Grain size quantification by optical microscopy, electron backscatter diffraction, and magnetic force microscopy.

Quantification of microstructure, especially grain size, in polycrystalline materials is a vital aspect to understand the structure-property relationships in these materials. In this paper, representative characterization techniques for determining the grain size, including optical microscopy (OM), electron backscatter diffraction (EBSD) in the scanning electron microscopy (SEM), and atomic force microscopy/magnetic force microscopy (AFM/MFM), are thoroughly evaluated in comparison, illustrated by rare-earth sintered Nd-Fe-B permanent magnets. Potential applications and additional information achieved by using aforementioned characterization techniques have been discussed and summarized.

Characterization of Pebax angioplasty balloon surfaces with AFM, SEM, TEM, and SAXS.

In the medical device industry, angioplasty balloons have been widely used in the less invasive treatment of heart disease by expanding and relieving clogged structures in various arterial segments. However, new applications using thin coatings on the balloon surface have been explored to enhance therapeutic value in the delivery of pharmaceuticals (drug-elution) or control thermal energy output (RF ablation). In this study, angioplasty balloon materials comprised of poly(ether-block-amide) (Pebax) were investigated via atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and small-angle X-ray scattering (SAXS) to characterize physical properties at the balloon surface that may affect coating adhesion. The soft segment of this Pebax 1074 material is polyethylene oxide (PEO) and the hard segment is nylon-12. The morphology of the hard segments of this block co-polymer are found via AFM stiffness measurements to be (40 ± 20) nm by (300 ± 150) nm and are oriented parallel to the surface of the balloon. SAXS measurements found the lamellar spacing to be (18.5 ± 0.5) nm, and demonstrate a preferential orientation in agreement with TEM and AFM measurements. Fixation of this balloon in resin, followed by cryo-sectioning is shown to provide a novel manner in which to investigate surface characteristics on the balloon such as material or coating thickness as well as uniformity in comparison to the bulk structure. These outputs were deemed critical to improve overall balloon processing such as molding and surface treatment options for robust designs toward better procedural outcomes targeting new therapeutic areas.

A new radioisotope tracing method of UHMWPE wear particle dispersion using 97Ru.

A new method of radioisotope labelling, using the reaction 92Zr(12C,α3n)97Ru, has been demonstrated. The method places radioactive 97Ru tracer atoms into ultra-high molecular weight polyethylene (UHMWPE). The radioisotope 97Ru (half-life t1/2=2.9 days) was implanted in 5 mm×5 mm UHMWPE samples to a maximum depth of 5 µm. The radioisotope is identified via a characteristic gamma-ray emission from its daughter 97Tc at 216 keV. The new method is advantageous since the concentration profile of the 97Ru label is almost constant starting at the surface. In order to show the efficacy of the method for wear measurements on prostheses, the labeled UHMWPE samples were worn in a model system. The model system involved bi-directional sliding actuation on a steel block. Debris transport, via the two pathways linking the polymer with the articulating steel surface and with the lubricant, respectively, has been quantified. Surface roughness of the steel and the load on the steel were varied. Changing the surface roughness of the steel from (110±30) to (340±90) nm increased the amount of debris dispersed in the lubricant from (21±3)% to (67±3)%. Furthermore, changing the load from 1 to 5 kg also increased debris transport along this pathway.