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

Insights into the biocompatibility of biodegradable metallic molybdenum for cardiovascular applications-a critical review

Atherosclerotic cardiovascular disease (ACD) is the leading cause of death worldwide. The gold standard of treatment is the implantation of a permanent stent implant that is often associated with complications such as thrombus formation, vascular neointimal response, and stent fracture, which altogether decrease the long-term safety and efficacy of the stent. Biodegradable metallic materials have become an attractive alternative because of the ability to facilitate a more physiological healing response while the metal degrades. Recently, Molybdenum (Mo) has been considered as a potential candidate due to its excellent mechanical and medical imaging properties. Moreover, the biomedical research studies performed to date have shown minimal adverse effects in vitro and in vivo. However, there are still concerns of toxicity at high doses, and the impact of the biochemical mechanisms of Mo on material performance especially in pathophysiological environments are yet to be explored. Mo is an essential co factor for enzymes such as xanthine oxidoreductase (XOR) that plays a critical role in vascular homeostasis and ACD progression. Herein, this review will focus on the biochemistry of Mo, its physiological and pathological effects with an emphasis on cardiovascular disease as well as the recent studies on Mo for cardiovascular applications and its advantages over other biodegradable metals. The limitations of Mo research studies will also be discussed and concluded with an outlook to move this revolutionary metallic biomaterial from the bench to the bedside.

An Electrolytic Elemental Iron Powder Effectively Regenerates Hemoglobin in Anemic Rats and Is Relatively Well Absorbed When Compared to Ferrous Sulfate Monohydrate

Elemental iron powders are used as food fortificants to reduce the incidence of iron deficiency anemia. However, many commercially available iron powders are relatively untested in vivo. The purpose of this study was to determine the hemoglobin regeneration efficiency (HRE) and relative iron bioavailability (RBV) of an electrolytic elemental iron powder (EIP), by treating anemic rats with 14 d iron repletion diets fortified with four different concentrations (12, 24, 36, or 48 mg iron/kg diet) of EIP and bakery-grade ferrous sulfate monohydrate (FS; FeSO4•H2O), or no added iron (control); n = 9-12/group. The HRE of FS was significantly higher (p ≤ 0.05) than EIP at each concentration of dietary iron tested. For EIP, the HREs (ratios) of diets containing 12, 24, 36, and 48 mg iron/kg were 0.356, 0.205, 0.197, and 0.163, respectively. For both EIP and FS, HRE was inversely associated with increasing dietary iron. The RBVs (%) of iron from EIP in diets at 12, 24, 36, and 48 mg iron/kg as compared to FS were 64.5, 59.1, 50.6, and 54.3%, respectively. Overall, findings show that at the concentrations of iron tested, EIP has RBVs greater than 50% and is an effective fortification agent to replenish hemoglobin and correct iron deficiency anemia.

Hemoglobin Regeneration Efficiency and Relative Iron Bioavailability of Four Elemental Iron Powders in Rats

Effective food fortification strategies using elemental iron powders (EIPs) are needed to combat iron deficiency anemia. The purpose of this study was to determine hemoglobin regeneration efficiency (HRE) and relative iron bioavailability (RBV) of four food-grade EIPs (El-Lyte (EL), Hi-Sol (HS), H-325 (H3), and A-131 (A1)) by treating anemic rats with 14 d iron repletion diets (uncooked and cooked), fortified with a 12, 24, or 36 mg iron/kg diet of the EIPs, ferrous sulfate monohydrate (FS, FeSO4•H2O), or no added iron (control), n = 9-12/group. The ability of EL and HS to maintain hemoglobin for 6 weeks on the 6 mg iron/kg diet was also studied. The dissolution rate of iron from the EIPs was measured in hydrochloric acid at pH 1.0. Compared to FS, the EL, HS, and A1 EIPs had >50% overall RBV, with the following order: HS > A1 > EL > H3 (p ≤ 0.05); the effect of cooking was not significant (p > 0.05). Dissolution testing revealed that the mean RBV of the EIPs was positively associated with the percentage of iron solubility. In the 6-week maintenance study, EL and HS maintained hemoglobin as well as FS. Overall, the findings show that at the concentrations of iron tested, these EIPs are effective fortification agents to replenish hemoglobin and correct iron deficiency anemia.

Iron-Gold Composites for Biodegradable Implants: In Vitro Investigation on Biodegradation and Biomineralization

The biocompatibility and biodegradation of iron (Fe) make it a suitable candidate for developing biodegradable metallic implants. However, the degradation rate of Fe in a physiological environment is extremely slow and needs to be enhanced to a rate compatible with tissue growth. Incorporating noble metals improves the Fe degradation rate by forming galvanic couples. This study incorporated gold (Au) into Fe at very low concentrations of 1.25 and 2.37 μg/g to improve the degradation rate. The electrochemical corrosion test of the samples revealed that the Au-containing samples showed a four-time and nine-time faster degradation rate than pure Fe. Furthermore, the immersion test and long-term electrochemical impedance spectroscopy conducted in simulated body fluid (SBF) revealed that the Au-incorporated samples exhibited increased bioactivity and degraded faster than pure Fe. Integrating nanogold into a Fe matrix increased the in situ formation of hydroxyapatite on the sample's surface and did not cause toxicity to L929-murine fibroblast cells. It is suggested that Fe-Au composites with low concentrations of Au can be used to tailor the biodegradation rate and promote the biomineralization of Fe-based implants in the physiological environment.

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.

Advances in the development of biodegradable coronary stents: A translational perspective

Implantation of cardiovascular stents is an important therapeutic method to treat coronary artery diseases. Bare-metal and drug-eluting stents show promising clinical outcomes, however, their permanent presence may create complications. In recent years, numerous preclinical and clinical trials have evaluated the properties of bioresorbable stents, including polymer and magnesium-based stents. Three-dimensional (3D) printed-shape-memory polymeric materials enable the self-deployment of stents and provide a novel approach for individualized treatment. Novel bioresorbable metallic stents such as iron- and zinc-based stents have also been investigated and refined. However, the development of novel bioresorbable stents accompanied by clinical translation remains time-consuming and challenging. This review comprehensively summarizes the development of bioresorbable stents based on their preclinical/clinical trials and highlights translational research as well as novel technologies for stents (e.g., bioresorbable electronic stents integrated with biosensors). These findings are expected to inspire the design of novel stents and optimization approaches to improve the efficacy of treatments for cardiovascular diseases.

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Bioresorbable stents can overcome the limitations of non-degradable stents.

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3D printing of shape-memory polymeric stents can lead to better clinical outcomes.

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Advances in Mg-, Fe- and Zn-based stents from a translational perspective.

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Electronic stents integrated with biosensors can covey stent status in real time.

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Development in the assessment of stent performance in vivo.

Biodegradable iron-silicon implants produced by additive manufacturing

Due to many negative and undesirable side effects from the use of permanent implants, the development of temporary implants based on biocompatible and biodegradable materials is a promising area of modern medicine. In the presented study, we have investigated complex-shaped iron-silicon (Fe-Si) scaffolds that can be used as potential biodegradable framework structures for creating solid implants for bone grafting. Since iron and silicon are biocompatible materials, and their alloy should also have biocompatibility. It has been demonstrated that cells UC-MSC and 3T3 were attached to, spread, and proliferated on the Fe-Si scaffolds' surface. Most of UC-MSC and 3T3 remained viable, only single dead cells were observed. According to the results of biological testing, the scaffolds have shown that deposition of calcium phosphate particles occurs on day one in the scaffold at the defect site that can be used as a primary marker of osteodifferentiation. These results demonstrate that the 3D-printed porous iron-silicon (Fe-Si) alloy scaffolds are promising structures for bone grafting and regeneration.

Design, mechanical and degradation requirements of biodegradable metal mesh for pelvic floor reconstruction

Pelvic organ prolapse (POP) is the herniation of surrounding tissue and organs into the vagina and or rectum, and is a result of weakening of pelvic floor muscles, connective tissue,...

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.

Evolution of the ε and γ phases in biodegradable Fe-Mn alloys produced using laser powder-bed fusion

The key feature of Fe-Mn alloys is gradual degradability and non-magneticity, with laser power bed fusion (LPBF) parameters influencing the microstructure and chemical composition. Our study focuses on biodegradable Fe-Mn alloys produced by mechanically mixing pure metal feedstock powders as part of the LPBF process. The Mn content and, consequently, the γ-ε phase formation in LPBF samples are directly correlated with an adapted energy-density (E) equation by combining the five primary LPBF parameters. We varied laser power (P) in a range of 200-350 W and scanning speed at 400 and 800 mm/s, and a comprehensive study was performed on samples with similar E. The study also showed an almost linear correlation between the LPBF's laser power and the material's hardness and porosity. The corrosion resistance was significantly reduced (from 13 to 400 μm/year) for the LPBF samples compared to a conventionally produced sample due to the dual-phase microstructure, increased porosity and other defects. The static immersion test showed that the process parameters greatly influence the quantity of oxides and the distribution of their diameters in the LPBF samples and, therefore, their corrosion stability. The most challenging part of the study was reducing the amount of ε phase relative to γ phase to increase the non-magnetic properties of the LPBF samples.

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.