Degradation Rate Of Magnesium Alloy Research Articles

Fabrication and corrosion behavior of TiO2 nanotubes on AZ91D magnesium alloy

Abstract The major drawback of magnesium alloys in biomedical applications is the rapid degradation rate and the lack of biological activity. In this study, TiO2 nanotubes were fabricated on the surface of AZ91D magnesium alloy (TiO2-Mg) to overcome such limitations. The corrosion behavior of TiO2-Mg nanotubes was studied in simulated body fluid solution using open circuit potentials (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests. The high polarization resistance and open circuit potentials of TiO2-Mg nanotubes indicate the formation of highly stable TiO2 layer in simulated body fluid than that of titanium layer on magnesium alloy (Ti-Mg). TiO2 nanotubes on AZ91D magnesium alloy (AZ91D) can effectively decrease the degradation rate of magnesium alloy, thus can be further applied in orthopedic implants.

Do biodegradable magnesium alloy intramedullary interlocking nails prematurely lose fixation stability in the treatment of tibial fracture? A numerical simulation

Intramedullary interlocking nailing is an effective technique used to treat long bone fractures. Recently, biodegradable metals have drawn increased attention as an intramedullary interlocking nailing material. In this study, numerical simulations were implemented to determine whether the degradation rate of magnesium alloy makes it a suitable material for manufacturing biodegradable intramedullary interlocking nails. Mechano-regulatory and bone-remodeling models were used to simulate the fracture healing process, and a surface corrosion model was used to simulate intramedullary rod degradation. The results showed that magnesium alloy intramedullary rods exhibited a satisfactory degradation rate; the fracture healed and callus enhancement was observed before complete dissolution of the intramedullary rod. Delayed magnesium degradation (using surface coating techniques) did not confer a significant advantage over the non-delayed degradation process; immediate degradation also achieved satisfactory healing outcomes. However, delayed degradation had no negative effect on callus enhancement, as it did not cause signs of stress shielding. To avoid risks of individual differences such as delayed union, delayed degradation is recommended. Although the magnesium intramedullary rod did not demonstrate rapid degradation, its ability to provide high fixation stiffness to achieve earlier load bearing was inferior to that of the conventional titanium alloy and stainless steel rods. Therefore, light physiological loads should be ensured during the early stages of healing to achieve bony healing; otherwise, with increased loading and degraded intramedullary rods, the fracture may ultimately fail to heal.

In vitro and in vivo degradation and mechanical properties of ZEK100 magnesium alloy coated with alginate, chitosan and mechano-growth factor

The biocompatibility, ultimate loading capacity and biodegradability of magnesium alloy make it an ideal candidate in biomedical fields. Fabrications of multilayered coatings carrying sodium alginate (ALG), chitosan (CHI) and mechano-growth factor (MGF) on fluoride-pretreated ZEK100 magnesium alloy have been obtained via layer by layer (LBL) to reduce the degradation rate of magnesium alloy in this study. The modified surfaces of ZEK100 substrates were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) and CARE EUT-1020 tester. Results reveal that multilayer-coated magnesium alloy can be successfully obtained with smooth surface morphology, and the mechanical properties of coated samples are almost the same as those of uncoated samples. However, the fatigue life of coated ZEK100 is slightly larger than that of uncoated samples after 1day of immersion. By comparing the degradation of uncoated and multilayer-coated ZEK100 samples in vitro and in vivo, respectively, it is found that the degradation rate of ZEK100 samples can be inhibited by LBL modification on the surface of the sample; and the corrosion rate in vivo is lower than that in vitro, which help solve the rapid degradation problem of magnesium alloy. In terms of the visible symptom of tissues in the left femur medullary cavity and material responses on the surface, multilayer-coated ZEK100 magnesium alloy has a good biocompatibility. These results indicate that multilayer-coated ZEK100 may be a promising material for bone tissue repair.

A Study of Anticorrosion Coatings for Surface Modification of Biodegradable Magnesium Alloy

Magnesium alloys material would dissolve easily in body fluid which contains chloride ion, and the corrosion products are necessary to the human body. Due to the suitable mechanical property, biocompatibility and biodegradability, magnesium alloys are promising in the development of bio-absorbable orthopedic implants for interventional therapy and bone tissue engineering. However, a rapid corrosion rate resulted form the intrinsically active response of magnesium alloys to chloride-containing blood plasma and human body fluid remains the problem. Subsequently, a better understanding of the interaction between magnesium alloys and human body environment is the prerequisite to lower the corrosion rate. The surface modification technique could change the surface composition and the degradation rate of magnesium alloys. In this study, Diamond-like carbon films (DLC) are deposited on AZ31 magnesium alloy by combining plasma enhanced unbalance magnetron sputtering physical vapor deposition (PEUMS-PVD) and microwave electron cyclotron resonance plasma enhanced chemical vapor deposition (MW-ECR PECVD) techniques. In these techniques, the SiC interlayer is introduced between metallic substrates and DLC films by using methane (CH4) and silicon target in order to increase the coating’s adherence. The corrosion behavior of the DLC films in simulated body fluid and biocompatibility have been measured and evaluated synthetically by the surface analysis technique, electrochemical measurement and hemocompatibility experiments.The present study demonstrated that DLC films were successfully formed by PECVD on Mg alloy substrate. Both films are composed of graphite that had a disorderedgraphite-like structure. Silicon component of Si/SiC intermediate layers suppresses the formation of sp2 graphitic clusters and increases the sp3 bonding and the hydrogen content in the DLC films. Based on these observations, it might be concludedthat DLC films on the Mg alloy substrate leads to a moderate increase in degradation resistance. As a hard DLC film was formed on the Mg alloy substrate, further study is worthwhile to check biocompatibility of these coatings and improve the quality of the film.

Corrosion Performance of Nitrided Based Coating on AZ9I Mg Alloy in Hank’s Solution

The use of Magnesium alloys as bioresorsable metallic implant is interesting to study due to the properties of magnesium ions which can be found naturally in bone tissue as well as are essential to human metabolism. However, its fast degradation rate and excess of these ions in the body may cause undesirable health effects. Therefore, surface treatment such as coating can offer an alternative solution to slow down the fast degradation rate of magnesium alloy. Thus, in this study, attempt has been made to coat the AZ91 magnesium alloy substrate with TiN, AlN and TiAlBN coatings using single hot press target with r.f. magnetron sputtering technique. During deposition, target power, working pressure and bias voltage were optimized for each coating deposition. Coating microstructure and its crystal phases are analysed using SEM and glancing angle X-ray diffraction analysis (GAXRD). Corrosion properties were evaluated using potentiodynamic polarization using Hank’s Solution as a medium to simulate body fluid. Result showed that TiAlBN coating is acting most successfully as a protection layer by slowing down the penetration of corrosion towards AZ91 Mg alloy substrate. SEM micrographs show a minimum damage to the substrate’s surface seen after subjected to corrosion test. In conclusion, TiAlBN coating is able to protect AZ91 Mg alloy substrate surface from corrosion and able to slow down their degradation rate. The better performance of TiAlBN coating create interest to further works on exploring the potential of this hard coated on AZ91 Mg alloy for biomaterial application.

Rapid coating of AZ31 magnesium alloy with calcium deficient hydroxyapatite using microwave energy.

Due to their unique biodegradability, magnesium alloys have been recognized as suitable metallic implant materials for degradable bone implants and bioresorbable cardiovascular stents. However, the extremely high degradation rate of magnesium alloys in physiological environment has restricted its practical application. This paper reports the use of a novel microwave assisted coating technology to improve the in vitro corrosion resistance and biocompatibility of Mg alloy AZ31. Results indicate that a dense calcium deficient hydroxyapatite (CDHA) layer was uniformly coated on a AZ31 substrate in less than 10min. Weight loss measurement and SEM were used to evaluate corrosion behaviors in vitro of coated samples and of non-coated samples. It was seen that CDHA coatings remarkably reduced the mass loss of AZ31 alloy after 7days of immersion in SBF. In addition, the prompt precipitation of bone-like apatite layer on the sample surface during immersion demonstrated a good bioactivity of the CDHA coatings. Proliferation of osteoblast cells was promoted in 5days of incubation, which indicated that the CDHA coatings could improve the cytocompatibility of the AZ31 alloy. All the results suggest that the CDHA coatings, serving as a protective layer, can enhance the corrosion resistance and biological response of magnesium alloys. Furthermore, this microwave assisted coating technology could be a promising method for rapid surface modification of biomedical materials.

Qualitative Study on Mechanical Environment Affecting the Degradation of the Magnesium Alloys

Objective Explore the degradation rule of the magnesium alloys in simple mechanical environment. Methods Select a kind of magnesium alloy of better degradation by experiment and prepare screws. The experiment totally contains five groups, they are control group one with no specific conditions, experimental group two with 0.1Mpa external pressure, experimental group three with 0.2Mpa external pressure, pig femoral experimental group four with 0.2N shear force, pig femoral experimental group five with 0.3N shear force. Record the volume of hydrogen every certain time interval and observe the surface morphology of magnesium alloy screws through Object Deformation Image Capture System when the experiment is over to reflect the degradation rate of magnesium alloys. And the experiment would be repeated once to ensure the test results. Results Compared to group one, when external pressure exists, the volume of hydrogen significantly increases. Group two and group three have no significant difference in results, but group three has a greater degree of degradation than group two by observing the surface morphology. The volume of hydrogen of group four and group five is smaller than that of the first group in that smaller volume of screws exposes in SBF. The volume of hydrogen of the fifth group is greater than that of group four. Group five has a greater degree of degradation than the fourth group by observing the surface morphology. The repeated experiment basically keeps the same conditions, but the volume of hydrogen of group three is greater than that of group two.Conclusion Mechanical environment has an impact on the degradation rate of magnesium alloys. The pressure of the environment affects the degradation rate of magnesium alloys. The greater the pressure, the faster the degradation rate. The external force affects degradation rate of magnesium alloys. The greater the shear force, the faster the degradation rate.

Surface coating reduces degradation rate of magnesium alloy developed for orthopaedic applications

Magnesium (Mg) or its alloys have shown great potential as promising biocorrosive or biodegradable implantation materials and/or internal fixators, owing to their good biocompatibility and osteoinductive potential. However, poor anticorrosion property or rapid biodegradation has limited their clinical applications where initial mechanical stabilisation is required. One of the practical approaches for decreasing its biodegradation is to introduce a coating on Mg or its alloys. The current study compared the two most widely used coating techniques, i.e., microarc oxidation (MAO) and electrophoresis deposition (EPD), for coating onto the Mg–Zr pin surface, both in vitro and in vivo , to determine which method can prevent Mg–Zr alloy degradation better. In vitro pH measurement and in vivo microcomputed tomographic evaluation were used for determining its degradation rate. Our in vitro and in vivo testing results indicated that EPD demonstrated better corrosion resistance than MAO, implying the potential of electrochemical technology for surface modification of Mg or its alloys developed for orthopaedic applications.

Surface characteristics and corrosion resistance of sol–gel derived CaO–P2O5–SrO–Na2O bioglass–ceramic coated Mg alloy by different heat-treatment temperatures

To improve the initial corrosion resistance and then make the degradation rate of magnesium alloys to meet the biomedical application, crack-free CaO–P2O5–SrO–Na2O bioglass-ceramic coatings were synthesized on AZ31 magnesium alloy substrates using a sol–gel dip-coating technique followed by a heat-treatment in the temperature range of 400–500 °C. The effects of heat-treatment on the phase constituents, surface characteristics and corrosion resistances of the coatings were investigated. It was shown that the crystallization of Ca2P2O7 occurred after the glass was treated at 400 °C. As the temperature increased from 400 °C to 450 °C, besides main phase Ca2P2O7, β-Ca(PO3)2 and Ca4P6O19 were identified as minor crystal phases in the glass–ceramic. No new phase was detected with the temperature increasing to 500 °C except for the further crystallization. Meanwhile, the water contact angles of the coatings decreased with the increase of heat-treatment temperature due to the great crystallization. The corrosion resistances of the coated magnesium alloys were studied by electrochemical corrosion techniques in the simulated body fluid. The results revealed that the coating heat-treated at 400 °C exhibited superior corrosion resistance because of less crystallization, suggesting that the calcium phosphate bioglass–ceramic coating can provide effective protection for magnesium alloy substrate to control its initial degradation in vivo and maintain the desired mechanical properties.

Control of Surface Degradation on Biodegradable Magnesium Alloys by Plasma-Based Technology

Despite the tremendous potential of biodegradable magnesium alloys in surgical implants, the intrinsic degradation rates of Mg-based biomedical implants may be too fast in the physiological environment, particularly in the early stage after surgery. This shortcoming has been hampering wider clinical applications. In this respect, surface modification by plasma-based techniques is a good means to tailor the surface structure and degradation rate of magnesium alloys. The work conducted in the Plasma Laboratory of the City University of Hong Kong in the past two to three years in this area is summarized and discussed in a chronological order in this paper. Different physiologically important elements such as aluminum, titanium, oxygen, zinc, and chromium have been plasma implanted into various biomedical magnesium alloys to alter the surface chemistry and corrosion behavior. This paper discusses the roles played by these plasma-implanted elements and the subsequent effects pertaining to the control of surface degradation from the perspective of orthopedic and cardiovascular applications.

Biocorrosion and osteoconductivity of PCL/nHAp composite porous film-based coating of magnesium alloy

The present study was aimed at designing a novel porous hydroxyapatite/poly(ε-caprolactone) (nHAp/PCL) hybrid nanocomposite matrix on a magnesium substrate with high and low porosity. The coated samples were prepared using a dip-coating technique in order to enhance the bioactivity and biocompatibility of the implant and to control the degradation rate of magnesium alloys. The mechanical and biocompatible properties of the coated and uncoated samples were investigated and an in vitro test for corrosion was conducted by electrochemical polarization and measurement of weight loss. The corrosion test results demonstrated that both the pristine PCL and nHAp/PCL composites showed good corrosion resistance in SBF. However, during the extended incubation time, the composite coatings exhibited more uniform and superior resistance to corrosion attack than pristine PCL, and were able to survive severe localized corrosion in physiological solution. Furthermore, the bioactivity of the composite film was determined by the rapid formation of uniform CaP nanoparticles on the sample surfaces during immersion in SBF. The mechanical integrity of the composite coatings displayed better performance (∼34% higher) than the uncoated samples. Finally, our results suggest that the nHAp incorporated with novel PCL composite membranes on magnesium substrates may serve as an excellent 3-D platform for cell attachment, proliferation, migration, and growth in bone tissue. This novel as-synthesized nHAp/PCL membrane on magnesium implants could be used as a potential material for orthopedic applications in the future.

Effect of Casting Method of AZ91 D Magnesium Alloy on the Degradation Behaviour in Simulated Body Fluid

Abstract Magnesium-based alloys as biodegradable orthopedic implants have been successful for their high degradation rates in the physiological environment and the consequent loss in the mechanical integrity. Casting method used in production of magnesium-based alloys influences the microstructure of implants due to cooling conditions. In this study, the effects of casting method (permanent mold casting and sand mold casting) on the degradation of AZ91D magnesium alloy in Hank's simulated body fluid at 36.5 ± 0.5°C have been investigated using immersion technique of cylindrical specimens. The specimens were subjected to simulated body fluid for 8 h and 24 h. The results have shown that the cooling rate from melt and grain size have great influence on the degradation rate of magnesium alloy.

Corrosion behavior of TiO2 films on Mg–Zn alloy in simulated body fluid

Magnesium alloys have been widely investigated in the field of biomaterials due to their moderate mechanical properties close to human bone and gradual degradation in human physiological environment without second surgeries. But results from clinical studies showed that magnesium implants suffered from too rapid degradation in human physiological environment. To reduce the degradation rate of magnesium alloys, surface modification is essential and effective besides element alloying. In this study, TiO2 films were deposited on Mg–Zn alloy by direct current reactive magnetron sputtering. The morphology and structure of the films were characterized by atomic force microscopy (AFM), scanning electron microscope (SEM) and X-ray diffraction (XRD). The corrosion resistance in simulated body fluid (SBF) at 37°C was evaluated by potentiodynamic polarization and hydrogen evolution tests. The corrosion behavior of the samples was investigated by SEM with energy dispersive spectroscopy (EDS) after immersion for different periods. The results showed that the compact films were composed of particles with the size of about 100nm and could effectively improve the corrosion resistance in SBF. After immersion for 10 days, the corrosion rates of the substrates and samples with TiO2 films were 4.13mm/y and 1.95mm/y, respectively. During the immersion, the TiO2 films could induce the growth of hydroxyapatite (HAp) to improve the bioactivity of the samples.