Understanding the effects of excimer laser treatment on corrosion behavior of biodegradable Mg-1Ca alloy in simulated body fluid

In this study,a KrF excimer laser was used to modify the biodegradable Mg-1Ca alloy and the time-evolution degradation behavior of the alloy before and after laser treatment was investigated in simulated body fluid(SBF)solution using immersion tests and electrochemical impedance spectroscopy(EIS).A 5μm melted layer with a homogeneous microstructure and an MgO film on the surface were achieved by laser radiation.Corrosion observations(hydrogen evolution,morphology and corrosion products)and EIS results revealed an improvement of corrosion resistance after laser treatment for 48 h.It was found a two-layer structure developed after 2 h immersion on both the untreated and laser-treated alloys,but the sequence of forming the two layers was opposite and greatly influenced by the laser-treated layer.The time-evolution corrosion processes on the untreated and laser-treated alloys were discussed,providing a better understanding of corrosion behavior of biodegradable Mg alloys modified by excimer laser.

Corrosion fatigue of the extruded Mg-Zn-Y-Nd alloy in simulated body fluid

Magnesium alloys were considered to be used as biodegradable implants due to their biocompatibility,biodegradability and nontoxicity.However,under the simultaneous action of corrosive environment and mechanical loading in human body,magnesium alloys are easy to be affected by corrosion fatigue and stress corrosion cracking.In this work,the fatigue behavior of the extruded Mg-Zn-Y-Nd alloy used for vascular stents was studied both in air and in simulated body fluid(SBF).It was revealed that the fatigue limit of as-extruded Mg-Zn-Y-Nd alloy in air is about 65 MPa at 10^7 cycles,while there is no limit in SBF and shows a linear relationship between the fatigue life and stress amplitudes.The fatigue crack source in air was formed by the inclusions and defects.However,the stress corrosion and hydrogen embrittlement are the main reasons for the formation of the fatigue initial crack source in SBF.

Evaluation of Bioactive Properties of α and β Wollastonite Bioceramics Soaked in a Simulated Body Fluid

Dense natural wollastonite bioceramics (CaSiO3) were prepared by a sintering method, varying the pressing load and sintering temperature, in order to obtain different phases of wollastonite, and different physical properties in the materials. The products were characterized by TGA-DTA, XRD, FT-IR, SEM-EDS, TEM and XPS techniques. The results indicate the presence of two polymorphic phases of wollastonite, the β-wollastonite and α-wollastonite with a transition temperature of the β phase to α phase at approximately 1250℃. These materials were soaked in a simulated body fluid (SBF) during 1, 2 and 3 weeks, to study their solubility and bioactivity. The effect of different wollastonite phases on the solubility of Ca and Si, as well as the capacity of producing layers of “newly formed apatite” on the surfaces of these materials in SBF solution were analyzed.

Reflections on the Mechanism of Calcium Phosphate Nucleation on Titanium in Simulated Body Fluids

The results and main findings of studies reported in the literature in relation to the deposition of calcium phosphate on Ti in simulated body fluids are summarized. The effects of the surface hydroxyl groups and the sign of surface charge on the nucleation of calcium phosphate are reviewed. One major controversy among the conclusions of different studies is the order of adsorption of the calcium ions and the phosphate ions in the initial stage of immersion. A simple model based on the amphoteric nature of the hydroxyl groups on Ti is proposed in an attempt to delineate the nucleation process for calcium phosphate on Ti in simulated body fluids. HPO4^2- ions interact with the hydroxyl groups via ion exchange and/or electrostatic attraction, and Ca^2＋ ions, via electrostatic attraction only. There is no preferential order of adsorption. Seemingly inconsistent results in different studies possibly arise from different prior treatments of the samples, which affect the adsorption properties.

Formation of Apatite in Simulated Body Fluid

It is confirmed that the essential condition for glasses and glass-ceramics to bond to living bone is the formation of an apatite layer on their surfaces in the body.It is proposed that a hydrated silica formed on the surfaces of these materials in the body plays an important role in forming the surface apatite layer,which has not been proved yet.It is shown experimentally that a pure hydrated silica gel can induce the apatite formation on its surface in a simulated body fluid when its starting pH is increased from 7.2 to 7.4.

Wear Behavior of Plasma Oxidized CoCrMo Alloy under Dry and Simulated Body Fluid Conditions

In this study, CoCrMo alloy was oxidized in plasma environment at the temperatures of 600 ℃ to 800 ℃ for 1 h to 5 h with 100% 02 gas and its tribological behavior was investigated. After the plasma oxidizing process, the compound and diffusion layers were formed on the surface. XRD results show that Cr203, a-Co and ε-Co phases diffracted from the modified layers after plasma oxidizing. The untreated and treated CoCrMo samples were subjected to wear tests both in dry and simulated body fluid conditions, and normal loads of 2 N and 10 N were used. For the sliding wear test, alumina balls were used as counter materials. It was observed that the wear resistance of CoCrMo alloy was increased after the plasma oxidizing process. The lowest wear rate was obtained from the samples that were oxidized at 800 ℃ for 5 h. It was detected that both wear environment and load have significant effects on the wear behavior of this alloy, and the wear resistance of oxidized CoCrMo alloy is higher when oxide-based counterface is used. The wear rates of both untreated and plasma oxidized samples increase under high loads.

Initial formation of corrosion products on pure zinc in simulated body fluid

Zinc was recently suggested to be a potential candidate material for degradable coronary artery stent.The corrosion behavior of pure zinc exposed to r-SBF up to 336 h was investigated by electrochemical measurements and immersion tests. The morphology and chemical composites of the corrosion products were investigated by scanning electron microscope, grazing-incidence X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectrometer. The results demonstrate that the initial corrosion products on the pure zinc mainly consist of zinc oxide/hydroxide and zinc/calcium phosphate compounds. The pure Zn encounters uniform corrosion with an estimated corrosion rate of 0.02-0.07 mmy;during the immersion, which suggests the suitability of pure Zn for biomedical applications.

Effect of corrosion on mechanical behaviors of Mg-Zn-Zr alloy in simulated body fluid

The main purpose of this paper is to investigate the effect of corrosion on mechanical behaviors of the Mg-Zn-Zr alloy immersed in simulated body fluid （SBF） with different immersion times. The corrosion behavior of the materials in SBF was determined by immersion tests. The surfaces of the corroded alloys were examined by SEM. The tensile samples of the extruded Mg-2Zn-0.8Zr magnesium alloy were immersed in the SBF for 0, 4, 7, 10, 14, 21 and 28 d. The tensile mechanical behaviors of test samples were performed on an electronic tensile testing machine. SEM was used to observe the fracture morphology. It was found that with extension of the immersion time, the ultimate tensile strength （UTS）, yield strength （YS） and elongation （EL） of the Mg-2Zn-0.8Zr samples decreased rapidly at first and then decreased slowly. The main fracture mechanism of the alloy transformed from ductile fracture to cleavage fracture with the increasing immersion times, which can be attributed to stress concentration and embrittlement caused by pit corrosion.

Corrosion Behavior ofAg-doped TiO2 Coatings on Commercially Pure Tita- nium in Simulated Body Fluid Solution

TiO2 films including different amounts of Ag obtained by sol-gel method on commercially pure titanium （CP-Ti） and the corrosion properties of Ag-doped TiO2 films were investigated by potentiodynamic polarisation and Electrochemical ImpedanceSpectroscopy （EIS） tests in Simulated Body Fluid （SBF） solution. The results were compared with untreated and un-doped samples. Surface characterizations before and after the corrosion tests were performed by the Scanning Electron Microscopy （SEM） and X-ray Diffraction （XRD） analysis. It was observed that Ag-doping for TiO2 films improved the corrosion resistance when compared with untreated and un-doped TiO2 film coated samples. The highest corrosion resistance was obtained from Ag-doped samples coated with a solution of 0.05 M Ag.

Fatigue Behaviors of a Ni-free ZrCuFeAlAg Bulk Metallic Glass in Simulated Body Fluid

Fatigue behaviors of a biocompatible Ni-free Zr60.14Cu22.31Fe4.85Al9.7Ag3 Zr-based bulk metallic glass （BMG） have been studied under three-point-bending test in a simulated body fluid （SBF） at 37 ℃ and compared with those in air at room temperature （RT）. The BMG shows a high fatigue limit of approximately 366 MPa in SBF, which was slightly lower than that in air （400 MPa）. The fatigue cracks tended to initiate from the defects such as cast-pores, inclusions and corners of the samples and propagate in a similar path in SBF and in air. Three distinct regions, i.e. a crack-initiation region, a stable crack-growth region and an unstable fast-fracture region were clearly observed on the fatigue-fractured surface. Although pitting occurred at the defects where crack initiated, it does not affect significantly the fatigue life of the BMG, because the lifetime in the present BMG is mainly determined by crack propagation. The high corrosion-fatigue limit of the studied BMG results from its excellent corrosion resistance in SBF and intrinsically good toughness.

Effects of different simulated fluids on anticorrosion biometallic materials

The corrosion behaviors of SUS316L stainless steel, Co Cr alloy and Ti 6Al 4V alloy in Ringer’s, PBS(-) and Hank’s solutions have been investigated. The results indicate that the corrosion of Ringer’s solution is the strongest, then followed by PBS(-) and Hank’s solution. The presence of HPO 2- 4, H 2PO - 4, SO 2- 4 and glucose in the PBS(-)and Hank’s solution probably reduces the corrosion inhibitor and corrosion current. The decrease of the solution’s pH significantly increases the corrosion rate and susceptibility to localized corrosion of SUS316L SS and Co Cr alloy. However, Ti 6Al 4V alloy exhibits an exceptional stability and has only a slight increase of corrosion rate with decreasing pH.

Super-hydrophobic stearic acid layer formed on anodized high purified magnesium for improving corrosion resistance of bioabsorbable implants

Magnesium and its alloys are ideal candidates for bioabsorbable implants.However,they can dissolve too rapidly in the human body for most applications.In this research,high purified magnesium(HP-Mg)was coated with stearic acid(SA)to slow the corrosion rate of magnesium in simulated body fluid at 37±1°C.HP-Mg was anodized(AC and DC voltages)to form an oxide/hydroxide layer,and then it was immersed in a SA solution.The SA coated layer surface,anodized layer,and the thickness of the oxide/hydroxide layer were investigated with Scanning Electron Microscopy(SEM).Electrochemical impedance spectroscopy(EIS)and potentiodynamic polarization(PDP)were used to estimate the corrosion rate of HP-Mg specimens.The results confirm that the hydrophobic coating can decrease the corrosion rate of HP-Mg by more than 1000x.The protectiveness of coated layer for anodized specimens with AC voltage continue for 2 and 3 weeks.For the HP-Mg coated anodized with DC voltage,the coated layer could improve the corrosion resistance for only a few days.

Physical and degradation properties of PLGA scaffolds fabricated by salt fusion technique

Tissue engineering scaffolds require a controlled pore size and interconnected pore structures to support the host tissue growth. In the present study, three dimensional （3D） hybrid scaffolds of poly lactic acid （PLA） and poly glycolic acid （PGA） were fabricated using solvent casting/particulate leaching. In this case, partially fused NaCl particles were used as porogen （200-300μ） to improve the overall porosity （≥90%） and internal texture of scaffolds. Differential scanning calorimeter （DSC） analysis of these porous scaffolds revealed a gradual reduction in glass transition temperature （Tg） （from 48°C to 42.5°C） with increase in hydrophilic PGA content. The potential applications of these scaffolds as implants were further tested for their biocompatibility and biodegradability in four simulated body fluid （SBF） types in vitro. Whereas, simulated body fluid （SBF） Type1 with the optimal amount of HCO 3 ions was found to be more appropriate and sensible for testing the bioactivity of scaffolds. Among three combinations of polymer scaffolds, sample B with a ratio of 75：25 of PLA： PGA showed greater stability in body fluids （pH 7.2） with an optimum degradation rate （9% to 12% approx）. X-ray diffractogram also confirmed a thin layer of hydroxyapatite deposition over sample B with all SBF types in vitro.

Development and assessment of a multifunctional chitosan-based coating applied on AZ31 magnesium alloy: Corrosion resistance and antibacterial performance against Klebsiella Pneumoniae

This work presents a simple method to functionalise the surface of AZ31 magnesium alloy by applying a duplex MgF_(2)/chitosan coating,which improves its corrosion resistance and provides it with some antibacterial performance.First,the effect of three chitosan solutions with different concentrations on the growth of the bacteria Klebsiella pneumoniae in nutritive medium(TSB)was evaluated by absorbance kinetics experiments,where the chitosan solution at 2%(m/V)was selected for the coating preparation.Before coating application,the AZ31 substrate was pretreated with hydrofluoric acid for 48 hours in order to form a MgF_(2)conversion layer.Subsequently,the coating was applied to the pretreated substrate through the dry-casting method.Samples of the alloy in each surface condition(bare,pretreated,and pretreated+coated with chitosan)were exposed to simulated body fluid(SBF)for 21 days at 37°C,with the solution renewed every 24 hours and the wastes stored.The surfaces were characterised by SEM-EDS,and XPS after the immersion tests,whereas the stored solutions were employed to measure the change in the Mg-ions concentration.Electrochemical impedance spectroscopy and potentiodynamic polarisation were performed in each surface condition to compare their corrosion resistance in SBF.The antibacterial activity of the functionalised surfaces was evaluated by the plate counting method and compared with bare samples.All results were correlated and demonstrate that the modified surface of AZ31 achieved a higher corrosion resistance when it was exposed to SBF,as well as a reduction of the bacterial growth during in vitro tests.

Gallium-containing magnesium alloy for potential use as temporary implants in osteosynthesis

In recent years magnesium alloys have been studied intensively with a view to their potential use in bioresorbable medical implants.In the present work the microstructure and the corrosion properties of a new bioresorbable Mg-4 wt%Ga-4 wt%Zn alloy and its variants with low Ca,Nd or Y additions were investigated.These alloys are of interest due to the efficacy of gallium as an element inhibiting bone resorption,osteoporosis,Paget's disease,and other illnesses.A severe plastic deformation technique of equal channel angular pressing(ECAP)was shown to provide the alloys with favorable mechanical properties.In addition,a desirable low rate of degradation in a simulated body fluid(Hanks'solution)was achieved.

Sol-gel Derived TiO_2-Bioactive glass-Hydroxyapatite Bioactive Coating on Titanium Alloy Substrate

Coating the hydroxyapatite （HA） on the titanium alloy surface can obtain a bioactive implant with high mechanical properties However, the bonding force between the titanium alloy and the HA was low due to their different coefficient of thermal expansion （CET）. Preparing the multi-layer coating with alleviated thermal stress on titanium alloy substrate is few reported. Fabrication of a TiO2-bioactive glass （BG）-HA bioactive coating was proposed to solve this problem. A particular TiO2 surface was prepared on the titanium alloy substrate by micro-arc oxidation treatment. The BG and HA coating were coated onto the TiO2 surface in turn by using a sol-gel method. The microstructure, surface morphology and phase composition of the coatings were analyzed. The bonding force of coatings was investigated by the nick apparatus. In vitro dissolution was performed by soaking the TiO2-BG-HA coated samples into the simulated body fluid for various periods. Micro-structural observations indicated that no delamination and crack occurred at the interface of HA/BG and BG/TiO2. The bonding between the substrate and coating consists of the mechanical interaction and the chemical bonding. The bonding force could reach about 45 N. The TiO2-BG-HA coating displayed the excellent forming ability of bone-like apatite when it was soaked into the simulated body fluid. This work suggests an innovative way to reduce the internal stress among coatings through varying BG composition to adjust its CTE, so as to enhance the bonding force.

Controlled Deposition of HAp Mimicking Tooth Enamel

Chemical compositions and mierosturcture of mature human tooth enamel were investigated by XRD , FTIR and SEM to further understand the characteristics of tooth enamel. In order to obtain apatite crystals chemically and structurally similar to those in tooth enamel, biomimetic way was employed. Self-assembled monolyers terminated with-SO3 H groups were used as deposition substrates and 1.5 SBF （ the concentrations of Ca^2＋ and PO4^3- ions 1.5 times ttum those in simulated body fluid ） with and without 5 ppm F^- were used as soaking medium. The XRD and FTIR results showed that both the deposited fluoride-substituted hydroxyapatite （ F-HAp ） crystals in 1.5 SBF with F^- and hydroxyapatite （ HAp ） crystals in 1.5 SBF were carbonate-contain ing, mimicking human tooth enamel in chemical compositions. The SEM photos showed that needle-like F-HAp crystals had large aspect ratios and grew in bundles, which were similar to the crystals in human tooth enomel. The results provide available information on dental restoration.

Effects of geosorbent and solution properties on sorption and desorption of PAHs

Characteristics of phenanthrene and pyrene’s sorption and desorption on two local soils in solutions of simulated groundwater,simulated lung fluid,and simulated saliva were studied with batch equilibrium experiments to understand the fate of PAHs in the karst region of southwestern China and to assess the environmental exposure and the health risk of PAHs.The results showed that the sorption and desorption isotherms of phenanthrene and pyrene on two target soils in the three solution systems could be adequately described by the Freundlich model,while the fitted isotherm parameters for the simulated groundwater solution distinguished notably from those for the simulated body fluid solutions.For the sorption experiments,in the simulated groundwater,the n values were 0.722 and 0.672 for phenanthrene and were 0.724 and0.663 for pyrene,respectively,on the yellow soil and the limestone soil;The log KF values were 3.118 and 3.323 for phenanthrene and were 3.648 and 3.846 for pyrene,respectively,on the yellow soil and the limestone soil.In the simulated body fluids,the n values for phenanthrene and pyrene ranged from 0.622 to 0.836 and from 0.590 to0.865,respectively,and the log KF values of phenanthrene and pyrene ranged from 2.845 to 3.327 and from 3.344 to3.779,respectively.For the desorption experiments,in the simulated groundwater,the n values were 0.662 and 0.744 for phenanthrene and were 0.702 and 0.647 for pyrene,respectively,on the yellow soil and the limestone soil.The log KF values were 3.666 and 3.686 for phenanthrene and were 4.128 and 4.225 for pyrene,respectively,on the yellow soil and the limestone soil.In the simulated body fluids,the n values for phenanthrene and pyrene ranged from 0.612 to 0.668 and from 0.631 to 0.819,respectively,and the log KF values of phenanthrene and pyrene ranged from 3.134 to 3.407 and from 3.533 to 3.839,respectively.The limestone soil had relatively higher log KF values but lower KOC values compared to those of the yellow soil,indicated that the nature of sorbent soils played the dominant role in sorption and desorption behaviors of PAHs.The experimental results showed a remarkable differences in sorption and desorption behaviors of PAHs in simulated body fluids and groundwater.The nonlinearities of measured isotherms and the measured sorption capacities of soils in simulated body fluids were significantly lower than corresponding those in the simulated groundwater,and HI values for simulated body fluids systems were significantly smaller than corresponding those for the simulated groundwater systems.The results underscore cautions in assessing environmental exposure and health risks of PAHs based on their sorption-desorption data in simulated groundwater as this is traditionally done.

Bone-inducing Activity of Biological Piezoelectric Ceramic

To simulate the piezoelectric effect of nature bone, two kinds of biological piezoelectric composite ceramics consisted of hydroxyapatite （ HA ） and lithium sodium potassium niobate （LNK） ceramic of which the ratio of HA/LNK was 1 ： 10 and 5 ： 5（ wt/ wt ） were prepared. Their piezoelectric property and growth of apatite crystal in the ceramics surface were investigated. With the increase of LNK amount, piezoelectric activity increased correspondingly. By immersing the poled piezoelectric ceramics in simulated body fluid （SBF） at 36.5 ℃ for 7, 14, and 21 days, apatite crystal was formed on negatively charged surfaces. After 21 days immersion in SBF, the thickest apatite crystal on the negatively charged surfaces increased to 3. 337 μn. The hotel biological piezoelectric ceramics show an excellent piezoelectric property and superior potential bioactivity.

The Effect of Material Surface Microstructure on the Enhancement of Bone-Bonding Ability of a Hydroxyapatite-Implant by Low-Intensity Pulsed Ultrasound (LIPUS)

Excellent firm bonding between the biomaterials and bone tissue (osseointegration and osteo-conductivity) has been desired for the stability in vivo of dental implants and artificial joints. Much has been learned about this concept, which has led to significant improvements in the design and surface modification of implants in the field of implant dentistry, orthopedic surgery. We have already reported that low-intensity pulsed ultrasound (LIPUS) irradiation can accelerate the bone bonding ability of the bio-conductive materials such as bioactive titanium and hydroxyapatite implant. However, it is still unclear whether the LIPUS could have same effect to different types of the bioactive-materials. Therefore, in this study, the differences of bone-like hydroxyapatite formation on some kind of hydroxyapatite surface in simulated body fluid (SBF) under the LIPUS irradiation were investigated. Two kinds of hydroxyapatite samples immersed in SBF was exposed to ultrasound waves, the bone-like apatite on the surface was analyzed by Scanning electron microscopy and X-ray diffraction. As a result, the enhancement of hydroxyapatite formation on the surface by LIPUS was confirmed, the initial epitaxial nucleation and crystal growth of apatite depended on crystal structure of the surface of matrix materials.