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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, 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.

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, Inês Ropio, Beatriz Romba, Joana Nobre, Célia Henriques, Jorge Carvalho Silva, J. I. Martins, João Paulo Borges, and Isabel Ferreira. "Cellulose-based electrospun fibers functionalized with polypyrrole and polyaniline for fully organic batteries." Journal of Materials Chemistry A 6 (2018): 256-265. AbstractWebsite

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.

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.

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.
Baptista, Ana Catarina, Miguel Brito, Ana Marques, and Isabel Ferreira. "Electronic control of drug release from gauze or cellulose acetate fibres for dermal applications." Journal of Materials Chemistry B 9 (2021): 3515-3522. AbstractWebsite

Electronic controlled drug release from fibres was studied using ibuprofen as a model drug, one of the most popular analgesics, to impregnate gauze and cellulose acetate (CA) membranes. Conductivity in the range of 1–10 mS cm−1 was obtained in polypyrrole (Ppy) functionalised gauze and CA fibres, providing voltage-controlled drug release in a system consisting of Ppy/Ibuprofen/Ppy membranes and an Ag electrode. SEM images evidenced the Ppy adhesion to fibres and Micro Raman spectra proved drug incorporation and release. A small wound adhesive built with these membranes retains ibuprofen at 1.5 V and quickly releases it when −0.5 V is applied.

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.
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, 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.

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.

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, 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.