1,230 research outputs found
In situ study of partially crystallized bioglass (R) and hydroxylapatite in vitro bioactivity using atomic force microscopy
The present work investigates, in situ, the in vitro
bioactivity of partially crystallized 45S5 Bioglass! (BG) as a
function of immersion time in a simulated body fluid (SBF)
using atomic force microscopy (AFM). The results obtained
for the crystallized BG! were compared to those of hydroxyapatite
c- and a-faces. The calcium phosphate layer grows on
the crystallized 45S5 B! by multiple two-dimensional nucleation
and fusion of these two-dimensional islands, which is
essentially the same mode as for the hydroxyapatite c-face.
The surface of the crystallized 45S5 BG! was almost fully
covered with a dense and compact calcium phosphate layer
after 24 h. The calcium phosphate formation on the crystallized
BG! arises from a low surface energy of the surface
layer and/or an effect of the layer to lower the resistance
when the growth units of calcium phosphate incorporate
into the growing island. These results indicate that the crystallized
45S5 BG! is suitable to be used as a filler for polymeric
matrix bioactive composites, as it maintains a high
bioactivity associated with a stiffer behavior (as compared to
standard BG!)
Structural Color and Iridescence in Transparent Sheared Cellulosic Films
Shear transparent cellulose free-standing thin films can develop iridescence similar to that found in petals of the tulip Queen of the Night. The iridescence of the film arises from the modulation of the surface into bands periodically spread perpendicular to the shear direction. Small amounts of nanocrystalline cellulose (NCC) rods in the precursor liquid-crystalline solutions do not disturb the optical properties of the solutions but enhance the mechanical characteristics of the films and affects their iridescence. Smaller bands periodicity, not affected by the NCC rods, slightly deviated from the shear direction is also observed. NCCs are crucial to tune and understand the film's surface features formation. Our findings could lead to new materials for application in soft reflective screens and devices
Modelling of ductile fracture in single point incremental forming using a modified GTN model
Understanding the deformation and failure mechanisms in single point incremental forming (SPIF) is of great importance for achieving improved formability. Furthermore, there will be added benefits for more in depth evaluation of the effect of localised deformation to the fracture mechanism in SPIF. Although extensive research has been carried out in recent years, questions still remain on the shear and particularly its effect to the formability in SPIF processes. In this work, a modified Gurson–Tvergaard-Needleman (GTN) damage model was developed with the consideration of shear to predict ductile fracture in the SPIF process due to void nucleation and coalescence with results compared with original GTN model in SPIF. A combined approach of experimental testing and SPIF processing was used to validate finite element results of the shear modified Gurson–Tvergaard-Needleman damage model. The results showed that the shear modified GTN model improved the modelling accuracy of fracture over the original GTN model under shear loading conditions. Furthermore, the shear plays a role under meridional tensile stress to accelerate fracture propagation in SPIF processes
Subset- and tissue-defined STAT5 thresholds control homeostasis and function of innate lymphoid cells
Innate lymphoid cells (ILCs) patrol environmental interfaces to defend against infection and protect barrier integrity. Using a genetic tuning model, we demonstrate that the signal-dependent transcription factor (TF) STAT5 is critical for accumulation of all known ILC subsets in mice and reveal a hierarchy of STAT5 dependency for populating lymphoid and nonlymphoid tissues. We apply transcriptome and genomic distribution analyses to define a STAT5 gene signature in natural killer (NK) cells, the prototypical ILC subset, and provide a systems-based molecular rationale for its key functions downstream of IL-15. We also uncover surprising features of STAT5 behavior, most notably the wholesale redistribution that occurs when NK cells shift from tonic signaling to acute cytokine-driven signaling, and genome-wide coordination with T-bet, another key TF in ILC biology. Collectively, our data position STAT5 as a central node in the TF network that instructs ILC development, homeostasis, and function and provide mechanistic insights on how it works at cellular and molecular levels
Source and pathway analysis of lead and polycyclic aromatic hydrocarbons in Lisbon urban soils
Fighting viral infections and virus-driven tumors with cytotoxic CD4+ T cells
CD4+ T cells have been and are still largely regarded as the orchestrators of immune responses, being able to differentiate into distinct T helper cell populations based on differentiation signals, transcription factor expression, cytokine secretion, and specific functions. Nonetheless, a growing body of evidence indicates that CD4+ T cells can also exert a direct effector activity, which depends on intrinsic cytotoxic properties acquired and carried out along with the evolution of several pathogenic infections. The relevant role of CD4+ T cell lytic features in the control of such infectious conditions also leads to their exploitation as a new immunotherapeutic approach. This review aims at summarizing currently available data about functional and therapeutic relevance of cytotoxic CD4+ T cells in the context of viral infections and virus-driven tumors
Antimicrobial functionalized genetically engineered spider silk
Genetically engineered fusion proteins offer potential as multifunctional biomaterials for medical use.
Fusion or chimeric proteins can be formed using recombinant DNA technology by combining nucleotide
sequences encoding different peptides or proteins that are otherwise not found together in nature. In the
present study, three new fusion proteins were designed, cloned and expressed and assessed for function,
by combining the consensus sequence of dragline spider silk with three different antimicrobial peptides.
The human antimicrobial peptides human neutrophil defensin 2 (HNP-2), human neutrophil defensins 4
(HNP-4) and hepcidin were fused to spider silk through bioengineering. The spider silk domain maintained
its self-assembly features, a key aspect of these new polymeric protein biomaterials, allowing the
formation of b-sheets to lock in structures via physical interactions without the need for chemical crosslinking.
These new functional silk proteins were assessed for antimicrobial activity against Gram e
Escherichia coli and Gram þ Staphylococcus aureus and microbicidal activity was demonstrated. Dynamic
light scattering was used to assess protein aggregation to clarify the antimicrobial patterns observed.
Attenuated-total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and circular dichroism
(CD) were used to assess the secondary structure of the new recombinant proteins. In vitro cell studies
with a human osteosarcoma cell line (SaOs-2) demonstrated the compatibility of these new proteins
with mammalian cells.Fundação para a Ciência e a Tecnologia (FCT) - Bolsa de doutoramento (SFRH/BD/28603/2006); Chimera project (PTDC/EBB-EBI/109093/2008); NIH and Tissue Engineering Resource Center EB003210, P41
EB002520, DE017207
Novel poly(L-lactic acid)/hyaluronic acid macroporous hybrid scaffolds : characterization and assessment of cytotoxicity
Poly(L-lactic acid), PLLA, a synthetic biodegradable polyester, is widely accepted in tissue engineering. Hyaluronic acid (HA), a natural polymer, exhibits an excellent biocompatibility, influences cell signaling, proliferation, and differentiation. In this study, HA crosslinking was performed by immersion of the polysaccharide in water-acetone mixtures containing glutaraldehyde (GA). The objective of this work is to produce PLLA scaffolds with the pores coated with HA, that could be beneficial for bone tissue engineering applications. PLLA tridimensional scaffolds were prepared by compression molding followed by salt leaching. After the scaffolds impregnation with soluble HA solutions of distinct concentration, a GA-crosslinking reaction followed by inactivation of the unreacted GA with glycine was carried out. An increase on surface roughness is shown by scanning electron microscopy (SEM) with the addition of HA. Toluidine blue staining indicates the present of stable crosslinked HA. An estimation of the HA original weight in the hybrid scaffolds was performed using thermal gravimetric analyses. FTIR-ATR and XPS confirmed the crosslinking reaction. Preliminary in vitro cell culture studies were carried out using a mouse lung fibroblast cell line (L929). SEM micrographs of L929 showed that cells adhered well, spread actively throughout all scaffolds, and grew favorably. A MTS test indicated that cells were viable when cultured onto the surface of all scaffolds, suggesting that the introduction of crosslinked HA did not increase the cytotoxicity of the hybrid scaffolds.Contract grant sponsor: Portuguese Foundation for Science and Technology (FCT) through POCTIContract grant sponsor: FEDER programs including project ProteoLight; contract grant number: PTDC/FIS/68517/2006Contract grant sponsor: European Union funded STREP Project HIPPOCRATES; contract grant number: NMP3-CT-2003-505758Contract grant sponsor: European NoE EXPERTISSUES; contract grant number: NMP3-CT-2004-500283Contract grant sponsor: Spanish Ministry of Science (The FEDER financial support); contract grant number: MAT2007-66759-C03-01The authors acknowledge the funding for research in the field of Regenerative Medicine through the collaboration agreement from the Conselleria de Sanidad (Generalitat Valenciana) and the Instituto de Salud Carlos III (Ministry of Science and Innovation). The European Union Financing, as part of the SOCRA-TES/Erasmus program is also gratefully acknowledged
Effects of Epitope Modification on T Cell Receptor–Ligand Binding and Antigen Recognition by Seven H-2Kd–restricted Cytotoxic T Lymphocyte Clones Specific for a Photoreactive Peptide Derivative
We tested for antigen recognition and T cell receptor (TCR)–ligand binding 12 peptide derivative variants on seven H-2Kd–restricted cytotoxic T lymphocytes (CTL) clones specific for a bifunctional photoreactive derivative of the Plasmodium berghei circumsporozoite peptide 252– 260 (SYIPSAEKI). The derivative contained iodo-4-azidosalicylic acid in place of PbCS S-252 and 4-azidobenzoic acid on PbCS K-259. Selective photoactivation of the N-terminal photoreactive group allowed crosslinking to Kd molecules and photoactivation of the orthogonal group to TCR. TCR photoaffinity labeling with covalent Kd–peptide derivative complexes allowed direct assessment of TCR–ligand binding on living CTL. In most cases (over 80%) cytotoxicity (chromium release) and TCR–ligand binding differed by less than fivefold. The exceptions included (a) partial TCR agonists (8 cases), for which antigen recognition was fivetenfold less efficient than TCR–ligand binding, (b) TCR antagonists (2 cases), which were not recognized and capable of inhibiting recognition of the wild-type conjugate, (c) heteroclitic agonists (2 cases), for which antigen recognition was more efficient than TCR–ligand binding, and (d) one partial TCR agonist, which activated only Fas (CD95), but not perforin/granzymemediated cytotoxicity. There was no correlation between these divergences and the avidity of TCR–ligand binding, indicating that other factors than binding avidity determine the nature of the CTL response. An unexpected and novel finding was that CD8-dependent clones clearly incline more to TCR antagonism than CD8-independent ones. As there was no correlation between CD8 dependence and the avidity of TCR–ligand binding, the possibility is suggested that CD8 plays a critical role in aberrant CTL function
Ultrafast measurements of mode-specific deformation potentials of BiTe and BiSe
Quantifying electron-phonon interactions for the surface states of
topological materials can provide key insights into surface-state transport,
topological superconductivity, and potentially how to manipulate the surface
state using a structural degree of freedom. We perform time-resolved x-ray
diffraction (XRD) and angle-resolved photoemission (ARPES) measurements on
BiTe and BiSe, following the excitation of coherent A
optical phonons. We extract and compare the deformation potentials coupling the
surface electronic states to local A-like displacements in these two
materials using the experimentally determined atomic displacements from XRD and
electron band shifts from ARPES.We find the coupling in BiTe and
BiSe to be similar and in general in agreement with expectations from
density functional theory. We establish a methodology that quantifies the
mode-specific electron-phonon coupling experimentally, allowing detailed
comparison to theory. Our results shed light on fundamental processes in
topological insulators involving electron-phonon coupling
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