Search

In this study, SuperLip, an innovative technology assisted by supercritical carbon dioxide (SC–CO2), was used to produce unloaded and vitamin D3 (VD3)-loaded nanoliposomes. Vesicles were produced using hydrogenated and nonhydrogenated phosphatidylcholine from food-grade lecithins at ratios of 30:70, 20:80 and 0:100. SuperLip was operated at 100 bar and 40 °C using water flow rates ranging from 2.5 to 10 mL/min. The results showed that unloaded liposomes produced by SuperLip presented a unimodal size distribution at a water flow rate of 10 mL/min, regardless of the phospholipid ratio, and mean diameters ranging from 125 to 141 nm. VD3-loaded liposomes also presented a unimodal size distribution at this water flow rate, but slightly higher diameters that ranged from 144 to 252 nm. Furthermore, the addition of 20% purified phospholipids to liposomes led to an increase in the mean size of VD3-loaded vesicles from 144 to 218 nm and an increase in the encapsulation efficiency from 66.7 to 88.9%.

Background Curcumin and vitamin D3 (VD3) are nutraceutical compounds that exert important roles in the human health. Nanoencapsulation in liposomes appears as a suitable target delivery system that can also enhance the bioavailability of these biomolecules. Methods Vesicles were prepared using different ratios of hydrogenated and non-hydrogenated phospholipids, obtained from soy and egg-yolk. A supercritical CO2 assisted process was used to produce the nanoliposomes. The operative parameters were 40 °C and 100 bar, using a water flow rate of 10 mL/min. Nanoliposomes were characterized by scanning electron microscopy and dynamic light scattering to determine their morphology and stability; whereas biomolecules encapsulation efficiency and release kinetics were measured by a UV/Vis spectrophotometer. Antioxidant activity and the effect of stress-induced conditions on the nanoliposomes were also investigated. Significant findings Nanoliposomes mean diameters ranged from 128 to 228 nm, with encapsulation efficiencies up to 95% for curcumin and 74% for VD3. The addition of 30% w/w of saturated phospholipids to the starting formulation promoted an increase in size of vesicles and a consequent increase in the encapsulation efficiency of both biomolecules. The antioxidant activity of curcumin was preserved after processing and the co-loaded nanovesicles demonstrated a good stability under different stress conditions.

With the aim of increasing the mechanical and biological properties of different materials, a supercritical CO2 (SC-CO2) assisted technique was used to include a polymer with a natural origin (levan) in membranes of cellulose acetate (CA) and polyvinylidenefluoride-co-hexafluoropropylene (PVDF-HFP). CA-levan membranes were characterized by interconnected pores ranging from 9 to 13 μm; due to levan addition, composite membranes increased their mechanical resistance and cells adhesion (from 8% to 30%). In the second system, the processing of a PVDF-HFP-DMSO-levan colloidal suspension system caused a morphological modification and the generation of a foam-like structure; a decrease of the mechanical resistance and an increase of cells adhesion (from 8% to 35%) were observed. Stress-strain responses for both systems were fitted using two different hyperelastic equations, Yeoh and Ogden; deviations from experimental data lower than 15% were obtained. In conclusion, SC-CO2 assisted process was able to generate composite structures with levan, accessible to the cells; i.e., transforming polymers like CA and PVDF-HFP in potentially useful materials for biological applications.

A supercritical CO2 drying process was used to prepare an innovative nanocomposite, formed by a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF HFP) aerogel loaded with RuO2 nanoparticles. The produced nanocomposites, at 10% and 60% w/w of RuO2, were tested for the electrochemical oxidation of model tannery wastewaters. The effect of the electrochemical oxidation parameters, like pH, temperature, and current density, on tannic acid, intermediates, and chemical oxygen demand (COD) removal, was investigated. In particular, the electrolysis of a simulated real tannery wastewater, using PVDF HFP_RuO2 60, was optimized working at pH 10, 40 °C, and setting the current density at 600 A/m2. Operating in this way, surfactants, sulfides, and tannins oxidation was achieved in about 2.5 h, ammonium nitrogen oxidation in 3 h, and COD removal in 5 h. When chloride-containing solutions were tested, the purification was due to indirect electrolysis, related to surface redox reactions generating active chlorine. Moreover, sulfide ions were converted into sulfates and ammonium nitrogen in gaseous N2.

In this short review, drug delivery systems, formed by polysaccharide-based (i.e., agarose, alginate, and chitosan) aerogels, are analyzed. In particular, the main papers, published in the period 2011–2020 in this research field, have been investigated and critically discussed, in order to highlight strengths and weaknesses of the traditional production techniques (e.g., freeze-drying and air evaporation) of bio-aerogels with respect to supercritical CO2 assisted drying. Supercritical CO2 assisted drying demonstrated to be a promising technique to produce nanostructured bio-aerogels that maintain the starting gel volume and shape, when the solvent removal occurs at negligible surface tension. This characteristic, coupled with the possibility of removing also cross-linking agent residues from the aerogels, makes these advanced devices safe and suitable as carriers for controlled drug delivery applications.

Poly(ʟ-lactide) (PLLA) films, even of high thickness, exhibiting co-crystalline and crystalline α phases with their chain axes preferentially perpendicular to the film plane (c⊥ orientation) have been obtained. This c⊥ orientation, unprecedented for PLLA films, can be achieved by the crystallization of amorphous films as induced by low-temperature sorption of molecules being suitable as guests of PLLA co-crystalline forms, such as N,N-dimethylformamide, cyclopentanone or 1,3-dioxolane. This kind of orientation is shown and quantified by two-dimensional wide-angle X-ray diffraction (2D-WAXD) patterns, as taken with the X-ray beam parallel to the film plane (EDGE patterns), which present all the hk0 arcs centered on the meridian. PLLA α-form films, as obtained by low-temperature guest-induced crystallization, also exhibit high transparency, being not far from those of the starting amorphous films.

A comparative analysis concerning bio-based gels production, to be used for tissue regeneration, has been performed in this review. These gels are generally applied as scaffolds in the biomedical field, thanks to their morphology, low cytotoxicity, and high biocompatibility. Focusing on the time interval 2015–2020, the production of 3D scaffolds of alginate, chitosan and agarose, for skin and bone regeneration, has mainly been investigated. Traditional techniques are critically reviewed to understand their limitations and how supercritical CO2-assisted processes could overcome these drawbacks. In particular, even if freeze-drying represents the most widespread drying technique used to produce polysaccharide-based cryogels, supercritical CO2-assisted drying effectively allows preservation of the nanoporous aerogel structure and removes the organic solvent used for gel preparation. These characteristics are essential for cell adhesion and proliferation.

A critical analysis of the major steps involved in the cellulose acetate industrial process is performed, with the aim of proposing possible improvements using supercritical CO2 based sub-processes. Once highlighted the main weakness of the traditional process, related to the (i) fine modulation of the acetylation reaction to obtain 2.5 acetate, (ii) acetic acid removal from the acetic dope, and (iii) treatment of the diluted acetic acid–water solution, the most attractive alternative resulted the adoption of a supercritical antisolvent extraction (SAE) performed on the acetic dope. Operating in this way, the problems related to the use of large quantities of water to remove acetic acid from the acetic dope are resolved, since it will be directly extracted by supercritical CO2. Micro- and nanoparticles, or filaments, of cellulose acetate can be produced. Finally, an acetic acid residue of 23 ppm, in the supercritical CO2 treated cellulose acetate, confirmed the success of this alternative process configuration.

The main techniques used for organic pollutant removal from water are adsorption, reductive and oxidative processes, phytoremediation, bioremediation, separation by membranes and liquid–liquid extraction. In this review, strengths and weaknesses of the different purification techniques are discussed, with particular attention to the newest results published in the scientific literature. This study highlighted that adsorption is the most frequently used method for water purification, since it can balance high organic pollutants removal efficiency, it has the possibility to treat a large quantity of water in semi-continuous way and has acceptable costs.

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 &deg, 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.

The addition of supercritical CO2 to a polymeric solution allows to achieve an expanded liquid, characterized by reduced viscosity and surface tension. Thanks to this peculiarity, polyvinylpyrrolidone (PVP) microparticles and microfibers loaded with quercetin (QT) were produced, using a supercritical CO2 assisted electrohydrodynamic process. The experiments were performed at different pressure, applied voltage, and polymer concentration; whereas, QT/PVP ratio was maintained constant at 3.5% w/w in all tested solutions. At 3% w/w PVP, particles with an average diameter of 0.77±0.24 μm were produced. At 15% w/w PVP, fibers were instead obtained, with an average diameter of 2.81±1.38 μm. The transition from electrospray to electrospinning occurred as a consequence of the polymer concentration that determined an increase in the solution viscosity. IR spectroscopy demonstrated the physical dispersion of QT into PVP fibers, and DSC showed that this drug was amorphous after processing. QT bioavailability was improved in the loaded fibers; it was released up to 30 times faster than from the unprocessed powder, and more than 90% of its native antioxidant activity was preserved.

BACKGROUND: Artemisia annua L. extraction is traditionally performed using hexane; the process is simple, but not selective. In this work, a strategy to concentrate artemisinin and the other similar active principles in the final extract is proposed, combining cheapness of maceration and selectivity of SC‐CO₂ processing. RESULTS: Hexane extraction produced a solid, waxy extract with a yield of 3.3% w/w with respect to the starting vegetable material. Then, SC‐CO₂ processing of this solid extract was performed operating at 0.8 kg h⁻¹ SC‐CO₂ flow rate and at different operative parameters. Very selective conditions were found operating at 90 bar and 50°C, obtaining a final product containing more than 71% w/w of active compounds (artemisinin, artemisin and dehydroartemisinin). CONCLUSION: Using this approach, a product more than 2.6 times richer in artemisinin than the one obtained by conventional techniques and about 2 times richer than direct CO₂ extraction, was obtained. Another relevant result is that the overall process scheme is cheaper than direct CO₂ extraction, since a high pressure extractor about 20 times smaller can be used, to process the waxy product obtained by hexane extraction. © 2018 Society of Chemical Industry

The recovery of active ingredients from vegetable matter is one of the most attractive research fields in the literature. The perspective that moves this large interest, is the possibility to selectively solubilize the compounds of interest in SC-CO2 and to avoid the use of organic solvents that pollute the environment, the products and the processed material. Nevertheless, care must be devoted in selecting process arrangement and extraction conditions, minimizing co-extracted compounds. Fractional extraction and/or fractional separation should be a possible solution. The addition of a co-solvent has been proposed in the case of less soluble compounds in pure SC-CO2; but, the so-called supercritical antisolvent extraction could represent a valuable solution for these compounds.

In this work, the comparison between PVDF-HFP porous structures loaded with 3% w/w curcumin (Cm), produced by supercritical assisted processes, was performed. In the case of membranes, different operative conditions (from 250 bar/35 °C to 150 bar/55 °C) and polymer concentrations (from 10 to 30% w/w) were tested. A cellular membranes morphology was observed and porosity values up to 89% were measured. Cm release was prolonged from 20 h to 26 h changing the PVDF-HFP membrane concentration from 20 to 30% w/w. PVDF-HFP-Cm aerogels were produced by supercritical drying, operating at 200 bar and 45 °C. A nanofibrous aerogels morphology was obtained with open and interconnected pores, reaching porosity values of 94%. The maximum Cm release was prolonged up to 44 h for 12% w/w PVDF-HFP aerogel. Kosmeyers-Peppas model produced a fair good representation of the Cm release experimental results for PVDF-HFP-Cm membranes and aerogels.

In this work, the effect of two processes, i.e., freeze-drying and supercritical CO2 (SC-CO2) drying, on the final morphology of agarose-based porous structures, was investigated. The agarose concentration in water was varied from 1 wt% up to 8 wt%. Agarose cryogels were prepared by freeze-drying using two cooling rates: 2.5 °C/min and 0.1 °C/min. A more uniform macroporous structure and a decrease in average pore size were achieved when a fast cooling rate was adopted. When a slower cooling rate was performed instead, cryogels were characterized by a macroporous and heterogenous structure at all of the values of the biopolymer concentration investigated. SC-CO2 drying led to the production of aerogels characterized by a mesoporous structure, with a specific surface area up to 170 m2/g. Moreover, agarose-based aerogels were solvent-free, and no thermal changes were detected in the samples after processing.

Co-crystallization of amorphous poly(2,6-dimethyl-1,4-phenylene) oxide (PPO) films, as induced by sorption at different temperatures of many liquid guest molecules, is explored. Both for co-crystalline (CC) and corresponding nanoporous-crystalline (NC) films, kinds of and degree of planar orientation, which are relevant for their properties and applications, can be controlled by the guest sorption procedure. In particular, crystalline polymer chain orientation preferentially perpendicular to the film plane is favored by bulky guest molecules and by low guest sorption temperatures, i.e. by slow guest uptakes. Guest sorption kinetics and Scanning Electron Microscopy ( SEM ) support a simple mechanism that rationalizes the kinds of planar orientation of crystalline PPO chains. Slow guest uptakes imply polymer co-crystallization in spatial confinement, producing lamellae that are oriented flat-on to the film surface and hence polymer chain axes preferentially perpendicular to the film plane (c⊥ orientation). Fast guest uptakes imply polymer co-crystallization leading to fibrils that are parallel to the film surface and hence to polymer chain axes being preferentially parallel to the film plane (c// orientation).

Supercritical fractional extraction and separation scheme, was used to process Artemisia annua L., producing extracts enriched in active antimalarial principles. The best results were obtained when extraction was performed at 100 bar, 40 °C and the first separator was operated at the same pressure and at −7 °C. Paraffinic co-extracted compounds were selectively recovered in the first separator, confirming the efficiency of the fractional cooling separation and a concentration of 35% w/w of active compounds was obtained in the second separator. Artemisinin was the major active compound in the extract; but, other two active compounds, artemisin and dehydroartemisinin, were also largely found. Other co-extracted compounds belonged to Artemisia essential oil. Different SC-CO2 flow rates were tested: an increase from 0.8 to 1.2 kg/h did not determine appreciable variations of the extraction rate of the various compounds, indicating that internal mass transfer resistance mainly controlled the extraction process.

This work proposes a modeling of the mechanical properties of porous polymers processed by scCO2, using a phenomenological approach. Tensile and compression tests of alginate/gelatin and cellulose acetate/graphene oxide were modeled using three hyperelastic equations, derived from strain energy functions. The proposed hyperelastic equations provide a fair good fit for mechanical behavior of the nanofibrous system alginate/gelatin (deviations lower than 10%), whereas, due to the presence of the solid in the polymer network, a four-parameter model must be used to fit the composite cellulose acetate/graphene oxide behavior. Larger deviations from the experimental data were observed for the system cellulose acetate/graphene oxide because of its microporous structure. A finite element method was, then, proposed to model both systems, it allowed a realistic description of observable displacements and effective stresses. The results indicate that materials processed using scCO2, when submitted to large stresses, do not obey Hooke&acute, s law and must be considered as hyperelastic.

A new process is proposed that can largely improve classical electrospray (ESPR) atomization, thanks to the addition of supercritical CO2 (SC-CO2) to the liquid mixture, in which a polymer is dissolved, forming an expanded liquid. The consequent reduction of surface tension and viscosity allows the production of micrometric or nanometric particles of controlled size and distribution at a production rate up to one hundred times that of the traditional process. The new process was applied to particle generation from a very high molecular weight polyvinylpyrrolidone (PVP) and tested at different polymer percentages by weight and at different pressures. Repeatable microparticle diameters and distributions were obtained, ranging between 0.55 and 2.25 &micro, m at PVP concentrations from 1 to 5% w/w and pressures between 80 and 120 bar.

Alginate-based aerogels with a cylindrical shape to be used for medical applications were produced by supercritical drying. First, alginate (Alg) solutions at different polymer concentrations (from 5% to 15% w/w) were extruded using a new custom-made device, in a coagulation bath of CaCl2 at 5% w/w or CuSO4 at 1.5% w/v, where hydrogels were generated; then, the corresponding aerogels were produced by supercritical drying at 200 bar and 45 °C for 4 h. Scanning electron microscopy showed that nanostructured morphology of native Ca- and Cu-Alg-hydrogels was preserved by supercritical drying. The same apparatus was also tested to produce alginate-chitosan (Alg-Ch) aerogels; they showed an hybrid morphology characterized by the microporosity of chitosan and the nanofibers of alginate, homogeneously distributed in the gel structure.

An evolution of traditional electrospray and electrospinning is proposed in this work, adding SC−CO2 in the liquid polymeric solution. This new process arrangement allows to overcome some intrinsic limitations of the traditional processes, namely surface tension and viscosity control. The influence of various process parameters was studied. The increase of electric potential difference did not significantly modify the particle size distributions and the fiber size distributions; but, the distributions became sharper as the electric potential difference increased. At low PVP percentages in the solution, electrospray was favored, forming small particles, due to low solution viscosity. The viscosity of the solution increased with PVP concentration: therefore, first large and very large particles were formed; then, the process was no more able to produce jet break-up, microfibers were obtained and the process was converted to electrospinning, producing microfibers with diameters down to about 1.4 μm. Using lower molecular weight PVP, smaller particles (down to 0.35 μm) were produced and the particles/fibers transition occurred at larger polymer percentages. Pressure and PVP percentage played opposite roles in generating the different morphologies; therefore, electrospray and electrospinning assisted by SC−CO2 are like two faces of the same medal: they could be performed using the same apparatus, properly setting the process conditions and polymer concentration.

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.

In this work is proposed a critical review of the scientific literature about the extraction of products of industrial interest from Cannabis sativa L., like cannabinoids, essential oil and seed oil, using supercritical and subcritical CO2. Traditional techniques are also reviewed and critically discussed to evidence the advantages of CO2 processing. The extracts can be also used in pharmaceutical and biomedical formulations, in form of co-precipitates and capsules, to improve active compounds bioavailability and performance. Further studies can be required, mainly based on the analysis of mass transfer resistances during extraction and on solubility data of the compounds to be extracted, to improve process selectivity and the purity of the extracts obtained.

Ampicillin loaded liposomes were entrapped in alginate aerogels to create a meta-carrier (a carrier within another carrier), to obtain a prolonged drug release. Liposomes with a diameter of 200 ± 77 nm and with an encapsulation efficiency of 69.5 ± 1.2% were produced using a supercritical assisted formation process (SuperLip). Then, they were entrapped into alginate gels, and the final loaded aerogels were obtained by supercritical CO2 drying. The successful entrapment of liposomes into aerogels was confirmed by EDX analysis. Drug release tests demonstrated that ampicillin release time from these meta-carriers was about 4 days; i.e., about twice than its release time from liposomes alone. Two mass transfer resistances in series operated in the overall drug release: one related to liposomes lipidic layers and one due to the presence of the alginate aerogel matrix.

Superabsorbent polymers (SAPs) are organic materials possessing high capacity to absorb and retain large volumes of water, saline and physiological solutions (at least 10–20 times their weight). The most commonly used SAPs are acrylated-based polymers that are not biodegradable or recyclable. To overcome these limits, carboxymethylcellulose (CMC) with hydroxyethylcellulose (HEC) hydrogels were synthetized in this work and dried using a supercritical assisted process at 200 bar and 45 °C. The solvent exchange procedure influenced the final aerogel morphology and, thus, the aerogel swelling ratio (SR). A solvent exchange starting from 50 % v/v ethanol, preserved the native gel nanofibrous morphology, producing a SR up to 20 times larger than the ones reported in the literature using the same process, corresponding to a water uptake larger than 500 times the weight of the dried aerogel.

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.

Safety, easiness, and ecologically friendly preparation methods are key features in the fabrication of a portable supercapacitor. In this work, it is reported the use of supercritical CO2 (SC–CO2)-assisted gel drying for the direct preparation in a one-step of a novel porous and portable supercapacitor device. It consists of three layers, grown together and able to uptake a large amount of an ionic liquid, of an aerogel of Poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP): the middle layer is formed by PVDF-HFP alone and the top, and bottom layers are formed by PVDF-HFP aerogels containing dispersed molybdenum disulfide (MoS2) nanosheets (i.e., PVDF-HFP + MoS2). The produced supercapacitor device (PVMS) is characterized by a mesoporous structure with high surface area, taking advantage from both non-flammability and electrochemical stability of PVDF-HFP and high capacitance of MoS2 due to its fast ionic conductivity. The supercapacitor, at the optimized operative conditions, achieves an excellent specific capacitance of 176 F/g and a very high energy density of 97.8 Wh/Kg at a power density of 0.65 of kW/kg (current density 0.6 A/g), that still remains 76.4 Wh/kg at 5.1 kW/kg (current density 5 A/g, specific capacitance of 138.2 F/g). The device shows good stability in an ionic liquid electrolyte, suggesting that the proposed process can be a new opportunity to produce highly bulky improved supercapacitors.

The properties of alginate/gelatin (A/G) interpenetrated polymer networks have been studied by dissipative particle dynamics (DPD) simulations. The simulation predicted some mechanical properties of A/G blends with different A/G ratios in water. Results from new synthesized aerogels have been used to validate the range of exploitation of the DPD simulations. Good mechanical and morphological properties of the aerogels have been achieved from aerogels derived from hydrogels with water content higher than 95%. DPD simulation results indicated that an optimal shear viscosity is reached for a composition of 95% water, 3% alginate and 2% gelatin. Furthermore, this approach can be of great interest in designing novel materials.

Supercritical CO 2 (SC-CO 2 ) extraction coupled with fractional separation of the extracts, has been used to concentrate the active principles of Ruta graveolens . Using 250 bar, 40 °C for the extraction process and cooling the first separator to −10 °C, an efficient extraction and fractionation was obtained. Different particle sizes of the vegetable matter were tested (from 0.20 to 0.80 mm); they indicated that the extraction process was faster when particle size was smaller; i.e., internal mass transfer controlled the process. Fractional separation allowed the selective elimination of cuticular waxes, that represented about 78% w/w of the total extract produced by SC-CO 2 processing. The extract collected in the second separator was concentrated in active compounds up to 87% w/w. For comparison purposes, extraction was also performed using an organic solvent: the extract obtained using ethyl-acetate, contained low percentages of active compounds, mainly due to the co-extraction of large quantities of waxes.

This work focuses on the modelling of the mechanical performance of cellulose acetate-graphene oxide nanocomposite membranes, produced by supercritical CO2 assisted phase inversion, using a set of algorithms able to build and integrate two different parametric variational 3D finite element (FE) models. These models simulate micro- and nano-level morphology of the nanocomposite using a multiscale approach. Microlevel is characterized by interconnected spherical pores; whereas, nanolevel is a composites whose filler is formed by graphene oxide sheets. Information about nanocomposite morphology, derived from electron scanning microscopy analyses, was used to build periodic representative volume elements. A numerical-experimental correlation was performed comparing FE model results with the experimental ones obtained by compression tests, at different weight percentages of graphene oxide with respect to the polymer loaded in the membrane. A good approximation of the experimental trend of Young modulus was obtained by FE simulations.

Chitosan (CH) is one of the polymers most frequently proposed in form of hydrogels for tissue engineering (TE) applications. It is often crosslinked with the aim of improving its stability and mechanical properties. In this work, a supercritical carbon dioxide (SC-CO2) gel drying process was proposed to obtain CH scaffolds and, for the first time, the simultaneous elimination of unreacted glutaraldehyde (GTA), taking advantage of its solubility in supercritical mixtures. SC-CO2 gel dried crosslinked CH aerogels showed a nanofibrous structure characterized by an average diameter of about 100 nm. No collapse of the nanostructure was observed in the aerogels, due to the peculiarities of supercritical fluids (e.g., near zero surface tension). Moreover, crosslinked CH showed a thermally stable structure, as determined by TGA analysis. The hypothesis that a supercritical mixture is able to efficiently extract GTA residues entrapped in the gel matrix was also verified: negligible residues of GTA were found at the end of release experiments; in particular, at the best operating conditions, a GTA concentration equal to 0.013 ppm was detected. Therefore, the produced crosslinked CH aerogels can be effectively and safely used for TE applications.

The extraction of pyrethrins from chrysanthemum flowers has been performed using supercritical CO2 (SC-CO2) extraction coupled to fractional separation, with the aim of producing complete and selective extraction of these insecticidal principles. 90 bar, 40 °C were selected as the operative conditions for a first step of extraction, to work at moderate SC-CO2 density; two separators in series operating at −10 °C and at a pressure equal to that of extraction, and 25 °C, 15 bar, were used for fractional separation, respectively. A second SC-extraction step, performed at 200 bar 40 °C, demonstrated that many undesired compounds were co-extracted at these process conditions. The comparison with liquid extraction, using petroleum ether, showed that using SC-CO2 and an exhaustive processing, 30% more pyrethrins were extracted. Using the fractional separation, the produced extracts contained about 99% w/w pyrethrins if the process was stopped after about 80 min. Another suggested duration of the extraction process can be set at about 250 min, at which about 63% w/w pyrethrins were contained in the extracted material. The adopted process strategy could be readily extended to the supercritical processing of several other materials and to the industrial scale.