Effect of nitrogen on blood compatibility of nickel-free high nitrogen stainless steel for biomaterial

Surface Modification of an Absorbable Bimodal Fe-Mn-Ag Alloy by Nitrogen Plasma Immersion Ion Implantation

Recently, Fe-Mn-based alloys have been increasingly catching the attention of the scientific community, because of their tunable and outstanding mechanical properties, and suitable degradation behavior for biomedical applications. In spite of these assets, their corrosion rate (CR) is, in general, too low to satisfy the requirements that need to be met for cardiovascular device applications, such as stents. In fact, the CR is not always the same for all of the degradation stages of the material, and in addition, a finely tuned release rate, especially during the first steps of the corrosion pattern, is often demanded. In this work, a resorbable bimodal multi-phase alloy Fe-3Mn-1Ag was designed by mechanical alloying and spark plasma sintering (SPS) to accelerate the corrosion rate. The presence of several phases, for example α-Fe, α-Mn, γ-FeMn and Ag, provided the material with excellent mechanical properties (tensile strength UTS = 722 MPa, tensile strain A = 38%) and a higher corrosion rate (CR = 3.2 ± 0.2 mm/year). However, higher corrosion rates, associated with an increased release of degradation elements, could also raise toxicity concerns, especially at the beginning of the corrosion pattern. In this study, The focus of the present work was the control of the CR by surface modification, with nitrogen plasma immersion ion implantation (N-PIII) treatment that was applied to mechanically polished (MP) samples. This plasma treatment (PT) improved the corrosion resistance of the material, assessed by static degradation immersion tests (SDITs), especially during the first degradation stages. Twenty-eight days later, the degradation rate reached the same value of the MP condition. Nitrogen compounds on the surface of the substrate played an important role in the corrosion mechanism and corrosion product formation. The degradation analysis was carried out also by potentiodynamic tests in modified Hanks' balanced salt solution (MHBSS), and Dulbecco's phosphate buffered saline solution (DPBSS). The corrosion rate was higher in MHBSS for both conditions. However, there was no significant difference between the corrosion rate of the PT in DPBSS (CR = 1.9 ± 0.6 mm/year) and in MHBSS (CR = 2 ± 1.4 mm/year). The cell viability was assessed with human vein endothelial cells (HUVECs) via an indirect metabolic activity test (MTT assay). Due to the lower ion release of the PT condition, the cell viability increased significantly. Thus, nitrogen implantation can control the in vitro corrosion rate starting from the very first stage of the implantation, improving cell viability.

Analytical review on the biocompatibility of surface-treated Ti-alloys for joint replacement applications

INTRODUCTION

With the advancement of joint replacements such as total hip replacement (THR), Titanium (Ti) and its alloys are widely used as implant materials. The bearing surface of Ti improves the longevity of implants. In this perception, researchers design a Ti-alloy that increases the wear and corrosion resistance to enhance osteogenesis and mechanical stability.

AREAS COVERED

: This paper is dedicated to finding the major causes of the failure of THR. Further, this paper provides an overview of the application of metallic alloys and their influencing factors that influence biocompatibility. The most contributing part of this paper focuses on the post-treatment impact on Ti-alloys biocompatibility.

EXPERT OPINION

This paper revealed and discussed that Ti alloys' biocompatibility for orthopedic applications mainly depends on antibacterial activities that decide tissue-implant compatibility. Therefore, performing surface treatment enhances the biocompatibility of Ti alloys. It was also observed that more water contact angle (WCA) induces bacterial growth and enhances cell adhesion. In contrast, the treated surface increases the antibacterial activities at lower WCA. Surface heat treatment with sintering or micro-arc oxidation achieves suitable antibacterial or antimicrobial activities.

High-manganese and nitrogen stabilized austenitic stainless steel (Fe-18Cr-22Mn-0.65N): a material with a bright future for orthopedic implant devices

The rationale behind the success of nickel free or with extremely low nickel austenitic high manganese and nitrogen stabilized stainless steels is adverse influences of nickel ion on human body. Replacement of nickel by nitrogen and manganese provides a stable microstructure and facilitates better biocompatibility in respect of the conventional 316L austenitic stainless steel (316L SS). In this investigation, biocompatibility of the high-manganese and nitrogen stabilized (Fe-18Cr-22Mn-0.65N) austenitic stainless steel was studied and found highly promising.In vitrocell culture and cell proliferation (MTT) assays were performed on this stainless steel and assessed in respect of the 316L SS. Both the steels exhibited similar cell growth behavior. Furthermore, an enhancement was observed in cell proliferation on the Fe-18Cr-22Mn-0.65N SS after surface modification by ultrasonic shot peening (USP). The mean percent proliferation of the MG-63 cells increased from ≈88% for Un-USP to 98% and 105% for USP 3-2 and USP 2-2 samples, respectively for 5 d of incubation. Interestingly,in vivoanimal study performed in rabbits for 3 and 6 weeks showed callus formation and sign of union without any allergic reaction.

Corrosion behavior of high nitrogen nickel-free austenitic stainless steel in the presence of artificial saliva and Streptococcus mutans

High nitrogen nickel-free austenitic stainless steels (HNSs) have great potentials to be used in dentistry owing to its exceptional mechanical properties, high corrosion resistance, and biocompatibility. In this study, HNSs with nitrogen of 0.88 wt% and 1.08 wt% displayed much lower maximum pit depths than 316L stainless steel (SS) after 21 d of immersion in abiotic artificial saliva (2.2 μm and 1.7 μm vs. 4.5 μm). Microbiologically influenced corrosion (MIC) evaluations revealed that Streptococcus mutans biofilms led to much severer corrosion of 316L SS than HNSs. Corrosion current densities of HNSs were two orders of magnitude lower than that of 316L SS after incubation of 7 d (37.5 nA/cm² and 29.9 nA/cm² vs. 5.63 μA/cm²). The pitting potentials of HNSs were at least 550 mV higher than that of 316L SS in the presence of S. mutans, confirming the better MIC resistance of HNSs. Cytotoxicity assay confirmed that HNSs were not toxic to MC3T3-E1 cells and allowed better sessile cell growth on them than on 316L SS. It can be concluded that HNSs are more suitable dental materials than the conventional 316L SS.

Biomechanical compatibility of high strength nickel free stainless steel bone plate under lightweight design

High nitrogen nickel-free stainless steel (HNNFSS) has excellent mechanical properties, corrosion resistance and biocompatibility, but its strength advantage is not fully used even though with one time higher than that of the conventional 316 L stainless steel. In this work, the lightweight design of HNNFSS bone plate was studied using finite element analysis, and the effect of lightweight plate fixation on histological and biomechanical behavior of healing bone were also researched on fractured rabbit femur. The finite element analysis results showed that the lightweight plate within 18.2% thickness reduction had higher bending strength and more homogeneous stress distribution compared with 316 L stainless steel plate. There was no obvious difference in radiography, histology analysis of callus and expression pattern of insulin like growth factor-1(IGF-1) of callus between the lightweight HNNFSS plate group and 316 L stainless steel plate group in animal test, and the IGF-1 concentrations of callus and the biomechanical bending test results also showed no statistical significance (p > 0.05), even though the data of the lightweight HNNFSS plate group were relatively better than that of 316 L stainless steel plate group. Therefore, the high nitrogen nickel-free stainless steel has the lightweight potential to keep good fixing function and improve bone healing compared with 316 L stainless steel plate.

In vitro mesenchymal stem cell response to a CO2 laser modified polymeric material

With an ageing world population it is becoming significantly apparent that there is a need to produce implants and platforms to manipulate stem cell growth on a pharmaceutical scale. This is needed to meet the socio-economic demands of many countries worldwide. This paper details one of the first ever studies in to the manipulation of stem cell growth on CO2 laser surface treated nylon 6,6 highlighting its potential as an inexpensive platform to manipulate stem cell growth on a pharmaceutical scale. Through CO2 laser surface treatment discrete changes to the surfaces were made. That is, the surface roughness of the nylon 6,6 was increased by up to 4.3μm, the contact angle was modulated by up to 5° and the surface oxygen content increased by up to 1atom %. Following mesenchymal stem cell growth on the laser treated samples, it was identified that CO2 laser surface treatment gave rise to an enhanced response with an increase in viable cell count of up to 60,000cells/ml when compared to the as-received sample. The effect of surface parameters modified by the CO2 laser surface treatment on the mesenchymal stem cell response is also discussed along with potential trends that could be identified to govern the mesenchymal stem cell response.

Modification of a commercial thromboelastography instrument to measure coagulation dynamics with three-dimensional biomaterials

Three-dimensional synthetic constructs with complex geometries have immense potential for use in a multitude of blood-contacting applications. Understanding coagulation phenomena is arguably the most critical aspect for applications involving synthetic biomaterials; however, real-time evaluation of the clot formation while interfacing with these materials is difficult to achieve in a reproducible and robust manner. Here, work representing first steps toward addressing this deficit is presented, wherein modified consumables for a clinical instrument (a Thromboelastograph(®)) have been fabricated. Thromboelastography (TEG) measures viscoelastic properties throughout clot formation and therefore provides clinically relevant coagulation measurements in real time (i.e., kinetics and strength of clot formation). Through our modification, TEG consumables can readily accommodate three-dimensional materials (e.g., those for regenerative tissue applications). The authors performed proof-of-concept experiments using polymer scaffolds with a range of surface properties and demonstrated that variations in surface properties resulted in differences in blood plasma coagulation dynamics. For example, the maximum rate of thrombus generation ranged from 22.2 ± 2.2 (dyn/cm(2))/s for fluorocarbon coated scaffolds to 8.7 ± 1.0 (dyn/cm(2))/s for nitrogen-containing scaffolds. Through this work, the ability to make real-time coagulation activity measurements during constant coagulation factor interface with biomedically relevant materials is demonstrated.

Biological behaviour of human umbilical artery smooth muscle cell grown on nickel-free and nickel-containing stainless steel for stent implantation

To evaluate the clinical potential of high nitrogen nickel-free austenitic stainless steel (HNNF SS), we have compared the cellular and molecular responses of human umbilical artery smooth muscle cells (HUASMCs) to HNNF SS and 316L SS (nickel-containing austenitic 316L stainless steel). CCK-8 analysis and flow cytometric analysis were used to assess the cellular responses (proliferation, apoptosis, and cell cycle), and quantitative real-time PCR (qRT-PCR) was used to analyze the gene expression profiles of HUASMCs exposed to HNNF SS and 316L SS, respectively. CCK-8 analysis demonstrated that HUASMCs cultured on HNNF SS proliferated more slowly than those on 316L SS. Flow cytometric analysis revealed that HNNF SS could activate more cellular apoptosis. The qRT-PCR results showed that the genes regulating cell apoptosis and autophagy were up-regulated on HNNF SS. Thus, HNNF SS could reduce the HUASMC proliferation in comparison to 316L SS. The findings furnish valuable information for developing new biomedical materials for stent implantation.

Osteoinduction and long-term osseointegration promoted by combined effects of nitrogen and manganese elements in high nitrogen nickel-free stainless steel

High nitrogen nickel-free stainless steel promoted osteoinduction and long-term osseointegration of implants by combined effects of N and Mn elements.

Effect of cold deformation on pitting corrosion of 00Cr18Mn15Mo2N0.86 stainless steel for coronary stent application

The high nitrogen nickel-free stainless steel has offered an alternative to further improve the performance of the coronary stents, and simultaneously avoids the potential harms of nickel element. Both cold deformation and pitting corrosion are very important for coronary stents made of stainless steel. In this work, the effect of cold deformation on the pitting corrosion resistance of a high nitrogen nickel-free stainless steel (00Cr18Mn15Mo2N0.86) in 0.9% saline solution was investigated. The results showed that the pitting corrosion of the steel was nearly unchanged with increases of the cold deformation up to 50%, indicating that the higher nitrogen content can reduce the negative effect of cold deformation on the pitting corrosion resistance, which is beneficial for the long term service of coronary stents in blood vessel.

Study of biocompatibility of medical grade high nitrogen nickel-free austenitic stainless steel in vitro

Adverse effects of nickel ions being released into the living organism have resulted in development of high nitrogen nickel-free austenitic stainless steels for medical applications. Nitrogen not only replaces nickel for austenitic structure stability but also improves steel properties. The cell cytocompatibility, blood compatibility and cell response of high nitrogen nickel-free austenitic stainless steel were studied in vitro. The mechanical properties and microstructure of this stainless steel were compared to the currently used 316L stainless steel. It was shown that the new steel material had comparable basic mechanical properties to 316L stainless steel and preserved the single austenite organization. The cell toxicity test showed no significant toxic side effects for MC3T3-E1 cells compared to nitinol alloy. Cell adhesion testing showed that the number of MC3T3-E1 cells was more than that on nitinol alloy and the cells grew in good condition. The hemolysis rate was lower than the national standard of 5% without influence on platelets. The total intracellular protein content and ALP activity and quantification of mineralization showed good cell response. We conclude that the high nitrogen nickel-free austenitic stainless steel is a promising new biomedical material for coronary stent development.

Effect of cold working on biocompatibility of Ni-free high nitrogen austenitic stainless steels using Dalton's Lymphoma cell line

The aims of the present work are to explore the effect of cold working on in-vitro biocompatibility of indigenized low cost Ni-free nitrogen containing austenitic stainless steels (HNSs) and to compare it with conventionally used biomedical grade, i.e. AISI 316L and 316LVM, using Dalton's Lymphoma (DL) cell line. The MTT assay [3-(4,5-dimethythiazol 2-yl)-2,5-diphenyltetrazolium bromide] was performed on DL cell line for cytotoxicity evaluation and cell adhesion test. As a result, it was observed that the HNS had higher cell proliferation and cell growth and it increases by increasing nitrogen content and degree of cold working. The surface wettability of the alloys was also investigated by water contact angle measurements. The value of contact angles was found to decrease with increase in nitrogen content and degree of cold working. This indicates that the hydrophilic character increases with increasing nitrogen content and degree of cold working which further attributed to enhance the surface free energy (SFE) which would be conducive to cell adhesion which in turn increases the cell proliferation.

An overview of recent advances in designing orthopedic and craniofacial implants

Great deal of research is still going on in the field of orthopedic and craniofacial implant development to resolve various issues being faced by the industry today. Despite several disadvantages of the metallic implants, they continue to be used, primarily because of their superior mechanical properties. In order to minimize the harmful effects of the metallic implants and its by-products, several modifications are being made to these materials, for instance nickel-free stainless steel, cobalt-chromium and titanium alloys are being introduced to eliminate the toxic effects of nickel being released from the alloys, introduce metallic implants with lower modulus, reduce the cost of these alloys by replacing rare elements with less expensive elements etc. New alloys like tantalum, niobium, zirconium, and magnesium are receiving attention given their satisfying mechanical and biological properties. Non-oxide ceramics like silicon nitride and silicon carbide are being currently developed as a promising implant material possessing a combination of properties such as good wear and corrosion resistance, increased ductility, good fracture and creep resistance, and relatively high hardness in comparison to alumina. Polymer/magnesium composites are being developed to improve mechanical properties as well as retain polymer's property of degradation. Recent advances in orthobiologics are proving interesting as well. This paper thus deals with the latest improvements being made to the existing implant materials and includes new materials being introduced in the field of biomaterials.

Quantitative biocompatibility evaluation of nickel-free high-nitrogen stainless steel in vitro/in vivo

Coronary stents must not provoke an inflammatory response; however, some kinds of ions that are released from biometals induce biological reaction. In the present study, we quantitatively evaluated biological reaction of nickel-free high-nitrogen stainless steel (HNS) by endothelial cell culture, and a bioimaging system using NF-κB/luciferase transgenic mice to confirm the potential of HNS for the application of coronary stent. Endothelialization was greater with HNS than with commercial stainless steel (SUS316L). In vivo inflammatory response of HNS was lower than that of SUS316L. These differences may be related to the amounts of nickel ion eluted from the stents, as HNS did not elute nickel ion. These data suggest that HNS may be useful as a material for coronary artery stents.

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.

Reduction of in-stent restenosis risk on nickel-free stainless steel by regulating cell apoptosis and cell cycle

High nitrogen nickel-free austenitic stainless steel (HNNF SS) is one of the biomaterials developed recently for circumventing the in-stent restenosis (ISR) in coronary stent applications. To understand the ISR-resistance mechanism, we have conducted a comparative study of cellular and molecular responses of human umbilical vein endothelial cells (HUVECs) to HNNF SS and 316L SS (nickel-containing austenitic 316L stainless steel) which is the stent material used currently. CCK-8 analysis and flow cytometric analysis were used to assess the cellular responses (proliferation, apoptosis, and cell cycle), and quantitative real-time PCR (qRT-PCR) was used to analyze the gene expression profile of HUVECs exposed to HNNF SS and 316L SS, respectively. Flow cytometry analysis revealed that 316L SS could activate the cellular apoptosis more efficiently and initiate an earlier entry into the S-phase of cell cycle than HNNF SS. At the molecular level, qRT-PCR results showed that the genes regulating cell apoptosis and autophagy were overexpressed on 316L SS. Further examination indicated that nickel released from 316L SS triggered the cell apoptosis via Fas-Caspase8-Caspase3 exogenous pathway. These molecular mechanisms of HUVECs present a good model for elucidating the observed cellular responses. The findings in this study furnish valuable information for understanding the mechanism of ISR-resistance on the cellular and molecular basis as well as for developing new biomedical materials for stent applications.

Development of new metallic alloys for biomedical applications

New low modulus β-type titanium alloys for biomedical applications are still currently being developed. Strong and enduring β-type titanium alloy with a low Young's modulus are being investigated. A low modulus has been proved to be effective in inhibiting bone atrophy, leading to good bone remodeling in a bone fracture model in the rabbit tibia. Very recently β-type titanium alloys with a self-tunable modulus have been proposed for the construction of removable implants. Nickel-free low modulus β-type titanium alloys showing shape memory and super elastic behavior are also currently being developed. Nickel-free stainless steel and cobalt-chromium alloys for biomedical applications are receiving attention as well. Newly developed zirconium-based alloys for biomedical applications are proving very interesting. Magnesium-based or iron-based biodegradable biomaterials are under development. Further, tantalum, and niobium and its alloys are being investigated for biomedical applications. The development of new metallic alloys for biomedical applications is described in this paper.