Jorge Carvalho Silva

Development of a new chitosan hydrogel for wound dressing

Wound healing is a complex process involving an integrated response by many different cell types and growth factors in order to achieve rapid restoration of skin architecture and function. The present study evaluated the applicability of a chitosan hydrogel (CH) as a wound dressing. Scanning electron microscopy analysis was used to characterize CH morphology. Fibroblast cells isolated from rat skin were used to assess the cytotoxicity of the hydrogel. CH was able to promote cell adhesion and proliferation. Cell viability studies showed that the hydrogel and its degradation by‐products are noncytotoxic. The evaluation of the applicability of CH in the treatment of dermal burns in Wistar rats was performed by induction of full‐thickness transcutaneous dermal wounds. Wound healing was monitored through macroscopic and histological analysis. From macroscopic analysis, the wound beds of the animals treated with CH were considerably smaller than those of the controls. Histological analysis revealed lack of a reactive or a granulomatous inflammatory reaction in skin lesions with CH and the absence of pathological abnormalities in the organs obtained by necropsy, which supported the local and systemic histocompatibility of the biomaterial. The present results suggest that this biomaterial may aid the re‐establishment of skin architecture.

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.

WO3 nanoparticle-based conformable pH sensor.

pH is a vital physiological parameter that can be used for disease diagnosis and treatment as well as in monitoring other biological processes. Metal/metal oxide based pH sensors have several advantages regarding their reliability, miniaturization, and cost-effectiveness, which are critical characteristics for in vivo applications. In this work, WO3 nanoparticles were electrodeposited on flexible substrates over metal electrodes with a sensing area of 1 mm(2). These sensors show a sensitivity of -56.7 ± 1.3 mV/pH, in a wide pH range of 9 to 5. A proof of concept is also demonstrated using a flexible reference electrode in solid electrolyte with a curved surface. A good balance between the performance parameters (sensitivity), the production costs, and simplicity of the sensors was accomplished, as required for wearable biomedical devices.

Multitechnique surface analysis system: apparatus description

Abstract A new multitechnique surface analysis system is presented. It has been designed for research on ion-solid interactions and for survey analysis. SIMS, XPS and AES are the main techniques used. Primary sources are an argon source for standard SIMS and a cesium source for negative and cathionized SIMS, a twin anode (Mg and Al) X-ray source for XPS, and a small spot electron gun for AES and low resolution electron microscopy. The mass spectrometer is a modified quadrupole based probe with an energy analyzer. Dynamic and static SIMS are possible as well as depth profiling. Photoelectrons and Auger electrons are analyzed by a true hemispherical energy analyzer that can also be used for ion spectroscopy. A secondary electron detector is also available. Exchanging the samples is possible through a fast entry air lock. In this small chamber a sputter gun is used to clean the sample. The sample under analysis is supported by a XYZ manipulator and can be temperature controlled in the range 130–850 K.

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.

Chitosan-based nanoparticles as drug delivery systems for doxorubicin: Optimization and modelling.

In the present work, two drug delivery systems were produced by encapsulating doxorubicin into chitosan and O-HTCC (ammonium-quaternary derivative of chitosan) nanoparticles. The results show that doxorubicin release is independent of the molecular weight and is higher at acidic pH (4.5) than at physiological pH. NPs with an average hydrodynamic diameter bellow 200nm are able to encapsulate up to 70% and 50% of doxorubicin in the case of chitosan and O-HTCC nanoparticles, respectively. O-HTCC nanoparticles led to a higher amount of doxorubicin released than chitosan nanoparticles, for the same experimental conditions, although the release mechanism was not altered. A burst effect occurs within the first hours of release, reaching a plateau after 24h. Fitting mathematical models to the experimental data led to a concordant release mechanism between most samples, indicating an anomalous or mixed release, which is in agreement with the swelling behavior of chitosan described in the literature.

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.

Improving Learning in Science and Mathematics with Exploratory and Interactive Computational Modelling

Scientific research involves mathematical modelling in the context of an interactive balance between theory, experiment and computation. However, computational methods and tools are still far from being appropriately integrated in the high school and university curricula in science and mathematics. In this chapter, we present a new way to develop computational modelling learning activities in science and mathematics which may be fruitfully adopted by high school and university curricula. These activities may also be a valuable instrument for the professional development of teachers. Focusing on mathematical modelling in the context of physics, we describe a selection of exploratory and interactive computational modelling activities in introductory mechanics and discuss their impact on student learning of key physical and mathematical concepts in mechanics.

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.

An overview of inverted colloidal crystal systems for tissue engineering.

Scaffolding is at the heart of tissue engineering but the number of techniques available for turning biomaterials into scaffolds displaying the features required for a tissue engineering application is somewhat limited. Inverted colloidal crystals (ICCs) are inverse replicas of an ordered array of monodisperse colloidal particles, which organize themselves in packed long-range crystals. The literature on ICC systems has grown enormously in the past 20 years, driven by the need to find organized macroporous structures. Although replicating the structure of packed colloidal crystals (CCs) into solid structures has produced a wide range of advanced materials (e.g., photonic crystals, catalysts, and membranes) only in recent years have ICCs been evaluated as devices for medical/pharmaceutical and tissue engineering applications. The geometry, size, pore density, and interconnectivity are features of the scaffold that strongly affect the cell environment with consequences on cell adhesion, proliferation, and differentiation. ICC scaffolds are highly geometrically ordered structures with increased porosity and connectivity, which enhances oxygen and nutrient diffusion, providing optimum cellular development. In comparison to other types of scaffolds, ICCs have three major unique features: the isotropic three-dimensional environment, comprising highly uniform and size-controllable pores, and the presence of windows connecting adjacent pores. Thus far, this is the only technique that guarantees these features with a long-range order, between a few nanometers and thousands of micrometers. In this review, we present the current development status of ICC scaffolds for tissue engineering applications.