Biocompatible antimicrobial coatings may enhance the function of many orthopedic implants by combating infection. Hydroxyapatite is a choice mineral for such a coating as it is native to bone and ...silver would be a possible antimicrobial agent as it is also commonly used in biomedical applications. The aim of the research is to develop a silver-containing calcium phosphate (Ag/Ca-P) coating via electrochemical deposition on titanium substrates as this allows for controlled coating buildup on complex shapes and porous surfaces. Two different deposition approaches are explored: one-step Ag/Ca-P(1) deposition coatings, containing silver ions as microsized silver phosphate particles embedded in the Ca-P matrix; and via a two-step method (Ag/Ca-P(2)) where silver is deposited as metallic silver nanoparticle on the Ca-P coating. The Ag/Ca-P(1) coating displays a bacterial reduction of 76.1 ± 8.3% via Ag-ion leaching. The Ag/Ca-P(2) coating displays a bacterial reduction of 83.7 ± 4.5% via contact killing. Interestingly, by preincubation in phosphate-buffered saline solution, bacterial reduction improves to 97.6 ± 2.7 and 99.7 ± 0.4% for Ag/Ca-P(1) and Ag/Ca-P(2) coatings, respectively, due to leaching of formed AgCl x (x–1)– species. The biocompatibility evaluation indicates that the Ag/Ca-P(1) coating is cytotoxic towards osteoblasts while the Ag/Ca-P(2) coating shows excellent compatibility. The electrochemical deposition of highly bactericidal coatings with excellent biocompatibility will enable us to coat future bone implants even with complex or porous structures.
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IJS, KILJ, NUK, PNG, UL, UM
Quantitative bending and compression tests on micropillars made of two different amorphous alloys, with tip diameters ranging from 93 to 645
nm, are performed in situ in a transmission electron ...microscope (TEM). Under microcompression each pillar shows an intermittent plastic flow accommodated by inhomogeneous shear banding. However, the individual shear banding events are strongly size-dependent, i.e. in larger pillars the deformation is controlled by nucleation of shear bands, but in smaller pillars it becomes propagation-controlled. On the other hand, the yield stress is essentially size-independent. Microbending tests show further advantages by amplifying size effects and minimizing artifacts. An interesting finding is that by microbending, a switch from highly inhomogeneous to fully homogeneous deformation is observed at an experimentally accessible size regime near 200
nm, whereas it is not accessible under microcompression, even at a sub-100
nm scale. These size effects are well interpreted by a micromechanical model, leading to a deformation map in the stress-size space. A physical picture of nanoscale shear localization process is also provided.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
TiC/a-C:H nanocomposite coatings, deposited with closed-field unbalanced magnetron sputtering, have been scrutinized with atomic force, scanning and high-resolution transmission electron microscopy, ...nanoindentation and tribo-tests. These coatings consist of 2–5nm TiC nanocrystallites embedded in an amorphous hydrocarbon (a-C:H) matrix. A transition from a columnar to a glassy microstructure has been observed in the nanocomposite coatings with increasing substrate bias or carbon content. Microcracks induced by nanoindentation or sliding wear readily propagate through the column boundaries whereas the coatings without a columnar microstructure exhibit substantial toughness. The toughening of the nanocomposite coatings has been achieved effectively on two different scales, namely by restraining the formation of columns on a microscale and by manipulating the nanostructure on a nanoscale. The hardness (H) and elastic modulus (E) of the coatings are found to increase monotonically with increasing substrate bias, whereas the ratio of the hardness to the elastic modulus (H/E) remains approximately constant. In contrast, H/E increases with C content. Ball-on-disc tribo-tests confirm that the nanocomposite coatings possess superior wear resistance and strong self-lubrication effects with a coefficient of friction as low as 0.05 in ambient air and below 0.02 in dry air, under dry sliding against uncoated bearing steel balls. Physical arguments are presented to explain the toughening mechanism and the ultra-low friction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
► Complex nanoparticles have spherical shape with particle size around 100nm. ► Carboxymethyl chitosan coating improves encapsulation and controlled release. ► Encapsulation inhibits the ...oligomerization of indole-3-carbinol. ► Encapsulation significantly enhanced thermal- and photo-stabilities of I3C and DIM.
Indole-3-carbinol (I3C) and 3,3′-diindolylmethane (DIM) are two bioactive compounds from Cruciferous vegetables. The stability of these compounds is a major challenge for their pharmaceutical applications. In this study, zein and zein/carboxymethyl chitosan (CMCS) nanoparticles were prepared to encapsulate I3C and DIM by a combined liquid–liquid phase separation and ionic gelation method. After zein nanoparticles were coated with CMCS, the zeta potential was decreased from around −10 to −20mV, and encapsulation efficiency was greatly improved. Both nanoparticle formulations provided controlled release of I3C and DIM in PBS medium. Zein and zein/CMCS nanoparticles demonstrated similar protection for both I3C and DIM against ultraviolet (UV) light, attributed mainly to the contribution of the zein protein. Compared with zein nanoparticles, zein/CMCS nanoparticles exhibited better protection of I3C against degradation and better inhibition against its oligomerization to DIM under thermal condition (37°C). Based on our results, the encapsulation of hydrophobic bioactives in zein/CMCS nanoparticles is a promising approach to improve their stability against harsh conditions and provide controlled release for food/pharmaceutical applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
There is a growing awareness of the heterogeneity of obstructive sleep apnoea (OSA). Clinical trials of CPAP treatment on cardiovascular protection have been mostly negative. We aimed to assess the ...association between polysomnographic parameters and incident major adverse cardiovascular events (MACEs), and to investigate if the CPAP effect could be better delineated among clinical subgroups.
This sleep cohort study was conducted using a clinical database and territory-wide electronic health administration data in Hong Kong. Cox regressions were used to calculate HRs. Latent class analysis was used to cluster patients with OSA according to clinical and polysomnographic features.
Of 1860 eligible Chinese subjects who underwent polysomnography (2006-2013), 1544 (83%) had OSA. Over median follow-up of 8.3 years, 278 (14.9%) experienced MACEs. Apnoea-hypopnoea index (AHI) did not predict MACEs (HR: 0.95; 95% CI 0.76 to 1.17), whereas sleep time with oxygen saturation <90% (TST90) (HR: 1.41; 95% CI 1.10 to 1.81) was an independent predictor of MACEs, as were wake and nocturnal heart rate. In moderate-severe OSA (n=1108) who were indicated for CPAP treatment, regular CPAP was not associated with reduction of incident MACEs. Further cluster analysis identified a subgroup (n=333) who was younger, more obese, had more severe OSA (higher AHI and TST90) and more cardiovascular risks, in whom regular CPAP was associated with a lower risk of MACEs (HR:0.49, 95% CI 0.25 to 0.95).
OSA-related TST90 and mean heart rate, but not AHI, were robust predictors of MACEs. A clinical phenotype subgroup who demonstrated beneficial effect of CPAP treatment was identified.
Ultrashort pulsed laser ablation of stainless steels Villerius, V.; Kooiker, H.; Post, J. ...
International journal of machine tools & manufacture,
March 2019, 2019-03-00, 20190301, Volume:
138
Journal Article
Peer reviewed
Open access
This research investigated the ablation process of commercial stainless steels with ultrashort pulsed laser. Square hollows were ablated on stainless steel sheets using a picosecond laser with pulse ...duration of 0.25, 1 and 10 ps, respectively, and fluence ranging from 0.125 J/cm2 to 5 J/cm2. For each setting the surface quality and ablation efficiency were determined by optical microscopy and scanning electron microscopy (SEM). Processing windows producing high quality surfaces at high ablation efficiency were found at a fluence around 0.75 J/cm2 for the two shorter pulse lengths tested. Individual cones and periodic cone-like protrusions were found in the low fluence regime (<0.625 J/cm2) and high fluence regime (>0.875 J/cm2), respectively, both of which make the ablated surface rough. Emphasizing on the individual cones, it is found that the cones are caused by inclusions in the base materials, attributed to a higher fluence threshold required for ceramic-like inclusions. This novel theory explaining the creation mechanism is verified by multiple analysis methods like SEM and energy dispersive X-ray spectroscopy and stop-motion SEM imaging.
•Square hollows were ablated on stainless steel sheets using a picosecond laser.•Inclusions induced cones found in the low fluence regime (<0.625 J/cm2).•Periodic cone-like protrusions formed in the high fluence regime (>0.875 J/cm2).•Stop-motion SEM imaging revealed the formation mechanism of inclusions induced cones..•The process window is the widest for 0.25 ps pulse and narrows with increasing pulse duration.
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The intestinal epithelium is highly regenerative. Rapidly proliferating LGR5+ crypt base columnar (CBC) cells are responsible for epithelial turnover needed to maintain intestinal homeostasis. Upon ...tissue damage, loss of LGR5+ CBCs can be compensated by activation of quiescent +4 intestinal stem cells (ISCs) or early progenitor cells to restore intestinal regeneration. LGR5+ CBC self-renewal and ISC conversion to LGR5+ cells are regulated by external signals originating from the ISC niche. In contrast, little is known about intrinsic regulatory mechanisms critical for maintenance of LGR5+ CBC homeostasis. We found that LGR5 expression in intestinal crypt cells is controlled by the circadian core clock gene BMAL1 and the BMAL1-regulated RNA-binding protein MEX3A. BMAL1 directly activated transcription of Mex3a. MEX3A in turn bound to and stabilized Lgr5 mRNA. Bmal1 depletion reduced Mex3a and Lgr5 expression and led to increased ferroptosis, which consequently decreased LGR5+ CBC numbers and increased the number of crypt cells expressing +4 ISC marker BMI1. Together, these findings reveal a BMAL1-centered intrinsic regulatory pathway that maintains LGR5 expression in the crypt cells and suggest a potential mechanism contributing to ISC homeostasis.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Nanosized pillars with diameters ranging from 90 to 600nm of four amorphous alloys, Cu47Ti33Zr11Ni6Sn2Si1, Zr50Ti16.5Cu15Ni18.5, Zr61.8Cu18Ni10.2Al10 and Al86Ni9Y5, were fabricated and tested in situ ...in a transmission electron microscope. The major consideration when varying the composition was the change in bulk modulus and Poisson’s ratio, which may affect the deformation mode and ductility of metallic glasses (MGs) at the nanoscale. Differences between the deformation behavior of tapered (1.5–3°) and taper-free systems were also investigated. The yield stress of all the MGs measured through the in situ experiments is found to be essentially size independent, irrespective of tapering. With increasing size, all the MGs examined show a ductile-to-brittle transition under compression; the transition point, however, depends on the chemical composition of the specific MG investigated. The lower the μ/B ratio, the larger the pillar diameter above which more brittle behavior occurs. Al86Ni9Y5 taper-free MG showed a transition threshold to brittle behavior at the largest pillar diameter of 300nm. A micromechanical model is presented to explain the various dependencies.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Diamond-like carbon (DLC) films were deposited on nitrile butadiene rubber (NBR) by the DC magnetron sputtering under different bias voltages. Raman spectra revealed that the variation of bias ...voltage could tune the carbon bond structure in DLC films. Both the hardness and Young's modulus increased with the increasing bias voltage. Tribological tests revealed that the DLC-coated NBR prepared at the bias voltage of −200 V exhibited low wear rate due to its high hardness. The sealing property was studied by evaluating the leakage rate of volatile liquid in a simple apparatus. All DLC films resulted in less leakage rate as compared to the raw rubber under large stress. The lowest leakage rate occurred in the DLC-coated NBR prepared with a bias voltage of −200 V, which was associated with the theoretical calculations (Persson's theory). It was attributed to the synergetic effects of the variations of the Young's modulus and root-mean-square (Rms) roughness. The low Young's modulus and Rms, controlled by regulating bias voltage, could enhance actual contact area and reduce the leakage rate.
•Tribology property of diamond-like carbon film on rubber is tuned by bias voltage.•The coated diamond-like carbon film on rubber can impede the leakage.•Bias voltage can control the sealing property of coated nitrile butadiene rubber.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
The pulsed current electrochemical deposition of calcium phosphate (Ca-P) coatings on a titanium substrate was investigated in this study. The effects of applied voltage and H2O2 concentration in the ...electrolyte solution on the phase composition and coating morphology were studied using X-ray diffraction and scanning electron microscopy. At lower concentrations of H2O2, the coating consists of mixed phases of dicalcium phosphate dehydrate, octa-calcium phosphate, and hydroxyapatite, whereas increased H2O2 concentrations results in a dual phase of octa-calcium phosphate and hydroxyapatite being deposited. Furthermore, with increasing H2O2 concentration, the voltage must be reduced in order to avoid H2 evolution. The best conditions for Ca-P deposition were achieved at −1.4V and 1.5wt% H2O2. The morphological changes at different deposition times as well as the crystallographic orientation of deposited crystals were studied using scanning electron microscopy and transmission electron microscopy. It was found that the crystal growth of Ca-P coatings is a time-dependent process. During the first stage of deposition (t=1min), the electrolyte is supersaturated and randomly oriented polycrystals of Ca-P nucleate and form nanoplates. During the second stage (t=3min), crystals grow slightly in a more oriented fashion and form micro-sized plates. During the third stage (t>10min), the deposited crystals grow in a highly directional manner and the morphology of the coating consists of elongated ribbon-like single crystals.
•Pulsed current electrochemical deposition of calcium phosphate coatings on titanium;•Effects of voltage and H2O2 concentration in the electrolyte solution on the phase composition and coating morphology;•The nucleation and growth mechanism of Ca-P coatings change during the course of deposition;•Morphology of Ca-P coatings evolves from randomly oriented hydroxyapatite nanoplates to ribbon-like single crystals.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK, ZRSKP
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