Effects of Liposomes Contained in Thermosensitive Hydrogels as Biomaterials Useful in Neural Tissue Engineering

Indexación: Scopus.Advances in the generation of suitable thermosensitive hydrogels for the delivery of cells in neural tissue engineering demonstrate a delicate relationship between physical properties and capabilities to promote cell proliferation and differentiation. To improve the properties of these materials, it is possible to add liposomes for the controlled release of bioactive elements, which in turn can affect the physical and biological properties of the hydrogels. In the present investigation, different hydrogels based on Pluronic F127 have been formulated with the incorporation of chitosan and two types of liposomes of two different sizes. The rheological and thermal properties and their relation with the neurite proliferation and growth of the PC12 cell line were evaluated. Our results show that the incorporation of liposomes modifies the properties of the hydrogels dependent on the concentration of chitosan and the lipid type in the liposomes, which directly affect the capabilities of the hydrogels to promote the viability and differentiation of PC12 cells. © 2017 by the authors.http://www.mdpi.com/1996-1944/10/10/112

Detection of a multi-shell planetary nebula around the hot subdwarf O-type star 2MASS J19310888+4324577

(Abridged) The origin of hot subdwarf O-type stars (sdOs) remains unclear since their discovery in 1947. Among others, a post-Asymptotic Giant Branch (post-AGB) origin is possible for a fraction of sdOs. We are involved in a comprehensive ongoing study to search for and to analyze planetary nebulae (PNe) around sdOs with the aim of establishing the fraction and properties of sdOs with a post-AGB origin. We use deep Halpha and [OIII] images of sdOs to detect nebular emission and intermediate resolution, long-slit optical spectroscopy of the detected nebulae and their sdO central stars. These data are complemented with other observations for further analysis of the detected nebulae. We report the detection of an extremely faint, complex PN around 2MASS J19310888+4324577 (2M1931+4324), a star classified as sdO in a binary system. The PN shows a bipolar and an elliptical shell, whose major axes are oriented perpendicular to each other, and high-excitation structures outside the two shells. WISE archive images show faint, extended emission at 12 and 22 microns in the inner nebular regions. The internal nebular kinematics is consistent with a bipolar and a cylindrical/ellipsoidal shell, in both cases with the main axis mainly perpendicular to the line of sight. The nebular spectrum only exhibits Halpha, Hbeta and [OIII]4959,5007 emission lines, but suggests a very low-excitation ([OIII]/Hbeta = 1.5), in strong contrast with the absence of low-excitation emission lines. The spectrum of 2M1931+4324 presents narrow, ionized helium absorptions that confirm the previous sdO classification and suggest an effective temperature >= 60000 K. The binary nature of 2M1931+4324, its association with a complex PN, and several properties of the system provide strong support for the idea that binary central stars are a crucial ingredient in the formation of complex PNe.Comment: 8 pages, 7 figures, accepted in Astronomy and Astrophysic

Interaction of landscape varibles on the potential geographical distribution of parrots in the Yucatan Peninsula, Mexico

La interacción de las variables del paisaje en la distribución geográfica potencial de los loros en la península de Yucatán, México La pérdida, degradación y fragmentación de las zonas boscosas están poniendo en peligro a las poblaciones de loros. En este estudio se determinó la influencia de la fragmentación en relación con la cobertura vegetal, los usos del suelo y la configuración espacial de los fragmentos, sobre los modelos de distribución geográfica potencial de los loros en la península de Yucatán, México. Se utilizó la distribución geográfica potencial de ocho especies de loros, teniendo en cuenta los mapas publicados recientemente y obtenidos con el algoritmo de máxima entropía, y se incorporó el mapa de probabilidad de distribución de cada especie. Se calcularon 71 parámetros y variables que evalúan la fragmentación forestal, la configuración espacial de los fragmentos, la proporción ocupada por vegetación y los usos del suelo en 100 parcelas de aproximadamente 29 km² distribuidas al azar dentro de las zonas de presencia y ausencia predichas para cada especie. Además, se tuvo en cuenta la relación entre las variables ambientales y la probabilidad de distribución de las especies. Se empleó una regresión de mínimos cuadrados parciales para analizar la relación existente entre las variables empleadas y los modelos de distribución potencial. Ninguna de las variables ambientales analizadas determina por sí sola la presencia, la ausencia ni la probabilidad de distribución de los loros en la península. Se observó que para las ocho especies, ya sea debido a la presencia y la ausencia o a la probabilidad de distribución, las variables explicativas más importantes son la interacción entre tres variables, en especial la interacción entre la superficie forestal total, la longitud total de los perímetros de los fragmentos y la cantidad de bosque tropical subperennifolio de altura mediana. La fragmentación del hábitat influye sobre la distribución geográfica potencial de estas especies en combinación con otros factores ambientales asociados a la misma, como son la proporción de las diferentes coberturas vegetales y los usos del suelo que se desarrollan en las áreas deforestadas.La interacción de las variables del paisaje en la distribución geográfica potencial de los loros en la península de Yucatán, México La pérdida, degradación y fragmentación de las zonas boscosas están poniendo en peligro a las poblaciones de loros. En este estudio se determinó la influencia de la fragmentación en relación con la cobertura vegetal, los usos del suelo y la configuración espacial de los fragmentos, sobre los modelos de distribución geográfica potencial de los loros en la península de Yucatán, México. Se utilizó la distribución geográfica potencial de ocho especies de loros, teniendo en cuenta los mapas publicados recientemente y obtenidos con el algoritmo de máxima entropía, y se incorporó el mapa de probabilidad de distribución de cada especie. Se calcularon 71 parámetros y variables que evalúan la fragmentación forestal, la configuración espacial de los fragmentos, la proporción ocupada por vegetación y los usos del suelo en 100 parcelas de aproximadamente 29 km² distribuidas al azar dentro de las zonas de presencia y ausencia predichas para cada especie. Además, se tuvo en cuenta la relación entre las variables ambientales y la probabilidad de distribución de las especies. Se empleó una regresión de mínimos cuadrados parciales para analizar la relación existente entre las variables empleadas y los modelos de distribución potencial. Ninguna de las variables ambientales analizadas determina por sí sola la presencia, la ausencia ni la probabilidad de distribución de los loros en la península. Se observó que para las ocho especies, ya sea debido a la presencia y la ausencia o a la probabilidad de distribución, las variables explicativas más importantes son la interacción entre tres variables, en especial la interacción entre la superficie forestal total, la longitud total de los perímetros de los fragmentos y la cantidad de bosque tropical subperennifolio de altura mediana. La fragmentación del hábitat influye sobre la distribución geográfica potencial de estas especies en combinación con otros factores ambientales asociados a la misma, como son la proporción de las diferentes coberturas vegetales y los usos del suelo que se desarrollan en las áreas deforestadas.The loss, degradation, and fragmentation of forested areas are endangering parrot populations. In this study, we determined the influence of fragmentation in relation to vegetation cover, land use, and spatial configuration of fragments on the potential geographical distribution patterns of parrots in the Yucatan Peninsula, Mexico. We used the potential geographical distribution for eight parrot species, considering the recently published maps obtained with the maximum entropy algorithm, and we incorporated the probability distribution for each species. We calculated 71 metrics/variables that evaluate forest fragmentation, spatial configuration of fragments, the ratio occupied by vegetation, and the land use in 100 plots of approximately 29 km², randomly distributed within the presence and absence areas predicted for each species. We also considered the relationship between environmental variables and the distribution probability of species. We used a partial least squares regression to explore patterns between the variables used and the potential distribution models. None of the environmental variables analyzed alone determined the presence/absence or the probability distribution of parrots in the Peninsula. We found that for the eight species, either due to the presence/absence or the probability distribution, the most important explanatory variables were the interaction among three variables, particularly the interactions among the total forest area, the total edge, and the tropical semi–evergreen medium– height forest. Habitat fragmentation influenced the potential geographical distribution of these species in terms of the characteristics of other environmental factors that are expressed together with the geographical division, such as the different vegetation cover ratio and land uses in deforested areas

The origin of the planetary nebula M 1-16. A morphokinematic and chemical analysis

We investigated the origin of the Planetary Nebula (PN) M 1-16 using narrow-band optical imaging, and high- and low-resolution optical spectra to perform a detailed morpho-kinematic and chemical studies. M 1-16 is revealed to be a multipolar PN that predominantly emits in [O III] in the inner part of the nebula and [N II] in the lobes. A novel spectral unsharp masking technique was applied to the position-velocity (PV) maps to reveal a set of multiple structures at the centre of M 1-16 spanning radial velocities from $-$40km$\,$s$^{-1}$ to 20km$\,$s$^{-1}$, with respect to the systemic velocity. The morpho-kinematic model indicates that the deprojected velocity of the lobe outflows are $\geq$100km$\,$s$^{-1}$, and particularly the larger lobes and knots have a deprojected velocity of $\simeq$350km$\,$s$^{-1}$; the inner ellipsoidal component has a deprojected velocity of $\simeq$29km$\,$s$^{-1}$. A kinematical age of $\sim$8700yr has been obtained from the model assuming a homologous velocity expansion law and a distance of 6.2$\pm$1.9kpc. The chemical analysis indicates that M 1-16 is a Type I PN with a central star of PN (CSPN) mass in the range of $\simeq$0.618-0.713M$_\odot$ and an initial mass for the progenitor star between 2.0 and 3.0M$_\odot$ (depending on metallicity). An $T_\mathrm{eff}\simeq$140$\,$000K and log$(L/L_{\odot})$=2.3 was estimated using the 3MdB photoionisation models to reproduce the ionisation stage of the PN. All of these results have led us to suggest that M 1-16 is an evolved PN, contrary to the scenario of proto-PN suggested in previous studies. We propose that the mechanism responsible for the morphology of M 1-16 is related to the binary (or multiple star) evolution scenario.Comment: A&A in press. 11 pages, 9 figure

Multiple and Precessing Collimated Outflows in the Planetary Nebula IC 4634

With its remarkable double-S shape, IC 4634 is an archetype of point-symmetric planetary nebulae (PN). In this paper, we present a detailed study of this PN using archival HST WFPC2 and ground-based narrow-band images to investigate its morphology, and long-slit spectroscopic observations to determine its kinematics and to derive its physical conditions and excitation. The data reveal new structural components, including a distant string of knots distributed along an arc-like feature 40"-60" from the center of the nebula, a skin of enhanced [O III]/H-alpha ratio enveloping the inner shell and the double-S feature, and a triple-shell structure. The spatio-kinematical study also finds an equatorial component of the main nebula that is kinematically independent from the bright inner S-shaped arc. We have investigated in detail the bow shock-like features in IC 4634 and found that their morphological, kinematical and emission properties are consistent with the interaction of a collimated outflow with surrounding material. Indeed, the morphology and kinematics of some of these features can be interpreted using a 3D numerical simulation of a collimated outflow precessing at a moderate, time-dependent velocity. Apparently, IC 4634 has experienced several episodes of point-symmetric ejections oriented at different directions with the outer S-shaped feature being related to an earlier point-symmetric ejection and the outermost arc-like string of knots being the relic of an even much earlier point-symmetric ejection. There is tantalizing evidence that the action of these collimated outflows has also taken part in the shaping of the innermost shell and inner S-shaped arc of IC 4634.Comment: 16 pages, 11 figures, accepted for publication in The Astrophysical Journa

Observational Study of the Multistructured Planetary Nebula NGC 7354

We present an observational study of the planetary nebula (PN) NGC 7354 consisting of narrowband Halpha and [NII]6584 imaging as well as low- and high-dispersion long-slit spectroscopy and VLA-D radio continuum. According to our imaging and spectroscopic data, NGC 7354 has four main structures: a quite round outer shell and an elliptical inner shell, a collection of low-excitation bright knots roughly concentrated on the equatorial region of the nebula, and two symmetrical jet-like features, not aligned either with the shells' axes, or with each other. We have obtained physical parameters like electron temperature and electron density as well as ionic and elemental abundances for these different structures. Electron temperature and electron density slightly vary throughout the nebula. The local extinction coefficient c_Hbeta shows an increasing gradient from south to north and a decreasing gradient from east to west consistent with the number of equatorial bright knots present in each direction. Abundance values show slight internal variations but most of them are within the estimated uncertainties. In general, abundance values are in good agreement with the ones expected for PNe. Radio continuum data are consistent with optically thin thermal emission. We have used the interactive three-dimensional modeling tool SHAPE to reproduce the observed morphokinematic structures in NGC 7354 with different geometrical components. Our SHAPE model is in very good agreement with our imaging and spectroscopic observations. Finally, after modeling NGC 7354 with SHAPE, we suggest a possible scenario for the formation of the nebula.Comment: Accepted for publication in AJ, 12 pages, 8 figure

Unveiling the structure of the planetary nebula M 2-48: Kinematics and physical conditions

The kinematics and physical conditions of the bipolar planetary nebula M 2-48 are analysed from high and low dispersion long-slit spectra. Previous CCD narrow-band optical observations have suggested that this nebula is mainly formed by a pair of symmetric bow-shocks, an off-center semi-circular shell, and an internal bipolar structure. The bipolar outflow has a complex structure, characterised by a series of shocked regions located between the bright core and the polar tips. There is an apparent kinematic discontinuity between the bright bipolar core and the outer regions. The fragmented ring around the bright bipolar region presents a low expansion velocity and could be associated to ejection in the AGB-PN transition phase, although its nature remains unclear. The chemical abundances of the central region are derived, showing that M 2-48 is a Type I planetary nebula (PN)