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8144 KiB

Open AccessArticle

Nanocrystalline β-Ta Coating Enhances the Longevity and Bioactivity of Medical Titanium Alloys

by Linlin Liu, Jiang Xu and Shuyun Jiang

Metals 2016, 6(9), 221; https://doi.org/10.3390/met6090221 - 10 Sep 2016

Cited by 10 | Viewed by 7102

Abstract

A β-Ta nanocrystalline coating was engineered onto a Ti-6Al-4V substrate using a double cathode glow discharge technique to improve the corrosion resistance and bioactivity of this biomedical alloy. The new coating has a thickness of ~40 μm and exhibits a compact and homogeneous [...] Read more.

A β-Ta nanocrystalline coating was engineered onto a Ti-6Al-4V substrate using a double cathode glow discharge technique to improve the corrosion resistance and bioactivity of this biomedical alloy. The new coating has a thickness of ~40 μm and exhibits a compact and homogeneous structure composed of equiaxed β-Ta grains with an average grain size of ~22 nm, which is well adhered on the substrate. Nanoindentation and scratch tests indicated that the β-Ta coating exhibited high hardness combined with good resistance to contact damage. The electrochemical behavior of the new coating was systematically investigated in Hank’s physiological solution at 37 °C. The results showed that the β-Ta coating exhibited a superior corrosion resistance as compared to uncoated Ti-6Al-4V and commercially pure tantalum, which was attributed to a stable passive film formed on the β-Ta coating. The in vitro bioactivity was studied by evaluating the apatite-forming capability of the coating after seven days of immersion in Hank’s physiological solution. The β-Ta coating showed a higher apatite-forming ability than both uncoated Ti-6Al-4V and commercially pure Ta, suggesting that the β-Ta coating has the potential to enhance functionality and increase longevity of orthopaedic implants. Full article

(This article belongs to the Special Issue Metallic Biomaterials)

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6388 KiB

Open AccessFeature PaperArticle

Evaluation of Chill Cast Co-Cr Alloys for Biomedical Applications

by Ana Laura Ramirez-Ledesma, Hugo F. Lopez and Julio Alberto Juarez-Islas

Metals 2016, 6(8), 188; https://doi.org/10.3390/met6080188 - 16 Aug 2016

Cited by 8 | Viewed by 5759

Abstract

Binary Co-Cr alloys containing various Cr contents were vacuum induction melted and cast into wedge-shaped copper molds. It was intended to develop a microstructure (1) free from interdendritic segregation and porosity; (2) having minimal intermetallic precipitates; and (3) suitable for biomedical applications. The [...] Read more.

Binary Co-Cr alloys containing various Cr contents were vacuum induction melted and cast into wedge-shaped copper molds. It was intended to develop a microstructure (1) free from interdendritic segregation and porosity; (2) having minimal intermetallic precipitates; and (3) suitable for biomedical applications. The resultant microstructures were evaluated from sections obtained longitudinally and centrally in the plane normal to the diverging wedge faces. All ingots showed a dendritic microstructure with some characteristic features. For instance, in Co-20–30 wt. % Cr alloys, the chilled cast microstructures consisted of columnar dendrites without interdendritic segregation, a minimum of intermetallic precipitates, and the presence of a predominantly athermal HCP ε-martensite (>80 vol. %). In addition, the metastable FCC γ-Co phase was identified by X-ray diffraction and scanning electron microscopy. In the case of 35–44 wt. % Cr cobalt alloys, a eutectic constituent including the σ-phase were found to develop in the interdendritic regions. From this work, a Co-20 wt. % Cr alloy was chosen for further investigation after heat treating below the γ/ε transition temperature. The resultant tensile strength and ductility were further improved after applying a heat treatment at 730 °C for 30 min, obtaining values of elongation of 26% as compared with 2.55 < 5 of elongation in the as cast condition. Also, the alloy corrosion resistance in artificial saliva was investigated. It was found that the exhibited corrosion rates for the as-cast and heat-treated conditions are between those reported for other similar systems. Full article

(This article belongs to the Special Issue Metallic Biomaterials)

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6286 KiB

Open AccessArticle

Specific Yielding of Selective Laser-Melted Ti6Al4V Open-Porous Scaffolds as a Function of Unit Cell Design and Dimensions

by Volker Weißmann, Jan Wieding, Harald Hansmann, Nico Laufer, Andreas Wolf and Rainer Bader

Metals 2016, 6(7), 166; https://doi.org/10.3390/met6070166 - 18 Jul 2016

Cited by 34 | Viewed by 7158

Abstract

Bone loss in the near-vicinity of implants can be a consequence of stress shielding due to stiffness mismatch. This can be avoided by reducing implant stiffness, i.e., by implementing an open-porous structure. Three open-porous designs were therefore investigated (cubic, pyramidal and a twisted [...] Read more.

Bone loss in the near-vicinity of implants can be a consequence of stress shielding due to stiffness mismatch. This can be avoided by reducing implant stiffness, i.e., by implementing an open-porous structure. Three open-porous designs were therefore investigated (cubic, pyramidal and a twisted design). Scaffolds were fabricated by a selective laser-melting (SLM) process and material properties were determined by conducting uniaxial compression testing. The calculated elastic modulus values for the scaffolds varied between 3.4 and 26.3 GP and the scaffold porosities between 43% and 80%. A proportional linear correlation was found between the elastic modulus and the geometrical parameters, between the elastic modulus and the compressive strengths, as well as between the strut width-to-diameter ratio (a/d) and elastic modulus. Furthermore, we found a power-law relationship between porosity and the modulus of elasticity that characterizes specific yielding. With respect to scaffold porosity, the description of specific yielding behaviour offers a simple way to characterize the mechanical properties of open-porous structures and helps generate scaffolds with properties specific to their intended application. A direct comparison with human bone parameters is also possible. We generated scaffolds with mechanical properties sufficiently close to that of human cortical bone. Full article

(This article belongs to the Special Issue Metallic Biomaterials)

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4176 KiB

Open AccessArticle

Effects of Cr₂N Precipitation on the Antibacterial Properties of AISI 430 Stainless Steel

by Je-Kang Du, Chih-Yeh Chao, Yu-Ting Jhong, Chung-Hao Wu and Ju-Hui Wu

Metals 2016, 6(4), 73; https://doi.org/10.3390/met6040073 - 24 Mar 2016

Cited by 6 | Viewed by 5847

Abstract

Based on their mechanical properties and good corrosion resistance, some commercial Ni-Cr stainless steels have been widely applied as biomaterials, including the austenitic 304 stainless steel, the austenitic 316 stainless steel, the duplex 2205 stainless steel, and the ferritic 430 stainless steel. In [...] Read more.

Based on their mechanical properties and good corrosion resistance, some commercial Ni-Cr stainless steels have been widely applied as biomaterials, including the austenitic 304 stainless steel, the austenitic 316 stainless steel, the duplex 2205 stainless steel, and the ferritic 430 stainless steel. In order to reduce the occurrence of infections resulting from biomaterial implants, instruments, and medical devices, Cu²⁺ and Ag²⁺ ions have been added onto biomaterials for increasing the antibacterial properties, but they are known to damage biofilm. The occurrence of nanoparticles can also improve the antibacterial properties of biomaterials through various methods. In this study, we used Escherichia coli and analyzed the microstructures of American Iron and Steel Institute (AISI) 430 stainless steel with a 0.18 mass % N alloy element. During a lower temperature aging, the microstructure of the as-quenched specimen is essentially a ferrite and martensite duplex matrix with some Cr₂N precipitates formed. Additionally, the antibacterial properties of the alloy for E. coli ranged from 3% to 60%, consistent with the presence of Cr₂N precipitates. When aged at a lower temperature, which resulted in nano-Cr₂N precipitation, the specimen possessed the highest antibacterial activity. Full article

(This article belongs to the Special Issue Metallic Biomaterials)

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1773 KiB

Open AccessArticle

Comparison of the Influence of Phospholipid-Coated Porous Ti-6Al-4V Material on the Osteosarcoma Cell Line Saos-2 and Primary Human Bone Derived Cells

by Axel Deing, Thomas Ebel, Regine Willumeit-Römer and Bérengère J.C. Luthringer

Metals 2016, 6(3), 66; https://doi.org/10.3390/met6030066 - 17 Mar 2016

Cited by 2 | Viewed by 5265

Abstract

Biomaterial surface functionalization remains of great interest in the promotion of cell osteogenic induction. Previous studies highlighted the positive effects of porous Ti-6Al-4V and phospholipid coating on osteoblast differentiation and bone remodeling. Therefore, the first objective of this study was to evaluate the [...] Read more.

Biomaterial surface functionalization remains of great interest in the promotion of cell osteogenic induction. Previous studies highlighted the positive effects of porous Ti-6Al-4V and phospholipid coating on osteoblast differentiation and bone remodeling. Therefore, the first objective of this study was to evaluate the potential synergistic effects of material porosity and phospholipid coating. Primary human osteoblasts and Saos-2 cells were cultured on different Ti-6Al-4V specimens (mirror-like polished or porous specimens) and were coated or not with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) for three weeks or five weeks. Selected gene expressions (e.g., classical bone markers: alkaline phosphatase, osteocalcin, osteoprotegerin (OPG), receptor activator of nuclear factor kappa-β ligand (RANKL) and runt-related transcription factor 2) were estimated in vitro. Furthermore, the expressions of osteocalcin and osteopontin were examined via fluorescent microscopy at five weeks (immunocytochemistry). Consequently, it was observed that phospholipid coating potentiates preferences for low and high porosities in Saos-2 and primary cells, respectively, at the gene and protein levels. Additionally, RANKL and OPG exhibited different gene expression patterns; primary cells showed dramatically increased RANKL expression, whereas OPG expression was decreased in the presence of POPE. A synergistic effect of increased porosity and phospholipid coating was observed in primary osteoblasts in bone remodeling. This study showed the advantage of primary cells over the standard bone cell model. Full article

(This article belongs to the Special Issue Metallic Biomaterials)

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Review

Jump to: Research, Other

226 KiB

Open AccessReview

The Development of Coronary Artery Stents: From Bare-Metal to Bio-Resorbable Types

by Ming-Yun Ho, Chun-Chi Chen, Chao-Yung Wang, Shang-Hung Chang, Ming-Jer Hsieh, Cheng-Hung Lee, Victor Chien-Chia Wu and I-Chang Hsieh

Metals 2016, 6(7), 168; https://doi.org/10.3390/met6070168 - 20 Jul 2016

Cited by 38 | Viewed by 9850

Abstract

Coronary artery disease is the leading cause of death worldwide. Conventional balloon angioplasty is associated with high rates of complications such as coronary dissection and vessel recoil. The deployment of bare-metal stents (BMSs) can overcome these problems and achieve a better patency rate [...] Read more.

Coronary artery disease is the leading cause of death worldwide. Conventional balloon angioplasty is associated with high rates of complications such as coronary dissection and vessel recoil. The deployment of bare-metal stents (BMSs) can overcome these problems and achieve a better patency rate than simple balloon angioplasty. It has been shown that the stent design including structure platform, size, length, and strut thickness has a major influence on the clinical results. Even though angioplasty with BMS implantation is widely used in coronary interventions, the restenosis rate due to neointimal hyperplasia remains high. Therefore, drug-eluting stents (DESs) coated with anti-proliferative agents and polymers have been developed to reduce the restenosis rate and improve the clinical outcomes. Although the repeat revascularization rate of DESs is lower than that of BMSs, the long-term stent thrombosis rate is higher than for BMSs. Therefore, new and emerging generations of stents, in which, for example, thinner struts and bioresorbable polymers are used, are available for clinical use. However, there are only a limited number of clinical trials, in which these newer stents have been compared with BMSs and first- and second-generation DESs. The purpose of this review was to provide up-to-date information on the evolution of coronary artery stents from BMSs to DESs to bioresorbable stents (BRSs). Full article

(This article belongs to the Special Issue Metallic Biomaterials)

659 KiB

Open AccessReview

Porous Titanium for Dental Implant Applications

by Zena J. Wally, William Van Grunsven, Frederik Claeyssens, Russell Goodall and Gwendolen C. Reilly

Metals 2015, 5(4), 1902-1920; https://doi.org/10.3390/met5041902 - 21 Oct 2015

Cited by 80 | Viewed by 13061

Abstract

Recently, an increasing amount of research has focused on the biological and mechanical behavior of highly porous structures of metallic biomaterials, as implant materials for dental implants. Particularly, pure titanium and its alloys are typically used due to their outstanding mechanical and biological [...] Read more.

Recently, an increasing amount of research has focused on the biological and mechanical behavior of highly porous structures of metallic biomaterials, as implant materials for dental implants. Particularly, pure titanium and its alloys are typically used due to their outstanding mechanical and biological properties. However, these materials have high stiffness (Young’s modulus) in comparison to that of the host bone, which necessitates careful implant design to ensure appropriate distribution of stresses to the adjoining bone, to avoid stress-shielding or overloading, both of which lead to bone resorption. Additionally, many coating and roughening techniques are used to improve cell and bone-bonding to the implant surface. To date, several studies have revealed that porous geometry may be a promising alternative to bulk structures for dental implant applications. This review aims to summarize the evidence in the literature for the importance of porosity in the integration of dental implants with bone tissue and the different fabrication methods currently being investigated. In particular, additive manufacturing shows promise as a technique to control pore size and shape for optimum biological properties. Full article

(This article belongs to the Special Issue Metallic Biomaterials)

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