Generation of chitosan nanoporous structures for tissue engineering applications using a supercritical fluid assisted process

In recent years, considerable attention has been given to chitosan-based materials and their applications in the field of tissue engineering. However, the techniques proposed until now for the formation of chitosan scaffolds present some limitations such as: they are very time-consuming, use organic solvents, have difficulties in the obtainment and preservation of various levels of porosity and the 3-D structure. In this work, a new SC-CO₂ assisted process for the production of chitosan scaffolds is proposed; it consists of three steps: formation of a chitosan hydrogel by thermally induced phase separation; substitution of water with a suitable solvent; drying of the gel using SC-CO₂. Using this process, we produced chitosan nanostructured networks with filaments diameters around 50 nm, without any collapse of the gel nanostructure, characterized by a high porosity (>91%) and high compressive modulus (150 kPa).     

Generation of chitosan nanoporous structures for tissue engineering applications using a supercritical fluid assisted process

In recent years, considerable attention has been given to chitosan-based materials and their applications in the field of tissue engineering. However, the techniques proposed until now for the formation of chitosan scaffolds present some limitations such as: they are very time-consuming, use organic solvents, have difficulties in the obtainment and preservation of various levels of porosity and the 3-D structure. In this work, a new SC-CO₂ assisted process for the production of chitosan scaffolds is proposed; it consists of three steps: formation of a chitosan hydrogel by thermally induced phase separation; substitution of water with a suitable solvent; drying of the gel using SC-CO₂. Using this process, we produced chitosan nanostructured networks with filaments diameters around 50 nm, without any collapse of the gel nanostructure, characterized by a high porosity (>91%) and high compressive modulus (150 kPa).     

Supercritical extraction of borage seed oil coupled to conventional solvent extraction of antioxidants

This paper describes the extraction of borage seed oil by supercritical carbon dioxide (SC-CO₂) and the further extraction of antioxidants from the SC-CO₂-defatted borage meal with organic solvents (water, methanol, ethanol and ethyl acetate). The optimal conditions for oil extraction were obtained at 303 and 323 K at 200 bar, 2.5 h and a continuous flow of CO₂ of 1.5 L/h introduced through the bottom when the operating pressure and temperature were reached, attaining a yield of 60%. Borage oil is rich in unsaturated fatty acids; oleic acid, linoleic acid and linolenic acid accounted for 74% of the total fatty acid content under the above conditions. The highest extraction yield was achieved using water or methanol as extracting solvent from the SC-CO₂-defatted borage meal at 303 K and pressures of 200 and 150 bar for water and methanol, respectively. The most potent extracts, according to all methods tested, were obtained with water and methanol.     

Fat-soluble vitamin extraction by analytical supercritical carbon dioxide

Extraction of fat-soluble vitamins (A, D, E, and β-carotene) by supercritical carbon dioxide (SC-CO₂) was tested to replace conventional liquid extraction methods, which require large volumes of organic solvents. Supercritical fluid extraction (SFE) is a rapid extraction technique for fat-soluble vitamins enabling them to be accurately determined using only small volumes of organic solvents. Extractions were performed on ultra-high-temperature sterilized milk, milk powder, pork, liver paté (paté de fois), infant formula, and canned baby food to compare the methods. The proposed method is based on the extraction of fat-soluble vitamins and their esters by using SC-CO₂ with methanol as a modifier. HPLC analysis using photometric detection was used for the vitamin analysis. The results showed no significant differences between extraction methods. The proposed SFF method appears to be useful as a substitute for the traditional organic solvent method, mainly for vitamin A and γ-tocopherol. Some data in this paper were presented at the 5th International Symposium on Supercritical Fluids, Atlanta, Georgia, April 2000.     

Carbon dioxide: a renewable feedstock for the synthesis of fine and bulk chemicals

The syntheses of carbon dioxide (CO₂) based industrially important chemicals have gained considerable interest in view of the sustainable chemistry and “green chemistry” concepts. In this review, recent developments in the chemical fixation of CO₂ to valuable chemicals are discussed. The synthesis of five-member cyclic carbonates via, cycloaddition of CO₂ to epoxides is one of the promising reactions replacing the existing poisonous phosgene-based synthetic route. This review focuses on the synthesis of cyclic carbonates, vinyl carbamates, and quinazoline-2,4(1H,3H)-diones via reaction of CO₂ and epoxide, amines/phenyl acetylene, 2-aminobenzinitrile and other chemicals. Direct synthesis of dimethyl carbonate, 1,3-disubstituted urea and 2-oxazolidinones/2-imidazolidinones have limitations at present because of the reaction equilibrium and chemical inertness of CO₂. The preferred alternatives for their synthesis like transesterification of ethylene carbonate with methanol, transamination of ethylene carbonate with primary amine and transamination reaction of ethylene carbonate with diamines/β-aminoalcohols are discussed. These methodologies offer marked improvements for greener chemical fixation of CO₂ in to industrially important chemicals.     

Synthesis and encapsulation of yttria stabilized zirconia particles in supercritical carbon dioxide

Nanocrystalline oxide powders synthesized in supercritical CO₂ (SC-CO₂) generally consist in nanoparticle agglomerates, which are difficult to handle. In this work a particle encapsulation method in SC-CO₂ was developed to overcome this problem. By performing both the synthesis and encapsulation steps in the supercritical fluid, the agglomeration of particles can be limited, their handling can be improved and the powder behavior can be modified depending on the selected encapsulation agent. Poly(dimethylsiloxane)-graft-polyacrylate (PDMS-g-PA) phase separation method and methylmethacrylate (MMA) polymerization on particle surface are typical encapsulation processes usable in batch mode, with SC-CO₂ as a solvent, for ceramic powder encapsulation. This paper describes preliminary results concerning the synthesis of yttrium stabilized zirconia (YSZ) in SC-CO₂ and its encapsulation with PDMS-g-PA or PMMA in SC-CO₂. It has been shown that both phase separation and polymerization allow coating of the oxide particles, and clearly modify their properties. On the other hand, the use of a surfactant like PDMS-g-PA allows anchoring of MMA monomer and promotes polymerization on the particle surface. The choice of the surfactant is considered as a key parameter for a successful encapsulation process. This preliminary work offers new perspectives for synthesis and encapsulation of ceramic powders in SC-CO₂.     

Synthesis of novel bis- and tris-(cyclic carbonate)s and their use in preparation of polymer networks

Novel six-membered bis- and tris-(cyclic carbonate)s that are useful as cross-linking agents in the synthesis of structurally stable yet biodegradable polycarbonates and polyesters have been synthesized in good to moderate yield (85-45%). Cross-linked aliphatic polycarbonates, and polyesters were prepared by copolymerization of the bis-cyclic carbonate (3f) with trimethylene carbonate, and ε-caprolactone. The polymers swelled in a wide variety of organic solvents, including CHCl₃, CH₂Cl₂, ethyl acetate, acetone, DMSO, and DMF but not in protic polar solvents, such as methanol, ethanol, and water. Swelling ratios of trimethylene carbonate/3f and ε-caprolactone/3f networks at different feed ratios were investigated in dichloromethane. The glass transition temperature of the TMC/3f networks increased with increasing cross-link density.     

Digestive enzymes characterization of krill (Euphausia superba) residues deoiled by supercritical carbon dioxide and organic solvents

In this study, Enzyme activities of krill were characterized before and after lipid extraction by supercritical carbon dioxide (SC-CO₂) and organic solvent, n-hexane and acetone. Krill SC-CO₂ extraction was performed under the conditions of temperature range from 35 to 45 °C and pressure, 150–250 bar for 2.5 h with a constant flow rate of 22 g/min. Extraction yields of lipids increased with pressure and temperature. The digestive enzyme activities of protease, lipase and amylase of SC-CO₂ treated krill residues were slightly decreased comparing to organic solvent, n-hexane and acetone treated residues. In SC-CO₂ treated samples, all of the digestive enzymes showed slightly higher temperature stability. In the other hand the crude extracts of SC-CO₂ and n-hexane treated krill samples showed almost same optimum pH and pH stability for each of the digestive enzymes. It was also found in SDS-PAGE that there are no significant differences in protein patterns of the crude extracts of untreated, SC-CO₂, n-hexane and acetone treated krill indicating no denaturation of proteins.     

Synthesis of nanosized calcium carbonate (aragonite) via a polyacrylamide inducing process

A carbonation route for the synthesis of nanosized calcium carbonate (aragonite) was studied. In the process, polyacrylamide was used as an organic substrate to induce the nucleation and growth of calcium carbonate. The calcium carbonate particles were produced by means of carbonation of the mixture of calcium hydroxide and polyacrylamide by bubbling CO₂/N₂ gas mixture_. The operating parameters such as the concentration of organic substrate and temperature were varied to study their influences on the polymorph and crystal sizes of calcium carbonate particles. The morphology of the calcium carbonate particles was characterized with transmission electron micrograph (TEM). The synthesized calcium carbonate particles in the presence of organic substrate are the mixture of aragonite with needle shape and calcite with cubic shape. Fourier transform infrared spectroscopy (FTIR) analysis reveals the presence of aragonite and calcite. The polymorphs and their crystal sizes were characterized with X-ray diffraction (XRD). The calcium carbonate nucleated in the organic substrate exhibited different endothermic peak in differential thermal gravity (DTG) results compared to one coexisting with the organic substrate.     

Synthesis and characterization of hydrophobic calcium carbonate particles via a dodecanoic acid inducing process

A carbonation route for the synthesis of hydrophobic calcium carbonate was studied. In the process, dodecanoic acid was used as an organic substrate to induce the nucleation and growth of calcium carbonate. The calcium carbonate particles were produced by means of carbonation of the mixture of calcium hydroxide and dodecanoic acid by bubbling CO₂/N₂ gas mixture. The operating parameters such as temperature and the concentration of the organic substrate were varied to study their influences on the active ratio and contact angle of calcium carbonate particles. The morphology of the calcium carbonate particles was characterized with scanning electron microscopy (SEM). The synthesized calcium carbonate particles in the presence of the organic substrate are rod-like and ellipse-like particles. The polymorphs were characterized with X-ray diffraction (XRD).     

Perspectives on supercritical fluid processing of fats and oils

Over the past two decades, fats and oils processing using supercritical carbon dioxide (SC-CO₂) has developed from focusing only on extraction to fractionation of complex lipid mixtures, conducting reactions in supercritical fluid media and particle formation techniques for the delivery of bioactive lipid components. Extraction of specialty oils and column fractionation of deodorizer distillates to concentrate tocopherols have reached commercial scale. Even though significant progress has been made in fundamental aspects, many challenges lie ahead to better understand the phase behavior and solubility of multicomponent lipid mixtures in SC-CO₂ and to generate the much needed fundamental data, including transport properties, density and interfacial tension. Considering the increasing consumer demand for “natural” products and stricter government regulations on the use of organic solvents like hexane, the future of SC-CO₂ processing of lipids is bright. Based on the know-how accumulated, integrated processes can be developed, targeting ingredients for both food and non-food industrial applications, which would fit well into a larger biorefinery approach.     

Equation of state for the systems containing aqueous salt: Prediction of high pressure vapor-liquid equilibrium

An equation of state (EOS), which is based upon contributions to the Helmholtz energy, is presented for systems containing aqueous electrolyte solutions at high pressure. The Peng-Robinson equation of state is used to provide the Helmholtz energy of a reference system. The electrolyte terms consist three terms containing a modified Debye-Hückel term for long-range electrostatic interactions, the Born energy contribution for electrostatic works and a Margules term for short-range electrostatic interactions between ions and solvents. The binary and ternary interaction parameters of the equation of state are obtained by experimental osmotic coefficient data. Systems that were studied here are (water+ NaCl+SC-CO₂), (water+NH₄Cl+SC-CO₂), (water+Na₂SO₄+SC-CO₂) and (water+methanol+NaCl+SC-CO₂). It is found that the proposed equation of state is able to accurately represent the experimental data over a wide range of pressure, temperature and salt concentration.     

Lipase made active in hydrophobic media by coupling with polyethylene glycol

Lipases from various microorganisms were chemically modified with polyethylene glycol derivatives: 2,4-bis[O-methoxypoly(ethylene glycol)]-6-chloro-s-triazine (activated PEG₂, a chain-shaped polymer) and copolymer of polyoxyethylene allyl methyl diether and maleic anhydride (activated PM, a comb-shaped polymer). Because each polymer is amphipathic, the modified lipases become soluble not only in aqueous solution but also in hydrophobic media. They exhibit potent catalytic actions for ester synthesis and ester exchange reactions, the reverse reaction of hydrolysis, in transparent organic solvents and also in oily substrates without organic solvents. With PEG₂-lipases, macrocyclic lactone and gefarnate (geranyl farnesylacetate) were synthesized in high yields from 16-hydroxy-hexadecanoic acid ethyl ester and from farnesylacetic acid and geraniol in organic solvents, respectively. The modified lipase catalyzed the esterification preferentially with the (R)-isomer of secondary alcohols. Because the ester synthesis reactions with modified lipase proceeded in the transparent benzene system, the kinetic parameters (Michaelis constant and maximum velocity) were obtained by reciprocal plotting according to the Michaelis equation. With comb-shaped polymer as modifier, PM-lipase catalyzed effectively the reverse reaction of hydrolysis in organic solvents. The properties of each modified lipase are discussed in relation to those of the nonmodified lipase. Presented at the 84th Annual Meeting of the American Oil Chemists' Society held on April 25–29, 1993, in Anaheim, CA.     

Enzymatic conversion of corn oil into biodiesel in a batch supercritical carbon dioxide reactor and kinetic modeling

Synthesis of fatty acid methyl esters (FAME) as biodiesel from corn oil was studied in a batch supercritical carbon dioxide (SC-CO₂) bioreactor using immobilized lipase (Novozym 435) as catalyst. Effects of reaction conditions on the contents of FAME, monoacylglycerols (MAG), diacylglycerols (DAG), and triacyglycerols (TAG) were investigated at various enzyme loads (5–15%), temperatures (40–60 °C), substrate mole ratios (corn oil:methanol; 1:3–1:9), pressures (10–30 MPa), and times (1–8 h). The highest FAME content (81.3%) was obtained at 15% enzyme load, 60 °C, 1:6 substrate mole ratio, and 10 MPa in 4 h. A reaction kinetic model was used to describe the system, and the activation energy of the system was calculated as 72.9 kJ/mol. Elimination of the use of organic solvents, chemical catalysts and wastewater as well as reasonably high yields make the enzymatic synthesis of biodiesel in SC-CO₂ a promising green alternative to conventional biodiesel process.     

Supercritical carbon dioxide extraction of astaxanthin from Paracoccus NBRC 101723: Mathematical modelling study

Astaxanthin (AX) is a secondary metabolite that accumulates inside the cell during Paracoccus fermentation. The fermentation biomass was extracted using supercritical carbon dioxide (SC-CO₂). The solubility parameter of AX, CO₂ and entrainer solvents was calculated and validated with experimental results. The pressure and particle size of the biomass had a significant effect on the extraction of AX. A maximum recovery of 963.33 μg/g of AX was obtained after SC-CO₂ extraction at 40ºC, 350 bar and a run time of 60 min with ethanol (20% v/w) as an entrainer. Further, the experimental data has been modelled using non-linear regression analysis method.     

Polymeric microparticles prepared by supercritical antisolvent precipitation

This work has as main objective the development of a model process to obtain microparticles of an acrylate-methacrylate copolymer (Eudragit L100^® and Eudragit EPO^®) using supercritical carbon dioxide (SC-CO₂) as antisolvent (GAS). After studying the behaviour of the copolymers in SC-CO₂ at different operation conditions (pressure, temperature and presence of ethanol (EtOH)), efforts were invested in the optimization of Eudragit EPO^® precipitation from an organic solution using carbon dioxide as antisolvent in batch mode. After loading the precipitation vessel with a fixed quantity of the copolymer dissolution, the SC-CO₂ has been added until the pressure of operation has been reached. Three process parameters, namely, solution nature, presence of surfactants and organic solvent removal step, have been evaluated. Microparticles with mean diameter from about 2 to 12 μm are obtained.     

Study of a new polymer electrolyte poly(ethylene oxide): NaClO3 with several plasticizers for battery application

Sodium ion conducting thin film polymer electrolytes based on poly(ethylene oxide) (PEO) complexed with NaClO₃ were prepared by a solution‐casting method. Characterization by XRD, IR spectroscopy and AC conductivity has been carried out on these thin film electrolytes to analyse their properties. The conductivity studies show that the conductivity value of PEO:NaClO₃ complex increases with the increase in salt concentrations. Increase in conductivity was found in the electrolyte system by the addition of low molecular weight polymer poly(ethylene glycol) (PEG) and the organic solvents dimethylformamide (DMF) and propylene carbonate (PC). Using these electrolyte systems, cell parameters were measured from the discharge study with the application of load 100 kΩ at room temperature with common cell configuration Na|electrolyte|C:I₂:electrolyte. The open circuit voltage (OCV) ranges from 2.81 to 3.23 V and the short circuit current (SCC) ranges from 340 to 1180 µA. © 2001 Society of Chemical Industry     

Making fabrics water-repellent with fluorine-containing silane in supercritical carbon dioxide medium

It was shown that fluorine-containing silane, 2,2,3,3,4,4,5,5,5,6,6,7,7-tridecafluoro-N-[3-(triethoxysilyl)propyl]-heptane amide, is an effective water-repellent for different fabrics. Its application from solution in supercritical carbon dioxide followed by heat treatment gives the surfaces of fabrics stable water-repellent properties. The use of SC-CO₂ as a universal medium for treating fabrics allows eliminating the use of organic solvents, which significantly reduces the ecological load on the environment, simplifies the manufacturing process, and makes it safer. Translated from Khimicheskie Volokna, No. 1, pp. 39-44, January-February, 2009.     

Supercritical Carbon Dioxide Extraction of Carotenoids from Pumpkin (Cucurbita spp.): A Review

Carotenoids are well known for their nutritional properties and health promoting effects representing attractive ingredients to develop innovative functional foods, nutraceutical and pharmaceutical preparations. Pumpkin (Cucurbita spp.) flesh has an intense yellow/orange color owing to the high level of carotenoids, mainly α-carotene, β-carotene, β-cryptoxanthin, lutein and zeaxanthin. There is considerable interest in extracting carotenoids and other bioactives from pumpkin flesh. Extraction procedures able to preserve nutritional and pharmacological properties of carotenoids are essential. Conventional extraction methods, such as organic solvent extraction (CSE), have been used to extract carotenoids from plant material for a long time. In recent years, supercritical carbon dioxide (SC-CO₂) extraction has received a great deal of attention because it is a green technology suitable for the extraction of lipophylic molecules and is able to give extracts of high quality and totally free from potentially toxic chemical solvents. Here, we review the results obtained so far on SC-CO₂ extraction efficiency and quali-quantitative composition of carotenoids from pumpkin flesh. In particular, we consider the effects of (1) dehydration pre-treatments; (2) extraction parameters (temperature and pressure); the use of water, ethanol and olive oil singularly or in combination as entrainers or pumpkin seeds as co-matrix.     

Electrochemical performances of electric double layer capacitor with UV-cured gel polymer electrolyte based on poly[(ethylene glycol)diacrylate]-poly(vinylidene fluoride) blend

Poly[(ethylene glycol)diacrylate]-poly(vinylidene fluoride), a gel polymer blend with ethylene carbonate:dimethyl carbonate:ethylmethyl carbonate (EC:DMC:EMC, 1:1:1 volume ratio) and containing 1.0 M of lithium hexafluoro phosphate (LiPF₆) as liquid components, is employed as a gel polymer electrolyte for an electric double layer capacitor (EDLC). Its electrochemical characteristics is compared with that of liquid organic electrolyte mixture of ethylene carbonate, dimethyl carbonate and ethylmethyl carbonate in a 1:1:1 volume ratio containing 1.0 M LiPF₆ salt. The specific surface area of the activated carbon powder as an active material is 1908 m²/g. Liquid poly[(ethylene glycol)diacrylate] (PEGDA) oligomer with a high retention capability of liquid electrolytes is cured by UV irradiation and poly(vinylidene fluoride)-hexafluoropropylene (PVdF-HFP) copolymer with a porous structure endows polymer matrix with high mechanical strength.The specific capacitance of EDLC using the gel polymer electrolyte (GPE-EDLC) shows 120 F/g, which is better than the liquid organic electrolyte. Good cycling efficiency is observed for a GPE-EDLC with high retention capability of liquid components. The high specific capacitance and good cycling efficiency are most likely due to the polarization resistance of EDLC with the gel polymer electrolyte, which is lower than the liquid organic electrolyte. This may result from the distinguished adhesion between the activated carbon electrode and the gel polymer electrolyte, as well as high retention capability of liquid components.Power densities of GPE-EDLC and LOE-EDLC shows 1.88 kW/kg and 1.21 kW/kg, respectively. However, the energy densities are low in both electrolytes.The GPE-EDLC exhibits rectangular cyclic voltammogram similar to an ideal EDLC within operating voltage range of 0 V-2.5 V. It should be noted that a region of electric double layer means a wide voltage and a rapid formation. Redox currents of both EDLCs are not observed in the sweep region and the cyclic voltammograms are unchanged on repeated runs. The observed leakage current shows 49 μA after 720 s at a constant voltage of 2.5 V, due to the high ionic conductivity of 1.5 × 10⁻³ S cm⁻¹ during storage time. Swelling and well-developed pore structures of the GPE blend films allow ions and solvents to move easily.