In vitro corrosion resistance and dual antibacterial ability of curcumin loaded composite coatings on AZ31 alloy: Effect of amorphous calcium carbonate.

Rapid corrosion and bacterial infection are obstacles to put into use biodegradable magnesium (Mg) alloy as biomedical materials. In this research, an amorphous calcium carbonate (ACC)@curcumin (Cur) loaded poly-methyltrimethoxysilane (PMTMS) coating prepared by self-assembly method on micro-arc oxidation (MAO) coated Mg alloy has been proposed. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy are adopted to analyze the morphology and composition of the obtained coatings. The corrosion behaviour of the coatings is estimated by hydrogen evolution and electrochemical tests. The spread plate method without or with 808 nm near-infrared irradiation is applied to evaluate the antimicrobial and photothermal antimicrobial ability of the coatings. Cytotoxicity of the samples is tested by 3-(4,5)-dimethylthiahiazo(-z-y1)-2,5-di- phenytetrazoliumromide (MTT) and live/dead assay culturing with MC3T3-E1 cells. Results show that the MAO/ACC@Cur-PMTMS coating exhibited favourable corrosion resistance, dual antibacterial ability, and good biocompatibility. Cur was employed as an antibacterial agent and photosensitizer for photothermal therapy. The core of ACC significantly improved the loading of Cur and the deposition of hydroxyapatite corrosion products during degradation, which greatly promoted the long-term corrosion resistance and antibacterial activity of Mg alloys as biomedical materials.

Corrosion resistance and mechanisms of Nd(NO3)3 and polyvinyl alcohol organic-inorganic hybrid material incorporated MAO coatings on AZ31 Mg alloy.

This work reports the design and preparation of novel organic (polyvinyl alcohol, PVA)-inorganic (neodymium nitrate, Nd(NO3)3) hybrid coatings on micro-arc oxidation (MAO) coating for magnesium (Mg) alloy corrosion protection. X-ray diffractometer, X-ray photoelectron spectroscopy, fourier transform infrared spectroscopy, field emission scanning electron microscope, Energy Dispersive X-ray spectrometer and surface roughness were applied to characterize the chemical composition and surface morphology of the coatings. The corrosion resistance of the coatings was evaluated by electrochemical and salt spray tests. The results suggested that the formation of PVA-Nd3+ and PVA-Mg2+ complexes promoted the enrichment of Nd3+ on the surface, and thereby improved the sealing quality and compactness of the coating. Interestingly, when the coating was damaged, the Nd3+ ions were transformed to their carbonates and covered the active sites, and thus exhibiting self-healing function. Further, the corrosion resistance of PVA-Nd3+ modified MAO composite coating on AZ31 Mg alloy was improved.

In vitro degradation, photo-dynamic and thermal antibacterial activities of Cu-bearing chlorophyllin-induced Ca-P coating on magnesium alloy AZ31.

Surgical failures, caused by postoperative infections of bone implants, are commonly met, which cannot be treated precisely with intravenous antibiotics. Photothermal therapy (PTT) and photodynamic therapy (PDT) have attracted widespread attention due to their non-invasive antibacterial effects on tissues and no bacterial resistance, which may be an excellent approach to solve infections related to bone implants for biodegradable magnesium alloys. Herein, a sodium copper chlorophyllin (SCC) with a porphyrin ring induced Ca-P coating was prepared on AZ31 magnesium alloy via layer-by-layer (LbL) assembly. The morphology and composition of the samples were characterized through field emission scanning electron microscope (FE-SEM) with affiliated energy dispersive spectrometer (EDS), X-ray diffractometer (XRD), and Fourier infrared spectrometer (FTIR) and X-ray photoelectron spectrometer (XPS) as well. Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and hydrogen evolution experiments were employed to evaluate the corrosion behavior of the samples. Atomic absorption spectrophotometer was used to measure Cu elemental content of different immersion periods. Cytocompatibility and antibacterial performance of the coatings were probed using in vitro cytotoxicity tests (MTT assay), live/dead cell staining and plate counting method. The results showed that the obtained (Ca-P/SCC)10 coating exhibited good corrosion resistance, antimicrobial activity (especially under 808 nm irradiation) and biocompatibility. The antibacterial rates for E. coli and S. aureus were 99.9% and 99.8%, respectively; and the photothermal conversion efficiency was as high as 42.1%. Triple antibacterial mechanisms including photodynamic, photothermal reactions and copper-ions release were proposed. This coating exhibited a promising application for biodegradable magnesium alloys.

In vitro corrosion resistance of layer-by-layer assembled polyacrylic acid multilayers induced Ca-P coating on magnesium alloy AZ31.

Biodegradable magnesium (Mg)-based alloys have aroused great concern owing to their promising characteristics as temporary implants for orthopedic application. But their undesirably rapid corrosion rate under physiological conditions has limited the actual clinical application. This study reports the use of a novel biomimetic polyelectrolyte multilayer template, based on polyvinylpyrrolidone (PVP) and polyacrylic acid (PAA) via layer-by-layer (LbL) assembly, to improve the corrosion resistance of the alloy. Surface characterization techniques (field-emission scanning electron microscopy, Fourier transform infrared (FTIR) spectrophotometer and X-ray diffractometer) confirmed the formation of biomineralized Ca-P coating on AZ31 alloy. Both hydrogen evolution and electrochemical corrosion tests demonstrated that the corrosion protection of the polyelectrolyte-induced Ca-P coating on AZ31 alloy. The formation mechanism of biomineralized Ca-P coating was proposed.

In vitro corrosion of pure Mg in phosphate buffer solution-Influences of isoelectric point and molecular structure of amino acids.

Influences of proteins on degradation of magnesium alloys are of great significance but not well understood. In particular the roles of amino acids, the basic unit of proteins in regulating the progress of biodegradation of magnesium based materials remain unclear. This study aims to investigate the impacts of alanine, glutamic acid and lysine on degradation of pure magnesium in phosphate buffer solution through SEM, XPS, FTIR, potentiodynamic polarisation curves, electrochemical impedance spectroscopy and immersion tests. The changed contents of amino acids in solutions were detected by UV-vis spectrophotometer. Results demonstrate that the charges of the selected amino acids imposed significant contribution to suppressing the degradation of pure magnesium in phosphate buffer solution. The presence of amino acids led to the formation of phosphate-based corrosion products, increasing free corrosion potential, and reduction in corrosion current density and solution pH depending on their isoelectric points and molecular structures. A plausible corrosion mechanism organised by amino acids on pure magnesium was proposed.

Corrosion resistance and antibacterial properties of hydroxyapatite coating induced by gentamicin-loaded polymeric multilayers on magnesium alloys.

As a result of their good biocompatibility, bioactivity, and mechanical properties, magnesium (Mg) alloys have received considerable attention as next generation biodegradable implants. Herein, in order to achieve a proper degradation rate and good antibacterial ability, we reported a novel hydroxyapatite coating induced by gentamicin (GS)-loaded polymeric multilayers for the surface treatment of the Mg alloy. The coating was characterized by X-ray diffraction, fourier transform infrared spectroscopy and scanning electron microscopy. The as-prepared hydroxyapatite coating showed the compact morphology and a well-crystallized apatite structure. This coating could improve the adhesion strength and reduce the corrosion rate of the substrate in simulated body fluid solution. Meanwhile, the drug release and antibacterial experiments demonstrated that the GS loaded specimen revealed a significant antimicrobial performance toward Staphylococcus aureus and had a prolonged release profile of GS, which would be helpful to the long-term bactericidal activity of the Mg implant. This coating showed acceptable biocompatibility via MTT assay and Live/dead staining. Thus, the multilayers-hydroxyapatite coated Mg alloy could improve the corrosion resistance and biocompatibility while delivering vital drugs to the site of implantation.

Advances in functionalized polymer coatings on biodegradable magnesium alloys - A review.

Magnesium (Mg) and its alloys have become a research frontier in biodegradable materials owing to their superior biocompatibility and excellent biomechanical compatibility. However, their high degradation rate in the physiological environment should be well tackled prior to clinical applications. This review summarizes the latest progress in the development of polymeric coatings on biodegradable Mg alloys over the last decade, regarding preparation strategies for polylactic acid (PLA), poly (latic-co-glycolic) acid (PLGA), polycaprolactone (PCL), polydopamine (PDA), chitosan (CS), collagen (Col) and their composite, and their performance in terms of corrosion resistance and biocompatibility. Feasible perspectives and developing directions of next generation of polymeric coatings with respect to biomedical Mg alloys are briefly discussed. STATEMENT OF SIGNIFICANCE: Magnesium (Mg) and its alloys have become a research frontier in biodegradable materials owing to their superior biocompatibility and suitable biomechanical compatibility. However, the principal drawback of Mg-based implants is their poor corrosion resistance in physiological environments. Hence, it is vital to mitigate the degradation/corrosion behavior of Mg alloys for safe biomedical deployments. This review summarizes the latest progress in development of polymeric coatings on biomedical Mg alloys regarding preparation strategy, corrosion resistance and biocompatibility, including polylactic acid (PLA), poly (latic-co-glycolic) acid (PLGA), polycaprolactone (PCL), chitosan (CS), polydopamine (PDA), collagen (Col) and their composite. In addition, functionalized polymer coatings with Mg alloys exhibits a promising prospect owing to their ability of degradation along with biocompatibility, self-healing, drug-delivery and osteoinduction.

Corrosion resistance of a novel SnO2-doped dicalcium phosphate coating on AZ31 magnesium alloy.

A SnO2-doped dicalcium phosphate coating was prepared on AZ31 alloy by means of hydrothermal deposition. The results showed that the coating possessed a globular morphology with a long lamellar crystalline structure and a thickness of approximately 40 µm. The surface of the coating became smooth with an increase additive amount of the SnO2 nanoparticles. The corrosion current density and hydrogen evolution rate of the coating prepared in presence of SnO2 were reduced compared to the coating without SnO2 and the bare AZ31 substrate, indicating an improvement in the corrosion resistance of the SnO2-doped coating.

In Vitro Degradation of Pure Magnesium-The Effects of Glucose and/or Amino Acid.

The influences of glucose and amino acid (L-cysteine) on the degradation of pure magnesium have been investigated using SEM, XRD, Fourier transformed infrared (FTIR), X-ray photoelectron spectroscopy (XPS), polarization and electrochemical impedance spectroscopy and immersion tests. The results demonstrate that both amino acid and glucose inhibit the corrosion of pure magnesium in saline solution, whereas the presence of both amino acid and glucose accelerates the corrosion rate of pure magnesium. This may be due to the formation of -C=N- bonding (a functional group of Schiff bases) between amino acid and glucose, which restricts the formation of the protective Mg(OH)2 precipitates.

In vitro corrosion of pure magnesium and AZ91 alloy-the influence of thin electrolyte layer thickness.

In vivo degradation predication faces a huge challenge via in vitro corrosion test due to the difficulty for mimicking the complicated microenvironment with various influencing factors. A thin electrolyte layer (TEL) cell for in vitro corrosion of pure magnesium and AZ91 alloy was presented to stimulate the in vivo corrosion in the micro-environment built by the interface of the implant and its neighboring tissue. The results demonstrated that the in vivo corrosion of pure Mg and the AZ91 alloy was suppressed under TEL condition. The AZ91 alloy was more sensitive than pure Mg to the inhibition of corrosion under a TEL thickness of less than 200 µm. The TEL thickness limited the distribution of current, and thus localized corrosion was more preferred to occur under TEL condition than in bulk solution. The TEL cell might be an appropriate approach to simulating the in vivo degradation of magnesium and its alloys.

In vitro degradation of pure Mg in response to glucose.

Magnesium and its alloys are promising biodegradable biomaterials but are still challenging to be used in person with high levels of blood glucose or diabetes. To date, the influence of glucose on magnesium degradation has not yet been elucidated, this issue requires more attention. Herein, we present pure Mg exhibiting different corrosion responses to saline and Hank's solutions with different glucose contents, and the degradation mechanism of pure Mg in the saline solution with glucose in comparison with mannitol as a control. On one hand, the corrosion rate of pure Mg increases with the glucose concentration in saline solutions. Glucose rapidly transforms into gluconic acid, which attacks the oxides of the metal and decreases the pH of the solution; it also promotes the absorption of chloride ions on the Mg surface and consequently accelerates corrosion. On the other hand, better corrosion resistance is obtained with increasing glucose content in Hank's solution due to the fact that glucose coordinates Ca(2+) ions in Hank's solution and thus improves the formation of Ca-P compounds on the pure Mg surface. This finding will open up new avenues for research on the biodegradation of bio-Mg materials in general, which could yield many new and interesting results.

[Effect of health service and its influence factors in flood disaster areas].

OBJECTIVE: To explore the effect of health service and its influential factors in flood disaster areas. METHODS: Fifty-five towns were sampled randomly from Dongting Lake area suffering from flood in 1998. The health service level, effect, and its influence factors were investigated retrospectively. RESULTS: The incidence rate of notifiable infectious diseases was 11.7 per thousand, prevalence rate of chronic disease was 51.2 per thousand, infant mortality rate was 43.1 per thousand, neonatal mortality rate was 10.2 per thousand, and the total mortality rate was 554.3/100,000 in Dongting Lake area. The health investment level was significantly associated with the incidence rate of notifiable infectious diseases, the infant mortality rate, and total mortality rate. Duration of flood and income per capita were important factors for the effect of health investment. CONCLUSION: Increasing health investment and residents' income in the flood disaster area, shortening the duration of flood would play positive role in residents' health in the flood disaster area.

[Study on index of osteoporosis with height-shortening value for self-examination in middle-aged and elderly population].

OBJECTIVE: To probe into the application value of the height shortening value as the self-examination index of the middle-aged and aged group's osteoporosis or reduced bone mineral density in communities. METHODS: Four communities were selected by cluster sampling at random in Changsha city to be the objects of study, among which women were 45 years old or older and men were 60 years old. Difference and the percentage proportion of the height shortening between the height of the research objects which was measured at their youth and the height measured at this study, were calculated. Mineral density of the anteroposterior lumber spine L2-L4, the left femur neck of each object of study with the DPX-IQ dual energy X-ray (DEXA) were both examined. Results examined by DEXA were recognized as "Golden Standards" and different absolute and relative height shortening values were taken as positive cutoff points. Sensitivity, specificity and Youden's index were calculated to draw the receiver operator characteristic curve in order to get the positive cutoff which was most suitable to both sensitivity and specificity, and to calculate the predicative values of that self-examination method among different groups. RESULTS: 3 cm of height shortened seemed to be the positive cutoff of the self-examination of osteoporosis, and its sensitivity, specificity and Youden's index were 75.4%, 76.7% and 0.521 respectively. 2 cm of height shortened was suggested as the positive cutoff of the self-examination method of reduced bone mineral density, while its sensitivity, specificity and Youden's index were 81.7%, 75.6% and 0.573 respectively. In this self-examination method, positive predicative value was the highest (76.4%; 88.7%) among the women group aged over 65. CONCLUSION: Certain height-shortening value could be used as the rough index of screening osteoporosis of reduced bone mineral density, which set a simple and easy way of self-examination for the middle-aged and elderly population.

[Years of potential life of residents among different flood areas in Hunan province].

OBJECTIVE: To determine the damage of different types of floods on the residents health. METHODS: The methods of standard mortality rate (SMR) and years of potential life lost (YPLL) were used to analyze the death of sample residents from flood areas in Dongting Lake in Hunan province. RESULTS: The order of death causes in the soaked area, the collapsed area and the non-flood area was the same. But the mortality rates of residents injury, poisoning and malignant neoplasm diseases in the soaked area and the collapsed area were higher than those of non-flood area. The resident standard rates of years of potential life lost (SYPLL) in the soaked area and the collapsed area were higher than that of the controls, especially in the age group of 30 to 45. The flood-attributed SYPLL in the male was higher than that of the female. CONCLUSION: Flood actually affected the health of residents. The more serious the flood is, the worse the effect is. It is very important to decrease the resident mortality rate of the injury, poisoning and malignant neoplasm, and to pay attention to protect people of 30 to 45 years old in flood areas.

[A research on the public health index related to the comprehensive assessment on floods].

OBJECTIVE: To develop a public health index related to the comprehensive assessment on the impact caused by floods. METHODS: A Analytic hierarchy process (AHP) theory was used to establish the initial evaluation system on the impact of floods. Modified-Delphi process was used to screen and determine the indicators and their weights while synthetical scored method was used to establish the comprehensive assessment model. Percentile was used to differentiate the degree of floods. Finally, analysis of variance (ANOVA) and correlation analysis were used to test the differentiability of the model for different degree of floods and the independence of these indicators. RESULTS: The model of comprehensive assessment on the impact of floods was set up, including six first-ranking indicators and twenty-four sub-indicators. The values of comprehensive assessment were divided into five grades by the percentiles. Verified results indicated that there were significant difference among the five grades (F = 76.11, P < 0.01) and all indicators were independent. CONCLUSION: An index of comprehensive assessment on the impact of floods was established, which could be used to evaluate the impact of floods and to differentiate the degree of flood, which seemed to have the characteristic of reliability, comprehensiveness and practicability.

[A study on the health status of residents affected by flood disasters].

OBJECTIVE: To study the immediate and long-term effects of disasters caused by floods on residents health status. METHODS: Stratified sampling by ranks of flood disaster occurred in 1996 and 1998, flood disaster areas and control areas were carried out. A retrospective study was also carried out to study all diseases involved during 1996 - 1999. RESULTS: The incident rates of acute infectious disease in flooding areas in 1996 and 1998 were both higher than those of non-flooding areas (863.181/100 000 and 736.591/100 000, respectively). But there was no different between the incident rate of the first years in flooding areas and that of non-flooding areas. The prevalence rates of 8 kinds of chronic diseases related to circulatory system, nervous system, digestive system, injury and poisonous diseases in flooding areas were also higher than that in the non-flooding areas. The highest incidence rates of most diseases were in the mountainous flooding areas, followed by areas collapsed by flooding, and the lowest were seen in soakedareas by floods. The incidence rates of intestinal infectious diseases and respiratory infectious diseases were lower in areas where prevention and control measures were weak. CONCLUSION: Flood could lead to the increase of incidence rates both on acute infectious diseases and non-infectious diseases. Interventions on non-infectious diseases should also be enforced to stop the epidemics when preventing and controlling acute infectious disease.

[Study on hospitalization expenses of flood disaster areas' residents of Dongting Lake in Hunan province in 1998].

OBJECTIVE: To study the expenses of hospitalization among the population in the flood disaster areas of Dongting Lake in Hunan province in 1998. METHODS: Descriptive epidemiologic study were conducted to analyze hospitalization expenses of the residents of 55 villages in flood disaster areas in 1998; single factors analysis and logarithmic linear regression analysis were carried out to explore influencing factors about hospitalization expenses of the residents. RESULTS: The hospitalization rate was 4.59% with an average hospitalization expenses of 667.42 Yuan in the flood disaster areas' residents of Dongting Lake in 1998. Compared with populations without suffering from flood, hospitalization rate and the average hospitalization expenses of flood disaster Areas' residents of Dongting Lake in 1998 were higher and had significant difference. The average hospitalization expenses in 1998 was affected by flood types, family income, gender, age, literacy, occupation, outcome after leaving the hospital and hospital ranks. CONCLUSION: These results implied that the flood disease aggravated inhabitants' burden of disease in Dongting Lake areas; the factors influencing the average hospitalization expenses were multiple, and synthetic measures should be taken in the prevention and control of flood disaster.