Publications

Export 91 results:
Sort by: Author [ Title  (Desc)] Type Year
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 
{
Duarte AR, Shariati A, Rovetto LJ, Peters CJ. {Water cavities of sH clathrate hydrate stabilized by molecular hydrogen: Phase equilibrium measurements}. Journal of Physical Chemistry B. 2008;112. Abstract

In this experimental phase equilibrium study, we show for the first time that it is possible to stabilize structure sH of hydrogen clathrate hydrate with the help of some selected promoters. It was established that the formation pressures of these systems are significantly higher than that of structure sII of hydrogen clathrate hydrate when tetrahydrofuran (THF) is used as a promoter. Although no experimental evidence is available yet, it is estimated that the hydrogen storage capacity of structure sH can be as high as 1.4 wt {%} of H 2 , which is about 40{%} higher compared to the hydrogen storage capacity in structure sH. © 2008 American Chemical Society.

Barros AA, Aroso IM, Silva TH, Mano JF, Duarte AR, Reis RL. {Water and carbon dioxide: Green solvents for the extraction of collagen/gelatin from marine sponges}. ACS Sustainable Chemistry and Engineering. 2015;3:254-60. Abstract

Marine sponges are extremely rich in natural products and are considered a promising biological resource. The major objective of this work is to couple a green extraction process with a natural origin raw material to obtain sponge origin collagen/gelatin for biomedical applications. Marine sponge collagen has unique physicochemical properties, but its application is hindered by the lack of availability due to inefficient extraction methodologies. Traditional extraction methods are time consuming as they involve several operating steps and large amounts of solvents. In this work, we propose a new extraction methodology under mild operating conditions in which water is acidified with carbon dioxide (CO2) to promote the extraction of collagen/gelatin from different marine sponge species. An extraction yield of approximately 50{%} of collagen/gelatin was achieved. The results of Fourier transformed infrared spectroscopy (FTIR), circular dichroism (CD), and differential scanning calorimetry (DSC) spectra suggest a mixture of collagen/gelatin with high purity, and the analysis of the amino acid composition has shown similarities with collagen from other marine sources. Additionally, in vitro cytotoxicity studies did not demonstrate any toxicity effects for three of the extracts.

Duarte AR, Santo VE, Alves A, Silva SS, Moreira-Silva J, Silva TH, Marques AP, Sousa RA, Gomes ME, Mano JF, Reis RL. {Unleashing the potential of supercritical fluids for polymer processing in tissue engineering and regenerative medicine}. Journal of Supercritical Fluids. 2013;79:177-85. Abstractpdf

One of the major scientific challenges that tissue engineering and regenerative medicine (TERM) faces to move from benchtop to bedside regards biomaterials development, despite the latest advances in polymer processing technologies. A variety of scaffolds processing techniques have been developed and include solvent casting and particles leaching, compression molding and particle leaching, thermally induced phase separation, rapid prototyping, among others. Supercritical fluids appear as an interesting alternative to the conventional methods for processing biopolymers as they do not require the use of large amounts of organic solvents and the processes can be conducted at mild temperatures. However, this processing technique has only recently started to receive more attention from researchers. Different processing methods based on the use of supercritical carbon dioxide have been proposed for the creation of novel architectures based on natural and synthetic polymers and these will be unleashed in this paper. © 2013 Elsevier B.V. All rights reserved.

Duarte AR, Santo VE, Alves A, Silva SS, Moreira-Silva J, Silva TH, Marques AP, Sousa RA, Gomes ME, Mano JF, Reis RL. {Unleashing the potential of supercritical fluids for polymer processing in tissue engineering and regenerative medicine}. Journal of Supercritical Fluids. 2013;79:177-85. Abstractpdf

One of the major scientific challenges that tissue engineering and regenerative medicine (TERM) faces to move from benchtop to bedside regards biomaterials development, despite the latest advances in polymer processing technologies. A variety of scaffolds processing techniques have been developed and include solvent casting and particles leaching, compression molding and particle leaching, thermally induced phase separation, rapid prototyping, among others. Supercritical fluids appear as an interesting alternative to the conventional methods for processing biopolymers as they do not require the use of large amounts of organic solvents and the processes can be conducted at mild temperatures. However, this processing technique has only recently started to receive more attention from researchers. Different processing methods based on the use of supercritical carbon dioxide have been proposed for the creation of novel architectures based on natural and synthetic polymers and these will be unleashed in this paper. © 2013 Elsevier B.V. All rights reserved.

Tutak W, Farooque T, Simon GC. {Tissue Engineering and Regenerative Medicine}. Journal of Tissue Engineering and Regenerative Medicine. 2012;6:1-429. Abstractpdf
n/a
Turner NJ, Sicari BM, Keane TJ, Londono R, Crapo PM, Tottey S, Matsushima R, Shimatsu Y, Nam K, Kimura T, Fujisato T. {Tissue Engineering and Regenerative Medicine}. Journal of Tissue Engineering and Regenerative Medicine. 2012;6:1-429. Abstractpdf
n/a
Duarte AR, Mano JF, Reis RL. {Thermosensitive polymeric matrices for three-dimensional cell culture strategies}. Acta Biomaterialia. 2011;7. Abstract

A completely new strategy for cell culture focusing on the design of three-dimensional (3D) smart surfaces by supercritical fluid technology has been developed. This approach might overcome the limitations on cell expansion and proliferation of currently existing techniques. An alternative technology, based on supercritical carbon dioxide, was used to polymerize poly(N- isopropylacrylamide) (PNIPAAm) and to foam poly(d,l-lactic acid) (P D,L LA), creating a thermosensitive 3D structure which has proven to have potential as a substrate for cell growth and expansion. We demonstrated that the thermosensitive matrices promoted cell detachment, thus P D,L LA scaffolds have the potential to be used as substrates for cell growth and expansion avoiding enzymatic and mechanical methods of cell harvesting. The harvested cells were replated to evaluate their viability, which was not compromised. A major advantage of this technology is the fact that the prepared materials can be recovered and reused. Therefore, the same substrate can be recycled and reused for different batches. An indirect impact of the technology developed is related to the field of biotechnology, as this novel technology for cell expansion can be applied to any adherent cell cultures. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Duarte AR, Mano JF, Reis RL. {The role of organic solvent on the preparation of chitosan scaffolds by supercritical assisted phase inversion}. Journal of Supercritical Fluids. 2012;72:326-32. Abstract

The aim of this study was to evaluate the possibility of preparing chitosan porous matrixes using supercritical fluid technology. Supercritical immersion precipitation technique was used to prepare scaffolds of a natural biocompatible polymer, chitosan for tissue engineering purposes. The physicochemical and biological properties of chitosan make it an excellent material for the preparation of drug delivery systems and for the development of new biomedical applications in many fields from skin to bone or cartilage. Supercritical assisted phase inversion experiments were carried out and the effect of different organic solvents on the morphology of the scaffolds was assessed. Chitosan scaffold morphology, porosity and pore size were evaluated by SEM and micro-CT. A thermodynamic analysis of the process was carried out and insights on the solubility parameter and Flory-Huggins interaction parameters are given. The preparation of a highly porous and interconnected structure of a natural material, chitosan, using a clean and environmentally friendly technology constitutes a new processing technology for the preparation of scaffolds for tissue engineering using these materials. © 2011 Elsevier B.V.

Silva JM, Duarte AR, Caridade SG, Picart C, Reis RL, Mano JF. {Tailored freestanding multilayered membranes based on chitosan and alginate}. Biomacromolecules. 2014;15. Abstract

© 2014 American Chemical Society. Engineering metabolically demanding tissues requires the supply of nutrients, oxygen, and removal of metabolic byproducts, as well as adequate mechanical properties. In this work, we propose the development of chitosan (CHIT)/alginate (ALG) freestanding membranes fabricated by layer-by-layer (LbL) assembly. CHIT/ALG membranes were cross-linked with genipin at a concentration of 1 mg·mL {\textless} sup {\textgreater} -1 {\textless} /sup {\textgreater} or 5 mg·mL {\textless} sup {\textgreater} -1 {\textless} /sup {\textgreater} . Mass transport properties of glucose and oxygen were evaluated on the freestanding membranes. The diffusion of glucose and oxygen decreases with increasing cross-linking concentration. Mechanical properties were also evaluated in physiological-simulated conditions. Increasing cross-linking density leads to an increase of storage modulus, Young modulus, and ultimate tensile strength, but to a decrease in the maximum hydrostatic pressure. The in vitro biological performance demonstrates that cross-linked films are more favorable for cell adhesion. This work demonstrates the versatility and feasibility of LbL assembly to generate nanostructured constructs with tunable permeability, mechanical, and biological properties.

Coimbra P, Gil MH, Sousa HD, Duarte CM. {T O T S I U Rib N Tio T O T S I N}.. 2008:102-7. Abstract
n/a
Barros AA, Aroso IM, Silva TH, Mano JF, Duarte AR, Reis RL. {Surface modification of silica-based marine sponge bioceramics induce hydroxyapatite formation}. Crystal Growth and Design. 2014;14:4545-52. Abstract

Marine biomaterials are a new emerging area of research with significant applications. Recently, researchers are dedicating considerable attention to marine-sponge biomaterials for various applications. We have focused on the potential of biosilica from Petrosia ficidormis for novel biomedical/industrial applications. A bioceramic structure from this sponge was obtained after calcination at 750 °C for 6 h in a furnace. The morphological characteristics of the three-dimensional architecture were evaluated by scanning electron microscopy (SEM) and microcomputed tomography, revealing a highly porous and interconnected structure. The skeleton of P. ficidormis is a siliceous matrix composed of SiO2, which does not present inherent bioactivity. Induction of bioactivity was attained by subjecting the bioceramics structure to an alkaline treatment (2M KOH) and acidic treatment (2M HCl) for 1 and 3 h. In vitro bioactivity of the bioceramics structure was evaluated in simulated body fluid (SBF), after 7 and 14 days. Observation of the structures by SEM, coupled with spectroscopic elemental analysis (EDS), has shown that the surface morphology presented a calcium-phosphate CaP coating, similar to hydroxyapatite (HA). The determination of the Ca/P ratio, together with the evaluation of the characteristic peaks of HA by infrared spectroscopy and X-ray diffraction, have proven the existence of HA. In vitro biological performance of the structures was evaluated using an osteoblast cell line, and the acidic treatment has shown to be the most effective treatment. Cells were seeded on bioceramics structures and their morphology; viability and growth were evaluated by SEM, MTS assay, and DNA quantification, respectively, demonstrating that cells are able to grow and colonize the bioceramic structures. © 2014 American Chemical Society.

Duarte AR, Mano JF, Reis RL. {Supercritical phase inversion of starch-poly($ε$-caprolactone) for tissue engineering applications}. Journal of Materials Science: Materials in Medicine. 2010;21:533-40. Abstract

In this work, a starch-based polymer, namely a blend of starch-poly(epsilon-caprolactone) was processed by supercritical assisted phase inversion process. This processing technique has been proposed for the development of 3D structures with potential applications in tissue engineering applications, as scaffolds. The use of carbon dioxide as non-solvent in the phase inversion process leads to the formation of a porous and interconnected structure, dry and free of any residual solvent. Different processing conditions such as pressure (from 80 up to 150 bar) and temperature (45 and 55 degrees C) were studied and the effect on the morphological features of the scaffolds was evaluated by scanning electron microscopy and micro-computed tomography. The mechanical properties of the SPCL scaffolds prepared were also studied. Additionally, in this work, the in vitro biological performance of the scaffolds was studied. Cell adhesion and morphology, viability and proliferation was assessed and the results suggest that the materials prepared are allow cell attachment and promote cell proliferation having thus potential to be used in some for biomedical applications.

Duarte AR, Mano JF, Reis RL. {Supercritical fluids in biomedical and tissue engineering applications: a review}. International Materials Reviews. 2009;54:214-22. Abstractpdf

Over the past several years, the definition of a scaffold for tissue engineering has changed dramatically, from a material that acts only as an inert structural support for cell attachment to serving as a more complex and dynamic environment for tissue development. This paper is a review on the existing and on the new emerging techniques based on supercritical fluid technology for the preparation of scaffolds and particles for tissue engineering applications. Supercritical fluid technology has already proven to be feasible for many pharmaceutical applications and is now emerging as an alternative to conventional materials' processing methods for the preparation of three-dimensional structures and injectable particles suitable to be used in regenerative medicine. The basic principles underlying each technique are here presented as well as the advantages and disadvantages of each process. The state of the art is reviewed and the major conclusions of the studies reported in the literature are discussed.

Martins M, Craveiro R, Paiva A, Duarte AR, Reis RL. {Supercritical fluid processing of natural based polymers doped with ionic liquids}. Chemical Engineering Journal. 2014;241. Abstract

Some approaches have been developed in our group to investigate the role of novel ionic liquids as process and property modifiers of natural-based polymers. In our previous work, we proposed the use of ionic liquids as plasticizing agents for the creation of porous structures from a semi-crystalline natural-based polymer. The current work intended to complement the previous studies, evaluating the ability of ionic liquid (IL) to plasticize polymers such as blends of starch-poly-lactic acid (SPLA) and its effect on supercritical fluid foaming process (SCF) and providing more insights on the mechanisms involved. For this purpose, blends of starch with poly (lactic) acid, with different ratios of starch and poly-lactic acid of 50:50 and 30:70 were modified and processed using 1-butyl-3-methylimidazolium chloride ([bmim]Cl). Supercritical fluid foaming was studied at different soaking times (1, 3 and 6h) using carbon dioxide at 20.0MPa and 40°C. The blends were characterized by different techniques, such as infra-red spectroscopy, differential scanning calorimetry and compression and tensile mechanical analysis. The morphology of the foamed structures was analyzed by scanning electron microscopy and micro-computed tomography. The results suggest that after 3h of soaking time an equilibrium state of carbon dioxide into the bulk samples is attained, yielding structures with 6{%} and 15{%} of porosity, for SPLA70 and SPLA50 respectively. The solubility of carbon dioxide within the matrices was studied for the same conditions and the results demonstrate a higher sorption degree in the samples doped with ionic liquid. Sorption and desorption diffusion coefficients of supercritical CO 2 in the SPLA matrix were determined for the raw polymer and for the SPLA doped with [bmim]Cl. It was found that the lower desorption diffusion coefficients are related with the higher porosity obtained by the foaming process. © 2013.

Duarte AR, Casimiro T, Aguiar-Ricardo A, Simplício AL, Duarte CM. {Supercritical fluid polymerisation and impregnation of molecularly imprinted polymers for drug delivery}. Journal of Supercritical Fluids. 2006;39:102-6. Abstract

Herein the preparation of molecularly imprinted polymers (MIPs) using supercritical fluid technology is evaluated. Poly(diethylene glycol dimethacrylate), polyDEGDMA, was synthesised in supercritical carbon dioxide (scCO2) using a carboxylic acid end-capped perfluoropolyether oil as stabiliser. Polymerisations were carried out in the presence of different concentrations of two different template drug molecules, salicylic acid and acetylsalicylic acid. Results suggest that molecular imprinted polymers were successfully prepared by supercritical polymerisation and then impregnated with the template in order to prepare controlled release systems. © 2006 Elsevier B.V. All rights reserved.

Duarte AR, Simplicio AL, Vega-González A, Subra-Paternault P, Coimbra P, Gil MH, de Sousa HC, Duarte CM. {Supercritical fluid impregnation of a biocompatible polymer for ophthalmic drug delivery}. Journal of Supercritical Fluids. 2007;42:373-7. Abstract

Supercritical fluid impregnation was tested to prepare a new ophthalmic drug delivery device. Poly(methylmethacrylate-co-ethylhexylacrylate-co-ethyleneglycoldimethacr ylate), P(MMA-EHA-EGDMA) has been proposed by Mariz [M. Mariz, Preparação de uma lente intra-ocular dotada de um sistema de libertação controlada de fármaco, Master Thesis, Universidade de Coimbra, 1999] as a promising matrix to be used for intraocular delivery of anti-inflammatory drugs used in eye surgery. This matrix was successfully impregnated with flurbiprofen, a non-steroidal anti-inflammatory agent. The success of the impregnation was evaluated by scanning electron microscopy (SEM) analysis and also by in vitro drug release studies. The effect of some operating parameters was evaluated, namely, pressure and contact time. The operating pressure will influence both the solubility of the drug in the supercritical fluid but also the sorption degree of the polymeric matrix in the presence of carbon dioxide. The solubility of the drug in carbon dioxide and the sorption degree are reported in previous studies. A comparison between the batch and the semi-continuous impregnation process is also presented. The supercritical fluid impregnation proved to be feasible for the preparation of a new ophthalmic drug delivery system. The drug release profiles suggest that the drug can be released up to three months, which is a major advantage for the prevention of the inflammatory response after ophthalmic surgery. © 2007 Elsevier B.V. All rights reserved.

Costa MS, Duarte AR, Cardoso MM, Duarte CM. {Supercritical antisolvent precipitation of PHBV microparticles}. International Journal of Pharmaceutics. 2007;328:72-7. Abstract

The micronization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) from organic solutions using supercritical antisolvent (SAS) technique has been successfully achieved. SAS experiments were carried out at different operational conditions and microspheres with mean diameters ranging from 3 to 9 $μ$m were obtained. The effect of CO2 and liquid flow, temperature and pressure on particle size and particle size distribution was evaluated. The microspheres were precipitated from a dichloromethane (DCM) solution. The best process conditions for this mixture were, according to our study, 40 °C, 100 bar, 1 mL min-1 liquid flow and 10 L min-1 carbon dioxide flow. Experiments with polymers containing different HV percentages were carried out. The powders obtained became more spherical as the HV content decreased. © 2006 Elsevier B.V. All rights reserved.

Craveiro R, Martins M, Santos GB, Correia N, Dionísio M, Barreiros S, Duarte AR, Reis RL, Paiva A. {Starch-based polymer-IL composites formed by compression moulding and supercritical fluid foaming for self-supported conductive materials}. RSC Advances. 2014;4. Abstract

In this work, blends of starch and poly-$ε$-caprolactone (PCL) doped with different concentrations of 1-butyl-3-methylimidazolium acetate ([BMIM]Ac) or 1-butyl-3-methylimidazolium chloride ([BMIM] Cl) were studied. The blends were characterized by mechanical analysis, infra-red spectroscopy (FTIR), differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS), evaluating the IL doping effect. The samples were subjected to supercritical carbon dioxide foaming and the morphology of the structures was assessed. DSC shows a single glass transition and melting endotherm for foamed and unfoamed samples, having no effect upon IL doping, and DRS shows increased molecular mobility for blends with higher IL concentrations, and some hindrance for lower ones. The conductivity for SPCL doped with 30{%} [BMIM] Cl, before and after foaming, is comparable to the conductivity of the IL but exhibits more stable conductivity values, opening doors for applications as self-supported conductive materials. © 2014 the Partner Organisations.

Duarte AR, Martins C, Coimbra P, Gil MH, de Sousa HC, Duarte CM. {Sorption and diffusion of dense carbon dioxide in a biocompatible polymer}. Journal of Supercritical Fluids. 2006;38:392-8. Abstract

Mass sorption and diffusion coefficients in one acrylate biocompatible copolymer contacted with supercritical (sc) carbon dioxide are reported. Equilibrium solubility of dense carbon dioxide in poly(methylmethacrylate-co-ethylhexylacrylate-co-ethyleneglycoldimethacr ylate) (P(MMA-EHA-EGDMA)) was studied by a gravimetric method in a temperature range from 308 to 323 K and a pressure range from 10.0 to 20.0 MPa. The cross-linked copolymer presented Fickian behavior and Fick's diffusion model was applied to determine the amount of carbon dioxide present and the diffusion coefficients. Diffusion coefficients for the sorption under supercritical conditions and desorption at ambient conditions were determined and compared. Samples of P(MMA-EHA-EGDMA) with different thickness were used for comparison of the maximum sorption degree. Polymerization conditions were also varied in order to evaluate the influence of the molecular weight of the copolymer in the CO2 sorption process. To investigate the possibility of impregnating this acrylate copolymer with an anti-inflammatory drug, a preliminary experiment was performed. © 2005 Elsevier B.V. All rights reserved.