3D Anastomosed Microvascular Network Model with Living Capillary Networks and Endothelial Cell-Lined Microfluidic Channels

This protocol describes detailed practical procedures for generating 3D intact and perfusable microvascular network that connects to microfluidic channels without appreciable leakage. This advanced 3D microvascular network model incorporates different stages of vascular development including vasculogenesis, endothelial cell (EC) lining, sprouting angiogenesis, and anastomosis in sequential order. The capillary network is first induced via vasculogenesis in a middle tissue chamber and then EC linings along the microfluidic channel on either side serve as artery and vein. The anastomosis is then induced by sprouting angiogenesis to facilitate tight interconnection between the artery/vein and the capillary network. This versatile device design and its robust construction methodology establish a physiological microcirculation transport model of interconnected perfused vessels from artery to vascularized tissue to vein

Microfluidic Perfusion for Regulating Diffusible Signaling in Stem Cells

Background Autocrine & paracrine signaling are widespread both in vivo and in vitro, and are particularly important in embryonic stem cell (ESC) pluripotency and lineage commitment. Although autocrine signaling via fibroblast growth factor-4 (FGF4) is known to be required in mouse ESC (mESC) neuroectodermal specification, the question of whether FGF4 autocrine signaling is sufficient, or whether other soluble ligands are also involved in fate specification, is unknown. The spatially confined and closed-loop nature of diffusible signaling makes its experimental control challenging; current experimental approaches typically require prior knowledge of the factor/receptor in order to modulate the loop. A new approach explored in this work is to leverage transport phenomena at cellular resolution to downregulate overall diffusible signaling through the physical removal of cell-secreted ligands. Methodology/Principal Findings We develop a multiplex microfluidic platform to continuously remove cell-secreted (autocrine\paracrine) factors to downregulate diffusible signaling. By comparing cell growth and differentiation in side-by-side chambers with or without added cell-secreted factors, we isolate the effects of diffusible signaling from artifacts such as shear, nutrient depletion, and microsystem effects, and find that cell-secreted growth factor(s) are required during neuroectodermal specification. Then we induce FGF4 signaling in minimal chemically defined medium (N2B27) and inhibit FGF signaling in fully supplemented differentiation medium with cell-secreted factors to determine that the non-FGF cell-secreted factors are required to promote growth of differentiating mESCs. Conclusions/Significance Our results demonstrate for the first time that flow can downregulate autocrine\paracrine signaling and examine sufficiency of extracellular factors. We show that autocrine\paracrine signaling drives neuroectodermal commitment of mESCs through both FGF4-dependent and -independent pathways. Overall, by uncovering autocrine\paracrine processes previously hidden in conventional culture systems, our results establish microfluidic perfusion as a technique to study and manipulate diffusible signaling in cell systems.National Institutes of Health (U.S.) (NIH grant No. EB007278)Swiss National Science FoundationSwiss National Science Foundatio

Ensemble Analysis of Angiogenic Growth in Three-Dimensional Microfluidic Cell Cultures

We demonstrate ensemble three-dimensional cell cultures and quantitative analysis of angiogenic growth from uniform endothelial monolayers. Our approach combines two key elements: a micro-fluidic assay that enables parallelized angiogenic growth instances subject to common extracellular conditions, and an automated image acquisition and processing scheme enabling high-throughput, unbiased quantification of angiogenic growth. Because of the increased throughput of the assay in comparison to existing three-dimensional morphogenic assays, statistical properties of angiogenic growth can be reliably estimated. We used the assay to evaluate the combined effects of vascular endothelial growth factor (VEGF) and the signaling lipid sphingoshine-1-phosphate (S1P). Our results show the importance of S1P in amplifying the angiogenic response in the presence of VEGF gradients. Furthermore, the application of S1P with VEGF gradients resulted in angiogenic sprouts with higher aspect ratio than S1P with background levels of VEGF, despite reduced total migratory activity. This implies a synergistic effect between the growth factors in promoting angiogenic activity. Finally, the variance in the computed angiogenic metrics (as measured by ensemble standard deviation) was found to increase linearly with the ensemble mean. This finding is consistent with stochastic agent-based mathematical models of angiogenesis that represent angiogenic growth as a series of independent stochastic cell-level decisions

The Role of Ethnic Directors in Corporate Social Responsibility: Does Culture matter? The Cultural Trait Theory Perspectives

This paper investigates the effect of cultural differences between ethnic directors on corporate social responsibility (CSR) of Public Liability Companies (PLCs) in Nigeria. Using the cultural trait theory, the study focuses on how the ethnic directors are influenced when making decisions concerning CSR. Adopting multiple regression analysis of data, the study investigates the three major ethnic groups (Yoruba, Igbo and Hausa) and finds cultural differences between the ethnic directors affect the adoption of CSR. Empirical results indicate that ethnic directors (Yoruba, Igbo and Hausa) were positively and significantly related to CSR. The paper contributes to the corporate governance and CSR debate concerning how ethnic directors’ decisions impact on CSR activities, particularly on the directors who are individualistic and collectivists towards CSR

Influence of shear stress and size on viability of endothelial cells exposed to gold nanoparticles

Screening nanoparticle toxicity directly on cell culture can be a fast and cheap technique. Nevertheless, to obtain results in accordance with those observed in live animals, the conditions in which cells are cultivated should resemble the one encountered in live systems. Microfluidic devices offer the possibility to satisfy this requirement, in particular with endothelial cell lines, because they are capable to reproduce the flowing media and shear stress experienced by these cell lines in vivo. In this work, we exploit a microfluidic device to observe how human umbilical vein endothelial cells (HUVEC) viability changes when subject to a continuous flow of culture medium, in which spherical citrate-stabilized gold nanoparticles of different sizes and at varying doses are investigated. For comparison, the same experiments are also run in multiwells where the cells do not experience the shear stress induced by the flowing medium. We discuss the results considering the influence of mode of exposure and nanoparticle size (24 and 13 nm). We observed that gold nanoparticles show a lower toxicity under flow conditions with respect to static and the HUVEC viability decreases as the nanoparticle surface area per unit volume increases, regardless of size

Sourcing Technological Knowledge Through Foreign Inward Licensing to Boost the Performance of Indian Firms: The Contingent Effects of Internal R&D and Business Group Affiliation

Sourcing technological knowledge from abroad is becoming a popular strategy among emerging market firms (EMFs). Combining the Knowledge-Based View and the Resource Dependence Theory, we argue that augmenting technological knowledge through foreign licensing enables EMFs to access state-of-the-art technological knowledge, reduce operational costs and risks associated to the innovation process, and develop a knowledge-based competitive advantage, ultimately boosting their financial performance. Using data about Indian firms observed from 2001 to 2013, we find that firms with a higher share of foreign inward technology licenses report better financial performance. However, the positive impact of technological knowledge accessed through inward licensing on firm performance is contingent upon: (1) the internal knowledge developed through R&D activity, and (2) the affiliation with business groups. While Indian firms with higher level of internal R&D are able to better leverage the value of foreign technological knowledge, thus reaching higher performance, firms affiliated to business groups gain fewer benefits from licensed foreign technological knowledge than non-business-group affiliated firms

Study on chemotaxis and chemokinesis of bone marrow-derived mesenchymal stem cells in hydrogel-based 3D microfluidic devices

BACKGROUND: Controlling the fate of mesenchymal stems cells (MSCs) including proliferation, migration and differentiation has recently been studied by many researchers in the tissue engineering field. Especially, recruitment of stem cells to injury sites is the first and crucial step in tissue regeneration. Although significant progress has been made in the chemotactic migration of MSCs, MSC migration in three dimensional environments remains largely unknown. We developed a 3D hydrogel-based microfluidic-device to study the migration behavior of human MSCs in the presence of stromal-cell derived factor-1α (SDF-1α), interleukin 8 (IL-8) and Substance P (SP) which have been utilized as chemoattractant candidates of human mesenchymal stem cells (hMSCs). RESULTS: We systematically investigated the chemotactic migration behaviors of hMSCs and their responses to SDF-1α, IL-8, and SP. SDF-1α was shown to be the most fascinating chemoattractant candidate among those factors at a certain time point. We also found that each chemokine showed different chemoattractant abilities according to their concentration. In the case of SP, this factor showed chemokinesis not chemotaxis. Especially at a 7–8 × 10(−8) M concentration range, the chemokinesis ability driven by SP was further increased. The data suggest that some factors at the optimal concentration exhibit chemokinesis or chemotaxis in a 3D hydrogel-based microfluidic device. CONCLUSION: In this study on chemotaxis and chemokinesis of hMSCs, the system parameters such as chemokine concentration, system stability, and 2D or 3D microenvironment are critically important to obtain meaningful results