1.
Interaction between a high purity magnesium surface and PCL and PLA coatings during dynamic degradation.
Chen, Y, Song, Y, Zhang, S, Li, J, Zhao, C, Zhang, X
Biomedical materials (Bristol, England). 2011;(2):025005
Abstract
In this study, polycaprolactone (PCL) and polylactic acid (PLA) coatings were prepared on the surface of high purity magnesium (HPMs), respectively, and electrochemical and dynamic degradation tests were used to investigate the degradation behaviors of these polymer-coated HPMs. The experimental results indicated that two uniform and smooth polymer films with thicknesses between 15 and 20 µm were successfully prepared on the HPMs. Electrochemical tests showed that both PCL-coated and PLA-coated HPMs had higher free corrosion potentials (E(corr)) and smaller corrosion currents (I(corr)) in the modified simulated body fluid (m-SBF) at 37 °C, compared to those of the uncoated HPMs. Dynamic degradation tests simulating the flow conditions in coronary arteries were carried out on a specific test platform. The weight of the specimens and the pH over the tests were recorded to characterize the corrosion performance of those samples. The surfaces of the specimens after the dynamic degradation tests were also examined. The data implied that there was a special interaction between HPM and its polymer coatings during the dynamic degradation tests, which undermined the corrosion resistance of the coated HPMs. A model was proposed to illustrate the interaction between the polymer coatings and HPM. This study also suggested that this reciprocity may also exist on the implanted magnesium stents coated with biodegradable polymers, which is a potential obstacle for the further development of drug-eluting magnesium stents.
2.
Improvement of lactic acid production from cellulose with the addition of Zn/Ni/C under alkaline hydrothermal conditions.
Zhang, S, Jin, F, Hu, J, Huo, Z
Bioresource technology. 2011;(2):1998-2003
Abstract
The effect of Zn, Ni and activated carbon on the yield of lactic acid from cellulose was investigated to improve the lactic acid yield under alkaline hydrothermal conditions. The results showed that the lactic acid yield increased greatly in the presence of Zn, Ni and activated carbon. Central composite response surface method (RSM) design experimentation was used to find the optimal concentrations of Zn, Ni, activated carbon and NaOH, which indicated that 0.02 g Zn, 0.03 g Ni, 0.07 g activated carbon and 2.5 mol/L NaOH were the optimal concentrations. Under this condition, the highest lactic acid yield was 42%, which was much higher than previous results using only NaOH (15%). The confirmatory experiments on lactic acid yield proved that the proposed model of lactic acid yield can accurately predict the lactic acid yield from cellulose.