A method of assessing peripheral stent abrasiveness under cyclic deformations experienced during limb movement.

Poor outcomes of peripheral arterial disease stenting are often attributed to the inability of stents to accommodate the complex biomechanics of the flexed lower limb. Abrasion damage caused by rubbing of the stent against the artery wall during limb movement plays a significant role in reconstruction failure but has not been characterized. Our goals were to develop a method of assessing the abrasiveness of peripheral nitinol stents and apply it to several commercial devices. Misago, AbsolutePro, Innova, Zilver, SmartControl, SmartFlex, and Supera stents were deployed inside electrospun nanofibrillar tubes with femoropopliteal artery-mimicking mechanical properties and subjected to cyclic axial compression (25%), bending (90°), and torsion (26°/cm) equivalent to five life-years of severe limb flexions. Abrasion was assessed using an abrasion damage score (ADS, range 1-7) for each deformation mode. Misago produced the least abrasion and no stent fractures (ADS 3). Innova caused small abrasion under compression and torsion but large damage under bending (ADS 7). Supera performed well under bending and compression but caused damage under torsion (ADS 8). AbsolutePro produced significant abrasion under bending and compression but less damage under torsion (ADS 12). Zilver fractured under all three deformations and severely abraded the tube under bending and compression (ADS 15). SmartControl and SmartFlex fractured under all three deformations and produced significant abrasion due to strut penetration (ADS 20 and 21). ADS strongly correlated with clinical 12-month primary patency and target lesion revascularization rates, and the described method of assessing peripheral stent abrasiveness can guide device selection and development. STATEMENT OF SIGNIFICANCE: Poor outcomes of peripheral arterial disease stenting are related to the inability of stents to accommodate the complex biomechanics of the flexed lower limb. Abrasion damage caused by rubbing of the stent against the artery wall during limb movement plays a significant role in reconstruction failure but has not been characterized. Our study presents the first attempt at assessing peripheral stent abrasiveness, and the proposed method is applied to compare the abrasion damage caused by Misago, AbsolutePro, Innova, Zilver, SmartControl, SmartFlex, and Supera peripheral stents using artery-mimicking synthetic tubes and cyclic deformations equivalent to five life-years of severe limb flexions. The abrasion damage caused by stents strongly correlates with their clinical 12-month primary patency and target lesion revascularization rates, and the described methodology can be used as a cost-effective and controlled way of assessing stent performance, which can guide device selection and development.

Safe balloon inflation parameters for resuscitative endovascular balloon occlusion of the aorta.

BACKGROUND: Noncompressible hemorrhage is a leading cause of preventable death in civilian and military trauma populations. Resuscitative endovascular balloon occlusion of the aorta (REBOA) is a promising method for controlling noncompressible hemorrhage, but safe balloon inflation parameters are not well defined. Our goal was to determine the balloon inflation parameters associated with benchtop flow occlusion and aortic/balloon rupture in ex vivo human aortas and test the hypothesis that optimal balloon inflation characteristics depend on systolic pressure and subject demographics. METHODS: Aortic occlusion parameters in human thoracic aortas (TAs) and abdominal aortas (AAs) from 79 tissue donors (median ± SD age, 52 ± 18 years [range, 13-75 years]; male, 52; female, 27) were recorded under 100/40, 150/40, and 200/40 mm Hg flow pressures for ER-REBOA and Coda balloons. Rupture tests were done with Coda balloons only without flow. RESULTS: In the TA, the average balloon inflation volumes and pressures resulting in 100/40 mm Hg flow occlusion were 11.7 ± 3.8 mL and 174 ± 65 mm Hg for the ER-REBOA, and 10.6 ± 4.3 mL and 94 ± 57 mm Hg for the Coda balloons. In the AA, these values were 6.2 ± 2.6 mL and 110 ± 47 mm Hg for the ER-REBOA, and 5.9 ± 2.2 mL and 71 ± 30 mm Hg for the Coda. The average balloon inflation parameters associated with aortic/Coda balloon rupture were 39.1 ± 6.5 mL and 1,284 ± 385 mm Hg in the TA, and 27.7 ± 7.7 mL and 1,410 ± 483 mm Hg in the AA. Age, sex, and systolic pressure all had significant effects on balloon occlusion and rupture parameters. CONCLUSION: Optimal balloon inflation parameters depend on anatomical, physiological, and demographic characteristics. Pressure-guided rather than volume-guided balloon inflation may reduce the risk of aortic rupture. These results can be used to help improve the safety of REBOA procedures and devices.

Termination of Ge surfaces with ultrathin GeS and GeS2 layers via solid-state sulfurization.

Reactions of Ge with S vapor, of interest as a potential approach for forming thin passivation layers on Ge surfaces, have been studied by photoelectron spectroscopy and Raman spectroscopy. Exposure of Ge(100) and Ge(111) to S drives the formation of Ge sulfide near-surface layers. At low temperatures, the reaction products comprise a thin GeS interlayer terminated by near-surface GeS2. Above 400 °C, exposure to sulfur gives rise to single-phase GeS2 layers whose thickness increases with temperature. Arrhenius analysis of the GeS2 thickness yields an activation energy (0.63 ± 0.08) eV, close to the barrier that controls Ge oxidation by O radicals. XPS measurements after extended ambient exposure show a stable, ultrathin near-surface GeS2 without significant oxidation, indicating that Ge-sulfides may provide an effective surface passivation for Ge surfaces.

High-resolution Thermal Micro-imaging Using Europium Chelate Luminescent Coatings.

Micro-electronic devices often undergo significant self-heating when biased to their typical operating conditions. This paper describes a convenient optical micro-imaging technique which can be used to map and quantify such behavior. Europium thenoyltrifluoroacetonate (EuTFC) has a 612 nm luminescence line whose activation efficiency drops strongly with increasing temperature, due to T-dependent interactions between the Eu3+ ion and the organic chelating compound. This material may be readily coated on to a sample surface by thermal sublimation in vacuum. When the coating is excited with ultraviolet light (337 nm) an optical micro-image of the 612 nm luminescent response can be converted directly into a map of the sample surface temperature. This technique offers spatial resolution limited only by the microscope optics (about 1 micron) and time resolution limited by the speed of the camera employed. It offers the additional advantages of only requiring comparatively simple and non-specialized equipment, and giving a quantitative probe of sample temperature.

Temperature-activated layer-breathing vibrations in few-layer graphene.

We investigated the low-frequency Raman spectra of freestanding few-layer graphene (FLG) at varying temperatures (400-900 K) controlled by laser heating. At high temperature, we observed the fundamental Raman mode for the lowest-frequency branch of rigid-plane layer-breathing mode (LBM) vibration. The mode frequency redshifts dramatically from 81 cm(-1) for bilayer to 23 cm(-1) for 8-layer. The thickness dependence is well described by a simple model of coupled oscillators. Notably, the LBM Raman response is unobservable at room temperature, and it is turned on at higher temperature (>600 K) with a steep increase of Raman intensity. The observation suggests that the LBM vibration is strongly suppressed by molecules adsorbed on the graphene surface but is activated as desorption occurs at high temperature.

Observation of low energy Raman modes in twisted bilayer graphene.

Two new Raman modes below 100 cm(-1) are observed in twisted bilayer graphene grown by chemical vapor deposition. The two modes are observed in a small range of twisting angle at which the intensity of the G Raman peak is strongly enhanced, indicating that these low energy modes and the G Raman mode share the same resonance enhancement mechanism, as a function of twisting angle. The ~94 cm(-1) mode (measured with a 532 nm laser excitation) is assigned to the fundamental layer breathing vibration (ZO' mode) mediated by the twisted bilayer graphene lattice, which lacks long-range translational symmetry. The dependence of this mode's frequency and line width on the rotational angle can be explained by the double resonance Raman process that is different from the previously identified Raman processes activated by twisted bilayer graphene superlattice. The dependence also reveals the strong impact of electronic-band overlaps of the two graphene layers. Another new mode at ~52 cm(-1), not observed previously in the bilayer graphene system, is tentatively attributed to a torsion mode in which the bottom and top graphene layers rotate out-of-phase in the plane.