Static and dynamic compressive strains influence nitric oxide production and chondrocyte bioactivity when encapsulated in PEG hydrogels of different crosslinking densities

SummaryObjectiveMechanical loading is an important regulator of chondrocytes; however, many of the mechanisms involved in chondrocyte mechanotransduction still remain unclear. Here, poly(ethylene glycol) (PEG) hydrogels are proposed as a model system to elucidate chondrocyte response due to cell deformation, which is controlled by gel crosslinking (ρx).MethodsBovine articular chondrocytes (50×106cells/mL) were encapsulated in gels with three ρxs and subjected to static (15% strain) or dynamic (0.3Hz or 1Hz, 15% amplitude strain) loading for 48h. Cell deformation was examined by confocal microscopy. Cell response was assessed by total nitric oxide (NO) production, proteoglycan (PG) synthesis (35SO42−-incorporation) and cell proliferation (CP) ([3H]-thymidine incorporation). Oxygen consumption was assessed using an oxygen biosensor.ResultsAn increase in ρx led to lower water contents, higher compressive moduli, and higher cell deformations. Chondrocyte response was dependent on both loading regime and ρx. For example, under a static strain, NO was not affected, while CP and PG synthesis were inhibited in low ρx and stimulated in high ρx. Dynamic loading resulted in either no effect or an inhibitory effect on NO, CP, and PG synthesis. Overall, our results showed correlations between NO and CP and/or PG synthesis under static and dynamic (0.3Hz) loading. This finding was attributed to the hypoxic environment that resulted from the high cell-seeding density.ConclusionThis study demonstrates gel ρx and loading condition influence NO, CP, and PG synthesis. Under a hypoxic environment and certain loading conditions, NO appears to have a positive effect on chondrocyte bioactivity

Despite NAIS concerns electronic identification use by cow-calf producers is increasing

The proposed U.S. National Animal Identification System has generated concerns among producers relative to implementation of the system. Many of these concerns stem from the USDA’s Bovine Identification Working Group’s recommendations to use electronic Identification Plan Bovine Working Group has recommended radio frequency identification as the technology to individually identify cattle. Understanding and implementing an electronic identification system for cow-calf producers is believed to be one of the greatest challenges of implementing the National Animal Identification System

Phase Separation in a ternary DPPC DOPC POPC System with Reducing Hydration

The maintenance of plasma membrane structure is vital for the viability of cells. Disruption of this structure can lead to cell death. One important example is the macroscopic phase separation observed during dehydration associated with desiccation and freezing, often leading to loss of permeability and cell death. It has previously been shown that the hybrid lipid 1 palmitoyl 2 oleoyl sn glycero 3 phosphocholine POPC can act as a line active component in ternary lipid systems, inhibiting macroscopic phase separation and stabilising membrane microdomains in lipid vesicles [1]. The domain size is found to decrease with increasing POPC concentration until complete mixing is observed. However, no such studies have been carried out at reduced hydration. To examine if this phase separation is unique to vesicles in excess water, we have conducted studies on several binary and ternary model membrane systems at both reduced hydration powder type samples and oriented membrane stacks and in excess water supported lipid bilayers at 0.2 mol fraction POPC, in the range where microdomain stabilisation is reported. Differential scanning calorimetry DSC and Fourier transform infrared spectroscopy FTIR are used to map phase transition temperatures, with X ray and neutron scattering providing details of the changes in lipid packing and phase information within these boundaries. Atomic force microscopy AFM is used to image bilayers on a substrate in excess water. In all cases, macroscopic phase separation was observed rather than microdomain formation at this molar ratio. Thus POPC does not stabilise microdomains under these conditions, regardless of the type of model membrane, hydration or temperature. Thus we conclude that the driving force for separation under these conditions overcomes any linactant effects of the hybrid lipi

The hydrology of glacier-bed overdeepenings : sediment transport mechanics, drainage system morphology, and geomorphological implications

Evacuation of basal sediment by subglacial drainage is an important mediator of rates of glacial erosion and glacier flow. Glacial erosion patterns can produce closed basins (i.e., overdeepenings) in glacier beds, thereby introducing adverse bed gradients that are hypothesised to reduce drainage system efficiency and thus favour basal sediment accumulation. To establish how the presence of a terminal overdeepening might mediate seasonal drainage system evolution and glacial sediment export, we measured suspended sediment transport from Findelengletscher, Switzerland during late August and early September 2016. Analyses of these data demonstrate poor hydraulic efficiency of drainage pathways in the terminus region but high sediment availability. Specifically, the rate of increase of sediment concentration with discharge was found to be significantly lower than that anticipated if channelised flow paths were present. Sediment availability to these flow paths was also higher than would be anticipated for discrete bedrock-floored subglacial channels. Our findings indicate that subglacial drainage in the terminal region of Findelengletscher is dominated by distributed flow where entrainment capacity increases only marginally with discharge, but flow has extensive access to an abundant sediment store. This high availability maintains sediment connectivity between the glacial and proglacial realm and means daily sediment yield is unusually high relative to yields exhibited by similar Alpine glaciers. We present a conceptual model illustrating the potential influence of ice-bed morphology on subglacial drainage evolution and sediment evacuation mechanics, patterns and yields, and recommend that bed morphology should be an explicit consideration when monitoring and evaluating glaciated basin sediment export rates

Holonomy groups and W-symmetries

Irreducible sigma models, i.e. those for which the partition function does not factorise, are defined on Riemannian spaces with irreducible holonomy groups. These special geometries are characterised by the existence of covariantly constant forms which in turn give rise to symmetries of the supersymmetric sigma model actions. The Poisson bracket algebra of the corresponding currents is a W-algebra. Extended supersymmetries arise as special cases.Comment: pages 2

On manifolds with nonhomogeneous factors

We present simple examples of finite-dimensional connected homogeneous spaces (they are actually topological manifolds) with nonhomogeneous and nonrigid factors. In particular, we give an elementary solution of an old problem in general topology concerning homogeneous spaces

Social information behaviour in Bookshops: implications for digital libraries

We discuss here our observations of the interaction of bookshop customers with the books and with each other. Contrary to our initial expectations, customers do not necessarily engage in focused, joint information search, as observed in libraries, but rather the bookshop is treated as a social space similar to a cafe. Our results extend the known repertoire of collaborative behaviours, supporting further development of models of user tasks and goals. We compare our findings with previous work and discuss possible implications of our observations for the design of digital libraries as places of both information access and social interaction

D-Brane Probes of Special Holonomy Manifolds

Using D2-brane probes, we study various properties of M-theory on singular, non-compact manifolds of G_2 and Spin(7) holonomy. We derive mirror pairs of N=1 supersymmetric three-dimensional gauge theories, and apply this technique to realize exceptional holonomy manifolds as both Coulomb and Higgs branches of the D2-brane world-volume theory. We derive a ``G_2 quotient construction'' of non-compact manifolds which admit a metric of G_2 holonomy. We further discuss the moduli space of such manifolds, including the structure of geometrical transitions in each case. For completeness, we also include familiar examples of manifolds with SU(3) and Sp(2) holonomy, where some of the new ideas are clarified and tested.Comment: 79 pages, Late

Thermal and photochemical control of nitro-nitrito linkage isomerism in single-crystals of [Ni(medpt)(NO₂)(η²-ONO)]

The known complex [Ni(medpt)(η1-NO2)(η2-ONO)] 1 (medpt = 3,3′-diamino-N-methyldipropylamine) crystallises in the monoclinic space group P21/m with 1.5 molecules in the asymmetric unit with two different η1-NO2 ligand environments in the crystal structure. At 298 K the molecule (A) sitting in a general crystallographic site displays a mixture of isomers, 78% of the η1-NO2 isomer and 22% of an endo-nitrito–(η1-ONO) form. The molecule (B) sitting on a crystallographic mirror plane adopts the η1-NO2 isomeric form exclusively. However, a variable temperature crystallographic study showed that the two isomers were in equilibrium and upon cooling to 150 K the η1-ONO isomer converted completely to the η1-NO2 isomer, so that both independent molecules in the asymmetric unit were 100% in the η1-NO2 form. A kinetic analysis of the equilibrium afforded values of ΔH = −9.6 (±0.4) kJ mol−1, ΔS = −21.5 (±1.8) J K−1 mol−1 and EA = −1.6 (±0.05) kJ mol−1. Photoirradiation of single crystals of 1 with 400 nm light, at 100 K, resulted in partial isomerisation of the η1-NO2 isomer to the metastable η1-ONO isomer, with 89% for molecule (A), and 32% for molecule (B). The crystallographic space group also reduced in symmetry to P21 with Z′ = 3. The metastable state existed up to a temperature of 150 K above which temperature it reverted to the ground state. An analysis of the crystal packing in the ground and metastable states suggests that hydrogen bonding is responsible for the difference in the conversion between molecules (A) and (B)