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.     

Electrochemical characterization of AISI 316L stainless steel in contact with simulated body fluid under infection conditions

Titanium and cobalt alloys, as well as some stainless steels, are among the most frequently used materials in orthopaedic surgery. In industrialized countries, stainless steel devices are used only for temporary implants due to their lower corrosion resistance in physiologic media when compared to other alloys. However, due to economical reasons, the use of stainless steel alloys for permanent implants is very common in developing countries. The implantation of foreign bodies is sometimes necessary in the modern medical practice. However, the complex interactions between the host and the can implant weaken the local immune system, increasing the risk of infections. Therefore, it is necessary to further study these materials as well as the characteristics of the superficial film formed in physiologic media in infection conditions in order to control their potential toxicity due to the release of metallic ions in the human body. This work presents a study of the superficial composition and the corrosion resistance of AISI 316L stainless steel and the influence of its main alloying elements when they are exposed to an acidic solution that simulates the change of pH that occurs when an infection develops. Aerated simulated body fluid (SBF) was employed as working solution at 37 °C. The pH was adjusted to 7.25 and 4 in order to reproduce normal body and disease state respectively. Corrosion resistance was measured by means of electrochemical impedance spectroscopy (EIS) and anodic polarization curves.     

The influence of complexing agent and proteins on the corrosion of stainless steels and their metal components

The present work is devoted to the problem of biodegradation of orthopaedic implants manufactured from stainless steel. In vitro simulations of the biocompatibility of two types of stainless steel, AISI 304 and AISI 316L, and their individual metal components, i.e. iron, chromium, nickel and molybdenum, were carried out in simulated physiological solution (Hank's) containing complexing agents. Knowledge of the effects of the chemical and biological complexing agents, EDTA and proteins, respectively, on the corrosion resistance of a metal should provide a better understanding of the processes occurring in vivo on its surface. The behavior of stainless steels and metal components was studied under open circuit and under potentiostatic conditions. The concentration of dissolved corrosion products in the form of released ions was determined by differential pulse polarography (DPP) and atomic emission spectrometry using inductively coupled plasma (ICP-AES). The composition of solid corrosion products formed on the surface was analyzed by energy dispersive X-ray spectroscopy (EDS) and their morphology was viewed by scanning electron microscopy (SEM). The addition of EDTA and proteins to physiological solution increased the dissolution of pure metals and stainless steels. The effect of particular protein differs on different metals and alloys.     

Titanium: The implant material of today

The use of metals for the replacement of structural components of the human body has been with us for some considerable time. The metals originally used were stainless steels which have gradually been replaced by cobalt-chromium alloys. Although titanium has been used since the late forties, it is only relatively recently that it has gained widespread interest. Titanium and its alloys are being used more and more in preference to the cobalt-chromium alloys and has broadened the field of applications. The features which make titanium such an interesting material are its excellent corrosion resistance in the biological environment, combined with an exception degree of biocompatibility which it shares with only a handful of other materials. In this review the background to the clinical use of titanium is discussed with particular attention to the biological aspects of the material. While there are now many clinical uses for titanium and its alloys their main areas of application are in the field of dentistry and orthopaedics and these are described in some detail.     

Fatigue and Corrosion Fatigue of High-Nitrogen Austenitic Stainless Steel

High nitrogen contents in solid solution as well as appropriate strengthening mechanisms in austenitic stainless steels can result in very high corrosion resistance. This is true in both air environment and in simulated human body fluids (corrosion fatigue). High cycle corrosion fatigue data are listed and compared with similar data for titanium base and cobalt base implant materials. Thus high nitrogen austenitic stainless steels are candidates to replace other stainless steels as implant materials.     

Impact of wear debris on striated muscle‐ a comparative in‐vivo study with titanium and stainless steel

Wear debris and corrosion products of metal implants induce biological events that may have severe consequences for skeletal muscle microcirculation. We therefore studied in vivo leukocyte‐endothelial cell interaction and leukocyte transmigration in skeletal muscle after confrontation with characterised titanium and stainless steel fretting corrosion particles, and compared these results with those of the bulk materials. Using the hamster dorsal skinfold chamber preparation and intravital microscopy, we could demonstrate in 30 animals that stainless steel induces a more pronounced inflammatory answer in contrast to the implant material titanium. However we were not able to show a general benefit of bulk vs. debris. Overall the study suggests that not only the bulk properties of orthopaedic implants but also the microcirculatory implications of inevitable wear debris may play a role in determining biocompatibility and ultimately longlivety of an implant. The skinfold chamber is a feasible and versatile model for observation of the dynamic process of microvascular response after foreign‐body implantation, and offers much perspective. With a minimum of adverse host reaction, our results indicate that titanium still represents the gold standard in metallic implant material, even in the case of generated wear debris, which shows a comparatively low inflammatory potential.     

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.     

The abrasive corrosion behavior of plasma-nitrided alloy steels in chloride environments

Both corrosion and abrasive corrosion behavior of plama-nitrided type 304 and 410 stainless steels and 4140 low alloy steel were investigated in 3% NaCl solution (pH = 6.8) by electrochemical corrosion measurements. Surface morphology and alloying elements after corrosion and abrasion corrosion tests were examined by scanning electron microscopy and energy dispersive analysis of X-rays. The results indicated that the plasma-nitrided SAE 4140 steel containing -(Fe,Cr)_{2 – 3}N and -(Fe,Cr)₄N surface nitrides which produce a thick and dense protective layer exhibited a significant decrease of corrosion currents by inhibition of the anodic dissolution of iron, whereas the plasma-nitrided type 304 and 410 stainless steels containing the segregation of chromium nitride CrN exhibited a extensive pitting corrosion by acceleration of the anodic dissolution of iron. It is concluded that the susceptibility to pitting is consistent with the degree of chromium segregation, and decreases as follows: 304 stainless steel > 410 stainless steel > 4140 steel. Also, the results of abrasive corrosion testing for the plasma-nitrided alloys are strongly related to the subtleties of the nitrided microstructures resulting in a pitting and spalling type of abrasive corrosion of type 304 and 410 stainless steels, and excellent abrasive corrosion resistance for SAE 4140 steel.     

Compatibility of ferritic and duplex stainless steels as implant materials: in vitro corrosion performance

The pitting corrosion, crevice corrosion and accelerated leaching of iron, chromium and nickel of super-ferritic and duplex stainless steels, and for effective comparison the presently used 316L stainless steel, have been studied in an artificial physiological solution (Hank's solution) by the potentiodynamic anodic polarization method. The results of the above studies have shown the new super-ferritic stainless steel to be immune to pitting and crevice corrosion attack. The pitting and crevice corrosion resistances of duplex stainless steel were found to be superior to those of the commonly used type 316L stainless steel implant materials. The accelerated leaching study conducted for the above alloys showed very little tendency for the leaching of metal ions when compared with 316L stainless steel. Thus the present study indicated that super-ferritic and duplex stainless steels can be adopted as implant materials due to their higher pitting and crevice corrosion resistance.     

Corrosion susceptibilities of various metals and alloys in synthetic geothermal brines

The corrosion susceptibilities of various pure metals and alloys were investigated in synthetic geothermal fluids. Rates of corrosion of AISI 1010 steel, types 304 and 316 stainless steels, Monel 400 and nickel were determined at three temperatures (296, 333 and 368 K); and those of the molybdenum, niobium and titanium were determined at 368 K only. Type 304 stainless steel appears to undergo an active-passive transition at a temperature range between 333 and 368 K. In the passive state type 304 steel has essentially the same corrosion rate as type 316. At 368 K the corrosion rate of pure nickel was approximately 2.5 times that of Monel, which in turn was twice that of type 316 stainless steel. The corrosion rates of Mo, Nb and Ti were less than one mdd at the highest experimental temperature.     

Comparison of the tissue reaction to implants made of a beta titanium alloy and pure titanium. Experimental study on rabbits

Commercially pure titanium (Ti cp) has been used successfully as an implant material in fracture fixation devices for many years. Ti cp is comparatively soft, but the mechanical properties, such as strength and ductility, can be adjusted by different means over a wide range. Titanium changes its crystal structure from a hexagonal (alpha) phase to the cubic (beta) phase at about 882 °C. Cubic titanium has the advantage of being very malleable (ductile), but in order to stabilize it at room temperature, additions of suitable alloying elements are required. In this study the soft tissue reaction to implants made from a beta titanium alloy (Ti–Mo–Zr–Al) with four different surface treatments is evaluated. The results are compared to Ti cp implants having the same surface conditions, and to electropolished stainless steel plates as controls. A minimum of four small plates of each group were implanted in rabbit tibiae for 3 months. Histomorphometric results show that the thickness of the soft tissue reaction layer, and the number of blood vessels, connective tissue cells (fibroblasts, fibrocytes), lymphocytes, and foreign body giant cells are not significantly different between beta titanium and Ti cp plates. For stainless steel plates the soft tissue reaction layer is thicker, and the numbers of macrophages and connective tissue cells are higher. Excellent biocompatibility was observed for this beta titanium alloy. The mechanical properties of this alloy surpass those of Ti cp, and because of the good tissue tolerance, this material seems to be advantageous and should enter into clinical testing.     

Anodischer Schutz durch Legierungsmaßnahmen

Anodic protection through alloying. The very heavy demands made on the resistance to corrosion of the metallic materials used in the chemical industry has at all times resulted in attempts to improve this property through special alloying techniques. In such techniques an important part is played by alloying elements which favourably influence the passivation of metals, the reason for this being that most of the materials used owe their resistance to the passive layers which are formed at their surfaces. Those elements which, by reducing over voltages, enable the cathodic reaction to be intensified are particularly important in this connection. They enable the passivating current to be raised and thus have effects similar to those of anodic protection. The effects of such elements, especially of Pt and Pd, on the corrosion behaviour of ferritic and austenetic stainless steels, of titanium, and of lead alloys, and also the opportunities for technical application, are described.     

TA15钛合金与铝合金和结构钢接触腐蚀与防护研究

通过测定TA15钛合金与铝合金和结构钢组成的电偶对的电偶电流的方法,研究了TA15钛合金在使用中与铝合金和结构钢接触时产生电偶腐蚀的敏感性.结果表明:TA15钛合金与铝合金和30CrMnSiA钢接触时会产生严重的电偶腐蚀,必须进行防护处理方可使用;与30CrMnSiNi2A钢接触产生的电偶腐蚀比较轻微.对铝合金和结构钢进行表面处理可以降低电偶腐蚀敏感性,表面处理后喷涂底漆可进一步降低电偶腐蚀敏感性.     

Nickel-free austenitic stainless steels for medical applications

Abstract

The adverse effects of nickel ions being released into the human body have prompted the development of high-nitrogen nickel-free 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 in medical stainless steels, the advantages of nitrogen in stainless steels, and emphatically, the development of high-nitrogen nickel-free stainless steels for medical applications. By combining the benefits of stable austenitic structure, high strength and good plasticity, better corrosion and wear resistances, and superior biocompatibility compared to the currently used 316L stainless steel, the newly developed high-nitrogen nickel-free stainless steel is a reliable substitute for the conventional medical stainless steels.     

Study of the properties of low-cost powder metallurgy titanium alloys by 430 stainless steel addition

Titanium is a lightweight metal with an outstanding combination of properties which make it the material of choice for many different applications. Nonetheless, its employment at industrial level is not widespread due to higher production costs with respect to competitor metals like steel and aluminium. In this work the production of low-cost titanium alloys is attempted by combining the utilisation of a powder metallurgy process and cheap alloying elements (i.e. commercial 430 stainless steel powder optimised for the powder metallurgy industry). Low-cost titanium alloys are fabricated by blending elemental titanium with stainless steel. The behaviour of the powders as well as that of the sintered materials are analysed and compared to that of a master alloy addition Ti6Al4V alloy. The produced low-cost titanium alloys show comparable properties to both wrought and powder metallurgy titanium alloys and, therefore, they are proposed as an alternative to obtain structural component made out of titanium alloys.     

Evaluation techniques of metallic biomaterials in vitro

Metals and alloys are widely used as biomedical materials and are important in medicine and they cannot be replaced with ceramics or polymers at present mainly because of their high strength and toughness. Since safety is the most important property of biomaterials, corrosion-resistant materials such as stainless steel, Co–Cr–Mo alloy, commercially pure titanium, and titanium alloys are employed as biomaterials. Evaluation techniques for corrosion with culturing cells, the characterization of reconstruction of surface oxide film, fretting fatigue, cytotoxicity, and biocompatibility are reviewed in this paper. These techniques are original and characteristics in the field of biomaterials that should contribute to the proper evaluations of biomaterials in vitro.     

Comparative study of some metallic biomaterials used as implants

The electrochemical behavior of two Ti alloys (TA and TAV) and two grades of stainless steels (SS₁ and SS₂), commonly used as biomedical implant materials, particularly for orthopedic and osteosynthesis applications, was investigated in Hank's solution at 37 °C and different pH. The aim was to distinguish between the behavior of these materials in artificial physiological solution through analysis of their corrosion potential variation with time and potentiodynamic polarization curves. Characterization of the modified surface layers was made by means of microscopic examinations, hardness measurements and X‐ray diffraction analysis. The results indicated that in neutral Hank's solution (pH = 7.2) SS₂ and SS₁ samples were of higher corrosion resistance than titanium alloys. The behavior was reversed in the acidic media (pH = 5.0 or 3.0), where TA had the least corrosion rate and the corrosion susceptibility increased in the order TA < TAV < SS₁ < SS₂.     

Evaluation techniques of metallic biomaterials in vitro

Metals and alloys are widely used as biomedical materials and are important in medicine and they cannot be replaced with ceramics or polymers at present mainly because of their high strength and toughness. Since safety is the most important property of biomaterials, corrosion-resistant materials such as stainless steel, Co–Cr–Mo alloy, commercially pure titanium, and titanium alloys are employed as biomaterials. Evaluation techniques for corrosion with culturing cells, the characterization of reconstruction of surface oxide film, fretting fatigue, cytotoxicity, and biocompatibility are reviewed in this paper. These techniques are original and characteristics in the field of biomaterials that should contribute to the proper evaluations of biomaterials in vitro.     

Beneficial effects of nitrogen on austenite antibacterial stainless steels

Nitrogen is a significant alloying element in austenite stainless steels. The aim of this paper is to evaluate the effects of nitrogen on the microstructure and properties of austenite antibacterial stainless steels. Two austenite antibacterial stainless steels containing copper and different nitrogen concentration (0.02 and 0.08 wt%, respectively) were fabricated. The microstructures and composition analysis were carried out using field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and Auger electron spectroscopy (AES). The epsilon copper-rich precipitates are spherical and less than 20 nm in size, with a cube-on-cube orientation relationship with the matrix. They are dispersed on the steel surface with a mean space of about 200 nm. Nitrogen cannot only improve the antibacterial property but enhance significantly the corrosion resistance in chloride media. Nitrogen compensates the harmful effect of epsilon copper precipitates on the corrosion resistance. The nitrogen concentration in the surface of N-2 steel is four times as much as in the surface of N-1 steel. Nitrogen enrichment in the steel surface improves the corrosion resistance. The presence of higher nitrogen increases the strength and decreases the ductility of austenite antibacterial stainless steel, which could be related to the variation of stacking-fault energy associated with nitrogen concentration.     

Modifying the properties of AISI 316L steel by glow discharge assisted low-temperature nitriding and oxynitriding

Apart from titanium, its alloys and CoCrMo alloys, austenitic steels are widely used in medical applications. In order to improve the frictional wear resistance of these steels, they are subjected to various surface treatments such that the good corrosion resistance of the steels is preserved.The paper analyzes the structure and phase composition of AISI 316L steel after subjecting it to low-temperature nitriding and oxynitriding under glow discharge conditions. The treatments produced diffusion-type surface layers composed of nitrogen-expanded austenite (known as the phase S, i.e. supersaturated solution of nitrogen in austenite) with a thin surface layer of chromium nitride (CrN) zone (after nitriding) or chromium oxide (Cr₂O₃) zone (after oxynitriding). It has been shown that the treatments substantially increase the hardness and frictional wear resistance of the steel without degrading its good corrosion resistance (examined in the Ringer physiological solution at a temperature of 37 °C).