AISI 316LVM Research Articles

SURFACE CHARACTERISTICS INFLUENCED BY LASER TEXTURING PARAMETERS ON BIOMEDICAL-GRADE AISI 316LVM STAINLESS STEEL

Surface roughness and wettability, which characterize the texture formed on the implant surface, are critical features for the functionality of the implant. Laser texturing is a promising processing method because of the advantages it provides in creating a particular surface topography on the surface of a metallic implant material with a nanosecond pulsed laser beam. Different experimental combinations were created using a fiber pulsed marking device on the surface of AISI 316LVM implant material using the hatch strategy; textures depending on the scan speed, frequency, and hatch distance were created on the surface. The surface roughness and wettability evaluated the effects of parameters on the texture form. Based on the experimental and statistical results, while the scan speed was the most significant parameter affecting the wettability behavior and surface roughness, the hatch strategy and frequency also affected the surface roughness to some extent. Many textured surfaces showed super-hydrophilic behavior with a contact angle of [Formula: see text]. It has been determined that surface textures with the same or close roughness values did not exhibit the same wettability behavior. The lowest surface roughness of 2 [Formula: see text]m with a [Formula: see text] contact angle was obtained at a hatch strategy of [Formula: see text]/[Formula: see text], a scan speed of 900 mm/s, a frequency of 100 kHz, and a hatch distance of 0.03 mm. Three-dimensional surface images show that while many craters formed the surface textures, overlapping consecutive beams and hatch strategies significantly affected the surface topography.

Investigation of the surface quality and machinability of AISI 316LVM

Surface quality has a significant effect on the reliability of an implant. The surface finish of the workpiece is influenced by machining parameters, tool wear and cooling–lubrication conditions. Typically, mineral oil-based conventional cutting fluids are employed for cooling and lubricating purposes in industrial machining processes. However, the use of these fluids places costly environmental and health responsibilities on companies. Consequently, it is preferable to utilize an affordable and environmentally friendly coolant/lubricant that does not generate liquid waste or have harmful side effects. In this work, we conducted experimental investigations to examine the effect of cutting forces, cutting temperature, tool wear and the quality of the machined surface on the machinability performance of medical grade AISI 316LVM austenitic stainless steel. Five different cutting conditions were employed in the machining experiments: dry cutting, flood, minimum quantity lubrication (MQL), cryogenic cutting with liquid carbon dioxide (LCO2) and cryogenic cutting with liquid nitrogen (LN2). Compared to the dry-cutting condition, the cutting temperature decreased by 42.1% under LN2 and flood conditions and by 40.4% under LCO2 conditions. The cutting tools exhibited small amounts of flank wear and nose wear, along with the formation of built-up edges (BUE); however, no crater wear was observed. The MQL method resulted in the lowest cutting forces, while the cryogenic methods yielded the highest cutting forces. Among the cutting conditions, the MQL and flood conditions produced the lowest roughness values and the best surface quality. Conversely, the cryogenic cutting conditions led to the highest roughness values and the poorest surface quality. Furthermore, the MQL condition resulted in the lowest dimensional deviations.

The development and characterization of bioactive coatings for local drug delivery in orthopedic applications

Layer-by-layer bioactive coatings on AISI 316LVM and Ti90Al6V4 alloy were developed, showing great promise for biomedicine, especially as part of implantable metal-based composites. A corrosion study of the coated and uncoated samples was performed using electrochemistry. It was proven that such coatings do not increase the corrosion susceptibility of substrate materials. Controlled-release of a nonsteroidal anti-inflammatory drug (diclofenac) from the coatings as well as their positive influence on osteoblast growth for several days was proven. The layer-by-layer structure and drug loading were also investigated by means of surface analytical techniques, i.e. ATR-FTIR, ToF-SIMS, and AFM. Finally, the suitability of the prepared coatings for potential orthopedic applications was proven using various cell testing methods.

Dexamethasone-Loaded Bioactive Coatings on Medical Grade Stainless Steel Promote Osteointegration.

In this study, a multilayer bioactive coating based on carboxymethyl cellulose (CMC) and dexamethasone (DEX) was prepared on medical-grade stainless steel (AISI 316LVM). Its aim was the controlled drug delivery of the incorporated anti‑inflammatory drug, which at the same time promotes osteogenic differentiation of mesenchymal stem cells. Due to DEX’s limited solubility in physiological fluids, which limits the loading capacity of coatings, it was further combined with β-cyclodextrin to increase its concentration in the bioactive coating. Controlled release of DEX from the multilayer coating was achieved in four steps: a “burst”, i.e., very fast, release step (in an immersion interval of 0–10 min), a fast release step (10–30 min), a slow-release step (60–360 min), and a plateau step (360–4320 min), following a zero-order release or Higuchi model release mechanism. Successful layer-by-layer coating formation was confirmed using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). It was shown that the application of the coating significantly increases the hydrophilic character of AISI 316LVM, and also significantly increases the surface roughness, which is known to promote cell growth. In addition, electrochemical measurements demonstrated that the coating application does not increase the susceptibility of medical-grade stainless steel to corrosion. In vitro cell testing using all cell types with which such coatings come into contact in the body (osteoblasts, chondrocytes, and mesenchymal stem cells (MSCs)) showed very good biocompatibility towards all of the mentioned cells. It further confirmed that the coatings promoted MSCs osteogenic differentiation, which is the desired mode of action for orthopedic implants.

Induced Biological Response in Contact with Ag-and Cu-Doped Carbon Coatings for Potential Orthopedic Applications.

Silver and copper as additives of various biomaterials have been reported as the potential solutions for biomedicine applications, mostly because of inducing bactericidal effects. The application of those admixtures in diamond-like carbon (DLC) coatings may be desirable for orthopedic implants. In the present manuscript, the biological effect of coatings with up to about 7 at.% and 14 at.% of, respectively, Cu and Ag is compared. The morphology, chemical structure, and composition of films deposited on AISI 316LVM and Ti6Al7Nb is characterized. The live/dead analysis conducted with Escherichia coli shows a higher bactericidal potential of silver than copper. Although the Cu-doped coatings can positively affect the proliferation of Saos-2 and EA.hy926 cell lines, the results of XTT test are on the verge of 70% of viability. Biological effect of silver on EA.hy926 cell lines is negative but that admixture ensures high proliferation of osteoblasts in contact with coatings deposited on titanium alloy (over 20% better than for substrate material). In that case, the viability is reaching about 85% for Ag-doped coatings on AISI 316LVM and 75% on Ti6Al7Nb. The results indicate that for the sake of bactericidal coatings that may promote osteointegration, the candidates are DLC with silver content no higher than 10 at.%.

Clindamycin-Based 3D-Printed and Electrospun Coatings for Treatment of Implant-Related Infections.

This study presents the development and characterisation of two novel bioactive coatings deposited on TiAlV and AISI 316LVM substrates. The coatings were prepared using 3D printing and electrospinning. The 3D-printed coating consisted of the cellulose nanofibril suspension, alginate, and carboxymethylcellulose (CMC), while CMC and polyethylene oxide were used to prepare the electrospun coating. Both coatings were loaded with the antibiotic clindamycin (CLIN), which is a bacteriostatic lincosamide known for its activity against streptococci, staphylococci, pneumococci, Bacteroides species, and other anaerobes. Initial characterisation of the coatings was performed by attenuated total reflectance Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and atomic force microscopy. Furthermore, the contact angle measurements, swelling rate, and biodegradability of the coatings were investigated. The released concentration of CLIN in PBS (pH = 7.4 at 25 °C) was determined by UV-VIS spectrophotometry. The coatings’ biocompatibility was determined using an MTT (3(4,5 dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide) assay using an osteoblast cell culture (hFOB 1.19, ATCC CRL 11372).

Tribocorrosion response of duplex layered CoCrMoC/CrN and CrN/CoCrMoC coatings on implant grade 316LVM stainless steel

The objective of this work was to improve the tribocorrosion performance of biomedical grade 316LVM stainless steel via the application of duplex layered coatings. Two different PVD coatings were deposited via magnetron sputtering: (1) an underlying CoCrMo carbon S-phase layer followed by an outermost CrN layer designated as CrN/S and; (2) an underlying CrN layer followed by an outermost CoCrMo carbon S-phase designated as S/CrN. Tribocorrosion of the coated and uncoated 316LVM was studied against an alumina ball which was made to slide in a reciprocation motion in Ringer's solution. The contributions of wear, corrosion and their synergy were elucidated by performing tests under open circuit, cathodic and anodic potential conditions. The resultant wear scars were analysed via SEM, EDS, optical microscopy and contact profilometry. Both coatings displayed superior tribocorrosion response to AISI 316LVM with CrN/S exhibiting the best performance. CrN/S displayed lowest coefficient of friction under all electrochemical conditions (~0.10–0.15) and a material loss under anodic condition with a 93% decrease when compared to 316LVM. The CrN/S scars exhibited a smooth morphology under all test conditions in contrast with the other two test materials which displayed shearing marks oriented along the sliding direction under OCP and anodic conditions. By considering the resultant scar morphologies, a hypothesis is being proposed to explain the tribocorrosion degradation mechanisms encountered.

Carboxymethyl cellulose/diclofenac bioactive coatings on AISI 316LVM for controlled drug delivery, and improved osteogenic potential

This work reports on the preparation and systematic testing of a novel multi-layered coating, comprised of the non-steroid anti-inflammatory drug diclofenac and biopolymer carboxymethyl cellulose. Drug release testing was performed on an Automated Transdermal Diffusion Cells Sampling System in combination with UV-VIS spectroscopy as the released drug concentration determination method. The results showed that most of the drug is released in the first six hours, whereas the overall released amount could be tailored through changes in the multi-layered coating composition. Biocompatibility tests performed on human osteoblast cells, showed cell viability improvement between 7% and 17% compared to the control sample. The expression of proteins playing important roles in extracellular matrix production and functioning was performed in order to obtain additional proof of the prepared materials’ osteointegration boosting capacity. Finally, electrochemical measurements confirmed that the coatings do not influence the corrosion susceptibility of AISI 316LVM stainless steel.

S-Phase Layer Development on 316 LVM Using Low Temperature Hybrid Thermochemical Treatment Process

This investigation focuses on the improvement of surface properties of medical grade austenitic stainless steel (AISI 316LVM). The aim is to develop a homogenous supersaturated hard layer of expanded austenite (s-phase) at the surface of AISI 316LVM using low temperature hybrid thermochemical heat treatment process. The s-phase layer produced by this process is able to improve the surface properties of AISI 316LVM, overcoming its drawback of low surface hardness and wear resistance, without impairing the corrosion resistance of the steel. During the heat treatment process, ammonia (NH3) and methane (CH4) gasses were introduced into the furnace with temperatures of 425°C and 475°C, at 6 and 12 hours with gas composition of 75% of NH3, 10% of CH4, and 15% of Nitrogen (N2). Characterization on the microstructure showed the formation of the S-phase layer with variation of thickness according to parameters used. The S-phase formation was confirmed with phase analysis using XRD. Besides, the surface hardness also significantly increased from 210.9 HV to 1170.0 HV. In conclusion, low temperature hybrid heat treatment process is able to produce a homogenous hard s-phase layer.

Radio-frequency plasma-enhanced chemical vapour deposition of carbon films on AISI 316LVM steel: Formation of a transition layer and metal whiskers, and their influence on coating properties

The process parameters for carbon coating synthesis can affect the entire zone of modification, including the coating itself and the transition layer close to the surface of the metal substrate. In this study, diamond-like carbon (DLC) coatings were synthesised using the radio frequency plasma-enhanced chemical vapour deposition method with a variable negative potential of the electrode called self-bias (Vb) that affects the temperature of the process. Three types of modification were distinguished according to the thickness and properties of the modification zone.The hardness of the mentioned zones was two to three times greater than that of the core material (AISI 316 LVM steel). Coatings deposited at temperatures up to 450 °C (Vb lower than 1000 V) have thicknesses lower than 5 μm. These coatings have good corrosion resistance but hardness on the level of 9 GPa. By increasing the process temperature above 500 °C (Vb above 1000 V), the corrosion resistance of the modification zone was depleted, an increase in hardness to a level of 14 GPa was observed. In these cases, the thickness of the modification zone was over 9 μm. The reason for the weak corrosion resistance was the formation of metal whiskers across DLC coating.

Analysis of the Enameled AISI 316LVM Stainless Steel

In this work, four different enamels were coated on AISI 316LVM stainless steel and the corrosion resistance of these samples was tested in 5 wt.% NaCl solution at room temperature. The preparation procedure of the enamels was optimized in terms of firing temperature, time and composition. First the thermal expansion was measured using dilatometry followed by electrochemical analysis using chronopotentiometry, electrochemical impedance spectroscopy and cyclic polarization. The topography of the most resistant sample was obtained by 3D-profilometry. All samples coated with enamel showed significantly higher corrosion and dilatation resistance compared with the uncoated stainless steel material.

Mechanical properties, chemical analysis and evaluation of antimicrobial response of Si-DLC coatings fabricated on AISI 316 LVM substrate by a multi-target DC-RF magnetron sputtering method for potential biomedical applications

In this study silicon doped diamond-like carbon (Si-DLC) coatings were synthesized on two substrates: silicon and AISI 316LVM stainless steel using a multi-target DC-RF magnetron sputtering method. The Si content in the films ranged between 4 and 16at.%, and was controlled by the electrical power applied in RF regime to Si cathode target.The character of the chemical bonds was revealed by FTIR analysis. With the addition of silicon the hydroxyl absorption (band in the range of 3200–3600cm−1) increased what suggests more hydrophilic character of the coating. There were also observed significant changes in bonding of Si atoms. For low content of dopant, Si-O-Si bond system is predominant, while for the highest content of silicon there is an evidence of the shift to Si-C bonds in close proximity to methyl groups. The Raman spectroscopy revealed that the G peak position is shifted to a lower wavenumber and the ID/IG ratio decreased with increasing Si content, which indicates an increase in the C-sp3 content. Regardless of the coatings’ composition, the improvement of hardness in comparison to pure substrate material (AISI 316 LVM) was observed. Although the reduction of the level of hardness from the level of 10.8GPa for pure DLC to about 9.4GPa for the silicon doped coatings was observed, the concomitant improvement of films adhesion with higher amount of Si was revealed. Although incorporation of the dopant to DLC coatings increases the number of E. coli cells which adhered to the examined surfaces, the microbial colonisation remains on the level of substrate material.The presented results prove the potential of Si-DLC coatings in biomedical applications from the point of view of their mechanical properties.

Effects of surface laser treatments on microstructure, tension, and fatigue behavior of AISI 316LVM biomedical wires

Recent developments in minimally invasive surgical techniques have led to a surge in advancing alternative manufacturing routes. In order to meet the functional needs of such small devices as cardiovascular stents, and guide wires, the use of new materials and delicate geometries has increased creating a new challenge for manufacturing and machining. In this work, two sets of laser parameters leading to different laser power output were employed to study the effects of systematic changes in microstructure and mechanical characteristics of AISI 316LVM biomedical grade wires. Uniaxial tension and cyclic strain-controlled fatigue with the use of flex bending machines were used in order to evaluate the mechanical properties. Surface quality, heat affected zone (HAZ), and subsequent mechanical response were also investigated. Improvements in the fatigue behavior of laser-treated wires were obtained but depended on the choice of laser parameters. Low power Nd:YAG laser-treated AISI 316LVM annealed wires exhibited better fatigue performance in both high cycle fatigue and low cycle fatigue compared to the annealed AISI 316LVM wires. In contrast, high power Nd:YAG laser-treated annealed wires exhibited poorer fatigue performance in both high cycle and low cycle fatigue. Nd:YAG laser-treated AISI 316LVM hard wires exhibited poorer fatigue performance in both high cycle fatigue and low cycle fatigue compared to the AISI 316LVM hard wires. The effects of laser processing conditions on the microstructural features responsible for these changes in fatigue behavior are discussed.

The effects of passivation parameters on pitting potential of biomedical stainless steel

Passivation is a chemical process in which the electrochemical condition of passivity is gained on the surface of metal alloys. Biomedical AISI 316LVM stainless steel (SS) can be passivized by means of nitric acid immersion in order to improve a protective oxide layer on the surface and consequently increase corrosion resistance of the SS in the physiological solutions. In this study, multiple regression analysis and artificial neural network (ANN) were employed for mathematical modeling of the AISI 316LVM SS passivation process after immersion in the nitric acid solution. The pitting potential, which represents the mea-sure of pitting corrosion resistance, was chosen as the response, while the passivation parameters were nitric acid concentration, temperature and passivation time. The comparison between experimental results and models predictions showed that only the ANN model provided statistically accurate predictions with a high coefficient of determination and a low mean relative error. Finally, based on the derived ANN equation, the effects of the passivation parameters on pitting potential were examined.

Enhancement of the Pitting Corrosion Resistance of AISI 316LVM Steel with Ta-Hf-C/Au Bilayers for Biomedical Applications

Tantalum carbide (TaC), hafnium carbide (HfC), and Ta-Hf-C mixed coatings with and without a gold (Au) interlayer were deposited on 316LVM steel substrates by the magnetron cosputtering technique in order to improve the corrosion resistance of steel substrates in a simulated biological fluid. To study the effect of the gold interlayer on pitting corrosion, the different systems were placed in contact with Ringer’s solution at pH 7.4 and a temperature of 37°C. The electrochemical properties of the coatings were determined using polarization curves. Subsequently, the surface morphologies were observed using scanning electron microscopy (SEM) in order to analyze the corrosion processes on the different surfaces. The gold interlayer was found to significantly improve the electrochemical properties of the system, showing a decrease in the pitting corrosion and deterioration rate, while it is expected that the binary and ternary carbides provide mechanical stability to the bilayers protecting the gold.

Influence of ALD process parameters on the physical and chemical properties of the surface of vascular stents

Studies of haemocompatibility of AISI 316LVM steel point to the need for nickel elimination from the surface and replacing it with other elements showing higher biotolerance. Such layers include titanium, carbon or silicon coatings. Therefore, the authors attempted to evaluate some selected physicochemical properties of TiO2 layers, grown by atomic layer deposition (ALD) method, on the surface of 316LVM steel at variable process temperature. ALD temperature has a major role in the final quality of the surface layer grown with the use of such method, regardless of the type of the base. It was observed that the growth of temperature had an adverse influence on corrosive resistance in the artificial plasma environment and contributed to formation of a double (porous) layer showing decreased tightness. Further on, assessment of the coating adhesion to the base showed that too low process temperature T=100°C had an adverse effect on mechanical properties, resulting in substantially reduced critical force. On the other hand, the performed surface wettability tests showed no influence of ALD temperature in the obtained angle values.

Potentiostatic, Potentiodynamic and Impedance Study of TiO2 Layers Deposited of 316 LVM Steel Used for Coronary Stents

Abstract The objective of the study is assessment of suitability of the ALD method for application of a TiO2 layer on surface of 316LVM steel used for production of vessel stents. Selection of the appropriate process parameters for application of the layer affects its electrochemical properties, which largely determine resistance of the biomaterial to corrosion in the blood environment, thus affecting its hemocompatibility. To assess resistance of the AISI 316LVM steel with modified surface to corrosion, voltammetric and impedance measurements were conducted. The proposed variant of surface processing allows safe deformation of the TiO2 layer without its delamination.

Novel chitosan/diclofenac coatings on medical grade stainless steel for hip replacement applications.

Corrosion resistance, biocompatibility, improved osteointegration, as well the prevention of inflammation and pain are the most desired characteristics of hip replacement implants. In this study we introduce a novel multi-layered coating on AISI 316LVM stainless steel that shows promise with regard to all mentioned characteristics. The coating is prepared from alternating layers of the biocompatible polysaccharide chitosan and the non-steroid anti-inflammatory drug (NSAID), diclofenac. Electrochemical methods were employed to characterize the corrosion behavior of coated and uncoated samples in physiological solution. It is shown that these coatings improve corrosion resistance. It was also found that these coatings release the incorporated drug in controlled, multi-mechanism manner. Adding additional layers on top of the as-prepared samples, has potential for further tailoring of the release profile and increasing the drug dose. Biocompatibility was proven on human-derived osteoblasts in several experiments. Only viable cells were found on the sample surface after incubation of the samples with the same cell line. This novel coating could prove important for prolongation of the application potential of steel-based hip replacements, which are these days often replaced by more expensive ceramic or other metal alloys.

Blasting and Passivation Treatments for ASTM F139 Stainless Steel for Biomedical Applications: Effects on Surface Roughness, Hardening, and Localized Corrosion

Due to the combination of good biofunctionality and biocompatibility at low cost, AISI 316 low carbon vacuum melting (LVM) stainless steel, as considered in ASTM F139 standard, is often the first choice for medical implants, particularly for use in orthopedic surgery. Proper surface finish must be provided to ensure adequate interactions of the alloy with human body tissues that in turn allows the material to deliver the desired performance. Preliminary studies performed in our laboratory on AISI 316LVM stainless steel surfaces modified by glass bead blasting (from industrial supplier) followed by different nitric acid passivation conditions disclosed the necessity to extend parameters of the surface treatments and to further consider roughness, pitting corrosion resistance, and surface and subsurface hardening measurements, all in one, as the most effective characterization strategy. This was the approach adopted in the present work. Roughness assessment was performed by means of amplitude parameters, functional parameters, and an estimator of the fractal dimension that characterizes surface topography. We clearly demonstrate that the blasting treatment should be carried out under controlled conditions in order to obtain similar surface and subsurface properties. Otherwise, a variation in one of the parameters could modify the surface properties, exerting a profound impact on its application as biomaterial. A passivation step is necessary to offset the detrimental effect of blasting on pitting corrosion resistance.

Long term and electrochemical corrosion investigation of cold worked AISI 316L and 316LVM stainless steels in simulated body fluid

AISI 316L and 316LVM stainless steels in annealed (solution quenched from 1050 °C) and rolled (10% and 20% cold work) conditions were assessed for their long term and electrochemical corrosion behavior in simulated body fluid (SBF) at 37 °C. The techniques used for the characterization of their corrosion resistance were the weight loss method, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. Scanning electron microscopy (SEM) was used to investigate the surface morphologies of the alloys after the polarization tests. Surface analysis of the films formed on the steels in SBF was carried out using X-ray photoelectron spectroscopy (XPS). The weight loss and corrosion rate decreased with increasing degree of cold working. The resistance of a passive film is directly related to the material's corrosion resistance and increases on cold working, indicating the formation of a larger protective oxide layer on the surface of cold worked samples. The corrosion current density (Icorr) decreased with increasing degree of cold working and, simultaneously, the corrosion potentials (Ecorr) became more positive. On observing the pit morphologies using SEM, shallower and smaller pits were associated with cold worked samples as compared to annealed samples. The XPS results indicated that the main elements in the passive oxide layer were Cr, Fe and Mo. The Cr-oxide (ox) : Cr-hydroxide (hy) ratio and the Fe-oxide (ox) : Fe-hydroxide (hy) ratio were observed to be higher for rolled materials than for annealed materials, indicating that the passive films on rolled materials are more protective and improve the corrosion resistance.