrombosis, while maintaining the prime requirements on biocompatibility, biodegradability, and mechanical behavior. This paper provides an overview of the existing stent types, their functionality, materials, and manufacturing conditions demonstrating the still huge potential for the development of promising stent solutions.

Long-Term Efficacy of Biodegradable Metal-Polymer Composite Stents After the First and the Second Implantations into Porcine Coronary Arteries

A biodegradable coronary stent is expected to eliminate the adverse events of an otherwise eternally implanting material after vessel remodeling. Both biocorrodible metals and biodegradable polymers have been tried as the matrix of the new-generation stent. Herein, we utilized a metal-polymer composite material to combine the advantages of the high mechanical strength of metals and the adjustable degradation rate of polymers to prepare the biodegradable stent. After coating polylactide (PLA) on the surface of iron, the degradation of iron was accelerated significantly owing to the decrease of local pH resulting from the hydrolysis of PLA, etc. We implanted the metal-polymer composite stent (MPS) into the porcine artery and examined its degradation in vivo, with the corresponding metal-based stent (MBS) as a control. Microcomputed tomography (micro-CT), coronary angiography (CA), and optical coherence tomography (OCT) were performed to observe the stents and vessels during the animal experiments. The MPS exhibited faster degradation than MBS, and the inflammatory response of MPS was acceptable 12 months after implantation. Additionally, we implanted another MPS after 1-year implantation of the first MPS to investigate the result of the MPS in the second implantation. The feasibility of the biodegradable MPS in second implantation in mammals was also confirmed.

Preclinical Evaluation of a Novel Sirolimus-Eluting Iron Bioresorbable Coronary Scaffold in Porcine Coronary Artery at 6 Months

OBJECTIVES

The aim of this study was to investigate the operability, 6-month efficacy, and safety of the novel sirolimus-eluting iron bioresorbable coronary scaffold (IBS) system compared with a cobalt-chromium everolimus-eluting stent (EES) (XIENCE Prime stent) in porcine coronary arteries.

BACKGROUND

Bioresorbable scaffolds have been considered the fourth revolution in percutaneous coronary intervention. However, the first-generation bioresorbable scaffold showed suboptimal results.

METHODS

Forty-eight IBS and 48 EES were randomly implanted into nonatherosclerotic swine. The operability, efficacy, and safety of the IBS and EES were evaluated using coronary angiography, optical coherence tomography, micro-computed tomography, scanning electron microscopy, and histopathologic evaluation at 7, 14, 28, 90, and 180 days after implantation.

RESULTS

The operability of the ultrathin IBS (∼70 μm) was comparable with that of the EES, except for its visibility. There was no statistically significant difference in area stenosis between the IBS and EES from 28 to 180 days. The IBS maintained its integrity up to 90 days without corrosion, while corrosion was observed in a few struts in 2 of 10 IBS at 180 days. The percentage of endothelialization of IBS was higher than that of XIENCE Prime stents within 14 days after implantation. The fibrin score was higher in the IBS group at 28 days but comparable with the EES group at 90 and 180 days. No scaffold or stent thrombosis was seen in either group. No abnormal histopathologic changes in scaffolded or stented vessel segments and 5 main remote organs were observed in either group.

CONCLUSIONS

Preclinical results suggest that the novel IBS has comparable operability, mid-term efficacy, and safety with the EES, and its corrosion profile in porcine coronary arteries is reasonable, which could support initial clinical study of the IBS.

Controlling the Degradation Rate of Biodegradable Mg-Zn-Mn Alloys for Orthopedic Applications by Electrophoretic Deposition of Hydroxyapatite Coating

Magnesium alloys as bioresorbable materials with good biocompatibility have raised a growing interest in the past years in temporary implant manufacturing, as they offer a steady resorption rate and optimal healing in the body. Magnesium exhibits tensile strength properties similar to those of natural bone, which determines its application in load-bearing mechanical medical devices. In this paper, we investigated the biodegradation rate of Mg-Zn-Mn biodegradable alloys (ZMX410 and ZM21) before and after coating them with hydroxyapatite (HAP) via the electrophoretic deposition method. The experimental samples were subjected to corrosion tests to observe the effect of HAP deposition on corrosion resistance and, implicitly, the rate of biodegradation of these in simulated environments. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) provided detailed information on the quality, structure, and morphology of the HAP coating. The obtained results demonstrate that coating of Mg-Zn-Mn alloys by HAP led to the improvement of corrosion resistance in simulated environments, and that the HAP coating could be used in order to control the biodegradation rate.

Are Fe-Based Stenting Materials Biocompatible? A Critical Review of In Vitro and In Vivo Studies

Fe-based materials have increasingly been considered for the development of biodegradable cardiovascular stents. A wide range of in vitro and in vivo studies should be done to fully evaluate their biocompatibility. In this review, we summarized and analyzed the findings and the methodologies used to assess the biocompatibility of Fe materials. The majority of investigators drew conclusions about in vitro Fe toxicity based on indirect contact results. The setup applied in these tests seems to overlook the possible effects of Fe corrosion and does not allow for understanding of the complexity of released chemical forms and their possible impact on tissue. It is in particular important to ensure that test setups or interpretations of in vitro results do not hide some important mechanisms, leading to inappropriate subsequent in vivo experiments. On the other hand, the sample size of existing in vivo implantations is often limited, and effects such as local toxicity or endothelial function are not deeply scrutinized. The main advantages and limitations of in vitro design strategies applied in the development of Fe-based alloys and the correlation with in vivo studies are discussed. It is evident from this literature review that we are not yet ready to define an Fe-based material as safe or biocompatible.

Anti-CD34-Grafted Magnetic Nanoparticles Promote Endothelial Progenitor Cell Adhesion on an Iron Stent for Rapid Endothelialization

Iron stents, with superior mechanical properties and controllable degradation behavior, have potential for use as feasible substitutes for nondegradable stents in the treatment of coronary artery occlusion. However, corrosion renders the iron surface hard to modify with biological molecules to accelerate endothelialization and solve restenosis. The objective of this study is to demonstrate the feasibility of using endothelial progenitor cells (EPCs) to rapidly adhere onto iron surfaces with the assistance of anti-CD34-modified magnetic nanoparticles. Transmission electron microscopy, Fourier transform infrared spectroscopy, Thermogravimetric analysis, XRD, and anti-CD34 immunofluorescence suggested that anti-CD34 and citric acid were successfully modified onto Fe3O4, and Prussian blue staining demonstrated the selectivity of the as-prepared nanoparticles for EPCs. Under an external magnetic field (EMF), numerous nanoparticles or EPCs attached onto the surface of iron pieces, particularly the side of the iron pieces exposed to flow conditions, because iron could be magnetized under the EMF, and the magnetized iron has an edge effect. However, the uniform adhesion of EPCs on the iron stent was completed because of the weakening edge effect, and the sum of adherent EPCs was closely linked with the magnetic field (MF) intensity, which was validated by the complete covering of EPCs on the iron stent upon exposure to a 300 mT EMF within 3 h, whereas almost no cells were observed on the iron stent without an EMF. These results verify that this method can efficiently promote EPC capture and endothelialization of iron stents.

The Fundamental Comparison of Zn-2Mg and Mg-4Y-3RE Alloys as a Perspective Biodegradable Materials

Biodegradable materials are of interest for temporary medical implants like stents for restoring damaged blood vessels, plates, screws, nails for fixing fractured bones. In the present paper new biodegradable Zn-2Mg alloy prepared by conventional casting and hot extrusion was tested in in vitro and in vivo conditions. Structure characterization and mechanical properties in tension and compression have been evaluated. For in vivo tests, hemispherical implants were placed into a rat cranium. Visual observation of the living animals, an inspection of implant location and computed tomography CT imaging 12 weeks after implantation were performed. Extracted implants were studied using scanning electron microscopy (SEM) on perpendicular cuts through corrosion products. The behaviour of zinc alloy both in in vitro and in vivo conditions was compared with commercially used Mg-based alloy (Mg-4Y-3RE) prepared by conventional casting and hot extrusion. Both compressive and tensile yield strengths of Zn and Mg-based alloys were similar; however, the brittleness of Mg-4Y-3RE was lower. Zn and Mg-based implants have no adverse effects on the behaviour or physical condition of rats. Moreover, gas bubbles and the inflammatory reaction of the living tissue were not detected after the 12-week period.

The Development of Magnesium-Based Resorbable and Iron-Based Biocorrodible Metal Scaffold Technology and Biomedical Applications in Coronary Artery Disease Patients

In the treatment of atherosclerotic disease patients, the adoption of second-generation drug-eluting stents (DES) in percutaneous coronary intervention reduced the occurrence of in-stent restenosis (ISR) and acute stent thrombosis (ST) when compared to bare metal stents and 1st generation DES. However, the permanent encaging of the vessel wall by any of the metallic stents perpetuates the inflammation process and prevents vasomotion in the treated segment. Aiming to overcome this issue, the bioresorbable scaffold (BRS) concept was developed by providing transient vascular radial support to the target segment during the necessary time to heal and disappearing after a period of time. Close to 20 years since BRS technology was first reported, the interventional cardiology field saw the rise and fall of several BRS devices. Although iron-based BRS is an emerging technology, currently, magnesium-alloy resorbable scaffolds devices are supported with the most robust data. This manuscript aims to review the concept of magnesium-based BRS devices, as well as their bioresorption mechanisms and the status of this technology, and the clinical outcomes of patients treated with magnesium BRS and to review the available evidence on iron-based BRS technology.

Study on a biodegradable antibacterial Fe-Mn-C-Cu alloy as urinary implant material

Biodegradable Fe based alloys have been investigated for fracture fixation and cardiovascular support to overcome complications of permanent implants. This study was focused on the development of a new Fe-Mn-C-Cu alloy with antibacterial and anti-encrustation properties as a urinary implant material. The microstructure and mechanical properties of the alloy were studied. The degradation behavior, antibacterial and anti-encrustation properties were evaluated by immersion test, antibacterial test and encrustation test, respectively. The results showed that Fe-Mn-C-Cu alloy was a non-magnetic, biodegradable, anti-bacterial and anti-encrustation alloy that could inhibit the biofilm and stone formations on its surface through the dual effects of degradation and Cu ions release. The study revealed the preliminary mechanisms of anti-infection and anti-encrustation for Fe-Mn-C-Cu alloy due to the continuous release of Cu²⁺ ions, which provides a new idea for application of biodegradable Fe-based material and the treatment of urinary tract infections and stones in the urinary system.

Cancellous-Bone-like Porous Iron Scaffold Coated with Strontium Incorporated Octacalcium Phosphate Nanowhiskers for Bone Regeneration

The repair of large bone defects poses a grand challenge in tissue engineering. Thus, developing biocompatible scaffolds with mechanical and structural similarity to human cancellous bone is in great demand. Herein, we fabricated a three-dimensional (3D) porous iron (Fe) scaffold with interconnected pores via a template-assisted electrodeposition method. The porous Fe scaffold with a skeleton diameter of 143 μm had the porosity >90%, an average pore size of 345 μm, and a yield strength of 3.5 MPa. Such structure and mechanical strength were close to those of cancellous bone. In order to enhance the biocompatibility of the scaffold, strontium incorporated octacalcium phosphate (Sr-OCP) was coated on the skeletons of the porous Fe scaffold. The coated Sr-OCP was in the form of nanowhiskers with a mean diameter of 300 nm and length of 30 μm. Such Sr-OCP coating could effectively reduce the release rate of the Fe ions to a level which was safe for the human body. Both in vitro cytotoxicity tests by extraction method and direct contact assay confirmed that the Sr-OCP coating could promote the cell adhesion and substantially enhance the biocompatibility of the porous Fe scaffolds. Thus, the cancellous-bone-like porous structure with compatible mechanical properties and excellent biocompatibility enables the present Sr-OCP coated porous Fe scaffold to be a promising candidate for bone repair and regeneration.

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.

Vascular Intervention: From Angioplasty to Bioresorbable Vascular Scaffold

Coronary artery disease (CAD) is the leading cause of mortality and morbidity worldwide. Clinically, CAD can be potentially managed through surgical artery bypass. However, due to the highly invasive nature, surgical intervention has been gradually replaced by percutaneous transluminal coronary angioplasty and recently by percutaneous coronary revascularization using metallic stents. However, the permanent presence of metallic scaffolds inevitably impairs arterial physiology and may induce a variety of adverse effects, such as inflammation, restenosis, thrombosis, and neoatherosclerosis. To address these limitations, revascularization using bioresorbable vascular scaffolds (BVSs) has emerged as the most promising approach. After angioplasty, BVSs provide temporarily mechanical support and are completely resorbed over defined time. This transient nature allows favorable arterial remodeling and avoids thrombosis and in-stent restenosis. However, the theoretical advantages of BVSs have yet to be demonstrated. In this chapter, we first review the evolution of nonsurgical vascular intervention approaches over the past few decades. Next, we discuss the current status of BVS development and propose potential approaches to addressing the limitations associated with the current BVSs.

Cardiovascular stents: overview, evolution, and next generation

Compared to bare-metal stents (BMSs), drug-eluting stents (DESs) have been regarded as a revolutionary change in coronary artery diseases (CADs). Releasing pharmaceutical agents from the stent surface was a promising progress in the realm of cardiovascular stents. Despite supreme advantages over BMSs, in-stent restenosis (ISR) and long-term safety of DESs are still deemed ongoing concerns over clinically application of DESs. The failure of DESs for long-term clinical use is associated with following factors including permanent polymeric coating materials, metallic stent platforms, non-optimal drug releasing condition, and factors that have recently been supposed as contributory factors such as degradation products of polymers, metal ions due to erosion and degradation of metals and their alloys utilizing in some stents as metal frameworks. Discovering the direct relation between stent materials and associating adverse effects is a complicated process, and yet it has not been resolved. For clinical success it is of significant importance to optimize DES design and explore novel strategies to overcome all problems including inflammatory response, delay endothelialization, and sub-acute stent thrombosis (ST) simultaneously. In this work, scientific reports are reviewed particularly focusing on recent advancements in DES design which covers both potential improvements of existing and recently novel prototype stent fabrications. Covering a wide range of information from the BMSs to recent advancement, this study mostly sheds light on DES's concepts, namely stent composition, drug release mechanism, and coating techniques. This review further reports different forms of DES including fully biodegradable DESs, shape-memory ones, and polymer-free DESs.

Magnetoelastic galfenol as a stent material for wirelessly controlled degradation rates

The gold standard of care for coronary artery disease, a leading cause of death for in the world, is balloon angioplasty in conjunction with stent deployment. However, implantation injuries and long-term presence of foreign material often promotes significant luminal tissue growth, leading to a narrowing of the artery and severely restricted blood flow. A promising method to mitigate this process is the use of biodegradable metallic stents, but thus far they have either degraded too slowly (iron) or disappeared prematurely (magnesium). The present work investigates the use of a unique type of magnetic material, galfenol (iron-gallium), for postoperative wireless control of stent degradation rates. Due to its magnetoelastic property, galfenol experiences longitudinal micron-level elongations when exposed to applied magnetic fields, allowing generation of a microstirring effect that affect its degradation behavior. In vitro indirect cytotoxicity tests on primary rat aortic smooth muscle cells indicated that galfenol byproducts must be concentrated approximately seven times from collected 60 day degradation medium to cause ∼15% of death from all cells. Surface and cross-sectional characterization of the material indicate that galfenol (Fe₈₀ Ga₂₀ ) degradation rates (∼0.55% per month) are insufficient for stenting applications. While this material may not be ideal for comprising the entire stent, there is potential for use in combination with other materials. Furthermore, the ability to control degradation rates postimplantation opens new possibilities for biodegradable stents; additional magnetoelastic materials should be investigated for use in stenting applications. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 232-241, 2019.