Composite Gels Based on Poly (Vinyl alcohol) for Biomedical Uses

Nowadays, poly (vinyl alcohol) (PVA) hydrogels are being studied for several biomedical applications such as joint replacement, wound dressings and controlled drug-releasing devices, among others. Reinforced PVA hydrogels show good mechanical properties and are a suitable option to replace cartilages. Furthermore, these materials can prevent loss of body fluids, be a barrier against bacteria and also permeable to oxygen, for these all interesting properties, they are used like wound dressings. For drug delivery systems a material that can control the dose and release at the site of action is desirable, this can be accomplished using hydrogels, which are loaded with a drug, and then they can release it when an external stimulus (light, temperature, magnetic field, etc.) takes place. The aim of this work was to obtain composite hydrogels for the previously mentioned biomedical applications. Hydroxyapatite (HA) reinforced PVA gels were prepared for potential uses as cartilage replacement, HA improves the mechanical, tribological and fixing properties of the polymer, reaching values similar to that of the cartilages. For wound dressings, the hydrogel was reinforced with bentonite (clay) in order to increase the dimensional stability and antimicrobial properties. Gels with controlled drug release capability under magnetic stimulation (ferrogels) were also synthesized and characterized here.Fil: Hoppe, Cristina Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); ArgentinaFil: Alvarez, Vera Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); ArgentinaFil: Maiolo, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); ArgentinaFil: Gonzalez, Jimena Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentin

Why Matrix theory works for oddly shaped membranes

We give a simple proof of why there is a Matrix theory approximation for a membrane shaped like an arbitrary Riemann surface. As corollaries, we show that noncompact membranes cannot be approximated by matrices and that the Poisson algebra on any compact phase space is U(infinity). The matrix approximation does not appear to work properly in theories such as IIB string theory or bosonic membrane theory where there is no conserved 3-form charge to which the membranes couple.Comment: 8 pages, 4 figures, revtex; references adde

On Finite Noncommutativity in Quantum Field Theory

We consider various modifications of the Weyl-Moyal star-product, in order to obtain a finite range of nonlocality. The basic requirements are to preserve the commutation relations of the coordinates as well as the associativity of the new product. We show that a modification of the differential representation of the Weyl-Moyal star-product by an exponential function of derivatives will not lead to a finite range of nonlocality. We also modify the integral kernel of the star-product introducing a Gaussian damping, but find a nonassociative product which remains infinitely nonlocal. We are therefore led to propose that the Weyl-Moyal product should be modified by a cutoff like function, in order to remove the infinite nonlocality of the product. We provide such a product, but it appears that one has to abandon the possibility of analytic calculation with the new product.Comment: 13 pages, reference adde

Structural and magnetic behavior of ferrogels obtained by freezing thawing of polyvinyl alcohol/poly (acrylic acid) (PAA)-coated iron oxide nanoparticles

Superparamagnetic ferrogels with high swelling ability and potential applications as solvent absorbers and stimuli-responsive drug delivery devices were obtained by a non-toxic and environmentally friendly route based on dispersion of poly(acrylic acid)-coated iron oxide nanoparticles (PAA-coated NPs) in poly(vinyl alcohol) (PVA) solutions followed by freezing–thawing. Presence of carboxylate groups arising from the PAA coating allowed hydrogen bonding formation between NPs and PVA and enabled the synthesis of optically homogenous, superparamagnetic materials formed by a homogenous distribution of NPs diffuse clusters in the PVA matrix. The addition of PAA-coated NPs produced a remarkable increase in crystallinity degree, thermal degradation and swelling percentage respect to the neat matrix, which demonstrates that ferrogels with improved properties can be obtained by this procedure. Thereafter, combination of a cryogenic technique with the use of non-toxic components and magnetic NPs coated by a pH sensitive polymer makes these ferrogels very promising for applications in the biomedical field.Fil: Moscoso Londoño, Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería; Argentina. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Sólidos Amorfos; ArgentinaFil: Gonzalez, Jimena Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata; ArgentinaFil: Muraca, D.. Universidade Estadual de Campinas. Instituto de Física ’Gleb Wataghin’. Laboratorio de Materiais e Baixas Temperaturas; Brasil;Fil: Hoppe, Cristina Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata; ArgentinaFil: Alvarez, Vera Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata; ArgentinaFil: López Quintela, A.. Universidad de Santiago de Compostela; España;Fil: Socolovsky, Leandro Martin. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Houssay. Instituto D/tec.y Cs.de la Ing.;Fil: Pirota, K. R.. Universidade Estadual de Campinas. Instituto de Física ’Gleb Wataghin’. Laboratorio de Materiais e Baixas Temperaturas; Brasil

The formin FHOD1 and the small GTPase Rac1 promote vaccinia virus actin-based motility

Vaccinia virus dissemination relies on the N-WASP– ARP2/3 pathway, which mediates actin tail formation underneath cell-associated extracellular viruses (CEVs). Here, we uncover a previously unappreciated role for the formin FHOD1 and the small GTPase Rac1 in vaccinia actin tail formation. FHOD1 depletion decreased the number of CEVs forming actin tails and impaired the elongation rate of the formed actin tails. Recruitment of FHOD1 to actin tails relied on its GTPase binding domain in addition to its FH2 domain. In agreement with previous studies showing that FHOD1 is activated by the small GTPase Rac1, Rac1 was enriched and activated at the membrane surrounding actin tails. Rac1 depletion or expression of dominant-negative Rac1 phenocopied the effects of FHOD1 depletion and impaired the recruitment of FHOD1 to actin tails. FHOD1 overexpression rescued the actin tail formation defects observed in cells overexpressing dominant-negative Rac1. Altogether, our results indicate that, to display robust actin-based motility, vaccinia virus integrates the activity of the N-WASP– ARP2/3 and Rac1–FHOD1 pathways.Fil: Alvarez, Diego Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. University of Yale. School of Medicine; Estados UnidosFil: Agaisse, Herve. University of Yale. School of Medicine; Estados Unido

Symmetries, Currents and Conservation Laws of Self-Dual Gravity

We describe an infinite-dimensional algebra of hidden symmetries for the self-dual gravity equations. Besides the known diffeomorphism-type symmetries (affine extension of w(infinity) algebra), this algebra contains new hidden symmetries, which are an affine extension of the Lorentz rotations. The full symmetry algebra has both Kac-Moody and Virasoro-like generators, whose exponentiation maps solutions of the field equations to other solutions. Relations to problems of string theories are briefly discussed.Comment: 14 pages, LaTeX, the paper was reformatte

String Field Theory and the Fuzzy Sphere

We use boundary string field theory to study open string tachyon condensation on a three-sphere closed string background. We consider the closed string background described by $SU(2)_k$ WZW model in the limit of large $k$. We compute the exact tachyon potential and analyse the decay modes.Comment: 14 pages, Latex, typos corrected, ref. adde

Oxygen Isotope Analysis of Human Bone Phosphate Evidences Weaning Age in Archaeological Populations

Acknowledgements With special thanks to Jean-Jacques Hublin and the MPI-EVA; to Annabell Reiner (MPI-EVA) and Bernd Steinhilber (Universitat Tubingen) for technical support;and to the Deutscher Akademischer Austausch Dienst for financial support to KB during this project (ref: A0970923). This research was funded by the Max Planck Society. TT was financed by the DFG Emmy Noether Program and acknowledges funding by the grant TU 148/2-1 for the Emmy Noether Group Bone Geochemistry. Thanks also tothe University of Aberdeen for support during the preparation of this manuscript.Peer reviewedPostprin

Open strings in Lie groups and associative products

Firstly, we generalize a semi-classical limit of open strings on D-branes in group manifolds. The limit gives rise to rigid open strings, whose dynamics can efficiently be described in terms of a matrix algebra. Alternatively, the dynamics is coded in group theory coefficients whose properties are translated in a diagrammatical language. In the case of compact groups, it is a simplified version of rational boundary conformal field theories, while for non-compact groups, the construction gives rise to new associative products. Secondly, we argue that the intuitive formalism that we provide for the semi-classical limit, extends to the case of quantum groups. The associative product we construct in this way is directly related to the boundary vertex operator algebra of open strings on symmetry preserving branes in WZW models, and generalizations thereof, e.g. to non-compact groups. We treat the groups SU(2) and SL(2,R) explicitly. We also discuss the precise relation of the semi-classical open string dynamics to Berezin quantization and to star product theory.Comment: 47 pages, 14 figure