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Temtem M, Pompeu D, Casimiro T, Mano JF, Aguiar-Ricardo A. "Supercritical CO 2 generating chitosan membranes and microparticles.". In: 8th World Biomaterials Congress 2008. Vol. 2.; 2008:. Abstract
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Temtem M, Silva LMC, Andrade PZ, dos Santos F, da Silva CL, Cabral JMS, Abecasis MM, Aguiar-Ricardo A. "Supercritical CO2 generating chitosan devices with controlled morphology. Potential application for drug delivery and mesenchymal stem cell culture." Journal of Supercritical Fluids. 2009;48(3):269-277. AbstractWebsite
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da Silva MS, Viveiros R, Coelho MB, Aguiar-Ricardo A, Casimiro T. "Supercritical CO2-assisted preparation of a PMMA composite membrane for bisphenol A recognition in aqueous environment." Chemical Engineering Science. 2012;68:94-100. AbstractPDFWebsite

This work reports a novel strategy to prepare affinity composite membranes using supercritical fluid technology. By blending molecularly imprinted polymeric particles with PMMA, a porous hybrid structure with affinity to the template molecule, bisphenol A, was prepared using a supercritical carbon dioxide (scCO2)-assisted method. Membranes were characterized in terms of morphology, mechanical performance and transport properties. The ability of the polymers and hybrid membranes to adsorb bisphenol A was tested in aqueous solutions and fitted to a linearized Langmuir equation, showing that adsorption takes place at homogeneous affinity binding sites within the imprinted surface. Filtration experiments showed that the imprinted hybrid membrane was able to adsorb higher amounts of template even in non-equilibrium dynamic binding conditions. The hybridization of the PMMA membrane herein reported conveys two important improvements over neat PMMA membrane: it introduced molecular affinity towards the template molecule and significantly increased the permeability of the porous structures, which are key parameters in processes that involve membranes. This technique could expand the applications of polymeric beads powders and enhance the efficiency of the membrane's transport properties. Our work presents a new method to confer affinity to a porous structure by immobilization of imprinted polymers, combining polymer synthesis and membrane formation using supercritical fluid technology.

Duarte ARC, Casimiro T, Aguiar-Ricardo A, Simplício AL, Duarte CMM. "Supercritical fluid polymerisation and impregnation of molecularly imprinted polymers for drug delivery." Journal of Supercritical Fluids. 2006;39(1):102-106. AbstractWebsite
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da Silva MS, Viveiros R, Aguiar-Ricardo A, Bonifacio VDB, Casimiro T. "Supercritical fluid technology as a new strategy for the development of semi-covalent molecularly imprinted materials." RSC Adv.. 2012;2:5075-5079. AbstractPDFWebsite

Molecularly imprinted polymeric particles with molecular recognition towards Bisphenol A (BPA) were synthesized for the first time using the semi-covalent imprinting approach in supercritical carbon dioxide (scCO2). The material{'}s affinity to BPA was achieved by co-polymerizing ethylene glycol dimethacrylate (EGDMA) with a template-containing monomer{,} Bisphenol A dimethacrylate (BPADM) in scCO2. Bisphenol A is then cleaved from the polymeric matrix by hydrolysis with tetrabutylammonium hydroxide (n-Bu4OH) also in a supercritical environment{,} taking advantage of the high diffusivity of scCO2. The selectivity of the molecular imprinted polymer (MIP) was assessed by evaluating its capability to bind BPA in comparison with progesterone and [small alpha]-ethinylestradiol. In addition{,} the cross-linked particles were used to prepare a PMMA-based hybrid imprinted membrane by a scCO2-assisted phase inversion method. Results show that the incorporation of MIP particles was able to confer molecular affinity to BPA to the membrane and that at dynamic conditions of filtration{,} this imprinted porous structure was able to adsorb a higher amount of BPA than the corresponding non-imprinted hybrid membrane. Our work represents a valuable greener alternative to conventional methods{,} for the synthesis of affinity materials which are able to maintain molecular recognition properties in water.

Casimiro T, Banet-Osuna AM, Ramos AM, da Ponte MN, Aguiar-Ricardo A. "Synthesis of highly cross-linked poly(diethylene glycol dimethacrylate) microparticles in supercritical carbon dioxide." European Polymer Journal. 2005;41(9):1947-1953. AbstractWebsite
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Costa E, De-Carvalho J, Casimiro T, da Silva CL, Cidade MT, Aguiar-Ricardo A. "Tailoring thermoresponsive microbeads in supercritical carbon dioxide for biomedical applications." Journal of Supercritical Fluids. 2011;56(3):292-298. AbstractWebsite
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Costa E, Coelho M, Ilharco LM, Aguiar-Ricardo A, Hammond PT. "Tannic acid mediated suppression of PNIPAAm microgels thermoresponsive behavior." Macromolecules. 2011;44(3):612-621. AbstractWebsite
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Montilla F, Clara E, Avilés T, Casimiro T, Aguiar Ricardo A, Nunes Da Ponte M. "Transition-metal-mediated activation of arylisocyanates in supercritical carbon dioxide." Journal of Organometallic Chemistry. 2001;626(1-2):227-232. AbstractWebsite
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Costa E, Lloyd MM, Chopko C, Aguiar-Ricardo A, Hammond PT. "Tuning Smart Microgel Swelling and Responsive Behavior through Strong and Weak Polyelectrolyte Pair Assembly." LangmuirLangmuir. 2012;28(26):10082-10090. AbstractWebsite

The layer-by-layer (LbL) assembly of polyelectrolyte pairs on temperature and pH-sensitive cross-linked poly(N-isopropylacrylamide)-co-(methacrylic acid), poly(NIPAAm-co-MAA), microgels enabled a fine-tuning of the gel swelling and responsive behavior according to the mobility of the assembled polyelectrolyte (PE) pair and the composition of the outermost layer. Microbeads with well-defined morphology were initially prepared by synthesis in supercritical carbon dioxide. Upon LbL assembly of polyelectrolytes, interactions between the multilayers and the soft porous microgel led to differences in swelling and thermoresponsive behavior. For the weak PE pairs, namely poly(l-lysine)/poly(l-glutamic acid) and poly(allylamine hydrochloride)/poly(acrylic acid), polycation-terminated microgels were less swollen and more thermoresponsive than native microgel, whereas polyanion-terminated microgels were more swollen and not significantly responsive to temperature, in a quasi-reversible process with consecutive PE assembly. For the strong PE pair, poly(diallyldimethylammonium chloride)/poly(sodium styrene sulfonate), the differences among polycation and polyanion-terminated microgels are not sustained after the first PE bilayer due to extensive ionic cross-linking between the polyelectrolytes. The tendencies across the explored systems became less noteworthy in solutions with larger ionic strength due to overall charge shielding of the polyelectrolytes and microgel. ATR FT-IR studies correlated the swelling and responsive behavior after LbL assembly on the microgels with the extent of H-bonding and alternating charge distribution within the gel. Thus, the proposed LbL strategy may be a simple and flexible way to engineer smart microgels in terms of size, surface chemistry, overall charge and permeability.The layer-by-layer (LbL) assembly of polyelectrolyte pairs on temperature and pH-sensitive cross-linked poly(N-isopropylacrylamide)-co-(methacrylic acid), poly(NIPAAm-co-MAA), microgels enabled a fine-tuning of the gel swelling and responsive behavior according to the mobility of the assembled polyelectrolyte (PE) pair and the composition of the outermost layer. Microbeads with well-defined morphology were initially prepared by synthesis in supercritical carbon dioxide. Upon LbL assembly of polyelectrolytes, interactions between the multilayers and the soft porous microgel led to differences in swelling and thermoresponsive behavior. For the weak PE pairs, namely poly(l-lysine)/poly(l-glutamic acid) and poly(allylamine hydrochloride)/poly(acrylic acid), polycation-terminated microgels were less swollen and more thermoresponsive than native microgel, whereas polyanion-terminated microgels were more swollen and not significantly responsive to temperature, in a quasi-reversible process with consecutive PE assembly. For the strong PE pair, poly(diallyldimethylammonium chloride)/poly(sodium styrene sulfonate), the differences among polycation and polyanion-terminated microgels are not sustained after the first PE bilayer due to extensive ionic cross-linking between the polyelectrolytes. The tendencies across the explored systems became less noteworthy in solutions with larger ionic strength due to overall charge shielding of the polyelectrolytes and microgel. ATR FT-IR studies correlated the swelling and responsive behavior after LbL assembly on the microgels with the extent of H-bonding and alternating charge distribution within the gel. Thus, the proposed LbL strategy may be a simple and flexible way to engineer smart microgels in terms of size, surface chemistry, overall charge and permeability.

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Fernandes L, Rial-Otero R, Temtem M, Veiga de Macedo C, Aguiar-Ricardo A, Capelo JL. "Ultrasonic energy as a tool in the sample treatment for polymer characterization through matrix-assisted laser desorption ionization time-of-flight mass spectrometry." Talanta. 2008;77(2):882-888. AbstractWebsite
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Ribeiro N, Casimiro T, Duarte C, Nunes Da Ponte M, Aguiar-Ricardo A, Poliakoff M. "Vapor-Liquid Equilibrium and Critical Line of the CO2 + Xe System. Critical Behavior of CO2 + Xe versus CO2 + n-Alkanes." Journal of Physical Chemistry B. 2000;104(4):791-795. AbstractWebsite
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Aguiar-Ricardo A, Temtem M, Casimiro T, Ribeiro N. "A visual acoustic high-pressure cell for the study of critical behavior of nonsimple mixtures." Review of Scientific Instruments. 2004;75(10 I):3200-3202. AbstractWebsite
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Aguiar-Ricardo A, Casimiro T, Costa T, Leandro J, Ribeiro N. "Visual and acoustic investigation of the critical behavior of mixtures of CO2 with a perfluorinated polyether." Fluid Phase Equilibria. 2006;239(1):26-29. AbstractWebsite
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