Improving biocompatibility of cobalt based alloy using chemical etching and mechanical treatment

Biomedical grade of cobalt based alloy have found a plethora of applications as medical devices especially in dental and articulation joints like in total ankle, knee and hip arthroplasty. However, the long‐term performance of this material is highly dependent on their ability to withstand in harsh aqueous environment effects such as corrosion and wear once they are used inside a human body. Loss of surface integrity and subsequent leaching of toxic metal ions as well as particles to the surrounding tissues may undermine biocompatibility of metallic implants, also potentially causing untimely loss of mechanical function and device failure. In this study, a biomedical grade of Co?Cr?Mo alloy surface was treated with various surface modification techniques such as chemical etching and mechanical roughening in order to improve its biocompatibility. Investigation was done to study which surface modification techniques possesses the positive effect in cell growth and exhibit excellent cell response on Co?Cr?Mo alloy. In‐vitro study showed that human osteoblast cells grown with good adherence and spread out with an intimate contact on the chemical treated surface after 14 days of incubation. It is believed that porous structure with grooves owned by chemical treated surface helps in anchoring the cells to the substrate surface and facilitates cells growth since more protein molecules expected to have more sites on this surface. Whilst on mechanical roughened surface, the cells appeared to show slightly less extended cell membranes and the cells remained retarded.     

Advanced biomaterials in hip joint arthroplasty. A review on polymer and ceramics composites as alternative bearings

Wear of total hip prosthesis is a significant clinical problem that nowadays involves a growing number of patients. To acquire further knowledge on the tribological phenomena that involve hip prosthesis, wear tests are conducted on new biomaterials to increase materials life in orthopaedic implants. Advances in biomaterials for biomedical purposes have enhanced in the last years evolving in new improved ceramic and polymeric materials producing the so-called composite materials.This paper aims to review the evolution and the current state of the art of the ceramics composites and polymers commonly used in orthopaedic field as hip joint implants. This is specified through a schematic overview by describing, in particular, the evolution of various composites materials. The authors propose commentary on the evolution and current use of biomaterials for orthopaedic application on the evolution and actually used biomaterials for orthopaedic applications.     

Engineered Functional Surfaces by Laser Microprocessing for Biomedical Applications

Metallic biomaterials are increasingly being used in various medical applications due to their high strength, fracture resistance, good electrical conductivity, and biocompatibility. However, their practical applications have been largely limited due to poor surface performance. Laser microprocessing is an advanced method of enhancing the surface-related properties of biomaterials. This work demonstrates the capability of laser microprocessing for biomedical metallic materials including magnesium and titanium alloys, with potential applications in cell adhesion and liquid biopsy. We investigate laser-material interaction, microstructural evolution, and surface performance, and analyze cell behavior and the surface-enhanced Raman scattering (SERS) effect. Furthermore, we explore a theoretical study on the laser microprocessing of metallic alloys that shows interesting results with potential applications. The results show that cells exhibit good adhesion behavior at the surface of the laser-treated surface, with a preferential direction based on the textured structure. A significant SERS enhancement of 6 × 10³ can be obtained at the laser-textured surface during Raman measurement.     

A review on nickel-free nitrogen containing austenitic stainless steels for biomedical applications

The field of biomaterials has become a vital area, as these materials can enhance the quality and longevity of human life. Metallic materials are often used as biomaterials to replace structural components of the human body. Stainless steels, cobalt–chromium alloys, commercially pure titanium and its alloys are typical metallic biomaterials that are being used for implant devices. Stainless steels have been widely used as biomaterials because of their very low cost as compared to other metallic materials, good mechanical and corrosion resistant properties and adequate biocompatibility. However, the adverse effects of nickel ions being released into the human body have promoted the development of “nickel-free nitrogen containing austenitic stainless steels” for medical applications. Nitrogen not only replaces nickel for austenitic structure stability but also much improves steel properties. Here we review the harmful effects associated with nickel and emphatically the advantages of nitrogen in stainless steel, as well as the development of nickel-free nitrogen containing stainless steels for medical applications. By combining the benefits of stable austenitic structure, high strength, better corrosion and wear resistance and superior biocompatibility in comparison to the currently used austenitic stainless steel (e.g. 316L), the newly developed nickel-free high nitrogen austenitic stainless steel is a reliable substitute for the conventionally used medical stainless steels.     

从可降解金属的角度审视医用镁合金的元素选择

进入21世纪以来,可降解金属成为医用金属材料研究的热点。镁及镁合金是过去10余年被广泛研究的代表性可降解金属材料。Web of Science检索显示,过去10余年有关医用镁合金的基础研究工作在全球范围内已经发表了3000余篇文章,人们对可降解镁合金与机体的力学、化学和生物学相互作用机制有了较深入的认识,初步开展了"医用镁合金的成分设计与性能优化"、"镁合金在体内的降解机制及其调控方法"、"镁合金降解产物的生物安全性与代谢途径"、"镁合金降解过程中的力学强度退化"等基础科学研究。尽管已有大量的新配方镁合金被设计与研究用于生物医学,但多为工程材料专家们的炒菜式思维,企业对投入费时费钱的生物医学验证坐等,医学转化成效低。在成百上千的已有材料配方中,迄今在全球上市的医用镁合金植入式医疗器械只有德国WE43系镁合金和韩国Mg-Ca-Zn合金,国内进入创新医疗器械的两个产品是以纯镁为材料。因此,拟从生物材料专家的视角出发,摒弃对力学性能的追求,从可降解金属的生物降解性和生物安全性两个最基本的判据出发,对元素周期表中适合可降解金属的元素进行初步筛选,在此基础上选出用于医用镁合金的合金化元素,换一个角度,从更佳的生物学性能和生物功能性出发,对未来医用镁合金材料设计指明可以尝试的新方向。     

Numerical investigation of the effect of porous titanium femoral prosthesis on bone remodeling

Porous titanium is a promising orthopedic implant material. As a potential use in total hip replacement, the effect of a porous titanium femoral prosthesis on bone remodeling is investigated in this paper. The stress and strain fields of a post-operative femur with a hip replacement are calculated by applying the three-dimensional finite element method. The effect of the implant material on the bone remodeling is evaluated by analyzing the loss of bone density following a strain magnitude based bone remodeling theory. Different implant materials, including currently used solid cobalt–chrome and solid titanium, potential porous titanium with different porosities, are considered in this study. This investigation confirms that bone loss around the implant strongly depends on the value of the elastic modulus of the prosthesis. There will be a sharp drop of the volume of the bone with density loss if a cobalt–chrome implant is replaced by a porous titanium implant. The numerical results show that both of the bone volume with density loss and the bone density loss rate decrease linearly with the increase of the porosity. However, increasing porosity will reduce the strength of porous titanium. With regard to material design for porous titanium-based femoral prosthesis, stress analysis is required to meet the strength requirement.     

Advanced Stellite alloys with improved metal-on-metal bearing for hip implants

Stellite 21 is a low-carbon Co–Cr–Mo alloy that has been used for hip implants for decades. The Stellite 21 implants can fail when the femoral head and the acetabular cup loosen because of limited metal-on-metal bearing. Two modified Stellite 21 alloys with better bearing capacities are proposed as replacements in this study: Cr-modified Stellite 21 with additional 10 wt.% Cr, and N-modified Stellite 21 with addition of 0.5 wt.% CrN. The wear and corrosion resistances of these alloys were investigated in simulated conditions experienced by hip implants in human bodies. The experimental results show that the proposed alloys all exhibit better wear resistance than the conventional hip implant material, but only Cr-modified Stellite 21 displays better corrosion resistance, thus this alloy should be considered for use in future hip implants.     

Experimental Study of the Creep Lifetime of the 1.25Cr 0.5Mo Steel Pipes

Abstract: In this paper, physical parameters for the creep constitutive equations of the low alloy ferritic steel 1.25Cr0.5Mo have been determined using experimental data. This alloy is used mostly in power generation and petrochemical industries because of its high temperature creep resistance. Test samples have been obtained from a new super‐heater pipe wall of a steam‐generating boiler in Tabriz Petrochemical Plant according to the ASTM standards. By conducting creep rupture tests for 1.25Cr0.5Mo steel, creep behaviour and creep‐rupture properties were examined for this material. Creep rupture tests have been carried out at four temperatures of 700, 725, 750 and 800 °C, under applied uni‐axial stresses of 30, 35, 40 and 50 MPa. The experimental data have been used to obtain the constitutive parameters using numerical optimisation techniques. Also the temperature and stress dependency of the creep lifetime for this alloy has been investigated using Larson–Miller and Monkman–Grant parameters. The results show good agreement with other test data such as ASTM and API. Finally, these constitutive equations have been used to study the creep behaviour of the super‐heater pipe. The results show that the super‐heater tube has been over designed in terms of the creep lifetime and this is in accordance with the in‐plant observations.     

Improved mechanical long-term reliability of hip resurfacing prostheses by using silicon nitride

Although ceramic prostheses have been successfully used in conventional total hip arthroplasty (THA) for many decades, ceramic materials have not yet been applied for hip resurfacing (HR) surgeries. The objective of this study is to investigate the mechanical reliability of silicon nitride as a new ceramic material in HR prostheses. A finite element analysis (FEA) was performed to study the effects of two different designs of prostheses on the stress distribution in the femur–neck area. A metallic (cobalt–chromium-alloy) Birmingham hip resurfacing (BHR) prosthesis and our newly designed ceramic (silicon nitride) HR prosthesis were hereby compared. The stresses induced by physiologically loading the femur bone with an implant were calculated and compared with the corresponding stresses for the healthy, intact femur bone. Here, we found stress distributions in the femur bone with the implanted silicon nitride HR prosthesis which were similar to those of healthy, intact femur bone. The lifetime predictions showed that silicon nitride is indeed mechanically reliable and, thus, is ideal for HR prostheses. Moreover, we conclude that the FEA and corresponded post-processing can help us to evaluate a new ceramic material and a specific new implant design with respect to the mechanical reliability before clinical application.     

Development of nitrogen-containing nickel-free austenitic stainless steels for metallic biomaterials—review

Metallic biomaterials—such as 316L stainless steel and cobalt-based alloys—have been used as biomaterials mainly because of their excellent mechanical and corrosion properties. However, the release of nickel trace elements—which cause toxicity—has prompted the development of nitrogen-containing nickel-free austenitic stainless steels. This paper reviews their development, traces the history of 316L stainless steel, and the improvement of properties by nitrogen addition. These steels are now available for production of implant devices such as bone plates and screws. Such production requires special techniques with nitrogen absorption treatment.     

Fabrication and biocompatibility of polyethyleneimine/heparin self-assembly coating on NiTi alloy

NiTi alloy has been used widely as biomaterials. But because of toxic effects possibly caused by excess Ni ions released during the corrosion process in the physiological environment, it is still a controversial material. Fabricating medicine-loaded coating, which is expected to decrease the release of Ni ions and improve the biocompatibility of the materials, is a potential way to solve the problem. In this paper, NiTi alloy is coated by polyethyleneimine/heparin films via layer-by-layer (LBL) self-assembly method. UV-Vis, FT-IR, atomic force microscopy (AFM) and contact angle measurements are used to characterize the microstructure of coatings and select the best fabrication conditions. Potentiodynamic polarization researches in sodium chloride and dynamic clotting time experiment are utilized to study its corrosion resistance capability and biocompatibility of coatings, respectively. The results indicate that PEI/heparin multilayer coating can improve the biocompatibility of NiTi alloy surface.     

超高分子量聚乙烯摩擦学性能研究进展

综述了超高分子量聚乙烯(UHMWPE)在摩擦学领域的研究进展,着重评述了UHMWPE材料在人工关节方面的应用以及在减摩耐磨材料方面的研究,并提出了UHMWPE作为减摩耐磨材料在研究与应用方面几个亟待解决的问题.     

Ni–Cr–Al Alloy for neutron scattering at high pressures

ABSTRACT

High-pressure devices used in neutron scattering require materials with high strength, low neutron attenuation, and no activation. They should also be non-magnetic. Only very few materials fulfil these criteria. Here, it is reported on the manufacture and properties of the Ni–Cr–Al alloy (57.0 wt-% Ni, 40.0 wt-% Cr, and 3.0 wt-% Al). The casting and heat treatment to obtain the material with the optimal yield strength are described in detail. Synchrotron powder diffraction reveals that phases of the Ni₂Cr, Cr, and Ni₃Al types are present. Aging has no significant effect on their lattice parameters and volume fractions. The alloy has no magnetic order down to at least 1.9?K as evidenced by magnetic measurements and diffraction with polarised neutrons.

This paper is part of a Thematic Issue on The Crystallographic Aspects of Metallic Alloys.     

Metallic Biomaterials

The improvement of medical health care during the past years has led to an increased use of implants. The requirements placed on implant materials are determined by medical progresses and biological demands. Metallic biomaterials are the dominating group of materials for use as highly tension loaded implants. Among the metals, titanium and specially developed titanium alloys have an outstanding position due to their combination of strength, elasticity and biocompatibility. In addition it is possible to develop “tailored materials” by functional coating the metals or by the production of composite materials.     

Effect of Zr on microstructure of metallic glass coatings prepared by gas tunnel type plasma spraying

Metallic glass is one of the most attractive advanced materials, and many researchers have conducted various developmental research works. Metallic glass is expected to be used as a functional material because of its excellent physical and chemical functions such as high strength and high corrosion resistance. However, the application for small size parts has been carried out only in some industrial fields. In order to widen the industrial application fields, a composite material is preferred for the cost performance. In the coating processes of metallic glass with the conventional deposition techniques, there is a difficulty to form thick coatings due to their low deposition rate. Thermal spraying method is one of the potential candidates to produce metallic glass composites. Metallic glass coatings can be applied to the longer parts and therefore the application field can be widened. The gas tunnel plasma spraying is one of the most important technologies for high quality ceramic coating and synthesizing functional materials. As the gas tunnel type plasma jet is superior to the properties of other conventional type plasma jets, this plasma has great possibilities for various applications in thermal processing. In this study, the gas tunnel type plasma spraying was used to form the metallic glass coatings on the stainless-steel substrate. The microstructure and surface morphology of the metallic glass coatings were examined using Fe-based metallic glass powder and Zr-based metallic glass powder as coating material. For the mechanical properties the Vickers hardness was measured on the cross section of both the coatings and the difference between the powders was compared.     

Polyethylene and cobalt–chromium molybdenium particles elicit a different immune response in vitro

Periprosthetic osteolysis is a major clinical problem that limits the long-term survival of total joint arthroplasties. Particles of prosthetic material stimulate immune competent cells to release cytokines, which may cause bone loss and loosening of the prosthesis. This study examined the following hypothesis. Polyethylene and titanium particles elicit a different immune response in vitro. To test these hypotheses, we used the human bone marrow cell culture model that we have established and previously used to examine particle associated cytokine release. Ultra high molecular weight polyethylene (UHMW-PE) induced a proliferation of CD14 positive cells (monocytes/macrophages) whereas cobalt chromium molybdenium (CoCrMb) particles demonstrated an increased proliferation of CD66b positive cells (granulocytes). Light and scanning microscopic evaluation revealed that the UHMW-PE particles, which have built large clusters of particles (Ø7, 5 μm), were mainly surrounded by the cells and less phagocytosed. On the other hand the smaller particles from CoCrMb have been phagocytosed by the cells. These results provide strong support for our hypothesis: that wear particles derived from prosthetic materials of different material can elicit significantly different biologic responses. In summary the results suggest that the “in vitro” response to wear particles of different biomaterials should be investigated by culture systems of various lineages of cells.     

Metallic Adhesive Layers for Ag‐Based First Surface Mirrors

Metallic thin films have been evaluated as adhesive layers for first surface mirrors. Thin films (0.5–4 nm thick) of Cr, Cu, Ge, Sn, and Ni, capped with an over layer of 100 nm of Ag have been deposited by means of ion assisted electron beam evaporation onto glass substrates. The specular reflectance, conductivity, morphology, adhesion, and abrasion resistance of the mirrors have been assessed and compared. This work demonstrates the superior Ni and Ge adhesion and abrasion resistance to Ag thin films, while Cr and again Ni are the best candidates in terms of reflectance enhancement. In particular, 4 nm of Ni increases the Ag reflectance from 95.7% to 96.7%, exhibits the strongest adhesion as determined by the cross hatch tape test and the lowest loss of material after the different abrasion tests is just 50% in comparison to 100% for Ag‐coated glass substrates.

     

Second generation (low modulus) titanium alloys in total hip arthroplasty

Titanium alloys ‐ type (α+β) ‐ like Ti6Al7Nb or Ti6Al4V are widely used in cementless total hip arthroplasty due to their lower modulus, biocompatibility and enhanced corrosion resistance in comparison to Stainless Steel or Cobalt‐Chromium implant materials. Several articles report about atrophy of the proximal femur in cases where long stems with a big diameter made of (α+β) Titanium alloys with a relatively high value of the Youngs’ Modulus (110 GPa) in comparison to the Youngs’ Modulus of cortical bone (15–25 GPa) have been implanted using a prosthesis design with distal anchorage technique. Meanwhile several implant manufacturers have developed a new group of biocompatible Beta‐Titanium alloys with a lower Youngs’ Modulus around 70 GPa. This article gives an overview of the current status of available low modulus Titanium alloys including their mechanical characteristics and future developments.     

Radiation-induced amorphization resistance and radiation tolerance in structurally related oxides

Ceramics destined for use in hostile environments such as nuclear reactors or waste immobilization must be highly durable and especially resistant to radiation damage effects. In particular, they must not be prone to amorphization or swelling. Few ceramics meet these criteria and much work has been devoted in recent years to identifying radiation-tolerant ceramics and the characteristics that promote radiation tolerance. Here, we examine trends in radiation damage behaviour for families of compounds related by crystal structure. Specifically, we consider oxides with structures related to the fluorite crystal structure. We demonstrate that improved amorphization resistance characteristics are to be found in compounds that have a natural tendency to accommodate lattice disorder.