Cyclic mechanical stretch (CMS) is an important physiological and pathological factor in the heart.
We examined whether CMS can affect localization of gap junctions with regard to the cell axis.
...Neonatal rat cardiomyocytes were cultured (7 days) on flexible 6-well plates. Thereafter, cells were kept static or stimulated with CMS (1 Hz; 0, 10, 20% elongation) for 0, 24, or 48 hours (with or without 10 micromol/L PD98059, 5 micromol/L BIM I (bisindolylmaleimide I), 2 micromol/L H8 N-(2-methlyamino-ethyl)-5-isoquinoline-sulfonamid, or 0.1 micromol/L angiotensin II. Additionally, cells were exposed to 24 hours of CMS followed by 24 hours of static recovery. CMS (24 hour, 10%) induced elongation of the cardiomyocytes and orientation 79+/-8 degrees toward the stretch direction. Moreover, the distribution of connexin (Cx)43 together with N-cadherin changed, so that both proteins were accentuated at the cell poles, whereas in nonstretched cells, they were distributed around the cell without preferential localization. Additional angiotensin II reduced polar Cx43 accentuation. The CMS-induced changes in Cx43 were reversible within 24 hours after end of stretch, and could be completely prevented by the MEK1/2 inhibitor PD98059 but not by BIM I or H8. Moreover, stretch resulted in Cx43 protein and Cx43-mRNA upregulation and in a significant upregulation of the phosphorylated forms of ERK1/2, glycogen synthase kinase 3beta and AKT. Furthermore, CMS resulted in a significant increase of the transcription factors activator protein 1 and CREB (cAMP response element-binding protein) in the nucleus.
CMS results in self-organization of cardiomyocytes leading to elongated cells orientated transverse to the stretch axis, enhanced Cx43 expression and Cx43 accentuation at the cell poles. The Cx43-changes seem to depend on the ERK1/2 signaling cascade.
The aim of our study was to elucidate how cyclic mechanical stretch is sensed by cardiomyocytes and in which way it affects cytoskeletal organization.
Neonatal rat cardiomyocytes, cultured on ...flexible membranes, were subjected to cyclic mechanical stretch (1 Hz, 10% elongation) for 24 h using either round or rectangular loading posts for equibi-axial or uni-axial stretch, respectively, using the FlexCell stretch system. Cells were treated either with vehicle, the focal adhesion kinase (FAK) inhibitor PF-573,228 (200 nM), or the stretch-activated ion channel blocker gadolinium (Gd3+; 100 μM).
Cyclic mechanical stretch (36 mm diameter silicone membrane, equibi-axial stretch, 10% elongation, 1 Hz) induced elongation of the cardiomyocytes together with accentuation of Cx43 at the cell poles, and with an orientation of the cell axis between the radial axis and the circumferential axis (mean deviation: 11° from the circumference). Moreover, stretch resulted in ca. 1.4 fold increased Cx43 expression. FAK was found to be phosphorylated at the edges of the cells. In order to find out, how cardiomyocytes might sense stretch, we investigated possible effects of Gd3+and PF-573,228. Gd3+ had no effect on elongation or polarization and did not affect stretch-induced Cx43 expression. Interestingly, the FAK inhibitor completely antagonized the stretch-induced elongation, orientation and Cx43-polarization. However, the stretch-induced Cx43 expression was insensitive to this treatment. In order to clarify our result that the cells in equibi-axial stretch did not exactly organize to the circumference or to the radial axis, we decided to use a uni-axial stretch protocol. In uni-axially stretched cells, we found that the cardiomyocytes also showed elongation, Cx43 polarization, and orientation near to the stretch axis, but not exactly in the stretch axis but ca. 25° oblique to it. Furthermore, we investigated the tubular system, the Golgi apparatus, the SR and the nucleus. After 24 h stretch the microtubules were localized nearly (but not completely) parallel to the stretch axis (i.e. in longitudinal cell axis). Moreover, the localization of nucleus and the Golgi was also changed: while under static conditions, the Golgi was distributed more or less around the nucleus, after stretch the Golgi was accentuated at one site of the nucleus facing a cell pole with the nucleus facing the opposite cell pole. The plus motor protein kinesin accentuated at the cell poles and at the cell periphery, while the minus motor protein dynein was found near to the Golgi apparatus.
The stretch signal sensing is mediated via FAK and leads to intracellular re-organization and orientation. The oblique orientation of the cell with regard to the direction of stretch may define a directed force vector which could allow the cell to orientate.
The stress behavior and the associated microstructure evolution of industrial Ti(C,N)/α-Al2O3 coatings subjected to thermal cycling are investigated by in situ energy dispersive synchrotron X-ray ...diffraction and transmission electron microscopy. Temperature-dependent stresses and changes in microstructural parameters (domain size and microstrain) are analyzed by in situ measurements at different temperatures between 25 and 800 °C, both in the heating up and cooling down step, including several thermal cycles. Transmission electron microscopy is used to evaluate defects before and after the thermal treatment. The introduction of high compressive stresses in α-Al2O3 by top-blasting is connected to a high defect density at the basal planes of the alumina layer. The stress relaxation of the alumina layer at high temperatures is associated with a successive annihilation of defects until a reversible temperature-dependent stress condition is set. Top-blasting does not change the initial microstructure and residual stress of the Ti(C,N) layer. Ti(C,N) shows a cyclic stress behavior associated with the heat treatment and an elastic deformation behavior in the temperature range investigated.
Investigations on comb crack resistance of milling inserts coated with chemical vapor deposition (CVD) Ti(C,N)/α-Al2O3 and Zr(C,N)/α-Al2O3 showed a distinct wear evolution in both systems. Wear ...studies revealed that the appearance of comb cracks is connected to the initial CVD cooling crack network. Micropillar compression tests indicated a brittle intergranular fracture mechanism for the Ti(C,N) layer and a transgranular fracture accompanied with signs of plastic deformation for the Zr(C,N) coating. Additionally, for the Zr(C,N) based system, a compressive stress condition in the temperature range of interest (200–600 °C) was determined by in-situ synchrotron X-ray diffraction. The set of residual compressive stresses together with the ability of the Zr(C,N) layer to deform plastically are key features that explain the enhanced resistance to comb crack wear of the Zr(C,N) based system in milling of cast iron.
The aim of this study was to analyze whether local application of 3% hydrogen peroxide (H2O2) additionally to standard antibiotic prophylaxis following implantation of cardiac implantable electronic ...devices (CIED) reduces the incidence of pocket infections (PI).
In this observational case-control study every patient from the group additionally treated with H2O2 was matched with two patients out of the control group for age, male-gender, body-mass-index and operation time. The incidence of PI within 365 days after device implantation was compared.
During the 5-year study period, 429 consecutive patients were additionally treated with H2O2 and matched with 858 patients undergoing standard treatment (mean age 69 ± 12 years, 876 males (67.4%), body-mass-index 28 ± 4.0 kg/m2 and operation time 45 ± 23 min). Except for a more frequent use of dual-platelet-inhibition in the H2O2-group, clinical characteristics were otherwise similar. A total of 23 (1.78%) PIs occurred, most of them (14/23; 61%) during the first 45 days after implantation procedure. The use of H2O2 was associated with a significant reduction (3/429 = 0.69% versus 20/858 = 2.33%; p = 0.04), although patients of the H2O2 treated group received more complex procedures increasing the risk of PI.
Intraoperative local application of 3% H2O2 seems to be associated with a significant reduced incidence of PI following implantation of CIED. Because of its non-randomized character this trial should be considered as a hypothesis generating study.
The deposition of ternary nitrides with the incorporation of carbon atoms into its structure has demonstrated to be a promising approach in the pursuit of wear-resistant and self-lubricating ...coatings. Firstly, both TiAlN and TiAlCN monolayers were deposited using direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) onto quenched and tempered AISI H11 tool steel to be used as references. Acetylene was used as a carbon precursor, producing DCMS and HiPIMS TiAlCN coatings with 9.0 and 21.7 at.% C, respectively.
Subsequently, TiAlN/TiAlCN multilayers of various designs were also developed as follows: 5×10/500, 5×50/500 and 5×100/500 nm. Residual stresses of the coating systems were determined by X-ray radiation utilising an ETA-diffractometer with a Cu-Kα radiation source applying the sin2ψ method. Additionally, residual stresses depth gradients of the substrate before and after the deposition of the coatings were determined in a LEDDI 8-circle diffractometer equipped with a W-X-ray tube and operated in the energy-dispersive mode of diffraction. Great reduction of the compressive residual stresses in the coatings was observed after the introduction of carbon into the TiAlN coating structure, shifting from −1047 ± 149 to −307 ± 211 MPa for the DCMS and from −7035 ± 1361 to +989 ± 187 MPa for the HiPIMS coatings. In the multilayer coatings, compressive residual stresses increase along with the increment of the TiAlN interlayer. Additionally, residual stresses of the substrate in the near-surface are dragged from low compressive stresses (−218 ± 61) to tensile stresses in the range of 1000 to 2000 MPa for all the DCMS/substrate systems, a behaviour only presented in HiPIMS by the TiAlN monolayer. Wear coefficients of all the evaluated HiPIMS systems are notoriously lower than their DCMS counterparts. Compared to TiAlN, TiAlCN HiPIMS presented a lower coefficient of friction but a higher wear coefficient, which in turn was not reduced by the introduction of the multilayer systems. Finally, Scratch test and Rockwell C adhesion tests have shown higher adhesion of DCMS coatings than HiPIMS coatings, and a detriment of the monolayers adhesion by the implementation of TiAlN/TiAlCN multilayer systems. The understanding of the residual stresses, both in the coating and in the substrate, and the way they affect the tribomechanical performance of the system coating/substrate continues to be of great importance, especially for coatings deposited by new technologies such as HiPIMS and self-lubricating coatings.
•Great reduction of compressive residual stresses with the carbon inclusion in TiAlN.•High superficial residual stresses on the substrate after DCMS deposition.•Adhesion of DCMS coatings systems to AISI H11 is always higher than HiPIMS.•Ceramic/ceramic multilayer designs did not improved adhesion or wear.
Energy‐dispersive diffraction under both laboratory and synchrotron conditions was applied to study the hoop stress in the near‐surface region of the inner wall of boreholes with a small diameter of ...2 mm. By use of different X‐ray beam cross sections for the sin2ψ measurements, it is demonstrated that the borehole‐to‐beam‐diameter ratio must be considered in the evaluation. A beam cross section which is comparable to the borehole diameter reduces the slope of the dhklϕψ–sin2ψ distributions and thus invalidates the result of stress analysis. A quantitative relationship is applied, which allows the results obtained under the above conditions to be scaled so that they reflect the actual residual stress state at the measurement position. Owing to the small diffraction angles, energy‐dispersive diffraction proves to be the only suitable experimental technique that allows a nondestructive and depth‐resolved analysis of the hoop stress component at the inner surface of boreholes with a large length‐to‐diameter ratio.
Energy‐dispersive diffraction is used for the nondestructive analysis of the hoop stress depth distribution at the inner surface of narrow boreholes. The results are corrected for the rotation effect, which is shown to have a significant influence on the measurements.
EDDIDAT is a MATLAB‐based graphical user interface for the convenient and versatile analysis of energy‐dispersive diffraction data obtained at laboratory and synchrotron sources. The main focus of ...EDDIDAT up to now has been on the analysis of residual stresses, but it can also be used to prepare measurement data for subsequent phase analysis or analysis of preferred orientation. The program provides access to the depth‐resolved analysis of residual stresses at different levels of approximation. Furthermore, the graphic representation of the results also serves for the consideration of microstructural and texture‐related properties. The included material database allows for the quick analysis of the most common materials and is easily extendable. The plots and results produced with EDDIDAT can be exported to graphics and text files. EDDIDAT is designed to analyze diffraction data from various energy‐dispersive X‐ray sources. Hence it is possible to add new sources and implement the device‐specific properties into EDDIDAT. The program is freely available to academic users.
EDDIDAT is a program that provides a graphical user interface for the evaluation of energy‐dispersive X‐ray diffraction data with the focus on depth‐resolved residual stress analysis.
Abstract Constrained thermal expansion and contraction during welding cause a compression-tension cycle and plastic deformation in the heat-affected zone, leading to work hardening. The nature of ...this hardening effect—isotropic or kinematic—determines the final local yield stress and thus affects the residual stress state. Therefore, mechanical hardening must be modeled correctly in welding simulations for accurately predicting welding residual stresses. Previous studies, relying on comparisons with experimental ex situ results, led to different recommendations regarding the choice of the hardening model and thus require clarification. In this work, the stress evolution in the heat-affected zone of a tungsten inert gas weld is studied in situ using energy-dispersive x-ray diffraction and a novel method of stress analysis based on crystallite anisotropy. Additionally, microstructural information is gathered through line profile analysis. Results are shown for both austenitic and ferritic high-alloy steels and compared to ex-situ results including a validation of the new method of stress analysis. Finally, conclusions on the nature of work hardening are drawn.
The relationship between residual stresses and microstructure associated with a laser powder bed fusion (LPBF) IN718 alloy has been investigated on specimens produced with three different scanning ...strategies (unidirectional Y-scan, 90° XY-scan, and 67° Rot-scan). Synchrotron X-ray energy-dispersive diffraction (EDXRD) combined with optical profilometry was used to study residual stress (RS) distribution and distortion upon removal of the specimens from the baseplate. The microstructural characterization of both the bulk and the near-surface regions was conducted using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). On the top surfaces of the specimens, the highest RS values are observed in the Y-scan specimen and the lowest in the Rot-scan specimen, while the tendency is inversed on the side lateral surfaces. A considerable amount of RS remains in the specimens after their removal from the baseplate, especially in the Y- and Z-direction (short specimen dimension and building direction (BD), respectively). The distortion measured on the top surface following baseplate thinning and subsequent removal is mainly attributed to the amount of RS released in the build direction. Importantly, it is observed that the additive manufacturing microstructures challenge the use of classic theoretical models for the calculation of diffraction elastic constants (DEC) required for diffraction-based RS analysis. It is found that when the Reuß model is used for the calculation of RS for different crystal planes, as opposed to the conventionally used Kröner model, the results exhibit lower scatter. This is discussed in context of experimental measurements of DEC available in the literature for conventional and additively manufactured Ni-base alloys.
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