Crevice corrosion - A newly observed mechanism of degradation in biomedical magnesium.

Crevice-induced corrosion is not desirable to occur in metallic magnesium (Mg) during many industrial applications. However, orthopedic implants made of Mg alloys have been demonstrated to degrade faster between the joining surface of bone plates and screws after implantation, suggesting the crevice corrosion may occur in the physiological environment. In this paper, a resin device is designed to parallel high purity magnesium (HP-Mg) plates with closely spaced slits. After a standard corrosion test in the phosphate-buffered saline (PBS) solution, the paralleled HP-Mg samples embedded in the custom-made resin device corrode faster than those without the resin device. The corrosion morphology of Mg with the resin device exhibits features of crevice corrosion with many deep holes and river-like texture. Moreover, implantation of the bone plate and screws in vivo demonstrates similar corrosion morphology as that of the in vitro test, suggesting the occurrence of crevice-enhanced corrosion in the bone-bone plate interface, as well as the contact area between the bone plate and the screws. STATEMENT OF SIGNIFICANCE: Understanding the corrosion behavior of Mg and Mg alloys after implantation is one of the main challenges for developing desirable biodegradable Mg alloys or effective methods to adjust the corrosion rate of Mg-based implants. In this paper, we attempted to understand the corrosion behaviors of HP-Mg at the joining surface between HP-Mg plates or HP-Mg screws and bone tissues after implantation. We designed an in vitro setup to mimic the crevice environment of the in vivo joining surface and found that the crevices existing on the HP-Mg would significantly accelerate the corrosion rate and change the corrosion morphology of HP-Mg plates. The in vivo implantation also showed similar corrosion morphology caused by crevice corrosion, which appeared at the joining surface between HP-Mg plates or HP-Mg screws and bone tissues. Then, we proposed a new corrosion mechanism of Mg-based alloys inside the crevice. The findings of this study can help us broaden our cognition on the corrosion behavior of Mg and Mg alloy-based orthopedic implants.

Fabrication and Application of a New-Type Photothermal Conversion Nano Composite Coating.

Photothermal conversion nanomaterials attract much attention for their high light/heat transform efficiency and controllable light absorption. In this work, the CuS semiconductor nanomaterials were prepared through the deposition method in the presence of citrate sodium and were characterized by TEM, XRD and UV-vis spectra. A new type of nano composite coating was obtained from acrylic resin by adding the CuS nanoparticles and other nanomaterials which could absorb the light of various infrared bands. The test showed that when exposed to infrared light, the plastic greenhouse model equipped with photothermal conversion coating gave out a more significant temperature rising than that of the common plastic greenhouse. The properties of photothermal conversion and heat insulation of photothermal conversion coating reach the best when the addition quantities of CuS and ZrC nanoparticles are 2%.