In the context of drug eluting stent, we present two-dimensional numerical models of mass transport of the drug in the wall and in the lumen to study the effect of the drug diffusion coefficients in the three principal media (blood, vascular wall, and polymer coating treated as a three-compartment problem) and the impact of different strut apposition configurations (fully embedded, half embedded, and not embedded). The different conditions were analyzed in terms of their consequence on the drug concentration distribution in the arterial wall. We apply the concept of the therapeutic window to the targeted vascular wall region and derive simple metrics to assess the efficiency of the various stent configurations. Although most of the drug is dispersed in the lumen, variations in the blood flow rate within the physiological range of coronary blood flow and the diffusivity of the drug molecule in the blood were shown to have a negligible effect on the amount of drug in the wall. Our results reveal that the amount of drug cumulated in the wall depends essentially on the relative values of the diffusion coefficients in the polymer coating and in the wall. Concerning the strut apposition, it is shown that the fully embedded strut configuration would provide a better concentration distribution.
Stenting is becoming the major interventional cardiology procedure worldwide. However restenosis remains a major limitation to the effectiveness of stents. Alterations to the local hemodynamics in the stented segment of the artery could be a potential factor in the development of in-stent restenosis. The characterization of wall shear stress and of blood flow patterns in a stented artery is therefore necessary for a good understanding of the role of hemodynamics in the development of in-stent restenosis. We have used a time-dependent 3D numerical model of a stented coronary artery to study the characteristics of the blood flow and the shear stress distribution. Our results show that the presence of the stent produces significant secondary flow that is limited to an annulus in the near wall region. Low shear stress zones were localized in the vicinity of the struts while the tips of the struts exhibited high values of shear stress. These results support the hypothesis that local hemodynamics may affect the development of in-stent restenosis and could influence the choice of stent geometries for future stent designs.
This paper investigates the embeddedness of digital entrepreneurship in the entrepreneurs' indigenous value system by examining the influence of 'Ubuntu' on digital entrepreneurship activities in the South African context. We do so through an interpretive field study of two innovation clusters in South Africa. Our findings reveal Ubuntu as the basis of a community orientation to digital entrepreneurship that offers an alternative to the prevalent heroic view in which digital entrepreneurship narratives are centred around the individual entrepreneur(s). They also highlight the tensions faced by digital entrepreneurs as they attempt to uphold the Ubuntu values of humility, reciprocity, and benevolence while operating in a competitive and fast-paced environment. In addition, our study indicates that the way entrepreneurs draw on their indigenous value system is dynamic, giving rise to what we call digital Ubuntu, reflecting a reworking of Ubuntu values into their increasingly digital reality. The concept of digital Ubuntu brings to light how indigenous values can become entangled with the capabilities of digital technologies and highlights the need for indigenous perspectives to advance our understanding of the diversity of digital phenomena, such as digital entrepreneurship, across cultural contexts.
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