Microfluidics with fluid walls

Microfluidics has great potential, but the complexity of fabricating and operating devices has limited its use. Here we describe a method - Freestyle Fluidics - that overcomes many key limitations. In this method, liquids are confined by fluid (not solid) walls. Aqueous circuits with any 2D shape are printed in seconds on plastic or glass Petri dishes; then, interfacial forces pin liquids to substrates, and overlaying an immiscible liquid prevents evaporation. Confining fluid walls are pliant and resilient; they self-heal when liquids are pipetted through them. We drive flow through a wide range of circuits passively by manipulating surface tension and hydrostatic pressure, and actively using external pumps. Finally, we validate the technology with two challenging applications - triggering an inflammatory response in human cells and chemotaxis in bacterial biofilms. This approach provides a powerful and versatile alternative to traditional microfluidics.The complexity of fabricating and operating microfluidic devices limits their use. Walsh et al. describe a method in which circuits are printed as quickly and simply as writing with a pen, and liquids in them are confined by fluid instead of solid walls

Multiple populations in globular clusters. Lessons learned from the Milky Way globular clusters

Recent progress in studies of globular clusters has shown that they are not simple stellar populations, being rather made of multiple generations. Evidence stems both from photometry and spectroscopy. A new paradigm is then arising for the formation of massive star clusters, which includes several episodes of star formation. While this provides an explanation for several features of globular clusters, including the second parameter problem, it also opens new perspectives about the relation between globular clusters and the halo of our Galaxy, and by extension of all populations with a high specific frequency of globular clusters, such as, e.g., giant elliptical galaxies. We review progress in this area, focusing on the most recent studies. Several points remain to be properly understood, in particular those concerning the nature of the polluters producing the abundance pattern in the clusters and the typical timescale, the range of cluster masses where this phenomenon is active, and the relation between globular clusters and other satellites of our Galaxy.Comment: In press (The Astronomy and Astrophysics Review

'Going private': a qualitative comparison of medical specialists' job satisfaction in the public and private sectors of South Africa

BACKGROUND: There is a highly inequitable distribution of health workers between public and private sectors in South Africa, partly due to within-country migration trends. This article elaborates what South African medical specialists find satisfying about working in the public and private sectors, at present, and how to better incentivize retention in the public sector. METHODS: Seventy-four qualitative interviews were conducted - among specialists and key informants - based in one public and one private urban hospital in South Africa. Interviews were coded to determine common job satisfaction factors, both financial and non-financial in nature. This served as background to a broader study on the impacts of specialist 'dual practice', that is, moonlighting. All qualitative specialist respondents were engaged in dual practice, generally working in both public and private sectors. Respondents were thus able to compare what was satisfying about these sectors, having experience of both. RESULTS: Results demonstrate that although there are strong financial incentives for specialists to migrate from the public to the private sector, public work can be attractive in some ways. For example, the public hospital sector generally provides more of a team environment, more academic opportunities, and greater opportunities to feel 'needed' and 'relevant'. However, public specialists suffer under poor resource availability, lack of trust for the Department of Health, and poor perceived career opportunities. These non-financial issues of public sector dissatisfaction appeared just as important, if not more important, than wage disparities. CONCLUSIONS: The results are useful for understanding both what brings specialists to migrate to the private sector, and what keeps some working in the public sector. Policy recommendations center around boosting public sector resources and building trust of the public sector through including health workers more in decision-making, inter alia. These interventions may be more cost-effective for retention than wage increases, and imply that it is not necessarily just a matter of putting more money into the public sector to increase retention

Boundary work: An interpretive ethnographic perspective on negotiating and leveraging cross-cultural identity

The complexity of global organizations highlights the importance of members’ ability to span diverse boundaries that may be defined by organization structures, national borders, and/or a variety of cultures associated with organization, nation-based societal and work cultures, industries, and/or professions. Based on ethnographic research in a Japan–US binational firm, the paper describes and analyzes the boundary role performance of the firm\u27s Japanese members. It contributes toward theory on boundary spanning by introducing a “cultural identity negotiation” conceptual framework. We show boundary spanning as a process shaped through the interplay of the contextual issues that make a boundary problematic; an individual\u27s multiple repertoires of cultural knowledge; and the individual boundary spanner\u27s “negotiation”, through interaction with others, of his/her cultural identities – the sense of “who I am” as a cultural being that is fundamental to an individual\u27s self-concept. At the same time, we make transparent the epistemological and methodological foundations of an interpretive ethnographic approach, demonstrating its value for understanding complex organizational processes. Research findings have practical implications for the selection and training of an organization\u27s employees, particularly of persons who may be considered “bicultural”

The multiple faces of self-assembled lipidic systems

Lipids, the building blocks of cells, common to every living organisms, have the propensity to self-assemble into well-defined structures over short and long-range spatial scales. The driving forces have their roots mainly in the hydrophobic effect and electrostatic interactions. Membranes in lamellar phase are ubiquitous in cellular compartments and can phase-separate upon mixing lipids in different liquid-crystalline states. Hexagonal phases and especially cubic phases can be synthesized and observed in vivo as well. Membrane often closes up into a vesicle whose shape is determined by the interplay of curvature, area difference elasticity and line tension energies, and can adopt the form of a sphere, a tube, a prolate, a starfish and many more. Complexes made of lipids and polyelectrolytes or inorganic materials exhibit a rich diversity of structural morphologies due to additional interactions which become increasingly hard to track without the aid of suitable computer models. From the plasma membrane of archaebacteria to gene delivery, self-assembled lipidic systems have left their mark in cell biology and nanobiotechnology; however, the underlying physics is yet to be fully unraveled

Parameterization of a coarse-grained model of cholesterol with point-dipole electrostatics

© 2018, Springer Nature Switzerland AG. We present a new coarse-grained (CG) model of cholesterol (CHOL) for the electrostatic-based ELBA force field. A distinguishing feature of our CHOL model is that the electrostatics is modeled by an explicit point dipole which interacts through an ideal vacuum permittivity. The CHOL model parameters were optimized in a systematic fashion, reproducing the electrostatic and nonpolar partitioning free energies of CHOL in lipid/water mixtures predicted by full-detailed atomistic molecular dynamics simulations. The CHOL model has been validated by comparison to structural, dynamic and thermodynamic properties with experimental and atomistic simulation reference data. The simulation of binary DPPC/cholesterol mixtures covering the relevant biological content of CHOL in mammalian membranes is shown to correctly predict the main lipid behavior as observed experimentally

The study of atmospheric ice-nucleating particles via microfluidically generated droplets

Ice-nucleating particles (INPs) play a significant role in the climate and hydrological cycle by triggering ice formation in supercooled clouds, thereby causing precipitation and affecting cloud lifetimes and their radiative properties. However, despite their importance, INP often comprise only 1 in 10³–10⁶ ambient particles, making it difficult to ascertain and predict their type, source, and concentration. The typical techniques for quantifying INP concentrations tend to be highly labour-intensive, suffer from poor time resolution, or are limited in sensitivity to low concentrations. Here, we present the application of microfluidic devices to the study of atmospheric INPs via the simple and rapid production of monodisperse droplets and their subsequent freezing on a cold stage. This device offers the potential for the testing of INP concentrations in aqueous samples with high sensitivity and high counting statistics. Various INPs were tested for validation of the platform, including mineral dust and biological species, with results compared to literature values. We also describe a methodology for sampling atmospheric aerosol in a manner that minimises sampling biases and which is compatible with the microfluidic device. We present results for INP concentrations in air sampled during two field campaigns: (1) from a rural location in the UK and (2) during the UK’s annual Bonfire Night festival. These initial results will provide a route for deployment of the microfluidic platform for the study and quantification of INPs in upcoming field campaigns around the globe, while providing a benchmark for future lab-on-a-chip-based INP studies

Consensus guidelines for the use and interpretation of angiogenesis assays

The formation of new blood vessels, or angiogenesis, is a complex process that plays important roles in growth and development, tissue and organ regeneration, as well as numerous pathological conditions. Angiogenesis undergoes multiple discrete steps that can be individually evaluated and quantified by a large number of bioassays. These independent assessments hold advantages but also have limitations. This article describes in vivo, ex vivo, and in vitro bioassays that are available for the evaluation of angiogenesis and highlights critical aspects that are relevant for their execution and proper interpretation. As such, this collaborative work is the first edition of consensus guidelines on angiogenesis bioassays to serve for current and future reference