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Temperature dependent stiffness and visco-elastic behaviour of lipid coated microbubbles using atomic force microscopy.
yesThe compression stiffness of a phospholipid microbubble was determined using force-spectroscopy as a function of temperature. The stiffness was found to decrease by approximately a factor of three from 0.08 N m 1, at 10 C, down to 0.03 N m 1 at 37 C. This temperature dependence indicates that the surface tension of lipid coating is the dominant contribution to the microbubble stiffness. The timedependent material properties, e.g. creep, increased non-linearly with temperature, showing a factor of two increase in creep-displacement, from 24 nm, at 10 C, to 50 nm, at 37 C. The standard linear solid model was used to extract the visco-elastic parameters and their determination at different temperatures allowed the first determination of the activation energy for creep, for a microbubble, to be determined.EPSR
From single steps to mass migration: the problem of scale in the movement ecology of the Serengeti wildebeest
A central question in ecology is how to link processes that occur over
different scales. The daily interactions of individual organisms ultimately
determine community dynamics, population fluctuations and the functioning
of entire ecosystems. Observations of these multiscale ecological
processes are constrained by various technological, biological or logistical
issues, and there are often vast discrepancies between the scale at which
observation is possible and the scale of the question of interest. Animal
movement is characterized by processes that act over multiple spatial and
temporal scales. Second-by-second decisions accumulate to produce
annual movement patterns. Individuals influence, and are influenced by,
collective movement decisions, which then govern the spatial distribution
of populations and the connectivity of meta-populations. While the
field of movement ecology is experiencing unprecedented growth in the
availability of movement data, there remain challenges in integrating
observations with questions of ecological interest. In this article, we present
the major challenges of addressing these issues within the context of the
Serengeti wildebeest migration, a keystone ecological phenomena that
crosses multiple scales of space, time and biological complexity.
This article is part of the theme issue ’Collective movement ecology’
Tattoo ink nanoparticles in skin tissue and fibroblasts
YesTattooing has long been practised in various societies all around the world and is becoming increasingly common and widespread
in the West. Tattoo ink suspensions unquestionably contain pigments composed of nanoparticles, i.e., particles of sub-100 nm
dimensions. It is widely acknowledged that nanoparticles have higher levels of chemical activity than their larger particle equivalents.
However, assessment of the toxicity of tattoo inks has been the subject of little research and ink manufacturers are not obliged
to disclose the exact composition of their products. This study examines tattoo ink particles in two fundamental skin components at
the nanometre level. We use atomic force microscopy and light microscopy to examine cryosections of tattooed skin, exploring the
collagen fibril networks in the dermis that contain ink nanoparticles. Further, we culture fibroblasts in diluted tattoo ink to explore
both the immediate impact of ink pigment on cell viability and also to observe the interaction between particles and the cells
The Effect of Polysialic Acid Expression on Glioma Cell Nano-mechanics
YesPolysialic acid (PolySia) is an important carbohydrate bio-polymer that is commonly over-expressed on tumours of neuroendocrine origin and plays a key role in tumour progression. PolySia exclusively decorates the neural cell adhesion molecule (NCAM) on tumour cell membranes, modulating cell-cell interactions, motility and invasion. In this preliminary study, we examine the nano-mechanical properties of isogenic C6 rat glioma cells - transfected cells engineered to express the enzyme polysialyltransferase ST8SiaII, which synthesises polySia (C6-STX cells) and wild type cells (C6-WT). We demonstrate that polySia expression leads to reduced elastic and adhesive properties but also more visco-elastic compared to non-expressing wild type cells. Whilst differences in cell elasticity between healthy and cancer cells is regularly assigned to changes in the cytoskeleton, we show that in this model system the change in properties at the nano-level is due to the polySia on the transfected cell membrane surface
Halogen Bonding with Phosphine: Evidence for Mulliken Inner Complexes and the Importance of Relaxation Energy
Intermolecular halogen bonding in complexes of phosphine and dihalogens has been
theoretically investigated using explicitly correlated coupled cluster methods and symmetry
adapted perturbation theory. The complexes H3P· · · ClF, H3P· · · BrF and H3P· · ·IF
are demonstrated to possess unusually strong interactions that are accompanied by an
increase in the induction component of the interaction energy and significant elongation
of the X–Y halogen distance on complex formation. The combination of these factors
is indicative of Mulliken inner complexes and criteria for identifying this classification
are further developed. The importance of choosing an electronic structure method that
describes both dispersion and longer range interactions is demonstrated, along with the
need to account for the change in geometry on complexation formation via relaxation
energy and overall stabilisation energies
Starling forces drive intracranial water exchange during normal and pathological states
Aim To quantify the exchange of water between cerebral
compartments, specifically blood, tissue, perivascular
pathways, and cerebrospinal fluid-filled spaces, on the basis
of experimental data and to propose a dynamic global
model of water flux through the entire brain to elucidate
functionally relevant fluid exchange phenomena.
Methods The mechanistic computer model to predict
brain water shifts is discretized by cerebral compartments
into nodes. Water and species flux is calculated between
these nodes across a network of arcs driven by Hagen-Poiseuille
flow (blood), Darcy flow (interstitial fluid transport),
and Starling’s Law (transmembrane fluid exchange). Compartment
compliance is accounted for using a pressurevolume
relationship to enforce the Monro-Kellie doctrine.
This nonlinear system of differential equations is solved implicitly
using MATLAB software.
Results The model predictions of intraventricular osmotic
injection caused a pressure rise from 10 to 22 mmHg, followed
by a taper to 14 mmHg over 100 minutes. The computational
results are compared to experimental data with
R2 = 0.929. Moreover, simulated osmotic therapy of systemic
(blood) injection reduced intracranial pressure from 25
to 10 mmHg. The modeled volume and intracranial pressure
changes following cerebral edema agree with experimental
trends observed in animal models with R2 = 0.997.
Conclusion The model successfully predicted time course
and the efficacy of osmotic therapy for clearing cerebral
edema. Furthermore, the mathematical model implicated
the perivascular pathways as a possible conduit for water
and solute exchange. This was a first step to quantify fluid
exchange throughout the brain
Multi-scale mechanical characterization of highly swollen photo-activated collagen hydrogels
Biological hydrogels have been increasingly sought after as wound dressings or scaffolds for regenerative medicine, owing to their inherent biofunctionality in biological environments. Especially in moist wound healing, the ideal material should absorb large amounts of wound exudate while remaining mechanically competent in situ. Despite their large hydration, however, current biological hydrogels still leave much to be desired in terms of mechanical properties in physiological conditions. To address this challenge, a multi-scale approach is presented for the synthetic design of cyto-compatible collagen hydrogels with tunable mechanical properties (from the nano- up to the macro-scale), uniquely high swelling ratios and retained (more than 70%) triple helical features. Type I collagen was covalently functionalized with three different monomers, i.e. 4-vinylbenzyl chloride, glycidyl methacrylate and methacrylic anhydride, respectively. Backbone rigidity, hydrogen-bonding capability and degree of functionalization (F: 16 ± 12–91 ± 7 mol%) of introduced moieties governed the structure–property relationships in resulting collagen networks, so that the swelling ratio (SR: 707 ± 51–1996 ± 182 wt%), bulk compressive modulus (Ec: 30 ± 7–168 ± 40 kPa) and atomic force microscopy elastic modulus (EAFM: 16 ± 2–387 ± 66 kPa) were readily adjusted. Because of their remarkably high swelling and mechanical properties, these tunable collagen hydrogels may be further exploited for the design of advanced dressings for chronic wound care
Investigation of Plasma Treatment on Micro-Injection Moulded Microneedle for Drug Delivery
YesPlasma technology has been widely used to increase the surface energy of the polymer surfaces for many industrial applications; in particular to increase in wettability. The present work was carried out to investigate how surface modification using plasma treatment modifies the surface energy of micro-injection moulded microneedles and its influence on drug delivery. Microneedles of polyether ether ketone and polycarbonate and have been manufactured using micro-injection moulding and samples from each production batch have been subsequently subjected to a range of plasma treatment. These samples were coated with bovine serum albumin to study the protein adsorption on these treated polymer surfaces. Sample surfaces structures, before and after treatment, were studied using atomic force microscope and surface energies have been obtained using contact angle measurement and calculated using the Owens-Wendt theory. Adsorption performance of bovine serum albumin and release kinetics for each sample set was assessed using a Franz diffusion cell. Results indicate that plasma treatment significantly increases the surface energy and roughness of the microneedles resulting in better adsorption and release of BSA
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