Is Cell Viability Always Directly Related to Corrosion Resistance of Stainless Steels?

It has been frequently reported that cell viability on stainless steels is improved by increasing their corrosion resistance. The question that arises is whether human cell viability is always directly related to corrosion resistance in these biostable alloys. In this work, the microstructure and in vitro corrosion behavior of a new class of medical-grade stainless steels were correlated with adult human mesenchymal stem cell viability. The samples were produced by a powder metallurgy route, consisting of mechanical alloying and liquid-phase sintering with a sintering aid of a eutectic Mn–Si alloy at 1050 °C for 30 and 60 min, leading to nanostructures. In accordance with transmission electron microscopic studies, the additive particles for the sintering time of 30 min were not completely melted. Electrochemical impedance spectroscopic experiments suggested the higher corrosion resistance for the sample sintered for 60 min; however, a better cell viability on the surface of the less corrosion-resistant sample was unexpectedly found. This behavior is explained by considering the higher ion release rate of the Mn–Si additive material, as preferred sites to corrosion attack based on scanning electron microscopic observations, which is advantageous to the cells in vitro. In conclusion, cell viability is not always directly related to corrosion resistance in stainless steels. Typically, the introduction of biodegradable and biocompatible phases to biostable alloys, which are conventionally anticipated to be corrosion-resistant, can be advantageous to human cell responses similar to biodegradable metals

Mechanical Properties of Natural Chitosan/Hydroxyapatite/Magnetite Nanocomposites for Tissue Engineering Applications

Chitosan (CS), hydroxyapatite (HA), and magnetite (Fe3O4) have been broadly employed for bone treatment applications. Having a hybrid biomaterial composed of the aforementioned constituents not only accumulates the useful characteristics of each component, but also provides outstanding composite properties. In the present research, mechanical properties of pure CS, CS/HA, CS/HA/magnetite, and CS/magnetite were evaluated by the measurements of bending strength, elastic modulus, compressive strength and hardness values. Moreover, the morphology of the bending fracture surfaces were characterized using a scanning electron microscope (SEM) and an image analyzer. Studies were also conducted to examine the biological response of the human Mesenchymal Stem Cells (hMSCs) on different composites. We conclude that, although all of these composites possess in-vitro biocompatibility, adding hydroxyapatite and magnetite to the chitosan matrix can noticeably enhance the mechanical properties of the pure chitosan

Neurobehavioural Toxicity of Bisphenol S in zebrafish (Danio rerio)

Elevated levels of contaminants from anthropogenic activities are a pernicious problem in various ecosystems. The presence of bisphenol analogues and especially bisphenol S (BPS) in the aquatic environment has been a growing issue of concern over the past few years. BPS concentrations in surface water range from <1- 65600 ng/L. Although these concentrations are much lower than the levels of BPS that cause acute toxicity, the sub-lethal effects of this exogenous compound under chronic exposure remain largely unknown. My thesis addressed this knowledge gap by evaluating how chronic exposure to three different field-relevant concentrations of BPS impact non-reproductive behaviours in zebrafish (Danio rerio). Furthermore, I investigated the possible molecular mechanisms underlying the intragenerational and transgenerational neurobehavioural effects of BPS. To this end, adult male and female zebrafish were exposed to either 1, 10, 30 µg/L BPS or 1 µg/L E2 as a positive control for 75 days. Subsequently, shoal cohesion, excursion from the shoals, group preferences, locomotor activity, anxiety and fear responses were assessed. The results suggest that environmentally relevant concentrations of BPS significantly reduced zebrafish sociality, anxiety and dysregulate the fear responses in adult male and female zebrafish. In the first data chapter, I found that exposure of adult zebrafish to all concentrations of BPS or E2 caused a marked decline in male and female group preference. Meanwhile, locomotor responses and the number of excursions from shoals did not change, and shoal cohesion was only decreased at the highest concentrations of BPS (30 µg/L) and E2. Similarly, in the second data chapter, I documented that 30 µg/L BPS and E2 induced a significant decrease in fear-related responses. At the same time, BPS, irrespective of exposure concentrations, and E2 significantly decreased bottom-dwelling behaviour in both male and female fish. The impaired behavioural responses were associated with a sex-specific dysregulation in the transcription of the neuropeptide signalling system, including isotocinergic and vasotocinergic neuro-endocrine systems, as well as a down-regulation in the transcription of enzymatic antioxidant genes (gpx1a, Cu/Zn-sod, Mn-sod, cat) in the brain of male and female adult zebrafish. In my final experiment, I exposed female zebrafish to various concentrations of BPS and E2 and afterwards bred them with untreated male zebrafish so as to investigate the transgenerational maternal effects of BPS on social behaviours and anxiety responses in offspring. Chronic maternal exposure to BPS (60 days) resulted in alteration in social behaviours and anxiety responses of male offspring in a dose-specific manner likely through oxidative stress and changes in the neuropeptide signalling system. These novel findings expand our current knowledge of the transgenerational effects of BPS, which has been quite limited to date. In summary, this thesis has made significant contributions to identifying the neurobehavioural consequences of chronic exposure to environmentally relevant BPS levels in fish

Drug-delivery Ca-Mg Silicate Scaffolds Encapsulated in PLGA

The aim of this work is to develop dual-functional scaffolds for bone tissue regeneration and local antibiotic delivery applications. In this respect, bioresorbable bredigite (Ca7MgSi4O16) porous scaffolds were fabricated by a foam replica method, loaded with vancomycin hydrochloride and encapsulated in poly lactic-co-glycolic acid (PLGA) coatings. Field emission scanning electron microscopy, Archimedes porosimetry and Fourier-transform infrared spectroscopy were used to characterize the structure of the scaffolds. The drug delivery kinetics and cytocompatibility of the prepared scaffolds were also studied in vitro. The bare sample exhibited a burst release of vancomycin and low biocompatibility with respect to dental pulp stem cells based on the MTT assay due to the fast bioresorption of bredigite. While keeping the desirable characteristics of pores for tissue engineering, the biodegradable PLGA coatings modified the drug release kinetics, buffered physiological pH and hence improved the cell viability of the vancomycin-loaded scaffolds considerably

Structure, Wettability, Corrosion and Biocompatibility of Nitinol Treated by Alkaline Hydrothermal and Hydrophobic Functionalization for Cardiovascular Applications

The main objective of this study is to hydrophobize nitinol (Ni-Ti alloy) for cardiovascular applications. For this purpose, medical nitinol samples were subjected to sodium hydroxide hydrothermal treatments at various temperatures, followed by hexadecyltrimethoxysilane (HDTMS) functionalization. Then, the structure, wettability, corrosion, cytocompatibility and cell adhesion of the prepared samples were evaluated. According to the results, porous blade-shaped layers of sodium titanate were formed on the substrate surface as a result of the alkaline treatment. These nano-rough features offered considerable hydrophobicity after HDTMS processing, where a maximum water contact angle of about 140° was obtained for the sample treated at 120 °C, followed by the HDTMS coating. In contrast to the individual application of the alkaline treatments, the subsequent HDTMS processing improved corrosion resistance in the simulated body fluid. Although all the samples presented appropriate cytocompatibility with respect to human umbilical vein endothelial cells, the cells did not show an adhesion tendency to the hydrophobic surfaces. It is concluded that alkaline hydrothermal and HDTMS processed nitinol can be considered for cardiovascular applications demanding hydrophobic surfaces

Fabrication of Nanostructured Medical-Grade Stainless Steel by Mechanical Alloying and Subsequent Liquid-Phase Sintering

Cataloged from PDF version of article.This article focuses on the microstructure of medical-grade P558 (ASTM F2581) stainless steel produced by mechanical alloying and liquid-phase sintering. Rietveld X-ray diffraction and transmission electron microscopy reflect that the mechanically alloyed stainless steel powder is a nanocrystal dispersed amorphous matrix composite.Mn-11.5 wt pct Si eutectic alloy as additive improves densification of the synthesized P558 alloy via liquid-phase sintering mechanism. X-ray mapping shows that after sintering at 1323 K (105°C) for 1 hour, a uniform distribution of dissolved Mn and Si is achieved. Moreover, the development of a nanostructured, fully austenitic stainless steel after sintering at the same temperature is realized by X-ray diffraction and transmission electron microscopy. © The Minerals, Metals & Materials Society and ASM International 201

Liquid-phase sintering of medical-grade P558 stainless steel using a new biocompatible eutectic additive

Cataloged from PDF version of article.One of the effective approaches to reduce residual pores in powder metallurgy parts is activated liquidphase sintering process using proper additives. In this work, for the first time, a new biocompatible additive (Mn–11.5 wt.% Si, a eutectic alloy) is experimented for liquid-phase sintering of nanocrystalline/amorphous P558 stainless steel powders. It is realized that by increasing the sintering aid content and temperature, the density is effectively increased: a sharp densification progress when the sintering temperature increases from 1000 °C to 1050 °C and a slower densification rate when it exceeds 1050 °C. This preliminary study opens up the development of high-density medical-grade stainless steels produced by powder metallurgy, where suitable additives can lower sintering temperature and time, which is promising for retarding grain growth and commercial applications. © 2012 Elsevier B.V. All rights reserve

Compositional homogeneity in a medical-grade stainless steel sintered with a Mn-Si additive

Cataloged from PDF version of article.In this paper, chemical composition uniformity in amorphous/nanocrystallization medical-grade stainless steel (ASTM ID: F2581) sintered with a Mn–Si additive was studied via scanning electron microscopy, energy dispersive X-ray spectroscopy, and transmission electron microscopy. The results show that as a result of sintering at 1000 °C, no dissociation of Mn–Si additive particles embedded in the stainless steel matrix occurs. In contrast, sintering at 1050 °C develops a relatively homogeneous microstructure from the chemical composition viewpoint. The aforementioned phenomena are explained by liquation of the Mn–Si eutectic additive, thereby wetting of the main powder particles, penetrating into the particle contacts and pore zones via capillary forces, and providing a path of high diffusivity. © 2012 Elsevier B.V. All rights reserved

Microstructural characterization of medical-grade stainless steel powders prepared by mechanical alloying and subsequent annealing

Cataloged from PDF version of article.The harmful effect of nickel ions released from conventional stainless steel implants has provided a high level of motivation for the further development of nickel-free stainless steels. In this paper, the microstructure of medical-grade nickel-free stainless steel powders, with the chemical composition of ASTM F2581, is studied during mechanical alloying and subsequent annealing. Rietveld X-ray diffraction and transmission electron microscopy evaluations reflect nanocrystallization, austenitization and amorphization of the powders due to mechanical activation. It is also realized that annealing of the as-milled powder can develop a single austenitic structure with nanometric crystallite sizes, implying a considerable inherent resistance to grain growth. This study demonstrates the merit of mechanical alloying and subsequent annealing in the development of nanostructured medical-grade stainless steels. (C) 2012 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserve

Bioperformance of chitosan/fluoride-doped diopside nanocomposite coatings deposited on medical stainless steel

This work focuses on the structure, bioactivity, corrosion, and biocompatibility characteristics of chitosan-matrix composites reinforced with various amounts of fluoride-doped diopside nanoparticles (at 20, 40, 60, and 80 wt%) deposited on stainless steel 316 L. Bioactivity studies reveal that the presence of the nanoparticles in the coatings induces apatite-forming ability to the surfaces. Based on electrochemical impedance spectroscopy and polarization experiments, the in vitro corrosion resistance of the substrate was enhanced by increasing the level of the nanoparticles in the coating. The sample containing 60% of the nanoparticles presented the highest osteoblast-like MG63 cell viability, in comparison to the other prepared and even control samples. Also, the cell attachment on the surfaces was improved with increasing the amount of the nanoparticles in the coatings. It is eventually concluded that the application of chitosan/fluoride-doped diopside nanocomposite coatings improves the bioperformance of metallic implants