972 research outputs found
Electrospun fibrinogen-PLA nanofibres for vascular tissue engineering
Here we report on the development of a new type of hybrid fibrinogen–polylactic acid (FBG–PLA) nanofibres (NFs) with improved stiffness, combining the good mechanical properties of PLA with the excellent cell recognition properties of native FBG. We were particularly interested in the dorsal and ventral cell response to the nanofibres' organization (random or aligned), using human umbilical endothelial cells (HUVECs) as a model system. Upon ventral contact with random NFs, the cells developed a stellate-like morphology with multiple projections. The well-developed focal adhesion complexes suggested a successful cellular interaction. However, time-lapse analysis shows significantly lowered cell movements, resulting in the cells traversing a relatively short distance in multiple directions. Conversely, an elongated cell shape and significantly increased cell mobility were observed in aligned NFs. To follow the dorsal cell response, artificial wounds were created on confluent cell layers previously grown on glass slides and covered with either random or aligned NFs. Time-lapse analysis showed significantly faster wound coverage (within 12 h) of HUVECs on aligned samples vs. almost absent directional migration on random ones. However, nitric oxide (NO) release shows that endothelial cells possess lowered functionality on aligned NFs compared to random ones, where significantly higher NO production was found. Collectively, our studies show that randomly organized NFs could support the endothelization of implants while aligned NFs would rather direct cell locomotion for guided neovascularization
An Evaluation of Mouse and Keyboard Interaction Indicators towards Non-intrusive and Low Cost Affective Modeling in an Educational Context
AbstractIn this paper we propose a series of indicators, which derive from user's interactions with mouse and keyboard. The goal is to evaluate their use in identifying affective states and behavior changes in an e-learning platform by means of non-intrusive and low cost methods. The approach we have followed study user's interactions regardless of the task being performed and its presentation, aiming at finding a solution applicable in any domain. In particular, mouse movements and clicks, as well as keystrokes were recorded during a math problem solving activity where users involved in the experiment had not only to score their degree of valence (i.e., pleasure versus displeasure) and arousal (i.e., high activation versus low activation) of their affective states after each problem by using the Self-Assessment-Manikin scale, but also type a description of their own feelings. By using that affective labeling, we evaluated the information provided by these different indicators processed from the original user's interactions logs. In total, we computed 42 keyboard indicators and 96 mouse indicators
A new scanning tunneling microscope reactor used for high-pressure and high-temperature catalysis studies
This is the published version. Copyright 2008 American Institute of PhysicsWe present the design and performance of a homebuilt high-pressure and high-temperature reactor
equipped with a high-resolution scanning tunneling microscope STM for catalytic studies. In this
design, the STM body, sample, and tip are placed in a small high pressure reactor 19 cm3
located within an ultrahigh vacuum UHV chamber. A sealable port on the wall of the reactor
separates the high pressure environment in the reactor from the vacuum environment of the STM
chamber and permits sample transfer and tip change in UHV. A combination of a sample transfer
arm, wobble stick, and sample load-lock system allows fast transfer of samples and tips between the
preparation chamber, high pressure reactor, and ambient environment. This STM reactor can work
as a batch or flowing reactor at a pressure range of 10−13 to several bars and a temperature range of
300–700 K. Experiments performed on two samples both in vacuum and in high pressure conditions
demonstrate the capability of in situ investigations of heterogeneous catalysis and surface chemistry
at atomic resolution at a wide pressure range from UHV to a pressure higher than 1 atm
Plasma polymerised nanoscale coatings of controlled thickness for efficient solid-phase presentation of growth factors
The engineering of biomaterial surfaces and scaffolds for specific biomedical and clinical application is of growing interest. Certain functionalised surfaces can capture and deliver bioactive molecules, such as growth factors (GF), enhancing the clinical efficacy of such systems. With a custom-made plasma polymerisation reactor described here we have developed bioactive polymer coatings based on poly(ethyl acrylate) (PEA). This remarkable polymer unfolds fibronectin (FN) upon adsorption to allow the GF binding region of FN to sequester and present GFs with high efficiency. We systematically evaluate process conditions and their impact on plasma polymerised PEA coatings and characterise the effect of plasma power and deposition time on thickness, wettability and chemical composition of the coatings. We demonstrate that functional substrate roughness can be maintained after deposition of the polymer coatings. Importantly, we show that coatings deposited at different conditions all maintain a similar or better bioactivity than spin coated PEA references. We show that in PEA plasma polymerised coatings FN assembles into nanonetworks with high availability of integrin and GF binding regions that sequester bone morphogenetic protein-2 (BMP-2). We also report similar mesenchymal stem cell adhesion behaviour, as characterised by focal adhesions, and differentiation potential on BMP-2 coated surfaces, regardless of plasma deposition conditions. This is a potent and versatile technology that can help facilitate the use of GFs in clinical applications
In-situ X-ray photoelectron spectroscopy studies of water on metals and oxides at ambient conditions
X-ray photoelectron spectroscopy (XPS) is a powerful tool for surface and interface analysis, providing the elemental composition of surfaces and the local chemical environment of adsorbed species. Conventional XPS experiments have been limited to ultrahigh vacuum (UHV) conditions due to a short mean free path of electrons in a gas phase. The recent advances in instrumentation coupled with third-generation synchrotron radiation sources enables in-situ XPS measurements at pressures above 5 Torr. In this review, we describe the basic design of the ambient pressure XPS setup that combines differential pumping with an electrostatic focusing. We present examples of the application of in-situ XPS to studies of water adsorption on the surface of metals and oxides including Cu(110), Cu(111), TiO2(110) under environmental conditions of water vapor pressure. On all these surfaces we observe a general trend where hydroxyl groups form first, followed by molecular water adsorption. The importance of surface OH groups and their hydrogen bonding to water molecules in water adsorption on surfaces is discussed in detail
Induced Water Condensation and Bridge Formation by Electric Fields in Atomic Force Microscopy
The influence of the Hall effect on the global stability of cool protostellar disks
The influence of the Hall effect on the global stability of cool Kepler disks
under the influence of an axial magnetic field is considered. For sufficiently
large magnetic Reynolds numbers Rm the magnetorotational instability (MRI)
exists in a finite interval of magnetic field amplitudes, _{min} < <
_{max}. For Kepler disks the pure MRI needs both rather high Rm
(representing the needed electrical conductivity) as well as _{min} of order
0.1 G. The magnetic field pattern resulting from our global and linear
calculations is of quadrupolar parity. For magnetic fields to
the rotation axis the Hall effect reduces the minimum magnetic Reynolds number
by about one order of magnitude. The _{min}, however, is even (sightly)
increased (see Fig. 6). For magnetic fields to the rotation axis the
Hall effect drives its own instability without the action of the Lorentz force.
The corresponding critical magnetic Reynolds number proves to be larger with
Hall effect (Rm ~ 10) than without Hall effect (Rm ~ 7) so that the Hall effect
for parallel fields even disturbs the formation of MHD-instability in cool
protoplanetary disks. If the disk is supercritical then the main result of the
Hall effect for positive fields is the strong reduction of the minimum magnetic
field amplitude which is necessary to start the instability. Observations must
show whether in star-forming regions the rotation axis and the magnetic field
orientation are correlated or are anticorrelated. If the magnetic fields are
high enough then our model predicts the dominance of fields antiparallel to the
rotation axis.Comment: 7 pages, 7 figures, Astron. Astrophys. (in press
The structure of mixed H2O-OH monolayer films on Ru(0001)
Scanning tunneling microscopy (STM) and x-ray absorption spectroscopy (XAS) have been used to study the structures produced by water on Ru(0001) at temperatures above 140 K. It was found that while undissociated water layers are metastable below 140 K, heating above this temperature produces drastic transformations whereby a fraction of the water molecules partially dissociate and form mixed H{sub 2}O-OH structures. XPS and XAS revealed the presence of hydroxyl groups with their O-H bond essentially parallel to the surface. STM images show that the mixed H{sub 2}O-OH structures consist of long narrow stripes aligned with the three crystallographic directions perpendicular to the close-packed atomic rows of the Ru(0001) substrate. The internal structure of the stripes is a honeycomb network of H-bonded water and hydroxyl species. We found that the metastable low temperature molecular phase can also be converted to a mixed H{sub 2}O-OH phase through excitation by the tunneling electrons when their energy is 0.5 eV or higher above the Fermi level. Structural models based on the STM images were used for Density Functional Theory optimizations of the stripe geometry. The optimized geometry was then utilized to calculate STM images for comparison with the experiment
Breakfast glycaemic index and exercise: combined effects on adolescents' cognition
The aim of the present study was to examine the combined effects of breakfast glycaemic index (GI) and a mid-morning bout of exercise on adolescents’ cognitive function. Participants were randomly allocated to a high or low GI breakfast group in a mixed research design, where each participant completed two experimental trials (exercise and resting). Forty-two adolescents (12.4±0.5 years old), undertook a bout of exercise (ten repeats of level one of the multi-stage fitness test; exercise trial) or continued to rest (resting trial) following consumption of either a high or low GI breakfast. A battery of cognitive function tests (visual search test, Stroop test and Sternberg paradigm) was completed 30 min before and 45 min following the exercise. Average heart rate during exercise was 170±15 beats.min-1. On the complex level of the Stroop test, response times improved across the morning following the low GI breakfast on both the exercise and resting trials, though the improvement was greatest on the exercise trial. However, response times only improved on the resting trial following the high GI breakfast (p = 0.012). On the 5 letter level of the Sternberg paradigm, response times improved across the morning following the low GI breakfast (regardless of exercise) and only on the exercise trial following the high GI breakfast (p = 0.019). The findings of the present study suggest that the combined effects of breakfast GI and exercise in adolescents depend upon the component of cognitive function examined. A low GI breakfast and mid-morning bout of exercise were individually beneficial for response times on the Sternberg paradigm, whereas they conferred additional benefits for response times on the Stroop test
Hurdles to uptake of mesenchymal stem cells and their progenitors in therapeutic products
Twenty-five years have passed since the first clinical trial utilising mesenchymal stomal/stem cells (MSCs) in 1995. In this time academic research has grown our understanding of MSC biochemistry and our ability to manipulate these cells in vitro using chemical, biomaterial, and mechanical methods. Research has been emboldened by the promise that MSCs can treat illness and repair damaged tissues through their capacity for immunomodulation and differentiation. Since 1995, 31 therapeutic products containing MSCs and/or progenitors have reached the market with the level of in vitro manipulation varying significantly. In this review, we summarise existing therapeutic products containing MSCs or mesenchymal progenitor cells and examine the challenges faced when developing new therapeutic products. Successful progression to clinical trial, and ultimately market, requires a thorough understanding of these hurdles at the earliest stages of in vitro pre-clinical development. It is beneficial to understand the health economic benefit for a new product and the reimbursement potential within various healthcare systems. Pre-clinical studies should be selected to demonstrate efficacy and safety for the specific clinical indication in humans, to avoid duplication of effort and minimise animal usage. Early consideration should also be given to manufacturing: how cell manipulation methods will integrate into highly controlled workflows and how they will be scaled up to produce clinically relevant quantities of cells. Finally, we summarise the main regulatory pathways for these clinical products, which can help shape early therapeutic design and testing
- …