The role of altered cyclic strain patterns on proliferation and apoptosis of vascular smooth muscle cells - implications for in-stent restenosis

Currently, Percutaneous Transluminal Coronary Angioplasty (PTCA) followed by stent implantation is the frontline treatment in the management of coronary artery disease. To-date the main drawback of stent implantation is in-stent restenosis. Restenosis is a partial re-occlusion of the arterial wall predominantly due to vascular smooth muscle cells (SMC) migration from the media to the intima and subsequent SMC proliferation. A stent procedure dramatically alters the level of strains and stresses in the coronary artery and hence the mechanical environment of the SMC. We hypothesised that there exists a direct causal relationship between the level of strain and vascular SMC proliferation and apoptosis within the vessel wall. Cyclic strain can be seen as made by different independent components: mean strain, amplitude and frequency. In this work, the role of each strain component (mean strain, amplitude and frequency) in controlling Bovine Aortic Smooth Muscle Cells (BASMC) proliferative and apoptotic capacity was investigated. Cyclic strain decreased SMC proliferation and increased apoptosis in a temporal manner. The mean cyclic strain had no significant effect on the proliferative and apoptotic behaviour of SMC whereas SMC behaviour was highly dependent on strain amplitude. This observation was further validated using human SMC. The role of mean strain and strain amplitude was further investigated using a novel in-house phantom mock arterial system where BASMC were cultured inside a perfused stented Sylgard mock artery under physiological levels of strain. Vascular SMC proliferation was significantly increased (+40%) and apoptosis decreased within the stented region in comparison to the more compliant upstream and downstream non-stented regions of the mock Sylgard artery. We therefore conclude that the decrease in strain amplitude experienced by vascular SMC within the stented region may be responsible for SMC accumulation due to enhanced proliferation and decreased apoptosis. This study provides important evidence for the use of more compliant stent designs to maintain the anti-proliferative effect of cyclic strain on vascular SMC and therefore reduce restenosis

An investigation of the SCOZA for narrow square-well potentials and in the sticky limit

We present a study of the self consistent Ornstein-Zernike approximation (SCOZA) for square-well (SW) potentials of narrow width delta. The main purpose of this investigation is to elucidate whether in the limit delta --> 0, the SCOZA predicts a finite value for the second virial coefficient at the critical temperature B2(Tc), and whether this theory can lead to an improvement of the approximate Percus-Yevick solution of the sticky hard-sphere (SHS) model due to Baxter [R. J. Baxter, J. Chem. Phys. 49, 2770 (1968)]. For SW of non vanishing delta, the difficulties due to the influence of the boundary condition at high density already encountered in an earlier investigation [E. Schoell-Paschinger, A. L. Benavides, and R. Castaneda-Priego, J. Chem. Phys. 123, 234513 (2005)] prevented us from obtaining reliable results for delta < 0.1. In the sticky limit this difficulty can be circumvented, but then the SCOZA fails to predict a liquid-vapor transition. The picture that emerges from this study is that for delta --> 0, the SCOZA does not fulfill the expected prediction of a constant B2(Tc) [M. G. Noro and D. Frenkel, J. Chem. Phys. 113, 2941 (2000)], and that for thermodynamic consistency to be usefully exploited in this regime, one should probably go beyond the Ornstein-Zernike ansatz.Comment: 40 pages, 13 figures. Previous Sec. 2 on the Yukawa potential has been removed. Only the square-well potential is considered in this versio

Relevance of electron spin dissipative processes to dynamic nuclear polarization via thermal mixing

The available theoretical approaches aiming at describing Dynamic Nuclear spin Polarization (DNP) in solutions containing molecules of biomedical interest and paramagnetic centers are not able to model the behaviour observed upon varying the concentration of trityl radicals or the polarization enhancement caused by moderate addition of gadolinium complexes. In this manuscript, we first show experimentally that the nuclear steady state polarization reached in solutions of pyruvic acid with 15 mM trityl radicals is substantially independent from the average internuclear distance. This evidences a leading role of electron (over nuclear) spin relaxation processes in determining the ultimate performances of DNP. Accordingly, we have devised a variant of the Thermal Mixing model for inhomogenously broadened electron resonance lines which includes a relaxation term describing the exchange of magnetic anisotropy energy of the electron spin system with the lattice. Thanks to this additional term, the dependence of the nuclear polarization on the electron concentration can be properly accounted for. Moreover, the model predicts a strong increase of the final polarization on shortening the electron spin-lattice relaxation time, providing a possible explanation for the effect of gadolinium doping.Comment: 13 pages, 12 figure

Role of the glassy dynamics and thermal mixing in the dynamic nuclear polarization and relaxation mechanisms of pyruvic acid

The temperature dependence of $^1$H and $^{13}$C nuclear spin-lattice relaxation rate $1/T_1$ has been studied in the 1.6 K - 4.2 K temperature range in pure pyruvic acid and in pyruvic acid containing trityl radicals at a concentration of 15 mM. The temperature dependence of $1/T_1$ is found to follow a quadratic power law for both nuclei in the two samples. Remarkably the same temperature dependence is displayed also by the electron spin-lattice relaxation rate $1/T_{1e}$ in the sample containing radicals. These results are explained by considering the effect of the structural dynamics on the relaxation rates in pyruvic acid. Dynamic nuclear polarization experiments show that below 4 K the $^{13}$C build up rate scales with $1/T_{\text{1e}}$, in analogy to $^{13}$C $1/T_1$ and consistently with a thermal mixing scenario where all the electrons are collectively involved in the dynamic nuclear polarization process and the nuclear spin reservoir is in good thermal contact with the electron spin system.Comment: 14 pages, 13 figure

Additive manufacturing of silicon carbide by selective laser sintering of PA12 powders and polymer infiltration and pyrolysis

Abstract In this work, we propose a novel hybrid additive manufacturing technique, which combines selective laser sintering (SLS) of polyamide powders and subsequent preceramic polymer infiltration and pyrolysis to manufacture Silicon Carbide components for complex architectures. By controlling the porosity of the sintered polymeric preform we are able to control the shrinkage upon the first infiltration and pyrolysis. This enabled the manufacturing of smaller features than those achievable with other manufacturing techniques. The mechanical strength of the resulting ceramic increased with the number of reinfiltration cycles up to 24 MPa, inversely the residual porosity decreased to 10 vol%. The microstructure showed two distinct phases of SiOC and SiC. The first was attributed to the interaction between the porous polyamide and the ceramic precursor during the first infiltration. SiC derived from the pyrolysis of the preceramic precursor alone

Brightness for different surround conditions: the effect of transient glare

We measured the effect of a transient glare source on the perceived brightness of a standard luminance (Lstd) patch (0.5 cd/m2) as a function of the surround luminance (Ls). In the experiment, both increment and decrement stimuli were dependent on the value of the Ls (0.01, 0.2, 0.4, 0.6, 0.8, 1.0, 1.5, or 2.0 cd/m2). We adopted a magnitude comparison paradigm using constant stimuli to determine the test matching luminance (Lm). When Ls was lower than the luminance of the patch, which corresponds to increments, Lm was lower than Lstd, and this effect was highest for the lowest Ls. There was a small but noticeable cusp as increments shifted to decrements. As Ls increased further (i.e., as the decrement grew), Lm flattened out below Lstd. The overall pattern of results could be interpreted in terms of the concept of contrast brightness, with consideration of the intrinsic differences in brightness evaluations between decrements and increments.Fil: Issolio, Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Investigación en Luz, Ambiente y Visión. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Instituto de Investigación en Luz, Ambiente y Visión; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Luminotecnia, Luz y Visión; ArgentinaFil: Colombo, Elisa Margarita. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Investigación en Luz, Ambiente y Visión. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Instituto de Investigación en Luz, Ambiente y Visión; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Luminotecnia, Luz y Visión; Argentin

Situating Vocational Learning and Teaching Using Digital Technologies - A Mapping Review of Current Research Literature

Context: The ongoing change of work life by digital technologies requires vocational education and training (VET) to adapt constantly. This "digital transformation" of work life gives therefore rise to the question how to advance the use of digital technologies in VET. A possible answer may be found by considering that VET should be transferable to work life. This goal may be achieved by coupling educational activities with examples of work situations. Such situated education may be accomplished by using digital technologies. Until five years ago this mainly consisted in using digital photos, videos, and the internet for educational scaffolding or learning tasks. In research this situated digital VET taxonomy is currently expanding. Hence, the use of digital technologies in VET may be advanced by considering current research literature on situated digital VET.Method: Here, we have searched and reviewed scientific publications on situated digital VET published in the past five years. In the peer-reviewed publications that we had selected, we first identified which digital technologies were used for situated VET and which educational activities were coupled with work situation examples. Subsequently, we identified the categories to which the publications could be grouped together by analyzing the content of their full texts. Results: Situated digital VET was accomplished in about half of the reviewed publications by a digital video on a work situation, and in almost half of the publications by a work situation presented in a 3D virtual environment. Digital videos on work situations mostly served all types of learning tasks and rather rarely educational scaffolding. Work situations presented in 3D virtual environments mostly served cognitive or behavioral learning tasks and never educational scaffolding. Situated digital VET was moreover accomplished by using the digital representation of a work situation that either had occurred previously or that was immediately taking place. Conclusions: Our findings suggest that retrospectively and immediately situated digital VET may be the two categories of an up-to-date basic taxonomy of situated digital VET. Hence, an important question to investigate for advancing the use of digital technologies in VET is the following: Which of the two identified types of situated digital VET can facilitate which kind of vocational learning? Based on the reviewed publications we are not able to give any answers to this. Hence, there is a massive need to investigate which kind of vocational learning can be facilitated by retrospectively, and which by immediately situated digital VET.