Cold drawn bioabsorbable ferrous and ferrous composite wires: an evaluation of in vitro vascular cytocompatibility

Radiopaque FeMnN-Mo composite drawn filled tubing wires for braided absorbable neurovascular devices

Flow diverter devices are small stents used to divert blood flow away from aneurysms in the brain, stagnating flow and inducing intra-aneurysmal thrombosis which in time will prevent aneurysm rupture. Current devices are formed from thin (∼25 μm) wires which will remain in place long after the aneurysm has been mitigated. As their continued presence could lead to secondary complications, an absorbable flow diverter which dissolves into the body after aneurysm occlusion is desirable. The absorbable metals investigated to date struggle to achieve the necessary combination of strength, elasticity, corrosion rate, fragmentation resistance, radiopacity, and biocompatibility. This work proposes and investigates a new composite wire concept combining absorbable iron alloy (FeMnN) shells with one or more pure molybdenum (Mo) cores. Various wire configurations are produced and drawn to 25-250 μm wires. Tensile testing revealed high and tunable mechanical properties on par with existing flow diverter materials. In vitro degradation testing of 100 μm wire in DMEM to 7 days indicated progressive corrosion and cracking of the FeMnN shell but not of the Mo, confirming the cathodic protection of the Mo by the FeMnN and thus mitigation of premature fragmentation risk. In vivo implantation and subsequent μCT of the same wires in mouse aortas to 6 months showed meaningful corrosion had begun in the FeMnN shell but not yet in the Mo filament cores. In total, these results indicate that these composites may offer an ideal combination of properties for absorbable flow diverters.

A Critical Review of Biodegradable Zinc Alloys toward Clinical Applications

Biodegradable zinc (Zn) alloys stand out as promising contenders for biomedical applications due to their favorable mechanical properties and appropriate degradation rates, offering the potential to mitigate the risks and expenses associated with secondary surgeries. While current research predominantly centers on the in vitro examination of Zn alloys, notable disparities often emerge between in vivo and in vitro findings. Consequently, conducting in vivo investigations on Zn alloys holds paramount significance in advancing their clinical application. Different element compositions and processing methods decide the mechanical properties and biological performance of Zn alloys, thus affecting their suitability for specific medical applications. This paper presents a comprehensive overview of recent strides in the development of biodegradable Zn alloys, with a focus on key aspects such as mechanical properties, toxicity, animal experiments, biological properties, and molecular mechanisms. By summarizing these advancements, the paper aims to broaden the scope of research directions and enhance the understanding of the clinical applications of biodegradable Zn alloys.

Benchtop proof of concept and comparison of iron- and magnesium-based bioresorbable flow diverters

OBJECTIVE

Bioresorbable flow diverters (BRFDs) could significantly improve the performance of next-generation flow diverter technology. In the current work, magnesium and iron alloy BRFDs were prototyped and compared in terms of porosity/pore density, radial strength, flow diversion functionality, and resorption kinetics to offer insights into selecting the best available bioresorbable metal candidate for the BRFD application.

METHODS

BRFDs were constructed with braided wires made from alloys of magnesium (MgBRFD) or iron (FeBRFD). Pore density and crush resistance force were measured using established methods. BRFDs were deployed in silicone aneurysm models attached to flow loops to investigate flow diversion functionality and resorption kinetics in a simulated physiological environment.

RESULTS

The FeBRFD exhibited higher pore density (9.9 vs 4.3 pores/mm2) and crush resistance force (0.69 ± 0.05 vs 0.53 ± 0.05 N/cm, p = 0.0765, n = 3 per group) than the MgBRFD, although both crush resistances were within the range previously reported for FDA-approved flow diverters. The FeBRFD demonstrated greater flow diversion functionality than the MgBRFD, with significantly higher values of established flow diversion metrics (mean transit time 159.6 ± 11.9 vs 110.9 ± 1.6, p = 0.015; inverse washout slope 192.5 ± 9.0 vs 116.5 ± 1.5, p = 0.001; n = 3 per group; both metrics expressed as a percentage of the control condition). Last, the FeBRFD was able to maintain its braided structure for > 12 weeks, whereas the MgBRFD was almost completely resorbed after 5 weeks.

CONCLUSIONS

The results of this study demonstrated the ability to manufacture BRFDs with magnesium and iron alloys. The data suggest that the iron alloy is the superior material candidate for the BRFD application due to its higher mechanical strength and lower resorption rate relative to the magnesium alloy.

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.

Osteogenic and angiogenic bioactive collagen entrapped calcium/zinc phosphates coating on biodegradable Zn for orthopedic implant applications

Zinc is becoming one of the leading candidate materials for biodegradable orthopedic implants owing to its attractive properties in terms of degradation behavior and mechanical properties. However, the insufficient surface bio-activities postpone its clinical application. In this study, an organic-inorganic collagen entrapped calcium/zinc phosphates coating was constructed on Zn surface to lessen Zn²⁺ releasing rate and to leverage the surface osteogenic and angiogenic properties. Collagen molecules were immobilized onto Zn substrate and subsequently coordinated with calcium and zinc ions to promote the CaZnP inorganic phase growth, ensuing an intertwined collagen-CaZnP hybrid system. Consequently, the hybrid coating was highly coalesced and compact. Such high quality warranted the contained Zn²⁺ releasing in a tolerable rate favorable for cells viability. The collagen-CaZnP coated Zn showed remarkedly stronger osteogenicity as compared to the untreated Zn, ascertained by the MC3T3-E1 osteoblast cell proliferation and differentiation assays, such as alkaline phosphatase expression and calcium nodule formation results. In addition, this hybrid coating supported human umbilical vein endothelial cells (HUVECs) migration and tube formation. The enhanced osteogenic and angiogenic properties could be ascribed to the nature of collagen and calcium/zinc phosphate components, the hybrid micro/nano-structure as well as the ability of controlling the Zn²⁺ release of Zn substrate into a suitable concentration range. Our strategy provides a new avenue to surface modification of biodegradable metals for bone regenerative perspective.

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.

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.

In vitro and in vivo studies to evaluate the feasibility of Zn-0.1Li and Zn-0.8Mg application in the uterine cavity microenvironment compared to pure zinc

Significant advances have been achieved in the research evaluating Zn and its alloys as degradable metallic biomaterials mainly for application in bone and blood vessels. In the present study, the degradation behaviors of Zn-0.1Li and Zn-0.8Mg alloys in simulated uterine fluid (SUF) were systematically investigated for 300 days. In vitro viability assays were conducted in different uterine cells (HUSMCs, HEECs, and HESCs), and histological examination after the in vivo implantation into the uterine cavity was performed using pure Zn as control. The immersion test results indicated that both Zn-0.1Li and Zn-0.8Mg alloys exhibited better corrosion resistance than pure Zn, with Zn₃(PO₄)₂⋅4H₂O and CaZn₂(PO₄)₂⋅2H₂O being the main corrosion products detected in the SUF in addition to ZnO. The cell cytotoxicity assays revealed that Zn-0.1Li and Zn-0.8Mg exhibited better cytocompatibility than Zn. Moreover, the in vivo experiments demonstrated that the Zn-0.1Li and Zn-0.8Mg alloys induced less inflammation in the uterine tissue than pure Zn, with CaCO₃ and Zn(HPO₄)⋅3H₂O being the major biocorrosion products in addition to ZnO. According to these results, zinc alloys appear to be suitable potential candidate materials for future intrauterine biomedical devices.

Accelerated discovery and mechanical property characterization of bioresorbable amorphous alloys in the Mg-Zn-Ca and the Fe-Mg-Zn systems using high-throughput methods

Ternary amorphous alloys in the magnesium (Mg)-zinc (Zn)-calcium (Ca) and the iron (Fe)-Mg-Zn systems are promising candidates for use in bioresorbable implants and devices. The optimal alloy compositions for biomedical applications should be chosen from a large variety of available alloys with best combination of mechanical properties (modulus, strength, hardness) and biological response (in situ degradation rates, cell adhesion and proliferation). As a first step towards establishing a database designed to enable such targeted material selection, amorphous alloy composition libraries were fabricated employing a combinatorial magnetron sputtering approach where Mg, Zn, and Ca/Fe are co-deposited from separate sources onto a silicon wafer substrate. Composition analysis using energy dispersive X-ray spectroscopy documented a composition range of ∼15-85 at% Mg, ∼6-55 at% Zn, and ∼5-60 at% Ca for the Mg-Zn-Ca library and ∼26-84 at% Mg, ∼10-61 at% Zn, and ∼7-55 at% Fe for the Fe-Mg-Zn library. X-ray diffraction measurements established that amorphous alloys (i.e., glasses) form in almost the entire range of composition at the high cooling rates during sputtering for both alloy libraries. Finally, the effective material modulus, the Oliver-Pharr hardness, and the yield strength values obtained using nanoindentation reveal a wide range of mechanical properties within both systems.

Innate glycosidic activity in metallic implants for localized synthesis of antibacterial drugs

The unexpected discovery presented herein is that industrialized metallic wires can perform conversion of the glucuronide prodrugs with ensuing antibacterial effects.

Assessment of the Biocompatibility and Biological Effects of Biodegradable Pure Zinc Material in the Colorectum

Little attention has been paid to the biocompatibility and biological effects of zinc as a material. Here, we therefore investigated the biocompatibility and anti-inflammatory and collagen-promoting effects of pure zinc material in the colorectum. Our in vitro results indicated that zinc toxicity and concentration were closely related. Low concentrations of zinc ions and pure zinc material extract had only minor effects on the viability of primary rectal mucosal epithelial cells; however, cytotoxicity was observed at concentrations greater than 0.017 μg/μL and 60%, respectively. In vivo experiments demonstrated that zinc pins degraded slowly in the colorectum (their volume decreasing by approximately 7.79% over 1 month) and did not cause serious adverse reactions. Pure zinc material was found to inhibit acute inflammation through increased expression of ENA-78 and F4/80. Moreover, zinc material heightened expression of collagen and VEGF, factors conducive to wound healing, in surrounding colorectal tissues. These preliminary results suggest that zinc shows great promise as an implant material for medical applications involving colorectal surgery.

Continuously Grooved Stent Struts for Enhanced Endothelial Cell Seeding

Purpose

Implantation of pre-endothelialized stents could enhance cellular recovery of a damaged vessel wall provided attached cells remain viable, functional and are present in sufficient numbers after deployment. The purpose of this study was to evaluate the feasibility of grooved stainless steel (SS) stents as a primary endothelial cell (EC) carrier with potentially enhanced EC protection upon stent deployment.

Materials and Methods

Attachment and behavior of enzymatically harvested human adult venous ECs seeded onto gelatin-coated vascular stents were evaluated in an in vitro setting. Smooth and grooved SS stents and smooth nitinol stents were studied.

Results

All cells expressed EC markers vWF and CD31. Using rotational seeding for a period of 16–24 h, ECs attached firmly to the stents with sufficient coverage to form a confluent EC monolayer. The grooved SS wire design was found to enable attachment of three times the number of cells compared to smooth wires. This also resulted in an increased number of cells remaining on the stent after deployment and after pulsatile flow of 180 ml/min for 24 h, which did not result in additional EC detachment.

Conclusions

The grooved stent provides a potential percutaneous means to deliver sufficient numbers of viable and functional cells to a vessel segment during vascular intervention. The grooves were found to offer a favorable surface for EC attachment and protection during stent deployment in an in vitro setting.

Electronic supplementary material

The online version of this article (doi:10.1007/s00270-017-1659-4) contains supplementary material, which is available to authorized users.

Accelerating degradation rate of pure iron by zinc ion implantation

Pure iron has been considered as a promising candidate for biodegradable implant applications. However, a faster degradation rate of pure iron is needed to meet the clinical requirement. In this work, metal vapor vacuum arc technology was adopted to implant zinc ions into the surface of pure iron. Results showed that the implantation depth of zinc ions was about 60 nm. The degradation rate of pure iron was found to be accelerated after zinc ion implantation. The cytotoxicity tests revealed that the implanted zinc ions brought a slight increase on cytotoxicity of the tested cells. In terms of hemocompatibility, the hemolysis of zinc ion implanted pure iron was lower than 2%. However, zinc ions might induce more adhered and activated platelets on the surface of pure iron. Overall, zinc ion implantation can be a feasible way to accelerate the degradation rate of pure iron for biodegradable applications.

Bioabsorbable zinc ion induced biphasic cellular responses in vascular smooth muscle cells

Bioabsorbable metal zinc (Zn) is a promising new generation of implantable scaffold for cardiovascular and orthopedic applications. In cardiovascular stent applications, zinc ion (Zn²⁺) will be gradually released into the surrounding vascular tissues from such Zn-containing scaffolds after implantation. However, the interactions between vascular cells and Zn²⁺ are still largely unknown. We explored the short-term effects of extracellular Zn²⁺ on human smooth muscle cells (SMCs) up to 24 h, and an interesting biphasic effect of Zn²⁺ was observed. Lower concentrations (<80 μM) of Zn²⁺ had no adverse effects on cell viability but promoted cell adhesion, cell spreading, cell proliferation, cell migration, and enhanced the expression of F-actin and vinculin. Cells treated with such lower concentrations of Zn²⁺ displayed an elongated shape compared to controls without any treatment. In contrast, cells treated with higher Zn²⁺ concentrations (80–120 μM) had opposite cellular responses and behaviors. Gene expression profiles revealed that the most affected functional genes were related to angiogenesis, inflammation, cell adhesion, vessel tone, and platelet aggregation. Results indicated that Zn has interesting concentration-dependent biphasic effects on SMCs with low concentrations being beneficial to cellular functions.

Uniform and accelerated degradation of pure iron patterned by Pt disc arrays

Pure iron has been confirmed as a promising biodegradable metal. However, the degradation rate of pure iron should be accelerated to meet the clinical requirements. In this work, two different designs of platinum disc arrays, including sizes of Φ20 μm × S5 μm and Φ4 μm × S4 μm, have been coated on the surface of pure iron. Corrosion tests showed the platinum discs formed plenty of galvanic cells with the iron matrix which significantly accelerated the degradation of pure iron. Simultaneously, due to the designability of the shape, size as well as distribution of Pt discs, the degradation rate as well as degradation uniformity of pure iron can be effectively controlled by coating with platinum discs. The cytotoxicity test results unveiled that Pt discs patterned pure iron exhibited almost no toxicity to human umbilical vein endothelial cells, but a significant inhibition on proliferation of vascular smooth muscle cells. In addition, the hemolysis rate of Pt discs patterned pure iron was lower than 1%. Moreover, Pt discs also effectively reduced the number of adhered platelets. All these results indicated that Pt discs patterning is an effective way to accelerate degradation and improve biocompatibility of pure iron.

In Vitro Cytotoxicity, Adhesion, and Proliferation of Human Vascular Cells Exposed to Zinc

Zinc (Zn) and its alloys have recently been introduced as a new class of biodegradable metals with potential application in biodegradable vascular stents. Although an in vivo feasibility study pointed to outstanding biocompatibility of Zn-based implants in vascular environments, a thorough understanding of how Zn and Zn²⁺ affect surrounding cells is lacking. In this comparative study, three vascular cell types-human endothelial cells (HAEC), human aortic smooth muscle cells (AoSMC), and human dermal fibroblasts (hDF)-were studied to advance the understanding of Zn/Zn²⁺-cell interactions. Aqueous cytotoxicity using a Zn²⁺ insult assay resulted in LD₅₀ values of 50 µM for hDF, 70 µM for AoSMC, and 265 µM for HAEC. Direct cell contact with the metallic Zn surface resulted initially in cell attachment, but was quickly followed by cell death. After modification of the Zn surface using a layer of gelatin-intended to mimic a protein layer seen in vivo-the cells were able to attach and proliferate on the Zn surface. Further experiments demonstrated a Zn dose-dependent effect on cell spreading and migration, suggesting that both adhesion and cell mobility may be hindered by free Zn²⁺.

In vitro studies on silver implanted pure iron by metal vapor vacuum arc technique

Pure iron has been verified as a promising biodegradable metal for absorbable cardiovascular stent usage. However, the degradation rate of pure iron is too slow. To accelerate the degradation of the surface of pure iron, silver ions were implanted into pure iron by metal vapor vacuum arc (MEVVA) source at an extracted voltage of 40keV. The implanted influence was up to 2×10(17)ions/cm(2). The composition and depth profiles, corrosion behavior and biocompatibility of Ag ion implanted pure iron were investigated. The implantation depths of Ag was around 60nm. The element Ag existed as Ag2O in the outermost layer, then gradually transited to metal atoms in zero valent state with depth increase. The implantation of Ag ions accelerated the corrosion rate of pure iron matrix, and exhibited much more uniform corrosion behavior. For cytotoxicity assessment, the implantation of Ag ions slightly decreased the viability of all kinds of cell lines used in these tests. The hemolysis rate of Ag ion implanted pure iron was lower than 2%, which was acceptable, whereas the platelet adhesion tests indicated the implantation of Ag ions might increase the risk of thrombosis.

Advances in Fe-based biodegradable metallic materials

This review systematically summarizes recent studies on Fe-based biodegradable metallic materials and discusses these findings in terms of their processing methods, mechanical properties, degradability and biocompatibility.

Cytocompatibility evaluation of different biodegradable magnesium alloys with human mesenchymal stem cells

In the last few years, the use of biodegradable magnesium (Mg) alloys has evoked great interest in the orthopedic field due to great advantages over long-term implant materials associated with various side effects like allergy and sensitization and consequent implant removal surgeries. However, degradation of these Mg alloys results in ion release, which may cause severe cytotoxicity and undesirable complications after implantation. In this study, we investigated the cytological effects of various Mg alloys on cells that play an important role in bone repair. Eight different magnesium alloys containing varying amounts of Al, Zn, Nd and Y were either incubated directly or indirectly with the osteosarcoma cell line Saos-2 or with uninduced and osteogenically-induced human mesenchymal stem cells (MSCs) isolated from bone marrow specimens obtained from the femoral shaft of patients undergoing total hip replacement. Cell viability, cell attachment and the release of ions were investigated at different time points in vitro. During direct or indirect incubation different cytotoxic effects of the Mg alloys on Saos-2 cells and osteogenically-induced or uninduced MSCs were observed. Furthermore, the concentration of degradation products released from the Mg alloys differed. Overall, Mg alloys MgNd2, MgY4, MgAl9Zn1 and MgY4Nd2 exhibit good cytocompatibility. In conclusion, this study reveals the necessity of cytocompatibility evaluation of new biodegradable magnesium alloys with cells that will get in direct contact to the implant material. Furthermore, the use of standardized experimental in vitro assays is necessary in order to reliably and effectively characterize new Mg alloys before performing in vivo experiments.