85 research outputs found
The effect of insulin-loaded chitosan particle-aggregated scaffolds in chondrogenic differentiation
Osteochondral defect repair requires a tissue engineering approach that aims at mimicking the physiological
properties and structure of two different tissues (cartilage and bone) using a scaffold–cell construct. One ideal
approach would be to engineer in vitro a hybrid material using a single-cell source. For that purpose, the scaffold
should be able to provide the adequate biochemical cues to promote the selective but simultaneous differentiation
of both tissues. In this work, attention was paid primarily to the chondrogenic differentiation by focusing
on the development of polymeric systems that provide biomolecules release to induce chondrogenic differentiation.
For that, different formulations of insulin-loaded chitosan particle–aggregated scaffolds were developed
as a potential model system for cartilage and osteochondral tissue engineering applications using insulin as a
potent bioactive substance known to induce chondrogenic differentiation. The insulin encapsulation efficiency
was shown to be high with values of 70.37!0.8%, 84.26!1.76%, and 87.23!1.58% for loadings of 0.05%, 0.5%,
and 5%, respectively. The in vitro release profiles were assessed in physiological conditions mimicking the cell
culture procedures and quantified by Micro-BCA! protein assay. Different release profiles were obtained that
showed to be dependent on the initial insulin-loading percentage. Further, the effect on prechondrogenic
ATDC5 cells was investigated for periods up to 4 weeks by studying the influence of these release systems on
cell morphology, DNA and glycosaminoglycan content, histology, and gene expression of collagen types I and II,
Sox-9, and aggrecan assessed by real-time polymerase chain reaction. When compared with control conditions
(unloaded scaffolds cultured with the standard chondrogenic-inducing medium), insulin-loaded scaffolds upregulated
the Sox-9 and aggrecan expression after 4 weeks of culture. From the overall results, it is reasonable to
conclude that the developed loaded scaffolds when seeded with ATDC5 can provide biochemical cues for
chondrogenic differentiation. Among the tested formulations, the higher insulin-loaded system (5%) was the
most effective in promoting chondrogenic differentiation.The authors would like to acknowledge the Portuguese Foundation for Science and Technology for the Ph. D. Grant to Patricia B. Malafaya (SFRH/BD/11155/2002). This work was partially supported and carried out under the scope of the European STREP Project HIPPOCRATES (NMP3-CT-2003-505758) and European NoE EXPERTISSUES (NMP3CT-2004-500283). The authors also like to acknowledge the Life and Health Sciences Research Institute (ICVS), University of Minho, for the use of their facilities, namely, to Luis Martins for histological sections slicing and H&E stain processing
dS-Holographic C-Functions with a Topological, Dilatonic Twist
Recently, the holographic aspects of asymptotically de Sitter spacetimes have
generated substantial literary interest. The plot continues in this paper, as
we investigate a certain class of dilatonically deformed ``topological'' de
Sitter solutions (which were introduced in hep-th/0110234). Although such
solutions possess a detrimental cosmological singularity, their interpretation
from a holographic perspective remains somewhat unclear. The current focus is
on the associated generalized -functions, which are shown to maintain their
usual monotonicity properties in spite of this exotic framework. These findings
suggest that such topological solutions may still play a role in our
understanding of quantum gravity with a positive cosmological constant.Comment: Latex, 30 pages; reference added and minor changes to tex
Reissner-Nordstrom-de Sitter black hole, planar coordinates and dS/CFT
We discuss the Reissner-Nordstrom-de Sitter black holes in the context of
dS/CFT correspondence by using static and planar coordinates. The boundary
stress tensor and the mass of the solutions are computed. Also, we investigate
how the RG flow is changed for different foliations. The Kastor-Traschen
multi-black hole solution is considered as well as AdS counterparts of these
configurations. In particular, we find that in planar coordinates the black
holes appear like punctures in the dual boundary theory.Comment: 30 pages, 3 eps figures, JHEP style v2: new references added,
misprints correcte
Non Linear Current Response of a Many-Level Tunneling System: Higher Harmonics Generation
The fully nonlinear response of a many-level tunneling system to a strong
alternating field of high frequency is studied in terms of the
Schwinger-Keldysh nonequilibrium Green functions. The nonlinear time dependent
tunneling current is calculated exactly and its resonance structure is
elucidated. In particular, it is shown that under certain reasonable conditions
on the physical parameters, the Fourier component is sharply peaked at
, where is the spacing between
two levels. This frequency multiplication results from the highly nonlinear
process of photon absorption (or emission) by the tunneling system. It is
also conjectured that this effect (which so far is studied mainly in the
context of nonlinear optics) might be experimentally feasible.Comment: 28 pages, LaTex, 7 figures are available upon request from
[email protected], submitted to Phys.Rev.
Moduli flow and non-supersymmetric AdS attractors
We investigate the attractor mechanism in gauged supergravity in the presence
of higher derivatives terms. In particular, we discuss the attractor behaviour
of static black hole horizons in anti-de Sitter spacetime by using the
effective potential approach as well as Sen's entropy function formalism. We
use the holographic techniques to interpret the moduli flow as an RG flow
towards the IR attractor horizon. We find that the holographic c-function obeys
the expected properties and point out some subtleties in understanding
attractors in AdS.Comment: 41 pages, 3 figures, JHEP style; V2: misprints corrected, expanded
references; V3: few typo's fixed in section
Galaxy Clusters Associated with Short GRBs. II. Predictions for the Rate of Short GRBs in Field and Cluster Early-Type Galaxies
We determine the relative rates of short GRBs in cluster and field early-type
galaxies as a function of the age probability distribution of their
progenitors, P(\tau) \propto \tau^n. This analysis takes advantage of the
difference in the growth of stellar mass in clusters and in the field, which
arises from the combined effects of the galaxy stellar mass function, the
early-type fraction, and the dependence of star formation history on mass and
environment. This approach complements the use of the early- to late-type host
galaxy ratio, with the added benefit that the star formation histories of
early-type galaxies are simpler than those of late-type galaxies, and any
systematic differences between progenitors in early- and late-type galaxies are
removed. We find that the ratio varies from R(cluster)/R(field) ~ 0.5 for n =
-2 to ~ 3 for n = 2. Current observations indicate a ratio of about 2,
corresponding to n ~ 0 - 1. This is similar to the value inferred from the
ratio of short GRBs in early- and late-type hosts, but it differs from the
value of n ~ -1 for NS binaries in the Milky Way. We stress that this general
approach can be easily modified with improved knowledge of the effects of
environment and mass on the build-up of stellar mass, as well as the effect of
globular clusters on the short GRB rate. It can also be used to assess the age
distribution of Type Ia supernova progenitors.Comment: ApJ accepted versio
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