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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, Ana Teresa Kullberg, Jorge Carvalho Silva, and João Paulo Borges. "Chitosan Inverted Colloidal Crystal scaffolds: Influence of molecular weight on structural stability." Materials Letters 193 (2017): 50-53. AbstractWebsite

Chitosan with three different molecular weights (538 ± 48, 229 ± 45 and 13 ± 3 kDa) was used to develop biodegradable Inverted Colloidal Crystal (ICC) scaffolds with uniform pore size and interconnected pore network. Mass loss and compression modulus were analyzed after hydrolytic degradation in order to understand the influence of molecular weight on structural and mechanical degradation of chitosan ICC structures. Results show that medium molecular weight chitosan (229 ± 45 kDa) retains ICC structure and compression modulus for an extended period (4 weeks) and is therefore the preferred one for the production of ICC for soft tissue engineering.

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.

João, Carlos, Coro Echeverria, Alexandre Velhinho, Jorge Carvalho Silva, Maria Helena Godinho, and João Paulo Borges. "Bio-inspired production of chitosan/chitin films from liquid crystalline suspensions." Carbohydrate polymers 155 (2017): 372-381. AbstractWebsite

Inspired by chitin based hierarchical structures observed in arthropods exoskeleton, this work reports the capturing of chitin nanowhiskers’ chiral nematic order into a chitosan matrix. For this purpose, highly crystalline chitin nanowhiskers (CTNW) with spindle-like morphology and average aspect ratio of 24.9 were produced by acid hydrolysis of chitin. CTNW were uniformly dispersed at different concentrations in aqueous suspensions. The suspensions liquid crystalline phase domain was determined by rheological measurements and polarized optical microscopy (POM). Chitosan (CS) was added to the CTNW isotropic, biphasic and anisotropic suspensions and the solvent was evaporated to allow films formation. The Films’ morphologies as well as the mechanical properties were explored. A correlation between experimental results and a theoretical model, for layered matrix’ structures with fibers acting as a reinforcement agent, was established. The results evidence the existence of two different layered structures, one formed by chitosan layers induced by the presence of chitin and another formed by chitin nanowhiskers layers. By playing on the ratio chitin/chitosan one layered structure or the other can be obtained allowing the tunning of materials’ mechanical 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.

K
Khili, Faouzia, João Borges Borges, Pedro L. Almeida, Rabah Boukherroub, and Amel Dakhlaoui Omrani. "Extraction of Cellulose Nanocrystals with Structure I and II and Their Applications for Reduction of Graphene Oxide and Nanocomposite Elaboration." Waste and Biomass Valorization 10 (2019): 1913-1927. AbstractWebsite

The aim of the present study is to investigate the effect of the hydrolysis process on the properties of nanocrystalline cellulose (NCC) isolated from different precursors and the subsequent use of the extracted NCC for the reduction of graphene oxide (GO). The raw materials (almond and peanut shells) chosen for the isolation of cellulose were selected on the basis of their abundance and their poorly investigation in the production of NCC. Microcrystalline cellulose (MCC) was firstly extracted by alkali and bleaching treatments, then hydrolyzed under different processes to produce NCC polymorphs with structure I (NCC-I) and NCC structure II (NCC-II). The Fourier transform infrared spectroscopy, the X-ray diffraction (XRD) and the 13C NMR studies of the alkali and bleached products confirmed the formation of cellulose type I with high purity and good crystallinity, while scanning electron microscopy (SEM) showed micrometric fibers with lengths reaching 80 µm. Sulfuric acid treatment of these microfibers results in NCC type I or II, depending on the hydrolysis process. SEM of the NCC samples exhibited nanorods with diameter and aspect ratio in the range of 20–40 and 20–25 nm, respectively. Thermogravimetric analysis (TGA) of the MCC and NCC products indicated stable materials with a degradation temperature reaching 240 and 200 °C for MCC and NCC, respectively. The other part of our work concerns the use of the obtained cellulose nanocrystals (type II) for the preparation of reduced graphene oxide composite (NCC/RGO), to demonstrate the reducing properties of the isolated NCCII.

L
Lakhdar, Allagui, João Paulo Borges, Abdesslam Amara, and Amel Omrani. "Template-free synthesis of sub-micrometric cobalt fibers with controlled shape and structure. Characterization and magnetic properties." Journal of Magnetism and Magnetic Materials 425 (2017): 6-11. AbstractWebsite

Sub-micrometric Co fibers were prepared via a modified polyol process at 90 °C under an external magnetic field of about 550 Oe, using ethelyne glycol as solvent and hydrazine as reducing agent. The structure, the size and the morphology of the as-elaborated products were highly controlled through properly monitoring the synthesis parameters (amount of NaOH added, the amount of the reducing agent, precursor’ concentration and precursors mixing protocol). The XRD characterization confirmed the formation of pure cobalt powders with either hexagonal compact (hcp) or face-centered-cubic (fcc) structure depending on the concentration of the metal precursor and sodium hydroxide. The scanning electron microscopy observations of the powders shows sub-micrometric fibers with about 0.4–0.6 µm in diameter and a length that could reach 15 µm. Fibers prepared at high reducing ratio were constituted of flower-like spheres that coalesce in the direction of the applied magnetic field. For their high contact surface, these fibers offer new opportunities for catalysis applications. The hysteresis loop measurements show an enhancement of the Hc of the as-obtained fibers compared to their bulk counterparts and permit to confirm the relationship between the structure and the magnetic properties of the materials.

Lima, Nuno, Ana Catarina Baptista, Bruno Morais M. Faustino, Sofia Taborda, Ana Marques, and Isabel Ferreira. "Carbon threads sweat-based supercapacitors for electronic textiles." Scientific Reports 10 (2020): 7703. AbstractWebsite

Flexible and stretchable energy-storage batteries and supercapacitors suitable for wearable electronics are at the forefront of the emerging field of intelligent textiles. In this context, the work here presented reports on the development of a symmetrical wire-based supercapacitor able to use the wearer’s sweat as the electrolyte. The inner and outer electrodes consists of a carbon-based thread functionalized with a conductive polymer (polypyrrole) which improves the electrochemical performances of the supercapacitor. The inner electrode is coated with electrospun cellulose acetate fibres, as the separator, and the outer electrode is twisted around it. The electrochemical performances of carbon-based supercapacitors were analyzed using a simulated sweat solution and displayed a specific capacitance of 2.3 F.g−1, an energy of 386.5 mWh.kg−1 and a power density of 46.4 kW.kg−1. Moreover, cycle stability and bendability studies were performed. Such energy conversion device has exhibited a stable electrochemical performance under mechanical deformation, over than 1000 cycles, which make it attractive for wearable electronics. Finally, four devices were tested by combining two supercapacitors in series with two in parallel demonstrating the ability to power a LED.

M
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.

Mano, Francisca, Marta Martins, Isabel Sá-Nogueira, Susana Barreiros, João Paulo Borges, Rui Reis, Ana Rita Duarte, and Alexandre Paiva. "Production of Electrospun Fast-Dissolving Drug Delivery Systems with Therapeutic Eutectic Systems Encapsulated in Gelatin." AAPS PharmSciTech 18 (2017): 2579-2585. AbstractWebsite

Fast-dissolving delivery systems (FDDS) have received increasing attention in the last years. Oral drug delivery is still the preferred route for the administration of pharmaceutical ingredients. Nevertheless, some patients, e.g. children or elderly people, have difficulties in swallowing solid tablets. In this work, gelatin membranes were produced by electrospinning, containing an encapsulated therapeutic deep-eutectic solvent (THEDES) composed by choline chloride/mandelic acid, in a 1:2 molar ratio. A gelatin solution (30% w/v) with 2% (v/v) of THEDES was used to produce electrospun fibers and the experimental parameters were optimized. Due to the high surface area of polymer fibers, this type of construct has wide applicability. With no cytotoxicity effect, and showing a fast-dissolving release profile in PBS, the gelatin fibers with encapsulated THEDES seem to have promising applications in the development of new drug delivery systems.

Marques, Ana, Davide Miglietta, G. Gaspar, Ana Catarina Baptista, A. Gaspar, P. Perdigão, Iris Soares, Catarina Bianchi, David Sousa, Bruno Morais M. Faustino, V. S. Amaral, T. Santos, A. P. Gonçalves, R. C. da Silva, Fabrizio Giorgis, and Isabel Ferreira. "Synthesis of thermoelectric magnesium-silicide pastes for 3D printing, electrospinning and low-pressure spray." Materials for Renewable and Sustainable Energy 8 (2019): 21. AbstractWebsite

In this work, eco-friendly magnesium-silicide (Mg2Si) semiconducting (n-type) thermoelectric pastes for building components concerning energy-harvesting devices through 3D printing, spray and electrospinning were synthetized and tested for the first time. The Mg2Si fine powders were obtained through the combination of ball milling and thermal annealing under Ar atmosphere. While the latter process was crucial for obtaining the desired Mg2Si phase, the ball milling was indispensable for homogenizing and reducing the grain size of the powders. The synthetized Mg2Si powders exhibited a large Seebeck coefficient of ~ 487 µV/K and were blended with a polymeric solution in different mass ratios to adjust the paste viscosity to the different requirements of 3D printing, electrospinning and low-pressure spray. The materials produced in every single stage of the paste synthesis were characterized by a variety of techniques that unequivocally prove their viability for producing thermoelectric parts and components. These can certainly trigger further research and development in green thermoelectric generators (TEGs) capable of adopting any form or shape with enhanced thermoelectric properties. These green TEGs are meant to compete with common toxic materials such as Bi2Te3, PbTe and CoSb that have Seebeck coefficients in the range of ~ 290–700 μV/K, similar to that of the produced Mg2Si powders and lower than that of 3D printed bulk Mg2Si pieces, measured to be ~ 4866 μV/K. Also, their measured thermal conductivities proved to be significantly lower (~ 0.2 W/mK) than that reported for Mg2Si (≥ 4 W/mK). However, it is herein demonstrated that such thermoelectric properties are not stable over time. Pressureless sintering proved to be indispensable, but difficultly achievable by long thermal annealing (even above 32 h) in inert atmosphere at 400 °C, at least for bulk Mg2Si pieces constituted by a mean grain size of 2–3 μm. Hence, for overcoming this sintering challenge and become the silicide’s extrusion viable in the production of bulk thermoelectric parts, alternative pressureless sintering methods will have to be further explored.

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.

Matos, Ricardo, Catarina Chaparro, Jorge Carvalho Silva, Manuel Valente, João Paulo Borges, and Paula I. P. Soares. "Electrospun composite cellulose acetate/iron oxide nanoparticles non-woven membranes for magnetic hyperthermia applications." Carbohydrate polymers 198 (2018): 9-16. AbstractWebsite

In the present work composite membranes were produced by combining magnetic nanoparticles (NPs) with cellulose acetate (CA) membranes for magnetic hyperthermia applications. The non-woven CA membranes were produced by electrospinning technique, and magnetic NPs were incorporated by adsorption at fibers surface or by addition to the electrospinning solution. Therefore, different designs of composite membranes were obtained. Superparamagnetic NPs synthesized by chemical precipitation were stabilized either with oleic acid (OA) or dimercaptosuccinic acid (DMSA) to obtain stable suspensions at physiological pH. The incorporation of magnetic NP into CA matrix was confirmed by scanning and transmission electron microscopy. The results showed that adsorption of magnetic NPs at fibers’ surface originates composite membranes with higher heating ability than those produced by incorporation of magnetic NPs inside the fibers. However, adsorption of magnetic NPs at fibers’ surface can cause cytotoxicity depending on the NPs concentration. Tensile tests demonstrated a reinforcement effect caused by the incorporation of magnetic NPs in the non-woven membrane.

N
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.

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Perdigão, Patrícia, Bruno Faustino, Jaime Faria, João Paulo Canejo, João Borges Borges, Isabel Ferreira, and Ana Catarina Baptista. "Conductive Electrospun Polyaniline/Polyvinylpyrrolidone Nanofibers: Electrical and Morphological Characterization of New Yarns for Electronic Textiles." Fibers 8 (2020): 24. AbstractWebsite

Advanced functionalities textiles embedding electronic fibers, yarns and fabrics are a demand for innovative smart cloths. Conductive electrospun membranes and yarns based on polyaniline/polyvinylpyrrolidone (PANI/PVP) were investigated using the chemical modification of PANI instead of using conventional coating processes as in-situ polymerization. PANI was synthesized from the aniline monomer and the influence of the oxidant-to-monomer ratio on electrical conductivity was studied. The optimized conductivity of pellets made with pressed PANI powders was 21 S·cm−1. Yarns were then prepared from the t-Boc-PANI/PVP electrospun membranes followed by PANI protonation to enhance their electrical properties. Using this methodology, electrospun membranes and yarns were produced with electrical conductivities of 1.7 × 10−2 and 4.1 × 10−4 S·cm−1.

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.

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.

Prezas, Pedro, Bruno Melo, Luís Costa, Manuel Valente, Maria Carmo Lança, José Ventura, Luís Pinto, and Manuel Prezas. "TSDC and impedance spectroscopy measurements on hydroxyapatite, β-tricalcium phosphate and hydroxyapatite/β-tricalcium phosphate biphasic bioceramics." Applied Surface Science 424 (2017): 28-38. AbstractWebsite

Bone grafting and surgical interventions related with orthopaedic disorders consist in a big business, generating large revenues worldwide every year. There is a need to replace the biomaterials that currently still dominate this market, i.e., autografts and allografts, due to their disadvantages, such as limited availability, need for additional surgeries and diseases transmission possibilities. The most promising replacement materials are biomaterials with bioactive properties, such as the calcium phosphate-based bioceramics group. The bioactivity of these materials, i.e., the rate at which they promote the growth and directly bond with the new host biological bone, can be enhanced through their electrical polarization.
In the present work, the electrical polarization features of pure hydroxyapatite (Hap), pure β-tricalcium phosphate (β-TCP) and biphasic hydroxyapatite/β-tricalcium phosphate composites (HTCP) were analyzed by measuring thermally stimulated depolarization currents (TSDC). The samples were thermoelectrically polarized at 500 °C under a DC electric field with a magnitude of 5 kV/cm. The biphasic samples were also polarized under electric fields with different magnitudes: 2, 3, 4 and 5 kV/cm. Additionally, the depolarization processes detected in the TSDC measurements were correlated with dielectric relaxation processes observed in impedance spectroscopy (IS) measurements.
The results indicate that the β-TCP crystalline phase has a considerable higher ability to store electrical charge compared with the Hap phase. This indicates that it has a suitable composition and structure for ionic conduction and establishment of a large electric charge density, providing great potential for orthopaedic applications.

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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.

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Raminhos, Joana, João Borges Borges, and Alexandre Velhinho. "Development of polymeric anepectic meshes: auxetic metamaterials with negative thermal expansion." Smart Materials and Structures 28 (2019): 045010. AbstractWebsite

his paper reports the application of additive manufacturing technology to fabricate bi-dimensional lightweight composite meshes capable of demonstrating auxetic properties (negative Poisson's ratio (NPR)) in combination with negative thermal expansion (NTE) behaviour, using as constituent materials polymers that do not exhibit NTE behaviour. To describe the combination of NPR and NTE characteristics, the designation of 'anepectic' is being proposed. Each mesh, obtained from varying either the material combination or the design parameters, was tested on a heated silicone bath to study the effects of the different combinations on the coefficient of thermal expansion (CTE). It was found that all meshes studied demonstrated a successful combination of NPR and NTE behaviours, and it was revealed that there is a possibility to tailor the meshes to activate the NTE behaviour within a chosen range of temperatures. For an extreme case, a Poisson's ratio of −0.056, along with a CTE of −1568 × 10−6 K−1 has been achieved.

Ramos, Diogo J., Henrique Carrêlo, João Paulo Borges, Nuria Calero Romero, Jenifer Santos Garcia, and Maria Teresa Cidade. "Injectable Hydrogels Based on Pluronic/Water Systems Filled with Alginate Microparticles for Biomedical Applications." Materials 12 (2019): 1-13. AbstractWebsite

A (model) composite system for drug delivery was developed based on a thermoresponsive hydrogel loaded with microparticles. We used Pluronic F127 hydrogel as the continuous phase and alginate microparticles as the dispersed phase of this composite system. It is well known that Pluronic F127 forms a gel when added to water in an appropriate concentration and in a certain temperature range. Pluronic F127 hydrogel may be loaded with drug and injected, in its sol state, to act as a drug delivery system in physiological environment. A rheological characterization allowed the most appropriate concentration of Pluronic F127 (15.5 wt%) and appropriate alginate microparticles contents (5 and 10 wt%) to be determined. Methylene blue (MB) was used as model drug to perform drug release studies in MB loaded Pluronic hydrogel and in MB loaded alginate microparticles/Pluronic hydrogel composite system. The latter showed a significantly slower MB release than the former (10 times), suggesting its potential in the development of dual cargo release systems either for drug delivery or tissue engineering.

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.

Ropio, Inês, Ana Catarina Baptista, Joana Nobre, J. Correia, F. Belo, S. Taborda, Morais B. M. Faustino, João Borges Borges, A. Kovalenko, and Isabel Ferreira. "Cellulose paper functionalised with polypyrrole and poly(3,4-ethylenedioxythiophene) for paper battery electrodes." Organic Electronics 62 (2018): 530-535. AbstractWebsite

A simple process of commercial paper functionalisation via in situ polymerisation of conductive polymers onto cellulose fibres was investigated and applied as electrodes in paper-based batteries. The functionalisation involved polypyrrole (PPy) and Poly (3,4-ethylenedioxythiophene) (PEDOT) as conductive polymers with the process of functionalisation optimised for each polymer individually with respect to oxidant-to-monomer ratios and polymerisation times and temperature. Paper with conductivity values of 44 mS/cm was obtained by exposing the samples to pyrrole vapour for a period of 30 min at room temperature; however, polymerisation at temperatures of 40 °C lead to higher conductivity values to up 141 mS/cm. Consequently, functionalised PPy and PEDOT papers were applied as cathodes in batteries with Al foil anodes and commercial paper soaked in an electrolyte solution of NaCl.

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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.

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, Isabel Ferreira, Carlos Novo, and João Borges Borges. "Towards the development of multifunctional chitosan-based iron oxide nanoparticles: Optimization and modelling of doxorubicin release." Carbohydrate Polymers 153 (2016): 212-221. AbstractWebsite

In the present work composite nanoparticles with a magnetic core and a chitosan-based shell were produced as drug delivery systems for doxorubicin (DOX). The results show that composite nanoparticles with a hydrodynamic diameter within the nanometric range are able to encapsulate more DOX than polymeric nanoparticles alone corresponding also to a higher drug release. Moreover the synthesis method of the iron oxide nanoparticles influences the total amount of DOX released and a high content of iron oxide nanoparticles inhibits DOX release. The modelling of the experimental results revealed a release mechanism dominated by Fickian diffusion.

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.

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.

Soares, Paula I. P., Coro Echeverria, Ana Catarina Baptista, Carlos João, Susete Fernandes, Ana Almeida, Jorge Carvalho Silva, Maria Helena Godinho, and João Paulo Borges. "Hybrid polysaccharide-based systems for biomedical applications." In Hybrid Polymer Composite Materials: Applications, edited by Manju Kumari Thakur, Vijay Kumar Thakur and Asokan Pappu, 107-149. USA: Woodhead Publishing, Elsevier, 2017. Abstract

Hybrid materials have been widely studied for structural applications. Polysaccharide-based fibers, especially cellulosic fibers, have been explored in the last two decades as substitutes of the traditional reinforcements made of glass or carbon fibers due to their mechanical properties. However, their biocompatibility, biodegradability, and chemistry have attracted the researchers and new developments in the field of smart and functional materials arise in diverse applications. This chapter will focus on the biomedical applications of polysaccharide-based smart and functional materials, namely those concerning biosensors and actuators, theranostic systems, and tissue-engineering applications. Special attention will be given to cellulose- and chitin/chitosan-based hybrid materials because these are the two most abundant polysaccharides and probably the most promising for the development of hybrid materials for biomedical applications. Biomimetic strategies for the development of smart and functional hybrid materials will also be highlighted.

Soares, Paula I. P., Diana Machado, César Laia, Laura Pereira, Joana Coutinho, Isabel Ferreira, Carlos Novo, and João Paulo Borges. "Thermal and magnetic properties of chitosan-iron oxide nanoparticles." Carbohydrate polymers 149 (2016): 382-390. AbstractWebsite

Chitosan is a biopolymer widely used for biomedical applications such as drug delivery systems, wound healing, and tissue engineering. Chitosan can be used as coating for other types of materials such as iron oxide nanoparticles, improving its biocompatibility while extending its range of applications.
In this work iron oxide nanoparticles (Fe3O4 NPs) produced by chemical precipitation and thermal decomposition and coated with chitosan with different molecular weights were studied. Basic characterization on bare and chitosan-Fe3O4 NPs was performed demonstrating that chitosan does not affect the crystallinity, chemical composition, and superparamagnetic properties of the Fe3O4 NPs, and also the incorporation of Fe3O4 NPs into chitosan nanoparticles increases the later hydrodynamic diameter without compromising its physical and chemical properties. The nano-composite was tested for magnetic hyperthermia by applying an alternating current magnetic field to the samples demonstrating that the heating ability of the Fe3O4 NPs was not significantly affected by chitosan.

Soares, Paula I. P., Joana Romão, Ricardo Matos, Jorge Carvalho Silva, and João Paulo Borges. "Design and engineering of magneto-responsive devices for cancer theranostics: Nano to macro perspective." Progress in Materials Science 116 (2021): 100742. AbstractWebsite

Design, research, and development of new and improved smart multifunctional devices is one of the main topics in the advanced functional materials agenda for the next decade. Smart materials that can be triggered by external stimuli are seen with high potential for innovative treatments and improved drug delivery systems by regulatory agencies like the FDA and EMA. The incorporation of magnetic nanostructures into complex systems produces multifunctional devices that can be spatiotemporally controlled by an external magnetic field. These magneto-responsive devices can be used for a multitude of biomedical applications, from diagnostic to the treatment of tumors, and are actively being developed and tested for cancer theranostics. Herein, we review the development of magneto-responsive devices for cancer theranostics, starting from the most straightforward architecture, single nanoparticles. We give some theoretical concepts about the design and production of such systems while providing a critical review of applications in clinical practice. Naturally, the review evolves to more complex architectures, from one-dimensional to three-dimensional magneto-responsive systems, demonstrating higher complexity and multifunctionality, and consequently, higher interest for clinical practice. The review ends with the main challenges in the design and engineering of magneto-responsive devices for cancer theranostics and future trends in this biomedical field.

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.

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.

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.

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.

Strohmeier, P., C. Honnet, H. Perner-Wilson, M. Teyssier, B. Fruchard, Ana Catarina Baptista, and J. Steimle. Demo of PolySense: How to Make Electrically Functional Textiles In CHI Conference on Human Factors in Computing Systems., 2020. Abstract

We demonstrate a simple and accessible method for enhancing textiles with custom piezo-resistive properties. Based on in-situ polymerization, our method offers seamless integration at the material level, preserving a textile's haptic and mechanical properties. We demonstrate how to enhance a wide set of fabrics and yarns using only readily available tools. During each demo session, conference attendees may bring textile samples which will be polymerized in a shared batch. Attendees may keep these samples. While the polymerization is happening, attendees can inspect pre-made samples and explore how these might be integrated in functional circuits. Examples objects created using polymerization include rapid manufacturing of on-body interfaces, tie-dyed motion-capture clothing, and zippers that act as potentiometers.

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Teixeira, Silvia Soreto, Manuel P. F. Graça, José Lucas, Manuel Almeida Valente, Paula I. P. Soares, Maria Carmo Lança, Tânia Vieira, Jorge Carvalho Silva, João Paulo Borges, Luiza-Izabela Jinga, Gabriel Socol, Cristiane Mello Salgueiro, José Nunes, and Luís C. Costa. "Nanostructured LiFe5O8 by a Biogenic Method for Applications from Electronics to Medicine." Nanomaterials 11 (2021): 193. AbstractWebsite

The physical properties of the cubic and ferrimagnetic spinel ferrite LiFe5O8 has made it an attractive material for electronic and medical applications. In this work, LiFe5O8 nanosized crystallites were synthesized by a novel and eco-friendly sol-gel process, by using powder coconut water as a mediated reaction medium. The dried powders were heat-treated (HT) at temperatures between 400 and 1000 °C, and their structure, morphology, electrical and magnetic characteristics, cytotoxicity, and magnetic hyperthermia assays were performed. The heat treatment of the LiFe5O8 powder tunes the crystallite sizes between 50 nm and 200 nm. When increasing the temperature of the HT, secondary phases start to form. The dielectric analysis revealed, at 300 K and 10 kHz, an increase of ε′ (≈10 up to ≈14) with a tanδ almost constant (≈0.3) with the increase of the HT temperature. The cytotoxicity results reveal, for concentrations below 2.5 mg/mL, that all samples have a non-cytotoxicity property. The sample heat-treated at 1000 °C, which revealed hysteresis and magnetic saturation of 73 emu g−1 at 300 K, showed a heating profile adequate for magnetic hyperthermia applications, showing the potential for biomedical applications.

Tipa, Cezar, Maria Teresa Cidade, Tânia Vieira, Jorge Carvalho Silva, Paula I. P. Soares, and João Paulo Borges. "A New Long-Term Composite Drug Delivery System Based on Thermo-Responsive Hydrogel and Nanoclay." Nanomaterials 11 (2021): 25. AbstractWebsite

Several problems and limitations faced in the treatment of many diseases can be overcome by using controlled drug delivery systems (DDS), where the active compound is transported to the target site, minimizing undesirable side effects. In situ-forming hydrogels that can be injected as viscous liquids and jellify under physiological conditions and biocompatible clay nanoparticles have been used in DDS development. In this work, polymer–clay composites based on Pluronics (F127 and F68) and nanoclays were developed, aiming at a biocompatible and injectable system for long-term controlled delivery of methylene blue (MB) as a model drug. MB release from the systems produced was carried out at 37 °C in a pH 7.4 medium. The Pluronic formulation selected (F127/F68 18/2 wt.%) displayed a sol/gel transition at approx. 30 °C, needing a 2.5 N force to be injected at 25 °C. The addition of 2 wt.% of Na116 clay decreased the sol/gel transition to 28 °C and significantly enhanced its viscoelastic modulus. The most suitable DDS for long-term application was the Na116-MB hybrid from which, after 15 days, only 3% of the encapsulated MB was released. The system developed in this work proved to be injectable, with a long-term drug delivery profile up to 45 days.

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Vieira, Tânia, Jorge Carvalho Silva, Botelho A. M. do Rego, João Borges Borges, and Célia Henriques. "Electrospun biodegradable chitosan based-poly(urethane urea) scaffolds for soft tissue engineering." Materials Science and Engineering: C 103 (2019): 109819. AbstractWebsite

The composition and architecture of a scaffold determine its supportive role in tissue regeneration. In this work, we demonstrate the feasibility of obtaining a porous electrospun fibrous structure from biodegradable polyurethanes (Pus) synthesized using polycaprolactone-diol as soft segment and, as chain extenders, chitosan (CS) and/or dimethylol propionic acid. Fourier transform infrared spectroscopy and proton nuclear magnetic resonance confirmed the syntheses. Fibre mats' properties were analysed and compared with those of solvent cast films. Scanning electron microscopy images of the electrospun scaffolds revealed fibres with diameters around 1 μm. From tensile tests, we found that Young's modulus increases with CS content and is higher for films (2.5 MPa to 6.5 MPa) than for the corresponding fibre mats (0.8 MPa to 3.2 MPa). The use of CS as the only chain extender improves recovery ratio and resilience. From X-ray diffraction, a higher crystalline degree was identified in fibre mats than in the corresponding films. Films' wettability was enhanced by the presence of CS as shown by the decrease of water contact angle. X-ray photoelectron spectroscopy revealed that while ester groups are predominant at the films' surface, ester and urethanes are present in similar concentrations at fibres' surface, favouring the interaction with water molecules. Both films and fibres undergo hydrolytic degradation. In vitro evaluation was performed with human dermal fibroblasts. No PU sample revealed cytotoxicity. Cells adhered to fibre mats better than to films and proliferation was observed only for samples of CS-containing PUs. Results suggest that electrospun fibres of CS-based polyurethanes are good candidate scaffolds for soft tissue engineering.

Vieira, Tânia, Jorge Carvalho Silva, João Paulo Borges, and Célia Henriques. "Synthesis, electrospinning and in vitro test of a new biodegradable gelatin-based poly(ester urethane urea) for soft tissue engineering." European Polymer Journal 103 (2018): 271-281. AbstractWebsite

Biodegradable polyurethanes have been studied as scaffolds for tissue engineering due to their adjustable physico-chemical properties. In this work, we synthesized a biodegradable gelatin-based poly(urethane urea) using polycaprolactone-diol, as soft segment, and isophorone diisocyanate and gelatin from cold water fish skin as hard segment. The synthesis was confirmed by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance and the influence of the amount of gelatin introduced in the polymer backbone was analyzed by thermal analysis. Gelatin-based poly(urethane urea) electrospun fibrous mats and solvent cast films were then produced and their physico-chemical and biological properties studied. They present an amorphous structure, elastomeric behavior and water contact angles typical of hydrophobic surfaces. Hydrolytic degradation was analyzed in phosphate buffer saline (PBS), lipase and trypsin solutions. No mass changes were detected during 37 days in PBS and trypsin while significant degradation by lipase was observed. Human foetal foreskin fibroblasts were seeded on the fibrous mats and films. Populations were evaluated by colorimetric cell viability assays and morphology by fluorescence imaging. The substrates supported cell adhesion and proliferation. The novel gelatin-based poly(urethane urea) fibrous mats offer attractive physico-chemical and biological properties for soft tissue engineering applications.