Supercritical Phase Inversion Research Articles

Supercritical Phase Inversion to Produce Photocatalytic Active PVDF-coHFP_TiO2 Composites for the Degradation of Sudan Blue II Dye.

TiO2-loaded poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-coHFP) membranes were produced by supercritical CO2-assisted phase inversion. Three different TiO2 loadings were tested: 10, 20, and 30 wt% with respect to the polymer. Increasing the TiO2 amount from 10 wt% to 20 wt% in the starting solution, the transition from leafy-like to leafy-cellular morphology was observed in the section of the membrane. When 30 wt% TiO2 was used, the entire membrane section showed agglomerates of TiO2 nanoparticles. These polymeric membranes were tested to remove Sudan Blue II (SB) dye from aqueous solutions. The adsorption/photocatalytic processes revealed that membrane morphology and TiO2 cluster size were the parameters that mainly affected the dye removal efficiency. Moreover, after five cycles of exposure of these membranes to UV light, SB removal was higher than 85%.

Production of fungistatic porous structures of cellulose acetate loaded with quercetin, using supercritical CO2

In this work, supercritical phase inversion was used to produce membranes of cellulose acetate, loaded with a highly hydrophobic drug, quercetin, with antifungal properties. Changing process parameters, such as polymer concentration (5%, 10% and 15% w/w), pressure (100 and 200 bar) and temperature (45 and 50 °C), different membrane morphologies and pores size were obtained. Operating in this way, it was possible to control quercetin release: the existence of macrovoids (i.e., finger-like structure) promoted a faster drug release (about 200 min); whereas, cellular structures favored a prolonged drug release (up to 1400 min). These membranes were tested against two types of fungi (Kluyveromyces lactis and Yarrowia lipolitica), obtaining an efficient and prolonged antifungal effect, overcoming the problems of quercetin hydrophobicity.

Supercritical Phase Inversion: A Powerful Tool for Generating Cellulose Acetate-AgNO3 Antimicrobial Membranes.

Antimicrobial composite membranes, formed by cellulose acetate loaded with AgNO3 particles, were produced by supercritical phase inversion. Different cellulose acetate concentrations were tested (15%, 20%, 30%(w/w)), whereas the active agent (i.e., silver nitrate) concentration was fixed at 0.1%(w/w) with respect to the quantity of polymer used. To determine the influence of the process parameters on membranes morphology, the pressure and temperature were varied from 150 to 250 bar and from 55 to 35 °C, respectively. In all cases, regularly porous membranes were produced with a uniform AgNO3 distribution in the membrane matrix. Silver release rate depended on membrane pore size, covering a time interval from 8 to 75 h.

Preparation and characterization of cellulose acetate-Laponite® composite membranes produced by supercritical phase inversion

Supercritical phase inversion was used to prepare new polymeric membranes, based on cellulose acetate and Laponite®, for tissue engineering applications. These composite membranes were characterized by a porous structure (porosity around 85%) with an average pore size ranging from about 9 to 13 μm depending on the initial weight ratio cellulose acetate/Laponite. This ratio also controlled thermal and mechanical properties of these membranes: Laponite modified membrane decomposition step and increased the membrane elasticity modulus up to 4 MPa while decreasing the percentage elongation at break from 240% to 180%. Laponite also increased material cells adhesion: thanks to its homogeneous inclusion into the membranes, a remarkable cells adhesion of around 80%, six times higher than the original material, was obtained.

Smart Membranes Production by Supercritical Phase Inversion to Increase Food Shelf-life

The freshness of minimally processed foods is also determined by their appearance; browning due to oxidative phenomena is one of the main reasons of discarded by consumers. To overcame this problem, the development of antioxidant active packaging has gained increasing interest in the food industry. In this work, a supercritical phase inversion process was tested to produce Curcumin (Cu) loaded Cellulose Acetate (CA) membranes, to be inserted in food packaging as antioxidant devices. Active membranes were produced at different process conditions (pressures ranging between 150-250 bar and temperatures ranging between 35-55 °C), polymer amount (12, 18, 24% w/w) and at constant ratio Cu/CA (10% w/w). Cu-loaded membranes showed an homogeneous cellular morphology with a mean pore size lower than 12 µm. Cu release was measured and a maximum release time of about 2 days was obtained; moreover, antioxidant tests were also performed on the loaded membranes, showing an activity up to 90%.

Production of antimicrobial membranes loaded with potassium sorbate using a supercritical phase separation process

The production of antimicrobial packaging is one of the most interesting challenges in the food industry; its scope is to prolong the shelf life of a food maintaining its safety and freshness. The major limitation of traditional techniques used to produce antimicrobial packaging, is the difficulty in controlling the release of the active agent from the device to the food surface. In this work, a supercritical phase inversion process has been tested to produce potassium sorbate (PS) loaded cellulose acetate (CA) membranes, to be inserted in food packaging. The membranes have been obtained at different process conditions (pressures 150–250 bar, temperatures 35–55 °C) and at different polymer concentrations (10, 15 and 20% w/w). PS to CA weight ratio has been maintained constant at 5% w/w for all the formulations. The best process parameter combination to obtain the longest PS release time (about 325 min) was 250 bar and 35 °C. The production of antimicrobial active packagings is one of the most attractive challenges in the food industry also catalyzed by consumers' demand for natural and safe foods and for environmental protection [1]. Antimicrobial food packaging reduces, inhibits or retards the growth of microorganisms that may be present in the food or packaging material itself [2], to extend the shelf life of the packed food. The most desired property is the controlled release of the antimicrobial agent to the food surface [3–6]. This characteristic is influenced by the technique used to produce the film. To overcome conventional processes limitations, it could be possible to use supercritical assisted processes, taking advantage of the properties of supercritical fluids, such as negligible surface tension, high diffusivity and low viscosity. In particular, a supercritical phase separation process has been successfully proposed to produce loaded polymeric membranes to be inserted in food packaging. [1] C.A. Campos, L.N. Gerschenson, S.K. Flores, Development of edible films and coatings with antimicrobial activity, Food Bioprocess Technol. 4 (2011) 849–875. [2] P. Appendini, J.H. Hotchkiss, Review of antimicrobial food packaging, Innov. Food Sci. Emerg. Technol. 3 (2002) 113–126. [3] M. Uz, S.A. Altınkaya, Development of mono and multilayer antimicrobial food packaging materials for controlled release of potassium sorbate, LWT—Food Sci. Technol. 44 (2011) 2302–2309. [4] P. Suppakul, J. Miltz, K. Sonneveld, S.W. Bigger, Active packaging technologies with an emphasis on antimicrobial packaging and its application, J. Food Sci. 68 (2003) 408–420. [5] A. Figoli, E. Mascheroni, S. Limbo, E. Drioli, Membrane for food packaging, chapter 10, in: V. Peinemann, S. Pereira Nunes, L. Giorno (Eds.), Membrane Technology: Volume 3: Membranes for Food Applications, Wiley-VCH Verlag GmbH & Co., Germany, 2010. [6] L. Vermeiren, F. Devlieghere, M. van Beest, N. de Kruif, J. Debevere, Development of the active packaging of foods, Trends Food Sci. Technol. 19 (1999) 77–86.

Porous nanostructured poly-l-lactide scaffolds prepared by phase inversion using supercritical CO2 as a nonsolvent in the presence of ammonium bicarbonate particles

Supercritical fluid technology has been utilized in the development of tissue engineering scaffolds. However, it results in some problems, such as the poorly interconnected pores and the inability to load growth factor due to the salt leaching process for removal of the solid porogen. In this study, ammonium bicarbonate (AB) particles were used as a porogen and mixed uniformly with poly-l-lactide (PLLA) solution. Supercritical CO2 was used to immerse and flush through the resulting compound to allow the occurrence of phase inversion, subsequently generating a nanofibrous network. As the decomposition temperature of AB crystals is 36°C, the temperature of the CO2 was increased to 40°C to decompose the porogen, and the decomposition products were removed by washing with CO2. The resulting PLLA scaffolds possessed both large pores and micro pores with a controllable pore size, a high porosity (>95%), an interconnected structure, a nanofibrous network, good mechanical properties (compressive strength up to 100kPa), and a very low organic solvent residue (12ppm). The results of Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) measurements indicated that the molecular structure and physical state of PLLA were not changed after supercritical processing. The results reveal that the application of AB particles as a porogen in the supercritical phase inversion process is feasible to produce tissue engineering scaffolds with a high-performance.

Nanostructured PVDF-HFP membranes loaded with catalyst obtained by supercritical CO 2 assisted techniques

Polymeric catalytic membrane reactors offer a larger flexibility over conventional reactors. The most-used method to generate polymer-based catalytic membranes is the phase inversion that, however, presents some limitations; in particular, the difficulty in generating a uniform distribution of the loaded materials. In this work, we use two new processes for the formation of membranes loaded with catalyst for potential applications in catalysis: supercritical assisted phase inversion and supercritical assisted gel drying, applied to formation of poly(vinylidene fluoride-co-hexafluoropropylene) membranes loaded with palladium nanoparticles. We analyzed the effect of process parameters (polymer concentration, catalyst concentration, pressure, temperature) on the membranes morphology. The supercritical phase inversion process produced cellular asymmetric structures with cell size ranging between 3 and 6 μm and nanoporous homogeneous networks, depending on the process conditions. Palladium nanoparticles homogeneous distributions were obtained only operating at selected process conditions, i.e., pressures larger than 150 bar and temperatures lower than 45 °C. Supercritical gel drying allowed homogeneous nanoporous membranes formation at all the tested process conditions: they were characterized by very high porosity (higher than 90%) and a very uniform catalyst distribution.

Supercritical phase inversion of starch-poly(ε-caprolactone) for tissue engineering applications

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.

Processing of novel bioactive polymeric matrixes for tissue engineering using supercritical fluid technology

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.

Dexamethasone-loaded scaffolds prepared by supercritical-assisted phase inversion

The aim of this study was to evaluate the possibility of preparing dexamethasone-loaded starch-based porous matrices in a one-step process. Supercritical phase inversion technique was used to prepare composite scaffolds of dexamethasone and a polymeric blend of starch and poly( l-lactic acid) (SPLA) for tissue engineering purposes. Dexamethasone is used in osteogenic media to direct the differentiation of stem cells towards the osteogenic lineage. Samples with different drug concentrations (5–15 wt.% polymer) were prepared at 200 bar and 55 °C. The presence of dexamethasone did not affect the porosity or interconnectivity of the polymeric matrices. Water uptake and degradation studies were also performed on SPLA scaffolds. We conclude that SPLA matrices prepared by supercritical phase inversion have a swelling degree of nearly 90% and the material presents a weight loss of ∼25% after 21 days in solution. Furthermore, in vitro drug release studies were carried out and the results show that a sustained release of dexamethasone was achieved over 21 days. The fitting of the power law to the experimental data demonstrated that drug release is governed by an anomalous transport, i.e., both the drug diffusion and the swelling of the matrix influence the release of dexamethasone out of the scaffold. The kinetic constant was also determined. This study reports the feasibility of using supercritical fluid technology to process in one step a porous matrix loaded with a pharmaceutical agent for tissue engineering purposes.

Formation of poly‐vinyl‐alcohol structures by supercritical CO2

AbstractPoly‐vinyl‐alcohol (PVA) porous structures have been prepared using a supercritical phase inversion process in which supercritical carbon dioxide (SC‐CO2) acts as the nonsolvent. First, we tested the versatility of the SC‐CO2 phase inversion process, forming PVA/dimethylsulfoxide (DMSO) solutions with polymer concentrations ranging from 1 to 35% (w/w) and changing the process parameters. We worked at temperatures from 35 to 55°C and pressures from 100 to 200 bar obtaining different membranes morphologies: dense films, membranes with coexisting morphologies, and microparticles. However, we did not produce symmetric or asymmetric porous membranes. To obtain this result, we used casting solutions formed by adding acetone to DMSO with the aim of modifying the affinity between SC‐CO2 and the liquid solvent. In this series of experiments, we obtained asymmetric membranes with skin layer thicknesses lower than 10 μm. The results obtained in this work have been explained considering that the membranes formation mechanism is related to the kinetics of the process; i.e. the affinity between the solvent (mixture of solvents) and SC‐CO2. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007