120 research outputs found
Fabrication of Plga/Hap and Plga/Phb/Hap Fibrous Nanocomposite Materials for Osseous Tissue Regeneration
The study presents the manufacturing of nanofibrous structures as osteoconductive, osteoinductive materials for osseous tissue regeneration. The fibrous structures were obtained by electrospinning of poly(l-lactide-coglicolide) (PLGA) with addition of hydroxyapatite (HAp) and of a blend of PLGA with polyhydroxybutyrate with HAp
added. The polymers used in the experiment were synthesised by an innovative method with a zirconium catalyst. First, the optimal electrospinning process parameters were selected. For the characterisation of the obtained osseous tissue reconstruction materials, the physical, macroscopic, functional, mechanical and thermal properties
as well as crystallinity index were studied. The study of the radiation sterilisation influence on average molar mass, thermal and mechanical properties was made in order to analyse the degradation effect
Nonlinear signalling networks and cell-to-cell variability transform external signals into broadly distributed or bimodal responses
We show theoretically and experimentally a mechanismbehind the emergence of wide or bimodal protein distributions in biochemical networks with nonlinear input-output characteristics (the dose-response curve) and variability in protein abundance. Large cell-to-cell variation in the nonlinear dose-response characteristics can be beneficial to facilitate two distinct groups of response levels as opposed to a graded response. Under the circumstances that we quantify mathematically, the two distinct responses can coexist within a cellular population, leading to the emergence of a bimodal protein distribution. Using flow cytometry, we demonstrate the appearance of wide distributions in the hypoxia-inducible factor-mediated response network in HCT116 cells. With help of our theoretical framework, we perform a novel calculation of the magnitude of cell-to-cell heterogeneity in the dose-response obtained experimentally
Fermiology via the electron momentum distribution
Investigations of the Fermi surface via the electron momentum distribution
reconstructed from either angular correlation of annihilation radiation (or
Compton scattering) experimental spectra are presented. The basis of these
experiments and mathematical methods applied in reconstructing
three-dimensional densities from line (or plane) projections measured in these
experiments are described. The review of papers where such techniques have been
applied to study the Fermi surface of metallic materials with showing their
main results is also done.Comment: 22 pages, 9 Figures, 4 Table
Different ways of dealing with Compton scattering and positron annihilation experimental data
Different ways of dealing with one-dimensional (1D) spectra, measured e.g. in
the Compton scattering or angular correlation of positron annihilation
radiation (ACAR) experiments are presented. On the example of divalent
hexagonal close packed metals it is shown what kind of information on the
electronic structure one can get from 1D profiles, interpreted in terms of
either 2D or 3D momentum densities. 2D and 3D densities are reconstructed from
merely two and seven 1D profiles, respectively. Applied reconstruction
techniques are particular solutions of the Radon transform in terms of
orthogonal Gegenabauer polynomials. We propose their modification connected
with so-called two-step reconstruction. The analysis is performed both in the
extended p and reduced k zone schemes. It is demonstrated that if positron wave
function or many-body effects are strongly momentum dependent, analysis of 2D
densities folded into k space may lead to wrong conclusions concerning the
Fermi surface. In the case of 2D ACAR data in Mg we found very strong many-body
effects. PACS numbers: 71.18.+y, 13.60.Fz, 87.59.FmComment: 17 pages, 9 figure
Collective ERK/Akt activity waves orchestrate epithelial homeostasis by driving apoptosis-induced survival.
Cell death events continuously challenge epithelial barrier function yet are crucial to eliminate old or critically damaged cells. How such apoptotic events are spatio-temporally organized to maintain epithelial homeostasis remains unclear. We observe waves of extracellular-signal-regulated kinase (ERK) and AKT serine/threonine kinase (Akt) activity pulses that originate from apoptotic cells and propagate radially to healthy surrounding cells. This requires epidermal growth factor receptor (EGFR) and matrix metalloproteinase (MMP) signaling. At the single-cell level, ERK/Akt waves act as spatial survival signals that locally protect cells in the vicinity of the epithelial injury from apoptosis for a period of 3-4 h. At the cell population level, ERK/Akt waves maintain epithelial homeostasis (EH) in response to mild or intense environmental insults. Disruption of this spatial signaling system results in the inability of a model epithelial tissue to ensure barrier function in response to environmental insults
Measurement and comparison of individual external doses of high-school students living in Japan, France, Poland and Belarus -- the "D-shuttle" project --
Twelve high schools in Japan (of which six are in Fukushima Prefecture), four
in France, eight in Poland and two in Belarus cooperated in the measurement and
comparison of individual external doses in 2014. In total 216 high-school
students and teachers participated in the study. Each participant wore an
electronic personal dosimeter "D-shuttle" for two weeks, and kept a journal of
his/her whereabouts and activities. The distributions of annual external doses
estimated for each region overlap with each other, demonstrating that the
personal external individual doses in locations where residence is currently
allowed in Fukushima Prefecture and in Belarus are well within the range of
estimated annual doses due to the background radiation level of other
regions/countries
Degradation, Bioactivity, and Osteogenic Potential of Composites Made of PLGA and Two Different SolâGel Bioactive Glasses
We have developed poly(l-lactide-co-glycolide) (PLGA) based composites using solâgel derived bioactive glasses (S-BG), previously described by our group, as composite components. Two different composite types were manufactured that contained either S2âhigh content silica S-BG, or A2âhigh content lime S-BG. The composites were evaluated in the form of sheets and 3D scaffolds. Sheets containing 12, 21, and 33Â vol.% of each bioactive glass were characterized for mechanical properties, wettability, hydrolytic degradation, and surface bioactivity. Sheets containing A2 S-BG rapidly formed a hydroxyapatite surface layer after incubation in simulated body fluid. The incorporation of either S-BG increased the tensile strength and Youngâs modulus of the composites and tailored their degradation rates compared to starting compounds. Sheets and 3D scaffolds were evaluated for their ability to support growth of human bone marrow cells (BMC) and MG-63 cells, respectively. Cells were grown in non-differentiating, osteogenic or osteoclast-inducing conditions. Osteogenesis was induced with either recombinant human BMP-2 or dexamethasone, and osteoclast formation with M-CSF. BMC viability was lower at higher S-BG content, though specific ALP/cell was significantly higher on PLGA/A2-33 composites. Composites containing S2 S-BG enhanced calcification of extracellular matrix by BMC, whereas incorporation of A2 S-BG in the composites promoted osteoclast formation from BMC. MG-63 osteoblast-like cells seeded in porous scaffolds containing S2 maintained viability and secreted collagen and calcium throughout the scaffolds. Overall, the presented data show functional versatility of the composites studied and indicate their potential to design a wide variety of implant materials differing in physico-chemical properties and biological applications. We propose these solâgel derived bioactive glassâPLGA composites may prove excellent potential orthopedic and dental biomaterials supporting bone formation and remodeling
Mitochondrial Variability as a Source of Extrinsic Cellular Noise
We present a study investigating the role of mitochondrial variability in
generating noise in eukaryotic cells. Noise in cellular physiology plays an
important role in many fundamental cellular processes, including transcription,
translation, stem cell differentiation and response to medication, but the
specific random influences that affect these processes have yet to be clearly
elucidated. Here we present a mechanism by which variability in mitochondrial
volume and functionality, along with cell cycle dynamics, is linked to
variability in transcription rate and hence has a profound effect on downstream
cellular processes. Our model mechanism is supported by an appreciable volume
of recent experimental evidence, and we present the results of several new
experiments with which our model is also consistent. We find that noise due to
mitochondrial variability can sometimes dominate over other extrinsic noise
sources (such as cell cycle asynchronicity) and can significantly affect
large-scale observable properties such as cell cycle length and gene expression
levels. We also explore two recent regulatory network-based models for stem
cell differentiation, and find that extrinsic noise in transcription rate
causes appreciable variability in the behaviour of these model systems. These
results suggest that mitochondrial and transcriptional variability may be an
important mechanism influencing a large variety of cellular processes and
properties
- âŚ