Ana Rita C. Duarte

The aim of this study was to evaluate the possibility of preparing starch-based porous matrixes using supercritical fluid technology. Supercritical immersion precipitation technique was used to prepare scaffolds of a polymeric blend of starch and poly(l-lactic acid) for tissue engineering purposes.Immersion precipitation experiments were carried out at different operational conditions and highly porous and interconnected scaffolds were obtained. Two organic solvents, dichloromethane and chloroform were tested, and from the results obtained chloroform was the more favourable for the process. The effect of polymer solution concentration (5 up to 20 wt{%}), temperature (35 up to 55 °C) and pressure (100 up to 200 bar) in the SPLA (50:50 wt{%}) membrane morphology, porosity and interconnectivity was evaluated. All the conditions tested were in the region of total miscibility between the organic solvent and carbon dioxide. Additionally, a blend with a different starch-poly(l-lactic acid) ratio (30:70 wt{%}) was tested. Bicontinuous structures were formed indicating that the L-L demixing process that governs the phase inversion is the spinodal decomposition. © 2008 Elsevier B.V. All rights reserved.

Equilibrium solubility of flurbiprofen, a nonsteroidal antiinflammatory agent, in supercritical carbon dioxide was measured by a static analytical method in the pressure range from (8.0 to 25.0) MPa, at temperatures of (303.0, 313.0, and 323.0) K. The cosolvent effect of ethanol in the solubility of the bioactive compound in supercritical carbon dioxide was investigated at 18 MPa and 313 K. The results obtained have a potential application in supercritical processes for this drug. Experimental solubility data were correlated with an empirical density-based Chrastil model.

The aim of this study was to develop a new process for the production of bioactive 3D scaffolds using a clean and environmentally friendly technology. The possibility of preparing composite scaffolds of Bioglass?? and a polymeric blend of starch and poly(l-lactic acid) (SPLA50) was evaluated. Supercritical phase-inversion technique was used to prepare inorganic particles loaded starch-based porous composite matrixes in a one-step process for bone tissue engineering purposes. Due to their osteoconductive properties some glasses and ceramics are interesting materials to be used for bone tissue engineering purposes; however their poor mechanical properties create the need of a polymeric support where the inorganic fraction can be dispersed. Samples impregnated with different concentrations of Bioglass?? (10 and 15{%} wt/wt polymer) were prepared at 200??bar and 55????C. The presence of Bioglass?? did not affect the porosity or interconnectivity of the polymeric matrixes. Dynamic mechanical analysis has proven that the modulus of the SPLA50 scaffolds increases when glass particles are impregnated within the matrix. In vitro bioactivity studies were carried out using simulated body fluid and the results show that a calcium-phosphate layer started to be formed after only 1??day of immersion. Chemical analysis of the apatite layer formed on the surface of the scaffold was performed by different techniques, namely EDS and FTIR spectroscopy and X-ray diffraction (XRD). The ion concentration in the simulated body fluid was also carried out by ICP analysis. Results suggest that a bone-like apatite layer was formed. This study reports the feasibility of using supercritical fluid technology to process, in one step, a porous matrix loaded with a bioactive material for tissue engineering purposes. ?? 2009 Elsevier B.V. All rights reserved.

This work addresses the preparation of 3D porous scaffolds of blends of chitosan and poly(l-lactic acid), CHT and PLLA, using supercritical fluid technology. Supercritical assisted phase-inversion was used to prepare scaffolds 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 regeneration. On the other hand, PLLA is a synthetic biodegradable polymer widely used for biomedical applications. Supercritical assisted phase-inversion experiments were carried out in samples with different polymer ratios and different polymer solution concentrations. The effect of CHT:PLLA ratio and polymer concentration and on the morphology and topography of the scaffolds was assessed by SEM and Micro-CT. Infra-red spectroscopic imaging analysis of the scaffolds allowed a better understanding on the distribution of the two polymers within the matrix. This work demonstrates that supercritical fluid technology constitutes a new processing technology, clean and environmentally friendly for the preparation of scaffolds for tissue engineering using these materials. © 2010 Elsevier B.V.

In situ ATR-IR spectroscopy was used to simultaneously measure the sorption and swelling of carbon dioxide at high pressures in a biocompatible acrylate copolymer poly(methylmethacrylate-co-ethylhexylacrylate-co- ethyleneglycoldimethacrylate), P(MMA-EHA-EGDMA). The $ν$ 3 band of CO 2 dissolved in the polymer (at 2335 cm -1 ) was used to calculate the sorption data and the polymer swelling was determined by analyzing the changes in the absorbance of the $ν$(CO) band (at 1730 cm -1 ) of the polymer. Transmission spectroscopy in the near-IR region was also used to study the sorption of CO 2 in the polymer using combinational and overtone bands. The experiments were carried out in a pressure range of 2.0-12.0 MPa and in a temperature range of 27-40 °C. The data for CO 2 sorption in this polymer obtained by in situ spectroscopic methods have been compared to the data obtained by the gravimetric technique. © 2005 Elsevier B.V. All rights reserved.