Understanding poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel as a multifunctional membrane in microfluidic cell culture platform

Cell culture technology developed at the turn of 20th century using Petri dish, which is not able to consider the microenvironment that the cells experience in vessels, has remained virtually unchanged for almost a century. However, such microenvironment associated with cell culture which usually consists of soluble factors, extracellular matrix cues, and cellular networks is difficult to reproduce experimentally with the traditional approach. In order to further elaborate complex mechanisms of cell biology through mimicking such microenvironment in vivo, the technical approaches together with developed microdevices are highly demanded within such a context. Microfluidic devices have been extensively developed and used for cell culture in the last two decades, which offer numerous advantages and a great potential for accurate and efficient control of the complex culturing microenvironment at cellular length scale. However, these devices are relatively complex in their fabrication and integration to fulfil multifunctional tasks for cell culture and drug testing simultaneously, which for example requires a membrane between the culture chamber and drug delivery reservoir to control microenvironment at cellular scale. This thesis is to primarily focus on the feasibility and reliability in the attempt of using poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel as an inserted membrane, based on its permeable and flexible tissue-like properties. PHEMA membrane is able to serve dual purposes in the microfluidic systems in cell culture: i) exchanging nutrients between culture chamber and drug delivery reservoir; and ii) sealing the microchannel circuits.</div

Dynamical Complexity of a Spatial Phytoplankton-Zooplankton Model with an Alternative Prey and Refuge Effect

The spatiotemporal dynamics of a phytoplankton-zooplankton model with an alternative prey and refuge effect is investigated mathematically and numerically. The stability of the equilibrium point and the traveling wave solution of the phytoplankton-zooplankton model are described based on theoretical mathematical work, which provides the basis of the numerical simulation. The numerical analysis shows that refuges have a strong effect on the spatiotemporal dynamics of the model according to the pattern formation. These results may help us to understand prey-predator interactions in water ecosystems. They are also relevant to research into phytoplankton-zooplankton ecosystems

Indole contributes to tetracycline resistance via the outer membrane protein OmpN in Vibrio splendidus

As an interspecies and interkingdom signaling molecule, indole has recently received attention for its diverse effects on the physiology of both bacteria and hosts. In this study, indole increased the tetracycline resistance of Vibrio splendidus. The minimal inhibitory concentration of tetracycline was 10 mu g/mL, and the OD600 of V. splendidus decreased by 94.5% in the presence of 20 mu g/mL tetracycline; however, the OD600 of V. splendidus with a mixture of 20 mu g/mL tetracycline and 125 mu M indole was 10- or 4.5-fold higher than that with only 20 mu g/mL tetracycline at different time points. The percentage of cells resistant to 10 mu g/mL tetracycline was 600-fold higher in the culture with an OD600 of approximately 2.0 (higher level of indole) than that in the culture with an OD600 of 0.5, which also meant that the level of indole was correlated to the tetracycline resistance of V. splendidus. Furthermore, one differentially expressed protein, which was identified as the outer membrane porin OmpN using SDS-PAGE combined with MALDI-TOF/TOF MS, was upregulated. Consequently, the expression of the ompN gene in the presence of either tetracycline or indole and simultaneously in the presence of indole and tetracycline was upregulated by 1.8-, 2.54-, and 6.01-fold, respectively, compared to the control samples. The combined results demonstrated that indole enhanced the tetracycline resistance of V. splendidus, and this resistance was probably due to upregulation of the outer membrane porin OmpN

What Drives Knowledge Payment in the Knowledge Payment Platform? An Empirical Study on the Purchase Behavior in the Emerging Market

Knowledge payment has become an emerging interactive mode. This research aims to investigate the influential factors driving knowledge demanders’ knowledge payment for online knowledge in emerging markets. By integrating flow experience theory and means-end chain theory, this paper reveals the relationships between each characteristic (product characteristics, demander characteristics, and platform characteristics), and knowledge demanders’ purchase intention. Hypotheses and theoretical model with product characteristics, demander characteristics, and platform characteristics of paid knowledge were proposed. 413 effective questionnaires were collected. A structural equation modeling was constructed and AMOS was used to illustrate the original estimate value of each path and correlations between items and factors. The results show that flow experience affects path dependence and perceived cost enjoyment, path dependence influences perceived cost performance. For product characteristics, perceived substitutability negatively influences perceived cost performance and purchase intention, and perceived cost performance affects purchase intention. For demander characteristics, perceived cost enjoyment positively affects purchase intention. For platform characteristics, perceived payment risk negatively influences purchase intention, while perceived payment convenience has no significant influence on purchase intention. The findings of the research provide some strategic enlightenment for content producers, knowledge payment platform managers