H.C. de Sousa

A detailed thermodynamic analysis of [C4mim][BF4]+ water as a case study to model ionic liquid aqueous solutions

Since determining experimentally a wide variety of thermophysical properties—even for a very small portion of the already known room temperature ionic liquids (and their mixtures and solutions)—is an impossible goal, it is imperative that reliable predictive methods be developed. In turn, these methods might offer us clues to understanding the underlying ion–ion and ion–molecule interactions. 1-Butyl-3-methylimidazolium tetrafluoroborate, one of the most thoroughly investigated ionic liquids, together with water, the greenest of the solvents, have been chosen in this work in order to use their mixtures as a case study to model other, greener, ionic liquid aqueous solutions. We focus our attention both on very simple methodologies that permit one to calculate accurately the mixtures molar volumes and heat capacities as well as more sophisticated theories to predict excess properties, pressure and isotope effects in the phase diagrams, and anomalies in some response functions to criticality, with a minimum of information. In regard to experimental work, we have determined: (a) densities as a function of temperature (278.15 < T/K < 333.15), pressure (1 < p/bar < 600), and composition (0 < xIL < 1), thus also excess molar volumes; (b) heat capacities and excess molar enthalpies as a function of temperature (278.15 < T/K < 333.15) and composition (0 < xIL < 1); and (c) liquid–liquid phase diagrams and their pressure (1 < p/bar < 700) and isotopic (H2O/D2O) dependences. The evolution of some of the aforementioned properties in their approach to the critical region has deserved particular attention.

Preparation and chemical and biological characterization of a pectin/chitosan polyelectrolyte complex scaffold for possible bone tissue engineering applications

In this work, porous scaffolds obtained from the freeze-drying of pectin/chitosan polyelectrolyte complexes were prepared and characterized by FTIR, SEM and weight loss studies. Additionally, the cytotoxicity of the prepared scaffolds was evaluated in vitro, using human osteoblast cells. The results obtained showed that cells adhered to scaffolds and proliferated. The study also confirmed that the degradation by-products of pectin/chitosan scaffold are noncytotoxic.

Dexamethasone-loaded poly(ɛ-caprolactone)/silica nanoparticles composites prepared by supercritical CO2 foaming/mixing and deposition

A supercritical carbon dioxide (scCO2)-assisted foaming/mixing method (SFM) was implemented for preparing dexamethasone (DXMT)-loaded poly(ε-caprolactone)/silica nanoparticles (PCL/SNPs) composite materials suitable for bone regeneration. The composites were prepared from PCL and mesoporous SNPs (MCM-41/SBA-15) by means of scCO2-assisted SFM at several operational pressures, processing times and depressurization conditions. DXMT was loaded into SNPs (applying a scCO2 solvent impregnation/deposition method - SSID) and into PCL/SNPs composites (using the SFM method). The effects of the employed operational and compositional variables on the physicochemical and morphological features as well as in the in vitro release profiles of DXMT were analyzed in detail. This work demonstrates that the above-referred scCO2-based methods can be very useful for the preparation of DXMT-loaded PCL/SNPs composites with tunable physicochemical, thermomechanical, morphological and drug release properties and suitable for hard-tissue regeneration applications.

Multifactor analysis on the effect of collagen concentration, cross-linking and fiber/pore orientation on chemical, microstructural, mechanical and biological properties of collagen type I scaffolds

This work evaluates the effect of processing variables on some physicochemical and mechanical properties of multi- and unidirectional laminar collagen type I scaffolds. The processing variables considered in this study included microstructure orientation (uni- and multidirectional fiber/pore controlled by freeze-drying methodology), cross-linking (chemical - using genipin and glutaraldehyde, and physical - using a dehydrothermal method), and collagen concentration (2, 5 and 8mg/ml). The biocompatibility of the scaffolds obtained in each of the evaluated manufacturing processes was also assessed. Despite previous research on collagen-based platforms, the effects that these processing variables have on the properties of collagen scaffolds are still not completely understood. Unidirectional scaffolds presented higher resistance to failure under stress than multidirectional ones. The cross-linking degree was found to decrease when the concentration of collagen increased whilst using chemical cross-linkers, and to increase with the concentration of collagen for the dehydrothermal cross-linked scaffolds. Pore orientation indexes of both unidirectional and multidirectional scaffolds were not influenced by collagen concentration. Cross-linked scaffolds were more hydrophobic than non-cross-linked ones, and presented water vapor permeability adequate for use in low-to-moderate exuding wounds. Pore size ranges were compatible with cell in-growth, independently of the employed cross-linking and freezing methodologies. Moreover, scaffolds cross-linked with glutaraldehyde presented higher in-growth of primary oral mucosa fibroblasts than those cross-linked with genipin or with the dehydrothermal treatment. This multi-factor analysis is expected to contribute to the design of collagen type I platforms, which are usable on several potential soft tissue-engineering applications.

Supercritical solvent impregnation of natural bioactive compounds in N-carboxybutyl chitosan membranes for the development of topical wound healing applications

Supercritical Solvent Impregnation (SSI) was used to load topical membrane-type wound dressing biomaterials with natural based bioactive compounds namelly quercetin as an antiinflammatory and thymol as anaesthetic and skin permeation enhancer. The biodegradable and biocompatible membranes where prepared as film- and foam-like structures of N-carboxybutylchitosan and agarose to study the influence of morphological structure on the fluid handling capacities of the materials. Results show that SSI is a feasible and advantageous process that permits to ‘tune’ the relative loaded amounts of the bioactive substances by changing the operational conditions. The process also promotes the size reduction of quercetin particles with a significant improvement in its solubility in aqueous solutions and consequently in its bioavailability. The prepared materials present a sustained delivery for quercetin and adequate fluid handling capacities that are in the typical and desired ranges for commercial wound dressings.

Adsorbent Derived from Pinus pinaster Tannin for Cationic Surfactant Removal

Abstract Pinus tannin gel (PTG) has proven to be an effective adsorbent for removing various cationic pollutants including heavy metals, dyes, and surfactants. The form of obtaining these condensed tannins from Pinus pinaster bark was conventional aqueous extraction using 5.0% ethanol as additive. The present study focused on the removal of the surfactant hexadecyltrimethylammonium bromide (CTAB) from aqueous solutions using PTG. Kinetic studies showed that the Lagergren, Ho, and Elovich models all adequately explained the kinetics of CTAB adsorption onto PTG, with r2 correlation coefficients of around 0.98. The influences of pH and temperature were found not to be critical, and the CTAB-PTG system was modeled theoretically according to the Langmuir hypothesis using linear, nonlinear, and multiparametric forms, obtaining the values of the activation energies and such system constants as k l .

Solubility of dense CO2 in two biocompatible acrylate copolymers

Abstract - Biocompatible polymers and copolymers are frequently being used as part of controlled delivery systems. These systems can be prepared using a “clean and environment friendly” technology like supercritical fluids. One great advantage of this process is that compressed carbon dioxide has excellent plasticizing properties and can swell most biocompatible polymeric matrixes, thus promoting drug impregnation processes. Mass sorption of two acrylate biocompatible copolymers contact with supercritical carbon dioxide is reported. Equilibrium solubility of dense carbon dioxide in poly(methylmethacrylate-co-ethylhexylacrylate) and poly(methylmethacrylate-co-ethylhexylacrylate-co-ethyleneglycoldimethacrylate) was studied by a static method at 10.0 MPa and 313 K. The reticulated copolymer had Fickean behavior and its diffusion coefficient was calculated, under operating conditions. Keywords : Biocompatible acrylate; Supercritical fluids. INTRODUCTION Knowledge of diffusion in and through polymers is important, not only for the design of polymeric materials but also in a number of chemical processes, such as polycondensation, foaming, creation of polymer composites, impregnation, modification of polymers and many others (Jespersen, 2002). This work is part of a research project designed for the study, development, preparation and characterization of controlled drug-release systems for ophthalmic applications. Determination of the best operating conditions involves the knowledge of the solubility of compressed carbon dioxide in the polymers. The use of supercritical fluids as solvents offers the possibility to develop new “clean and environment friendly” processes. Compressed carbon dioxide has excellent plasticizing properties and can swell most biocompatible polymeric matrixes, thus promoting drug impregnation processes (Leino and Urtti, 1996). Biologically active or medical ingredients can be incorporated into polymer substrates without interference in the activity of the active substance because supercritical fluids process are at a low temperature (Clifford, 1999). Carbon dioxide is the most commonly used fluid due to its nontoxic properties and the low operating temperatures involved in supercritical processes (T

Phosphonium ionic liquids as greener electrolytes for poly(vinyl chloride)-based ionic conducting polymers

Ionic liquid based ion-conducting polymers have been prepared and characterized by loading poly(vinyl chloride) (PVC) with one of two phosphonium-based ionic liquids (PhILs) (trihexyl(tetradecyl) phosphonium bis(trifluoromethylsulfonyl)imide, [P14,6,6,6][Tf2N] and trihexyl(tetradecyl) phosphonium chloride, [P14,6,6,6][Cl]) and a commonly used PVC plasticizer (di-isononyl phthalate, DINP). Different proportions of each charged (PhILs) and non-charged (DINP) additive were used to evaluate the influence of PhIL ionicity on the ionic conductivity of the PVC-based electrolyte and to study the effect of the thermomechanical properties of PVC on the diffusivity of ionic charges in between PVC molecular chains, and consequently on the electrochemical properties of the polymer. Films were characterized for their chemical, morphological, thermomechanical and electrical properties. The results show that both PhIL ionicity and PhIL–PVC compatibility play a major role in decreasing the electrical resistivity of PVC films. The lowest film resistivity (0.4 kΩ cm), corresponding to an estimated electrical conductivity of ∼2.4 μS cm−1, was observed for PVC films loaded with the highest tested amount of [P14,6,6,6][Tf2N] (45 wt% of PhIL at fixed DINP composition, 9 wt%). These films were also stable at temperatures up to 200 °C without using any further PVC thermal stabilizer. The polymer electrolytes presented in this work may be used as platforms to produce soft, safer and cost-effective ion-conducting materials by using non-volatile and electrochemically stable PhILs as liquid electrolytes incorporated into a cheap, stable and versatile polymer such as PVC.

SCF-assisted processing of dexamethasone-loaded poly(ε-caprolactone)/MCM-41 materials for biomedical applications

Biodegradable polymeric foams of proper pore sizes, geometries and densities, are already known to be useful biomaterials for several pharmaceutical, biomedical and tissue engineering applications. Moreover, the combination of these biodegradable polymeric foams with biocompatible inorganic nanoparticles and with bioactive substances may lead to the generation of novel composite biomaterials presenting improved chemical, physical and biological properties. This work reports preliminary results on the use of supercritical carbon dioxide (scCO2) processes, namely of scCO2-assisted foaming and of scCO2-assisted impregnation/deposition, for the development of dexamethasone-loaded composite biomaterials prepared with poly(E-caprolactone) (PCL) and with mesoporous MCM-41 silica nanoparticles (SNPs). Pure PCL and PCL/MCM-41 composite materials (90:10 and 70:30, wt.%) were processed by scCO2 foaming at different experimental density (801.4 and 901.2 Kg/m3), processing time (2 and 14 hours) and depressurization rate (0.22 and 3.0 L/min) conditions. In addition, mesoporous MCM-41 SNPs were loaded with dexamethasone (DXMT) by a scCO2 impregnation/deposition method at the above referred experimental conditions, and by DXMT sorption from aqueous and from ethanolic DXMT liquid solutions (at 37 oC and atmospheric pressure). All prepared materials were characterized by simultaneous differential thermal analysis (SDT) and texturometry. DXMT release studies were performed in order to evaluate and to compare the obtained DXMT release profiles from loaded MCM-41 SNPs. Obtained results demonstrated the feasibility of using scCO2 impregnation/deposition and scCO2 foaming methods for the development of DXMT-loaded PCL/MCM-41 composite materials to be applied in hard tissue biomedical applications.