Long term expansion profile of mesenchymal stromal cells at protein nanosheet-stabilised bioemulsions for next generation cell culture microcarriers.

Tremendous progress in the identification, isolation and expansion of stem cells has allowed their application in regenerative medicine and tissue engineering, and their use as advanced in vitro models. As a result, stem cell manufacturing increasingly requires scale up, parallelisation and automation. However, solid substrates currently used for the culture of adherent cells are poorly adapted for such applications, owing to their difficult processing from cell products, relatively high costs and their typical reliance on difficult to recycle plastics and microplastics. In this work, we show that bioemulsions formed of microdroplets stabilised by protein nanosheets displaying strong interfacial mechanics are well-suited for the scale up of adherent stem cells such as mesenchymal stromal cells (MSCs). We demonstrate that, over multiple passages (up to passage 10), MSCs retain comparable phenotypes when cultured on such bioemulsions, solid microcarriers (Synthemax II) and classic 2D tissue culture polystyrene. Phenotyping (cell proliferation, morphometry, flow cytometry and differentiation assays) of MSCs cultured for multiple passages on these systems indicate that, although stemness is lost at late passages when cultured on these different substrates, stem cell phenotypes remained comparable between different culture conditions, at any given passage. Hence our study validates the use of bioemulsions for the long term expansion of adherent stem cells and paves the way to the design of novel 3D bioreactors based on microdroplet microcarriers

Extreme Reversal in Mechanical Anisotropy in Liquid-Liquid Interfaces Reinforced with Self-Assembled Protein Nanosheets

The structuring of liquid–liquid and liquid–air interfaces may play an important role in novel microfabrication platforms and biotechnologies, from the spontaneous formation of microfilaments from liquid droplets and the 3D printing of liquids, to the culture of stem cells on emulsions. Understanding the mechanical anisotropy of associated liquid interfaces is essential for the development of such systems. Models of AFM indentation at liquid interfaces, based on the Young-Laplace model, currently do not allow the quantification of interfacial mechanical properties of associated molecular films. This report presents such a model and compares its predictions to interfacial mechanical properties characterised via interfacial shear rheology. An extreme reversal of mechanical anisotropy of liquid–liquid interfaces is observed, upon self-assembly of protein nanosheets, by 5 orders of magnitude. Results indicate that, although interfacial rheology is more sensitive than AFM indentation to the mechanics of molecular films in the low range of interfacial mechanics, AFM indentation allows the quantification of mechanical properties of stiffer molecular films, and remains better adapted to the characterisation of small samples and enables the characterisation of local heterogeneity

The culture of HaCaT cells on liquid substrates is mediated by a mechanically strong liquid-liquid interface

The mechanical properties of naturally-derived matrices and biomaterials are thought to play an important role in directing cell adhesion, spreading, motility, proliferation and differentiation. However, recent reports have indicated that cells may respond to local nanoscale physical cues, rather than bulk mechanical properties. We had previously reported that primary keratinocytes and mesenchymal stem cells did not seem to respond to the bulk mechanical properties of poly(dimethyl siloxane) (PDMS) substrates. In this study, we examine the mechanical properties of weakly crosslinked PDMS substrates and observe a liquid-like behaviour, with complete stress relaxation. We then report the observation that HaCaT cells, an epidermal cell line, proliferate readily at the surface of uncrosslinked liquid PDMS, as well as on low viscosity (0.77 cSt) fluorinated oil. These results are surprising, considering current views in the field of mechanotransduction on the importance of bulk mechanical properties, but we find that strong mechanical interfaces, presumably resulting from protein assembly, are formed at liquid–liquid interfaces for which cell adhesion and proliferation are observed. Hence our results suggest that cells sense the nanoscale mechanical properties of liquid–liquid interfaces and that such physical cues are sufficient to sustain the proliferation of adherent cells

Sequential decoupling of negative-energy states in Douglas-Kroll-Hess theory

Here, we review the historical development, current status, and prospects of Douglas--Kroll--Hess theory as a quantum chemical relativistic electrons-only theory.Comment: 15 page

Air-structured optical fiber drawn from a 3D-printed preform

© 2015 Optical Society of America. A structured optical fiber is drawn from a 3D-printed structured preform. Preforms containing a single ring of holes around the core are fabricated using filament made from a modified butadiene polymer. More broadly, 3D printers capable of processing soft glasses, silica, and other materials are likely to come on line in the not-so-distant future. 3D printing of optical preforms signals a new milestone in optical fiber manufacture

Classical and Quantum Equations of Motion for a BTZ Black String in AdS Space

We investigate gravitational collapse of a $(3+1)$-dimensional BTZ black string in AdS space in the context of both classical and quantum mechanics. This is done by first deriving the conserved mass per unit length of the cylindrically symmetric domain wall, which is taken as the classical Hamiltonian of the black string. In the quantum mechanical context, we take primary interest in the behavior of the collapse near the horizon and near the origin (classical singularity) from the point of view of an infalling observer. In the absence of radiation, quantum effects near the horizon do not change the classical conclusions for an infalling observer, meaning that the horizon is not an obstacle for him/her. The most interesting quantum mechanical effect comes in when investigating near the origin. First, quantum effects are able to remove the classical singularity at the origin, since the wave function is non-singular at the origin. Second, the Schr\"odinger equation describing the behavior near the origin displays non-local effects, which depend on the energy density of the domain wall. This is manifest in that derivatives of the wavefunction at one point are related to the value of the wavefunction at some other distant point.Comment: 9 pages, 1 figure. Minor Clarification and corrections. Accepted for Publication in JHE

Band structure engineering in (Bi1-xSbx)2Te3 ternary topological insulators

Three-dimensional (3D) topological insulators (TI) are novel quantum materials with insulating bulk and topologically protected metallic surfaces with Dirac-like band structure. The spin-helical Dirac surface states are expected to host exotic topological quantum effects and find applications in spintronics and quantum computation. The experimental realization of these ideas requires fabrication of versatile devices based on bulk-insulating TIs with tunable surface states. The main challenge facing the current TI materials exemplified by Bi2Se3 and Bi2Te3 is the significant bulk conduction, which remains unsolved despite extensive efforts involving nanostructuring, chemical doping and electrical gating. Here we report a novel approach for engineering the band structure of TIs by molecular beam epitaxy (MBE) growth of (Bi1-xSbx)2Te3 ternary compounds. Angle-resolved photoemission spectroscopy (ARPES) and transport measurements show that the topological surface states exist over the entire composition range of (Bi1-xSbx)2Te3 (x = 0 to 1), indicating the robustness of bulk Z2 topology. Most remarkably, the systematic band engineering leads to ideal TIs with truly insulating bulk and tunable surface state across the Dirac point that behave like one quarter of graphene. This work demonstrates a new route to achieving intrinsic quantum transport of the topological surface states and designing conceptually new TI devices with well-established semiconductor technology.Comment: Minor changes in title, text and figures. Supplementary information adde

Institutional Export Barriers on Exporters from Emerging Markets: Evidence from China

The emerging markets have become the increasingly important trading nations in the global economy. Given its significance to practitioners and policymakers, export barriers has been the popular topic in the international business studies. However, research about export barriers caused by the local institutions are under developed, though institutional voids and institutional inefficiency are reported as the major determinants for business development in emerging markets. This paper aims to fill in this gap by exploring the institutional export barriers in emerging markets. Based on existing studies on export barriers and institutional perspective, a conceptual framework is initially developed by separating formal and informal institutional export barriers. Then three specific institutional export barriers are identified, including government policy, weak legal system and informal and personal networks. In the meanwhile, this paper sheds light on how the institutional export barriers are developed and obstruct exporting in emerging markets