Célia Henriques

In vitro and in vivo evaluation of electrospun nanofibers of PCL, chitosan and gelatin: a comparative study.

Many polymers have been investigated with respect to their use in skin tissue engineering. However, directly comparable data on the role played by different polymers in assisting skin wound healing requires their in vitro and in vivo evaluation under the same conditions. Therefore, we performed a study in order to compare the performance of electrospun nanofiber mats from three different polymers concerning cell-scaffold interaction and wound healing promotion. A polyester (polycaprolactone, PCL), a protein (gelatin from cold water fish skin, GEL) and a polysaccharide (chitosan, CS) were the polymers chosen. Gelatin nanofibers were crosslinked with glutaraldehyde vapor. The scaffolds were characterized physico-chemically, in vitro by seeding with human fetal fibroblasts, HFFF2, and used in vivo as skin substitutes in a rat wound model with total skin removal. In vitro tests revealed that cells adhered and proliferated in all scaffolds. However, cells deep into the scaffold were only observed in the PCL and CS scaffolds. In in vivo tests CS scaffolds had the highest impact on the healing process by decreasing the extent of wound contraction and enhancing the production of a neodermis and re-epithelialization of the wound.

In vitro evaluation of crosslinked electrospun fish gelatin scaffolds.

Gelatin from cold water fish skin was electrospun, crosslinked and investigated as a substrate for the adhesion and proliferation of cells. Gelatin was first dissolved in either water or concentrated acetic acid and both solutions were successfully electrospun. Cross-linking was achieved via three different routes: glutaraldehyde vapor, genipin and dehydrothermal treatment. Solutions properties (surface tension, electrical conductivity and viscosity) and scaffolds properties (chemical bonds, weight loss and fiber diameters) were measured. Cellular viability was analyzed culturing 3T3 fibroblasts plated on the scaffolds and grown up to 7 days. The cells were fixed and observed with SEM or stained for DNA and F-actin and observed with confocal microscopy. In all scaffolds, the cells attached and spread with varying degrees. The evaluation of cell viability showed proliferation of cells until confluence in scaffolds crosslinked by glutaraldehyde and genipin; however the rate of growth in genipin crosslinked scaffolds was slow, recovering only by day five. The results using the dehydrothermal treatment were the less satisfactory. Our results show that glutaraldehyde treated fish gelatin is the most suitable substrate, of the three studied, for fibroblast adhesion and proliferation.

Evaluation of nanofibrous scaffolds obtained from blends of chitosan, gelatin and polycaprolactone for skin tissue engineering

Polymer blending is a strategy commonly used to obtain hybrid materials possessing properties better than those of the individual constituents regarding their use in scaffolds for Tissue Engineering. In the present work, the scaffolds produced by electrospinning solutions of polymeric blends obtained using a polyester (polycaprolactone, PCL), a polysaccharide (chitosan, CS) and a protein (gelatin extracted from cold water fish skin, GEL), were investigated. Solutions conductivity, shear viscosity and surface tension were determined. GEL-containing scaffolds were crosslinked with vapour phase glutaraldehyde (GTA). The scaffolds were characterized physico-chemically regarding fibre morphology, porosity, water contact angle, mechanical properties, chemical bonds and fibre and dimensional stability upon immersion in water and cell culture medium. The scaffolds were further tested in vitro for cell adhesion, growth and morphology of human foetal fibroblasts (cell line HFFF2). Results show that the nanofibrous scaffolds are hydrophilic and display the typical porosity of non-woven fibre mats. The CS/PCL and CS/PCL/GEL scaffolds have the highest elastic modulus (48MPa). Dimensional stability is best for the CS/PCL/GEL scaffolds. FTIR spectra confirm the occurrence of cross-linking reactions of GTA with both GEL and CS. Cell adhesion ratio ranked from excellent (close to 100%) to satisfactory (around 50%) in the order PCL/GEL>CS/GEL>CS/PCL/GEL>CS/PCL. Cell populations show an extended lag phase in comparison with the controls but cell proliferation occurs on all scaffolds until confluence is reached. In conclusion, all scaffolds studied possess characteristics that enable them to be used in skin tissue engineering but the CS/PCL/GEL scaffolds have better physical properties whereas the PCL/GEL scaffolds support a higher cell adhesion.

Dependence of metal surface properties on the valence-electron density in the stabilized jellium model

Abstract The stabilized jellium model is the simplest model which yields realistic results for the physical properties of simple metals. For the surface properties, its single input is the valence-electron density, which is described by the density parameter r s . We remark that the surface energy and the work function as a function of r s , within that model, are reasonably approximated by power laws and compare that behaviour with similar descriptions found in the literature and with experiment. We also present a simple relationship between the surface energy and the bulk modulus, which is well fitted by the power − 7 2 of the density parameter (when the effective valence is taken to be z ∗ =1 ). Another simple relationship between the work function and the bulk modulus is shown.

Cellulose-based electrospun fibers functionalized with polypyrrole and polyaniline for fully organic batteries

A novel cellulose-based bio-battery made of electrospun fibers activated by biological fluids has been developed. This work reports a new concept for a fully organic bio-battery that takes advantage of the high surface to volume ratio achieved by an electrospun matrix composed of sub-micrometric fibers that acts simultaneously as the separator and the support of the electrodes. Polymer composites of polypyrrole (PPy) and polyaniline (PANI) with cellulose acetate (CA) electrospun matrix were produced by in situ chemical oxidation of pyrrole and aniline on the CA fibers. The structure (CA/PPy|CA|CA/PANI) generated a power density of 1.7 mW g−1 in the presence of simulated biological fluids, which is a new and significant contribution to the domain of medical batteries and fully organic devices for biomedical applications.

Evanescent core pseudopotential: Applications to surfaces and clusters

A new local pseudopotential, called the “evanescent core” pseudopotential, has recently been proposed for sp-bonded metals. It is fitted to dominant density parameters of the solid state (valence, average equilibrium valence electron density, and interstitial valence electron density), and it yields an overall good description of physical properties such as binding energies and bulk moduli, in the framework of second-order perturbation theory. The potential, therefore, takes into account the atomic structure of the metal beyond the stabilized jellium model or structureless pseudopotential model. We present applications of the pseudopotential to surfaces and clusters of Na, Mg and Al, specifically: (i) Band-structure effects on surface tension and work functions; (ii) Cohesive energies and optimized structures of small clusters with two and six atoms (the latter with octahedral symmetry). The results are compared with those of the stabilized jellium model.

Metallic slabs: perturbative treatments based on jellium

Abstract We examine first-order perturbative results based on jellium for the surface energy of slabs of simple metals, using various local pseudo-potentials (Ashcroft, Heine–Abarenkov and evanescent core). The difference between the pseudo-potential and the jellium potential is averaged along the plane parallel to the surface. We compare these perturbative results with those of the stabilized-jellium model (a modification of the regular jellium model in which the perturbation appears in the energy functional right from the outset) and with the output of other perturbative and non-perturbative calculations.

The negative ionization of sputtered carbon atoms

The formation and survival probability of negative carbon ions sputtered from a graphite sample was determined. The energy distribution of C - ions was measured experimentally and the energy distribution of all sputtered carbon atoms was obtained from a computer simulation with the program TRIM.SP. From the two distributions, we obtained the probability that a carbon atom would capture an electron from the graphite and subsequently survive as it moves away from the surface. The results show two different situations. At low energy (below 25 eV), the sputtered particles are all negatively ionized when the affinity level crosses the graphite Fermi level and afterwards, the population decay follows a semi-classical rate equation. At higher energy (above 25 eV), a velocity-dependent fraction reaches the crossing distance as neutral atoms.