Structure and tribological performance of helium-implanted layer on Ti6Al4V alloy by plasma-based ion implantation

The present paper concentrates on tribological performance of Ti6Al4V alloy treated by helium plasmabased ion implantation with a voltage of -30 kV and a dose range of 1, 3, 6 and 9 ×1017 He/cm2. X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM) and Atomic force microscopy (AFM) were used to characterize composition, structure and surface morphology, respectively. The variation of hardness with indenting depth was measured and tribological performance was evaluated. The uniform cavities with a diameter of several nanometers are formed in the helium-implanted layer on Ti6Al4V alloy. Helium implantation enhances the ingress of O, C and N and produces TiO2, Al2O3, TiC, TiN in the near surface layer on their removal from the vacuum and exposure to normal atmospheric condition. In the near surface layer, the hardness of implanted samples increases remarkably comparing with the untreated sample, and the maximum peak increasing factor is up to 2.9 for the sample implanted with 3 ×1017 He/cm2. A decrease in surface roughness, resulting from the leveling effect of sputtering and re-deposition during implantation, has also been observed. Comparing with the untreated sample, implanted samples have a good wear resistance property. And the maximum increase in wear resistance reaches over seven times that of the untreated one for the sample implanted with 3×1017 He/cm2. The wear mechanism of implanted samples is abrasive-dominated.The present paper concentrates on tribological performance of Ti6Al4V alloy treated by helium plasmabased ion implantation with a voltage of -30 kV and a dose range of 1, 3, 6 and 9 ×1017 He/cm2. X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM) and Atomic force microscopy (AFM) were used to characterize composition, structure and surface morphology, respectively. The variation of hardness with indenting depth was measured and tribological performance was evaluated. The uniform cavities with a diameter of several nanometers are formed in the helium-implanted layer on Ti6Al4V alloy. Helium implantation enhances the ingress of O, C and N and produces TiO2, Al2O3, TiC, TiN in the near surface layer on their removal from the vacuum and exposure to normal atmospheric condition. In the near surface layer, the hardness of implanted samples increases remarkably comparing with the untreated sample, and the maximum peak increasing factor is up to 2.9 for the sample implanted with 3 ×1017 He/cm2. A decrease in surface roughness, resulting from the leveling effect of sputtering and re-deposition during implantation, has also been observed. Comparing with the untreated sample, implanted samples have a good wear resistance property. And the maximum increase in wear resistance reaches over seven times that of the untreated one for the sample implanted with 3×1017 He/cm2. The wear mechanism of implanted samples is abrasive-dominated

Impact of device landing zone calcification patterns on paravalvular regurgitation after transcatheter aortic valve replacement with different next-generation devices

$\bf Objective$ Residual paravalvular regurgitation (PVR) has been associated to adverse outcomes after transcatheter aortic valve replacement (TAVR). This study sought to evaluate the impact of device landing zone (DLZ) calcification on residual PVR after TAVR with different next-generation transcatheter heart valves. $\bf Methods$ 642 patients underwent TAVR with a SAPIEN 3 (S3; n=292), ACURATE neo (NEO; n=166), Evolut R (ER; n=132) or Lotus (n=52). Extent, location and asymmetry of DLZ calcification were assessed from contrast-enhanced CT imaging and correlated to PVR at discharge. $\bf Results$ PVR was ≥moderate in 0.7% of S3 patients, 9.6% of NEO patients, 9.8% of ER patients and 0% of Lotus patients (p<0.001), and these differences remained after matching for total DLZ calcium volume. The amount of DLZ calcium was significantly related to the degree of PVR in patients treated with S3 (p=0.045), NEO (p=0.004) and ER (p<0.001), but not in Lotus patients (p=0.698). The incidence of PVR ≥moderate increased significantly over the tertiles of DLZ calcium volume (p=0.046). On multivariable analysis, calcification of the aortic valve cusps, LVOT calcification and the use of self-expanding transcatheter aortic valve implantation (TAVI) prostheses emerged as predictors of PVR. $\bf Conclusions$ The susceptibility to PVR depending on the amount of calcium was mainly observed in self-expanding TAVI prostheses. Thus, DLZ calcification is an important factor to be considered in prosthesis selection for each individual patient, keeping in mind the trade-off between PVR reduction, risk of new pacemaker implantation and unfavourable valve ha emodynamics