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Godinho, Maria Helena, João Paulo Borges, João Carlos Bordado, Maria Teresa Cidade, and Assis Farinha Martins. "Preparation and liquid-crystalline properties of toluene-4-sulphonyl urethane of hydroxypropylcellulose." Liquid Crystals 14 (1993): 653-659. AbstractWebsite

A novel liquid-crystalline polymer, the toluene-4-sulphonyl urethane of hydroxypropylcellulose (TSUHPC), was prepared through chemical modification of hydroxypropylcellulose (HPC) of Mw = 60000 g mol−1. The resulting polymer was characterized by infrared spectroscopy, differential scanning calorimetry (DSC) and polarizing microscopy. It was found that thermotropic liquid crystal phases are formed between about 60°C and 110°C. Concentrated solutions of TSUHPC in acetone and N,N-dimethylacetamide exhibit cholesteric behaviour, at room temperature. When approaching the lyotropic mesophase to solid transition, either by cooling or by solvent evaporation, very interesting arborescent structures of a seemingly fractal nature may be observed, depending on the kinetics of the transition. A banded texture can be observed when the polymer is sheared near the transition to the isotropic phase.

Borges, João Paulo, Maria Helena Godinho, Assis Farinha Martins, Ana Catarina Trindade, and Mohamed Naceur Belgacem. "Cellulose-based composite films." Mechanics of composite materials 37 (2001): 257-264. AbstractWebsite

The mechanical and optical properties of cellulose-based composite films are investigated.It is shown that the use of toluene diisocyanate as a coupling agent and Avicel fibers as reinforcing elements give films with the highest mechanical characteristics. Using differential scanning calorimetry, it is also found that the glass transition temperature Tg of all the materials studied is below the room temperature and that the Tg increased with cross-linking and introduction of Avicel.

Borges, João Paulo, Maria Helena Godinho, Mohamed Naceur Belgacem, and Assis Farinha Martins. "New bio-composites based on short fibre reinforced hydroxypropylcellulose films." Composite interfaces 8 (2001): 233-241. AbstractWebsite

The present work deals with the preparation and the characterisation of solid films, having thickness between 15 and 40 μm, prepared with hydroxypropyl cellulose (HPC) and different amounts of commercial cellulose fibres (0; 0.5; 10 and 15% w/w) (system A) and with 1,4-butyl diisocyanate (BDI), as a cross-linking agent (system B). Before the preparation of these films, the surface energy of cellulose fibres, as such and after purification with different solvents, was determined by Inverse Gas Chromatography (IGC), which gave the values of dispersive energy and acid-base properties of their surfaces. The tensile and photo-elastic properties of the solid films obtained were studied. There were no significant changes in Young's modulus between the two systems. However, as expected, the values of the elongation and those of the fracture stress were systematically higher for system B in comparison with system A. The same trend was found for the birefringence, measured at the same elongation values for the films obtained from both systems.

Borges, João Paulo, Maria Helena Godinho, Assis Farinha Martins, DF Stamatialis, MN de Pinho, and Mohamed Naceur Belgacem. "Tensile properties of cellulose fiber reinforced hydroxypropylcellulose films." Polymer composites 25 (2004): 102-110. AbstractWebsite

The tensile properties of cross-linked and uncross-linked composite films (thickness ∼20–35 μm) prepared from Hydroxypropylcellulose (HPC) with incorporation of microcrystalline cellulose fibers (Avicel) were studied. The concentration of fibers in the composites ranged from 0 to 30 w/w% and cross-linked composites were obtained by the reaction of HPC-Avicel mixtures with 1,4-butyldiisocyanate. It was demonstrated that the inclusion of fibers in a HPC matrix produces composites with enhanced mechanical properties that are improved by cross-linking. Mechanical results seem to indicate that the elastic deformation of the cross-linked composites is predominantly dominated by the fiber content while the cross-linking affects mainly the plastic deformation. Maximum values of the Young's Modulus, yield stress and tensile stress were observed at 10 w/w% for the cross-linked and 20 w/w% for the uncross-linked composites. Furthermore cross-linked films with 10 w/w% of fibers present values of yield stress and tensile stress that are in average 15 to 20% higher than those obtained for uncross-linked composites with 20 w/w% of fibers. Studies in Polarizing Optical Microscopy and Atomic Force Microscopy (AFM) seem to indicate that tensile properties of these composites are correlated to the packing of fibers. For the concentration of the utilized cross-linking agent, and for a fiber content of 10 w/w%, an optimal packing of fibers throughout the matrix has been correlated to the minimal difference between the roughness parameters obtained by AFM analysis of the top and bottom surfaces of the films.

Prabaharan, Mani, João Paulo Borges, Maria Helena Godinho, and João F. Mano. "Liquid Crystalline Behaviour of Chitosan in Formic, Acetic, Monochloroacetic Acid Solutions." Materials Science Forum 514-516 (2006): 1010-1014. AbstractWebsite

The objective of this work was to prepare polysaccharide-based gels exhibiting liquid crystalline properties. Such systems may be used in some optical or in biomedical applications, where biodegradability is required. Chitosan is a derivative of chitin, widely used in a series of medical applications. Due to its rigid structure, chitosan or its derivatives may show lyotropic mesophases in certain conditions. In this work, chitosan solutions were prepared by mixing completely the polysaccharide with different concentration of formic, acetic and monochloroacetic acids at room temperature. X-ray diffraction patterns of the gels did not show the existence of a crystalline structure. Finger-prints texture observed by polarised optical microscopy was attributed to a cholesteric liquid crystalline phase that usually develops in concentrated solutions. Values of the nematic chiral pitch (P) were determined in function of acid solution concentration. The critical concentrations (C*) to form a lyotropic liquid crystalline phase in formic, acetic and monochloroacetic acids were determined, and the obtained values were confronted with the expected critical concentration based on the Flory formalism. The critical concentration values were found to be dependent upon the acid used.

Canejo, João Paulo, João Paulo Borges, Maria Helena Godinho, Pedro Brogueira, Paulo IC Teixeira, and Eugene M. Terentjev. "Helical Twisting of Electrospun Liquid Crystalline Cellulose Micro-and Nanofibers." Advanced Materials 20 (2008): 4821-4825. AbstractWebsite

Helically twisted fibers can be produced by electrospinning liquid-crystalline cellulose solutions. Fiber topographies are studied by atomic force microscopy, scanning electron microscopy (see figure) and polarized optical microscopy. The fibers have a nearly universal pitch-to-diameter ratio and comprise both right- and left-handed helices.

Ribeiro, Maximiano P., Ana Espiga, Daniela Silva, Patricia Baptista, Joaquim Henriques, Catarina Ferreira, Jorge Carvalho Silva, João Paulo Borges, Eduardo Pires, Paula Chaves, and Ilídio J. Correia. "Development of a new chitosan hydrogel for wound dressing." Wound repair and regeneration 17 (2009): 817-824. AbstractWebsite

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.

Almeida, Pedro L., Sudarshan Kundu, João Paulo Borges, Maria Helena Godinho, and Joao L. Figueirinhas. "Electro-optical light scattering shutter using electrospun cellulose-based nano-and microfibers." Applied Physics Letters 95 (2009): 043501. AbstractWebsite

Electrospun cellulose-based nano and microfibers and a nematic liquid crystal are used to assemble an electro-optical (EO) light-scattering device that shows enhanced characteristics when compared to similar devices. Based on the controlled scattering of light in the composite system, the device can achieve light transmission coefficients tunable from 1% up to around 89%. Simulation of the EO behavior indicates that the roughness of the polymer-liquid crystal interface is crucial for the optical performance of the device.

Godinho, Maria Helena, João Paulo Canejo, Luis FV Pinto, João Paulo Borges, and Paulo IC Teixeira. "How to mimic the shapes of plant tendrils on the nano and microscale: spirals and helices of electrospun liquid crystalline cellulose derivatives." Soft Matter 5 (2009): 2772-2776. AbstractWebsite

We show that suspended nano and microfibres electrospun from liquid crystalline cellulosic solutions will curl into spirals if they are supported at just one end, or, if they are supported at both ends, will twist into a helix of one handedness over half of its length and of the opposite handedness over the other half, the two halves being connected by a short straight section. This latter phenomenon, known as perversion, is a consequence of the intrinsic curvature of the fibres and of a topological conservation law. Furthermore, agreement between theory and experiment can only be achieved if account is taken of the intrinsic torsion of the fibres. Precisely the same behaviour is known to be exhibited by the tendrils of climbing plants such as Passiflora edulis, albeit on a lengthscale of millimetres, i.e., three to four orders of magnitude larger than in our fibres. This suggests that the same basic, coarse-grained physical model is applicable across a range of lengthscales.

Henriques, Célia, Ricardo Vidinha, David Botequim, João Paulo Borges, and Jorge Carvalho Silva. "A systematic study of solution and processing parameters on nanofiber morphology using a new electrospinning apparatus." Journal of nanoscience and nanotechnology 9 (2009): 3535-3545. AbstractWebsite

We assembled a new electrospinning apparatus and used poly(ethylene oxide) as a model polymer to perform a systematic study on the influence of solution and processing parameters on the morphology of electrospun nanofibers. Solution parameters studied were polymer concentration and molecular mass. The solvent used, 60 wt% water,40 wt% ethanol, was the same throughout the study. Processing parameters analyzed were: solution feed rate, needle tip-collector distance and electrostatic potential difference between the needle and collector. Solution viscosity increased both with polymer concentration and molecular mass. Polymer concentration plays a decisive role on the outcome of the electrospinning process: a low concentration led to the formation of beaded fibers; an intermediate concentration yielded good quality fibers; a high concentration resulted in a bimodal size distribution and at even higher concentration a distributed deposition. Fiber diameter increased with polymer molecular mass and higher molecular masses are associated with a higher frequency of splaying events. Fiber diameter increased linearly with solution feed rate. While an increase in needle-collector distance represents a weaker electric field, a greater distance to be covered by the fibers and a longer flight time, presumably favoring the formation of thinner fibers, as solvent evaporation leads to a local increase of concentration and viscosity, viscoelastic forces opposing stretching caused an increase of fiber diameter with needle-collector distance. A higher voltage applied at the needle is associated with a higher charging of the polymer and a higher electrical current through it ultimately leading to incomplete solvent evaporation and merged fibers being produced. Controlling the charging of the polymer independently of the electric field strength was achieved by applying a voltage to the collector while distance and potential difference were kept constant. The increased electrostatic repulsion associated with an increase of the high voltage applied to the needle led to the disappearance of merged fibers.

Borges, João Paulo, Maria Helena Godinho, Joao Luis Figueirinhas, MN de Pinho, and Mohamed Naceur Belgacem. "All-cellulosic based composites." In Cellulose Fibers: Bio-and Nano-Polymer Composites, edited by Susheel Kalia, B. S. Kaith and Inderjeet Kaur, 399-421. Springer Berlin Heidelberg, 2011. Abstract

The use of cellulosic fibers as load bearing constituents in composite materials has increased over the last decade due to their relative cheapness compared to conventional materials such as glass and aramid fibers, their ability to recycle, and because they compete well in terms of strength per weight of material. All-cellulosic based composites prepared from cellulose derivatives based matrices and microcrystalline cellulosic fibers made by direct coupling between fibers and matrix present interesting mechanical and gas permeation properties, thus being potential candidates for packaging materials. Both the cellulosic matrix and the reinforcing fibers are biocompatible and widely used in the pharmaceutical industry, which is very important for the envisaged application. In addition to their biocompatibility, cellulosic systems have the ability to form both thermotropic and lyotropic chiral nematic phases, and the composites produced from the latter show improved mechanical properties due to fiber orientation induced by the anisotropic matrix. The preparation and characterization (morphological, topographical, mechanical, gas barrier properties) of all-cellulosic based composites are described in this chapter.

Baptista, Ana Catarina, J. I. Martins, Elvira Fortunato, Rodrigo Martins, João Paulo Borges, and Isabel Ferreira. "Thin and flexible bio-batteries made of electrospun cellulose-based membranes." Biosens Bioelectron 26 (2011): 2742-5. AbstractWebsite

The present work proposes the development of a bio-battery composed by an ultrathin monolithic structure of an electrospun cellulose acetate membrane, over which was deposited metallic thin film electrodes by thermal evaporation on both surfaces. The electrochemical characterization of the bio-batteries was performed under simulated body fluids like sweat and blood plasma [salt solution–0.9% (w/w) NaCl]. Reversible electrochemical reactions were detected through the cellulose acetate structure. Thus, a stable electrochemical behavior was achieved for a bio-battery with silver and aluminum thin films as electrodes. This device exhibits the ability to supply a power density higher than 3 muW cm(-2). Finally, a bio-battery prototype was tested on a sweated skin, demonstrating the potential of applicability of this bio-device as a micropower source.

Soares, Paula I. P., Sérgio Dias, Carlos Novo, Isabel Ferreira, and João Paulo Borges. "Doxorubicin vs. ladirubicin: methods for improving osteosarcoma treatment." Mini reviews in medicinal chemistry 12 (2012): 1239-1249. AbstractWebsite

Osteosarcoma is the most common primary bone tumor in children and adolescents, with a 5-year disease free survival rate of 70%. Current chemotherapy regimens comprise a group of chemotherapeutic agents in which doxorubicin is included. However, tumor resistance to anthracyclines and cardiotoxicity are limiting factors for its usage. Liposomal formulations of doxorubicin improve its anti-cancer effects but are still insufficient. The research in this area has lead to the production of anthracyclines analogues, such as ladirubicin, the leading compound of alkylcyclines. This new anticancer agent has shown promising results in vivo and in vitro, being effective against osteosarcoma cell lines, including those with a multidrug resistant phenotype. In phase I clinical trials, this molecule caused mild side effects and did not induce significant cardiotoxicity at doses ranging from 1 to 16 mg/m2, resulting in a peak plasma concentration (Cmax) ranging from 0.5 to 1.5 μM. The recommended doses for phase II studies were 12 and 14 mg/m2 in heavily and minimally pretreated/non-pretreated patients, respectively. Phase II clinical trials in ovary, breast, colorectal cancer, NSCLC and malignant melanoma are underway. Given the improved molecular targeting efficacy of these new compounds, ongoing approaches have sought to improve drug delivery systems, to improve treatment efficacy while reducing systemic toxicity. The combination of these two approaches may be a good start for the discovery of new treatment for osteosarcoma.

Pimenta, Andreia F. R., Ana Catarina Baptista, Tânia Carvalho, Pedro Brogueira, Nuno Lourenço, Carlos Afonso, Susana Barreiros, Pedro Vidinha, and João Paulo Borges. "Electrospinning of Ion Jelly fibers." Materials Letters 83 (2012): 161-164. AbstractWebsite

Ion Jelly materials combine the chemical versatility and conductivity of an ionic liquid (IL) with the morphological versatility of a biopolymer (gelatin). They exhibit very interesting properties, such as conductivities up to 10− 4 S cm− 1, and high thermostability up to 180 °C, and have been used successfully to design electrochromic windows. In this work we report on the preparation of Ion Jelly fibers through electrospinning in order to obtain high surface area conductive materials. We have used the IL 1-(2-hydroxyethyl)-3-methyl-imidazolium tetrafluoroborate ([C2OHmim]BF4), which exhibits conveniently high ionic conductivity (over 10− 3 S cm− 1) and electrochemical stability (electrochemical window over 6.0 V). The morphology of the obtained fibers was quantified using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). We found that on average the effect of the IL on fiber diameter differs for lower and higher IL concentrations and that this effect was correlated with the initial conductivity and viscosity of Ion Jelly electrospinning solution. Moreover we also found that conductivities of Ion Jelly fibers are of the same order of magnitude as the conductivities of Ion Jelly dense films (~ 10− 4 S cm− 1). To the best of our knowledge, this is the first report on the incorporation of an IL into gelatin fibers using electrospinning. This opens up new opportunities for the application of gelatin fibers in electrochemical and biomedical devices.

Franco, Patrícia Q., Carlos João, Jorge Carvalho Silva, and João Paulo Borges. "Electrospun hydroxyapatite fibers from a simple sol–gel system." Materials Letters 67 (2012): 233-236. AbstractWebsite

This work reports the production of hydroxyapatite (HA) sub-micron fibers by combining electrospinning and a non-alkoxide sol–gel system, using cheap precursors. Phosphorus pentoxide (P2O5) and calcium nitrate tetrahydrate (Ca(NO3)2.4H2O) were used as precursors of phosphorus and calcium, respectively. The fibers were electrospun from a mixture of the gel formed from the system Ca(NO3)2.4H2O/P2O5 with polymeric solutions of polyvinylpyrrolidone (PVP) in water and ethanol/water mixtures. The fibers were analyzed for their morphology (Scanning Electron Microscopy, SEM), chemical composition (Fourier Transform Infrared Spectroscopy, FTIR) and structure (X-ray diffraction, XRD). The fibers obtained were composed mainly of type B carbonated HA with traces of β-tricalcium phosphate (β-TCP). SEM analysis revealed that increasing the concentration of water in the solvent system, used in the preparation of electrospinning solutions, led to fibers with smaller diameters and narrower diameter distribution.

Soares, Paula I. P., Isabel Ferreira, Rui Igreja, Carlos Novo, and João Paulo Borges. "Application of Hyperthermia for Cancer Treatment: Recent Patents Review." Recent Patents on Anti-Cancer Drug Discovery 7 (2012): 64-73. AbstractWebsite

Cancer is one of the main causes of death in the world and its incidence increases every day. Current treatments are insufficient and present many breaches. Hyperthermia is an old concept and since early it was established as a cancer treatment option, mainly in superficial cancers. More recently the concept of intracellular hyperthermia emerged wherein magnetic particles are concentrated at the tumor site and remotely heated using an applied magnetic field to achieve hyperthermic temperatures (42-45°C). Many patents have been registered in this area since the year 2000. This review presents the most relevant information, organizing them according to the hyperthermic method used: 1) external Radio- Frequency devices; 2) hyperthermic perfusion; 3) frequency enhancers; 4) apply heating to the target site using a catheter; 5) injection of magnetic and ferroelectric particles; 6) injection of magnetic nanoparticles that may carry a pharmacological active drug. The use of magnetic nanoparticles is a very promising treatment approach since it may be used for diagnostic and treatment. An ideal magnetic nanoparticle would be able to detect and diagnose the tumor, carry a pharmacological active drug to be delivered in the tumor site, apply hyperthermia through an external magnetic field and allow treatment monitoring by magnetic resonance imaging.

Baptista, Ana Catarina, Isabel Ferreira, and João Borges. "Cellulose-based bioelectronic devices." In Cellulose - Medical, Pharmaceutical and Electronic Applications, edited by Theo van de Ven and Louis Godbout. InTech, 2013.
Baptista, Ana Catarina, Isabel Ferreira, and João Paulo Borges. "Cellulose-based composite systems for biomedical applications." In Biomass based Biocomposites, edited by Vijay Kumar Thakur and A. S. Singha, 47-60. U.K.: Smithers Rapra Technology, 2013.
dos Santos, Renato, Ângelo Rocha, Ana Matias, Catarina Duarte, Isabel Sá-Nogueira, Nuno Lourenço, and João Paulo Borges. "Development of antimicrobial Ion Jelly fibers." RSC Advances 3 (2013): 24400-24405. Abstract

We report a method to obtain electrospun fibers based on ionic liquids and gelatin, exhibiting antimicrobial properties.

Baptista, Ana Catarina, Isabel Ferreira, and João Paulo Borges. "Electrospun fibers in composite materials for medical applications." Journal of Composites and Biodegradable Polymers 1 (2013): 56-65. AbstractWebsite

The development of nanoscaled materials has deserved a remarkable interest for biomedical applications. Biological tissues are essentially composite materials with particular mechanical properties that should be carefully considered during the design of innovative biomedical scaffolds. Electrospun membranes are often found in medical applications due to its high specific surface which creates a 3D porous structure that mimics the native extracellular matrix. These electrospun membranes can also be designed to have enhanced mechanical properties, biocompatibility and cellular response making them appealing and inspiring to be used in composites materials.
This paper reviews the new insights in the development of advanced nanostructured composites materials based on electrospun fibers. From tissue engineering to bioelectronics, these composite materials can be found in the most promising research developments for the medical applications.

Baptista, Ana Catarina, Paula I. P. Soares, Isabel Ferreira, and João Paulo Borges. "Nanofibers and nanoparticles in biomedical applications." In Bioengineered Nanomaterials, edited by Atul Tiwari and Ashutosh Tiwari. USA: CRC Press (Taylor & Francis Group), 2013.
Ferreira, Isabel, Ana Catarina Baptista, Joaquim Pratas Leitão, Jorge Soares, Elvira Fortunato, Rodrigo Martins, and João Paulo Borges. "Strongly Photosensitive and Fluorescent F8T2 Electrospun Fibers." Macromol Mater Eng 298 (2013): 174-180. AbstractWebsite

Electrospun fibers of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-bithiophene] (F8T2) with exceptional electro-optical performance are obtained. The I/T characteristics measured in fibers with 7–15 µm diameter and 1 mm length show a semiconductor behavior; their thermal activation energy is 0.5 eV and the dark conductivity at RT is 5 × 10−9 (Ω cm)−1. Besides exhibiting a photosensitivity of about 60 under white light illumination with a light power intensity of 25 mW · cm−2, the fibers also attain RT photoluminescence in the cyan, yellow, and red wavelength range under ultraviolet, blue, and green light excitation, respectively. Optical microscope images of F8T2 reveal homogeneous electrospun fibers, which are in good agreement with the uniformly radial fluorescence observed.

Soares, Paula I. P., Isabel Ferreira, and João Paulo Borges. "Application of Hyperthermia for Cancer Treatment: Recent Patents Review." In Topics in Anti-Cancer Research, Vol. 3, edited by Atta-ur-Rahman and Khurshid Zaman, 342-383. Bentham Science Publishers, 2014. Abstract

Cancer is one of the main causes of death in the world and its incidence increases every day. Current treatments are insufficient and present many breaches. Hyperthermia is an old concept and was early established as a cancer treatment option, mainly in superficial cancers. More recently, the concept of intracellular hyperthermia emerged wherein magnetic particles are concentrated at the tumor site and remotely heated using an applied magnetic field to achieve hyperthermic temperatures (42-45ºC). Many patents have been registered in this area since the year 2000. This chapter presents the most relevant information organized in two main categories according to the use or not of nanotechnology. The patents without nanotechnology were divided into the following subcategories: 1) external Radio-Frequency devices; 2) hyperthermic perfusion; 3) frequency enhancers; 4) applying heat to the target site using a catheter; and 5) injection of magnetic and ferroelectric particles. The patents with nanotechnology were divided into three subcategories: 1) hyperthermia devices; 2) nanoparticles; and 3) nanostructures. The use of magnetic nanoparticles is a very promising treatment approach since it may be used for diagnostic and treatment. Magnetic nanoparticle could be applied to detect and diagnose the tumor and to carry a pharmacological active drug to be delivered in the tumor site or apply hyperthermia through an external magnetic field.

Borges, João Paulo, João Paulo Canejo, Susete Fernandes, Pedro Brogueira, and Maria Helena Godinho. "Cellulose-Based Liquid Crystalline Composite Systems." In Nanocellulose Polymer Nanocomposites: Fundamentals and Applications, edited by Vijay Kumar Thakur, 215-235. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2014.
Soares, Paula I. P., Ana Alves, Laura Pereira, Joana Coutinho, Isabel Ferreira, Carlos Novo, and João Paulo Borges. "Effects of surfactants on the magnetic properties of iron oxide colloids." Journal of Colloid and Interface Science 419 (2014): 46-51. AbstractWebsite

Iron oxide nanoparticles are having been extensively investigated for several biomedical applications such as hyperthermia and magnetic resonance imaging. However, one of the biggest problems of these nanoparticles is their aggregation.
Taking this into account, in this study the influence of three different surfactants (oleic acid, sodium citrate and Triton X-100) each one with various concentrations in the colloidal solutions stability was analyzed by using a rapid and facile method, the variation in the optical absorbance along time.
The synthesized nanoparticles through chemical precipitation showed an average size of 9 nm and a narrow size distribution. X-ray diffraction pattern and Fourier Transform Infrared analysis confirmed the presence of pure magnetite. SQUID measurements showed superparamagnetic properties with a blocking temperature around 155 K. In addition it was observed that neither sodium citrate nor Triton X-100 influences the magnetic properties of the nanoparticles. On the other hand, oleic acid in a concentration of 64 mM decreases the saturation magnetization from 67 to 45 emu/g. Oleic acid exhibits a good performance as stabilizer of the iron oxide nanoparticles in an aqueous solution for 24 h, for concentrations that lead to the formation of the double layer.

Ferreira, José Luis, Susana Gomes, Célia Henriques, João Paulo Borges, and Jorge Carvalho Silva. "Electrospinning polycaprolactone dissolved in glacial acetic acid: Fiber production, nonwoven characterization, and In Vitro evaluation." Journal of Applied Polymer Science 131 (2014): 41068. AbstractWebsite

The electrospinning of polycaprolactone (PCL) dissolved in glacial acetic acid and the characterization of the resultant nonwoven fiber mats is reported in this work. For comparison purposes, PCL fiber mats were also obtained by electrospinning the polymer dissolved in chloroform. Given the processing parameters chosen, results show that 14 and 17 wt % PCL solutions are not viscous enough and yield beaded fibers, 20 and 23 wt % solutions give rise to high quality fibers and 26 wt % solutions yield mostly irregular and fused fibers. The nonwoven mats are highly porous, retain the high tensile strain of PCL, and the fibers are semicrystalline. Cells adhere and proliferate equally well on all mats, irrespective of the solvent used in their production. In conclusion, mats obtained by electrospinning PCL dissolved in acetic acid are also a good option to consider when producing scaffolds for tissue engineering. Moreover, acetic acid is miscible with polar solvents, which may allow easier blending of PCL with hydrophilic polymers and therefore achieve the production of electrospun nanofibers with improved properties.

João, Carlos, Joana Vasconcelos, Jorge Carvalho Silva, and João Paulo Borges. "An Overview of Inverted Colloidal Crystal Systems for Tissue Engineering." Tissue Engineering Part B-Reviews 20 (2014): 437-454. AbstractWebsite

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.

Quirós, Jennifer, João Paulo Borges, Karina Boltes, Ismael Rodea-Palomares, and Roberto Rosal. "Antimicrobial electrospun silver-, copper- and zinc-doped polyvinylpyrrolidone nanofibers." Journal of Hazardous Materials 299 (2015): 298-305. AbstractWebsite

The use of electrospun polyvinylpyrrolidone (PVP) nanofibers containing silver, copper, and zinc nanoparticles was studied to prepare antimicrobial mats using silver and copper nitrates and zinc acetate as precursors. Silver became reduced during electrospinning and formed nanoparticles of several tens of nanometers. Silver nanoparticles and the insoluble forms of copper and zinc were dispersed using low molecular weight PVP as capping agent. High molecular weight PVP formed uniform fibers with a narrow distribution of diameters around 500 nm. The fibers were converted into an insoluble network using ultraviolet irradiation crosslinking. The efficiency of metal-loaded mats against the bacteria Escherichia coli and Staphylococcus aureus was tested for different metal loadings by measuring the inhibition of colony forming units and the staining with fluorescent probes for metabolic viability and compromised membranes. The assays included the culture in contact with mats and the direct staining of surface attached microorganisms. The results indicated a strong inhibition for silver-loaded fibers and the absence of significant amounts of viable but non-culturable microorganisms. Copper and zinc-loaded mats also decreased the metabolic activity and cell viability, although in a lesser extent. Metal-loaded fibers allowed the slow release of the soluble forms of the three metals.

João, Carlos, Jorge Carvalho Silva, and João Paulo Borges. "Chitin-Based Nanocomposites: Biomedical Applications." In Eco-friendly Polymer Nanocomposites, edited by Vijay Kumar Thakur and Manju Kumari Thakur, 439-457. Springer India, 2015. Abstract

Chitin, the second most abundant polymer in nature, is a renewable, nontoxic, biodegradable, and antibacterial polysaccharide. This semicrystalline biopolymer exhibits hierarchical structure from nano to micro-scale and is responsible for interesting living tissue properties. Recently, the scientific interest in chitin nanofibrils for applications in biomedical and tissue engineering fields has increased due to their particular capabilities such as matrix reinforcements, bioactivity and morphology similar to natural tissues. This chapter is focused on composite materials reinforced with chitin nanofibrils and their biomedical applications.

Zamora-Mora, Vanessa, Paula I. P. Soares, Coro Echeverria, Rebeca Hernández, and Carmen Mijangos. "Composite chitosan/agarose ferrogels for potential applications in magnetic hyperthermia." Gels 1 (2015): 69-80. AbstractWebsite

Composite ferrogels were obtained by encapsulation of magnetic nanoparticles at two different concentrations (2.0 and 5.0 % w/v) within mixed agarose/chitosan hydrogels having different concentrations of agarose (1.0, 1.5 and 2.0% (w/v)) and a fixed concentration of chitosan (0.5% (w/v)). The morphological characterization carried out by scanning electron microscopy showed that dried composite ferrogels present pore sizes in the micrometer range. Thermogravimetric measurements showed that ferrogels present higher degradation temperatures than blank chitosan/agarose hydrogels without magnetic nanoparticles. In addition, measurements of the elastic moduli of the composite ferrogels evidenced that the presence of magnetic nanoparticles in the starting aqueous solutions prevents to some extent the agarose gelation achieved by simply cooling chitosan/agarose aqueous solutions. Finally, it is shown that composite chitosan/agarose ferrogels are able to heat in response to the application of an alternating magnetic field so that they can be considered as potential biomaterials to be employed in magnetic hyperthermia treatments.

Baptista, Ana Catarina, Alexandre Botas, Ana Almeida, Ana Nicolau, Bruno Falcão, Manuel Soares, Joaquim Pratas Leitão, Rodrigo Martins, João Paulo Borges, and Isabel Ferreira. "Down conversion photoluminescence on PVP/Ag-nanoparticles electrospun composite fibers." Optical Materials 39 (2015): 278-281. AbstractWebsite

The influence of Ag nanoparticles (Ag NPs) on the luminescence of electrospun nonwoven mats made of polyvinylpyrrolidone (PVP) has been studied in this work. The PVP fibers incorporating 2.1–4.3 nm size Ag NPs show a significant photoluminescence (PL) band between 580 and 640 nm under 325 nm laser excitation. The down conversion luminescence emission is present even after several hours of laser excitation, which denotes the durability and stability of fibers to consecutive excitations. As so these one-dimensional photonic fibers made using cheap methods is of great importance for organic optoelectronic applications, fluorescent clothing or counterfeiting labels.

Echeverria, Coro, Paula I. P. Soares, Ana Robalo, Laura Pereira, Carlos Novo, Isabel Ferreira, and João Paulo Borges. "One-pot synthesis of dual-stimuli responsive hybrid PNIPAAm-chitosan microgels." Materials & Design 86 (2015): 745-751. AbstractWebsite

The incorporation of magnetic nanoparticles into poly(N-isopropylacrylamide) (PNIPAAm) and chitosan microgels gives rise to hybrid systems that combine the microgels swelling capacity with the interesting features presented in magnetic nanoparticles. The presence of chitosan that act as surfactant for magnetic nanoparticles provides a simplistic approach which allows the encapsulation of magnetic nanoparticles without any previous surface modification. Spherical and highly monodisperse microgels with diameters in the range of 200 to 500 nm were obtained. The encapsulation of magnetic nanoparticles in the polymer matrix was confirmed by high resolution Scanning Electron Microscopy in transmission mode. Volume phase transition of the microgels was accessed by Dynamic Light Scattering measurements. It was observed that the thermosensitivity of the PNIPAM microgels still persists in the hybrid microgels; however, the swelling ability is compromised in the microgels with highest chitosan content. The heating performance of the hybrid magnetic microgels, when submitted to an alternating magnetic field, was also evaluated demonstrating the potential of these systems for hyperthermia treatments.

Mano, Francisca, Ivo Aroso, Susana Barreiros, João Paulo Borges, Rui Reis, Ana Rita Duarte, and Alexandre Paiva. "Production of Poly(vinyl alcohol) (PVA) Fibers with Encapsulated Natural Deep Eutectic Solvent (NADES) Using Electrospinning." ACS Sustainable Chemistry & Engineering 3 (2015): 2504-2509. AbstractWebsite

Functionalized electrospun fibers are of great interest for biomedical applications such as in the design of drug delivery systems. Nevertheless, in some cases the molecules of interest have poor solubility in water or have high melting temperatures. These drawbacks can be overcome using deep eutectic solvents. In this work, poly(vinyl alcohol) (PVA), a common biodegradable biopolymer, was used to produce new functionalized fibers with the eutectic mixture choline chloride:citric acid in a molar ratio of (1:1) ChCl:CA (1:1), which was used as a model system. Fibers were produced from an aqueous solution with 7.8% (w/v) and 9.8% (w/v) of 95% hydrolyzed PVA and a 2% (v/v) of ChCl:CA (1:1). Smooth, uniform fibers with an average diameter of 0.4 μm were obtained with a content of 19.8 wt % of ChCl:CA (1:1) encapsulated.

Neagu, Eugene, Maria Carmo Lança, Carlos Dias, and José Marat-Mendes. "Space charge and dipolar charge contribution at polar polymers polarization." IEEE Transactions on Dielectrics and Electrical Insulation 22 (2015): 1419-1426. AbstractWebsite

The thermally stimulated discharge current, the final thermally stimulated discharge current, DC conductivity and the final thermally stimulated discharge current with partially blocking electrode measures were used to analyze electrical behavior of Nylon 11. The objective was to discriminate between dipole related effects and space charge related effects. The space charge effects are dominant in the temperature range from room temperature to 170 °C. By using a Teflon-FEP partially blocking electrode, the space charge injected in the sample is diminished and the effects related to dipole movement can be observed. Beside the two known relaxations for Nylon 11, one associated with the glass transition around 60 °C and a second one associated with a molecular motion in the rigid-amorphous phase at 96 °C, a weak relaxation was observed around 168 °C. The peak around 96 °C is quite broad been composed of two narrow peaks. The final thermally stimulated discharge current method allows a better selection of the experimental conditions for sample charging (polarization) to have only a partial overlap between the nearby peaks. The peak's maximum current and temperature are dependent on the ratio between the charging and discharging time and temperature given a possibility to discriminate between dipolar and space charge effects. A pyroelectric current changes sign around 140 °C indicating that the amidegroup dipoles are frozen in opposite directions when the sample temperature is below 140 °C (amorphous and rigid-amorphous phase) or above (crystalline phase). The conductivity is controlled by the competition between n(E,T) and μ(E,T) indicating a space charge controlled conductivity mechanism.

Soares, Paula I. P., Frederik Lochte, Coro Echeverria, Laura Pereira, Joana Coutinho, Isabel Ferreira, Carlos Novo, and João Paulo Borges. "Thermal and magnetic properties of iron oxide colloids: influence of surfactants." Nanotechnology 26 (2015): 425704. AbstractWebsite

Iron oxide nanoparticles (NPs) have been extensively studied in the last few decades for several biomedical applications such as magnetic resonance imaging, magnetic drug delivery and hyperthermia. Hyperthermia is a technique used for cancer treatment which consists in inducing a temperature of about 41–45 °C in cancerous cells through magnetic NPs and an external magnetic field. Chemical precipitation was used to produce iron oxide NPs 9 nm in size coated with oleic acid and trisodium citrate. The influence of both stabilizers on the heating ability and in vitro cytotoxicity of the produced iron oxide NPs was assessed. Physicochemical characterization of the samples confirmed that the used surfactants do not change the particles' average size and that the presence of the surfactants has a strong effect on both the magnetic properties and the heating ability. The heating ability of Fe3O4 NPs shows a proportional increase with the increase of iron concentration, although when coated with trisodium citrate or oleic acid the heating ability decreases. Cytotoxicity assays demonstrated that both pristine and trisodium citrate Fe3O4 samples do not reduce cell viability. However, oleic acid Fe3O4 strongly reduces cell viability, more drastically in the SaOs-2 cell line. The produced iron oxide NPs are suitable for cancer hyperthermia treatment and the use of a surfactant brings great advantages concerning the dispersion of NPs, also allowing better control of the hyperthermia temperature.

Soares, Paula I. P., Ana Isabel Sousa, Jorge Carvalho Silva, Isabel Ferreira, Carlos Novo, and João Paulo Borges. "Chitosan-based nanoparticles as drug delivery systems for doxorubicin: optimization and modelling." Carbohydrate polymers 147 (2016): 304-312. AbstractWebsite

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 200 nm 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 24 h. 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.

Marques, Susana, Paula I. P. Soares, Coro Echeverria, Maria Helena Godinho, and João Paulo Borges. "Confinement of thermoresponsive microgels into fibres via colloidal electrospinning: experimental and statistical analysis." RSC Advances 6 (2016): 76370-76380. AbstractWebsite

The strategy of confining stimuli-responsive microgels in electrospun fibres would allow the fabrication of polymeric networks that combine the microgels swelling ability and properties with the interest features of the electrospun fibres. Colloidal electrospinning is an emerging method in which fibres containing microgels can be produced by a single-nozzle and designed through the solution carrier materials. The incorporation of poly(N-isopropylacrylamide) (PNIPAAM) and PNIPAAM-chitosan (PNIPAAM-CS) in poly(ethyleneoxyde) (PEO) fibres via colloidal electrospinning producing composite fibres was the main purpose of the present work{,} which was confirmed by means of Scanning Electron Microscopy (SEM). Dynamic light scattering was used to analyse the microgels hydrodynamic diameter ranging up to 900 nm depending on the composition and temperature of the surrounding medium. By performing a statistical analysis the relationship of the processing variables over the fibre size was evaluated following the response surface methodology (RSM). From the set of parameters aimed to minimize the fibre diameter{,} composite fibres with an average diameter of 63 nm were produced. Only the as-prepared microgels with higher monodispersity provided {"}bead-on-a-string{"} morphologies.

Soares, Paula I. P., César Laia, Alexandra Carvalho, Laura Pereira, Joana Coutinho, Isabel Ferreira, Carlos Novo, and João Paulo Borges. "Iron oxide nanoparticles stabilized with a bilayer of oleic acid for magnetic hyperthermia and MRI applications." Applied Surface Science 383 (2016): 240-247. AbstractWebsite

Iron oxide nanoparticles (Fe3O4, IONPs) are promising candidates for several biomedical applications such as magnetic hyperthermia and as contrast agents for magnetic resonance imaging (MRI). However, their colloidal stability in physiological conditions hinders their application requiring the use of biocompatible surfactant agents. The present investigation focuses on obtaining highly stable IONPs, stabilized by the presence of an oleic acid bilayer. Critical aspects such as oleic acid concentration and pH were optimized to ensure maximum stability. NPs composed of an iron oxide core with an average diameter of 9 nm measured using transmission electron microscopy (TEM) form agglomerates with an hydrodynamic diameter of around 170 nm when dispersed in water in the presence of an oleic acid bilayer, remaining stable (zeta potential of −120 mV). Magnetic hyperthermia and the relaxivities measurements show high efficiency at neutral pH which enables their use for both magnetic hyperthermia and MRI.

João, Carlos, Ana Catarina Baptista, Isabel Ferreira, Jorge Carvalho Silva, and João Paulo Borges. "Natural Nanofibres for Composite Applications." In Fibrous and Textile Materials for Composite Applications, edited by Sohel Rana and Raul Fangueiro, 261-299. Singapore: Springer Singapore, 2016. Abstract

Cellulose and chitin are the two most abundant natural polysaccharides. Both have a semicrystalline microfibrillar structure from which nanofibres can be extracted. These nanofibres are rod-like microcrystals that can be used as nanoscale reinforcements in composites due to their outstanding mechanical properties. This chapter starts by reviewing the sources, extraction methods and properties of cellulose and chitin nanofibres. Then, their use in the fabrication of structural and functional nanocomposites and the applications that have been investigated are reviewed. Nanocomposites are materials with internal nano-sized structures. They benefit from the properties of the nanofillers: low density, nonabrasive, nontoxic, low cost, susceptibility to chemical modifications and biodegradability. Diverse manufacturing technologies have been used to produce films, fibres, foams, sponges, aerogels, etc. Given their natural origin and high stiffness, these polymers have attracted a lot of attention not only in the biomedical and tissue engineering fields but also in areas such as pharmaceutics, cosmetics, agriculture, biosensors and water treatment.

João, Carlos, Rute Almeida, Jorge Carvalho Silva, and João Paulo Borges. "A simple sol-gel route to the construction of hydroxyapatite inverted colloidal crystals for bone tissue engineering." Materials Letters 185 (2016): 407-410. AbstractWebsite

Hydroxyapatite (HAp) scaffolds with uniform pore size and interconnected pore network were constructed based on the inverted colloidal crystal (ICC) geometry and a simple sol-gel formulation. Monodisperse polystyrene microspheres were self-assembled and annealed into a hexagonal close packed structure. HAp sol-gel was infiltrated in this template followed by thermal treatment for simultaneous HAp matrix sintering and polymeric colloidal crystal calcination. The resultant ICC scaffolds exhibit an ordered architecture that was able to offer a favorable environment for human osteoblasts adhesion and proliferation, an essential feature for bone ingrowth in tissue engineering applications.