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Item type:Publication, Access status: without files , Supercritical CO2 sorption kinetics and thymol impregnation of PCL and PCL-HA(Elsevier, 2016); ; ; ; The potential of supercritical carbon dioxide (scCO2) processing of polycaprolactone (PCL) and polycaprolactone-hydroxyapatite (PCL-HA) composites for obtaining functional porous scaffolds at moderate temperatures (35-40 °C) was analyzed and quantified. The effect of scCO2 sorption kinetics on the swelling, foam morphology and thermal behavior of the PCL and PCL-HA composites was studied. Sorption isotherms were determined using magnetic suspension balance at 10-30 MPa and 35-40 °C. Influence of the pressure, HA amount (10-20%) and procedure for HA powder preparation on the sorption kinetics was discussed. Supercritical solvent impregnation (SSI) of PCL and PCL-HA with thymol was investigated as environmentally friendly way to produce functional scaffolds with controlled microstructure. Moderately high pressures (13-17 MPa) and 10% of HA were proven to be favorable for creation of the PCL scaffolds with satisfying foam microstructure (mean pore size ∼200-300 μm), filler distribution and thymol impregnation yields (12-18%). This was due to the satisfactory high scCO2 solubility (0.25-0.30 g/g) and mass transfer rate (∼10-10 m2/s) in the polymer phase as well as its great plasticizing effect (-ΔTm = 26.4-27.4 °C). Higher saturation of the polymer phase with scCO2 (0.30-0.55 g/g), filler amount (20%) and thymol solubility in scCO2 (>5.5 g/kg) at pressures above 20 MPa resulted in decreased mass transfer rate and SSI efficiency.Publicationtype: Journal Article56 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Functionalization of polycaprolactone/hydroxyapatite scaffolds with Usnea lethariiformis extract by using supercritical CO₂(2016-01-01); ; ; ; Investigation of an integrated supercritical fluid extraction and supercritical solvent impregnation process for fabrication of microporous polycaprolactone-hydroxyapatite (PCL-HA) scaffolds with antibacterial activity is presented. The HA content and particle size as well as the operating conditions of the integrated process is optimized regarding the amount of impregnated antibacterial agent (Usnea lethariiformis extract) in the PCL-HA matrix, scaffold morphology and antibacterial activity against methicillin resistant Staphylococcus aureus (MRSA) strains. High pressure differential scanning calorimetry (HP-DSC) assay reveals that an increasing amount of HA results in decreasing melting temperature as well as crystallinity at an operating pressure of 17 MPa. The PCL-HA composites with micrometric sizes of the HA particles are convenient for being processed by the integrated process due to the simple preparation, a good interaction between the PCL matrix and filler and the advantageous impact on sorption. The scaffold obtained from PCL-HA with 20% of the HA shows the highest impregnation yield at 17 MPa and 35 °C (5.9%) and subsequently also the best bactericidal effect on the tested MRSA strains at an initial bacterial inoculum of 2 × 10- 4 CFU/mL.Publicationtype: Journal Article72 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , An integrated supercritical extraction and impregnation process for production of antibacterial scaffoldsThis chapter deals with integrated processes using carbon dioxide in supercritical conditions for the development of functionalized materials. The basics of the involved process units are presented to allow a general understanding, and for enabling to extend the design to a variety of applications. A conceptual design is proposed by integrating three steps for producing scaffolds with antibacterial properties. A setup for an integrated scCO2 extraction unit of natural compounds with posterior impregnation on solid matrices is described in detail including a final step of foaming, as a way of product formulation, by making use of the same supercritical fluid as being used for the prior extraction and impregnation steps. The strategy followed is based on minimizing the loss of extract matter in the tubes, vessels, and heat exchangers of the equipment by directly using the scCO2-extract solution for impregnation, avoiding the low efficiency of extract recovery and energy consumption occurring in a separation step forced by pressure reduction. Results of production of functionalized poly(caprolactone) scaffolds with natural compounds extracted from Patagonian Usnea lichen are presented as an example. To establish appropriate operating conditions for each of the processing steps, supercritical extraction of Usnea as well as sorption kinetics and resulting material properties have been studied in detail before arriving at an optimized overall process. 13.1 IntroductionSince the beginning of the eighties of the past century, supercritical extraction from solid natural resources is finding a growing number of industrial applications. Starting from food industry and stimulants (coffee, hops), a large variety of almost any lipid-containing seeds, spices or herbs has been extracted to obtain products of high purity and quality. Most of these high-price products are applied in cosmetics or pharmaceutical industry [1-3]. A distinction is made depending on whether the main aim is to extract a valuable component or to retrieve some undesired substance in order to increase the value of the source material, like in the case of extraction of aflotoxines from cork. Apart from extraction, high pressure can also be applied for modifying the original properties of the (natural) source material or to formulate an intermediate product. Treatment of rice with compressed or supercritical carbon dioxide (scCO2) generates certain properties that have advantages for posterior processing [4]. It has been proved that carbon dioxide induces swelling of plant cell structures, which in its turn improves fluid accessibility to extractable substances and, therefore, enhances the yield during the extraction process [5]. One important drawback is the energetic balance of high pressure extraction [6]. Principally, a high electrical input is required for condensing the CO2 after the product separation step. To overcome this important disadvantage, closed solvent loops should be considered and big pressure steps avoided. Consecutive processing steps have been designed in a way for improving the energetic balance in industrial processes, like decaffeination of green coffee beans, especially when the pressure level can be maintained at isobaric conditions throughout the process. To separate the extractable from the compressed solvent, an adsorption process can be included. However, this usually implies a further separation step for regenerating the adsorbent. Hence, the separation of the extract from the supercritical solvent needs to be envisaged in a smart way. One possibility is bonding the extracted substance to a substrate, guided in a certain way that the formulation of an end product is included in the process. A number of challenges need to be overcome: (i) Different kinetics of the materials in the different process steps (ii) Alteration of substrate properties (iii) Technical challenges, such as isobaric pumps (hermetic pumps) (iv) Product retrieval This chapter shows how different processing mechanisms may fit together to an integrated process, concentrating it on three steps: extraction, sorption, and formulation (Fig. 13.1). Different examples are given for research, pilot, and industrial-scale processes, focusing on a novel process for manufacturing antibacterial scaffolds or devices based on phytoextracts and biopolymers.Publicationtype: Book Part42 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Development of polycaprolactone scaffold with antibacterial activity by an integrated supercritical extraction and impregnation process(Elsevier, 2013-03-23); ; ; ; The present study is aimed to develop a process for production of functionalized scaffolds impregnated with natural compounds extracted from Patagonian Usnea lichen. A setup for an integrated supercritical CO2 extraction of natural compounds with posterior impregnation on solid matrices (polycaprolactone, PCL) is developed and presented here. In order to establish optimized operating conditions, supercritical extraction of Usnea as well as sorption kinetics and resulting material properties have been studied separately first. Usnea extracts isolated by supercritical carbon dioxide at 30 MPa and 40 C have shown strong antibacterial activity with values of the minimum inhibitory concentration (MIC) ranging from less than 1.25 μg/mL to 320 μg/mL against Listeria innocua and Methicillin-resistant Staphylococcus (MRS) strains. Useful scaffolds of PCL for tissue engineering containing a porous structure with pore diameters between 150 and 340 μm can be obtained when PCL is exposed to carbon dioxide at 35 C and 15 MPa. The degree of crystallinity of functionalized PCL was shown to be influenced by the incorporated antibacterial agent. The presented results showed that the impregnated PCL samples are promising bactericidal compounds against L. innocua. Screening of antibacterial activity of functionalized PCL against a Methicillin-resistant Staphylococcus aureus (MRSA) strain showed a higher activity when a low bacterial inoculum level (2 × 104 Colony-forming Units/mL [CFU/mL]) was assayed.Publicationtype: Journal Article62 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of different pre-treatment methods on isolation of extracts with strong antibacterial activity from lichen Usnea barbata using carbon dioxide as a solvent(Elsevier, 2013-01-24); ; ; ; Multiplication and spreading of multiresistant pathogenic bacteria that cause fatal infections in humans and animals have boosted research on implementation of newer technologies for producing natural substances with strong antibacterial activities. In this study, SFE from lichen Usnea barbata was investigated for different pre-treatment methods with respect to extracts' yield, usnic acid recovery and antibacterial activity against more than thirty methicillin resistant staphylococci strains. Extraction of U. barbata with subcritical carbon dioxide was studied as well. Extraction yield, usnic acid content and antibacterial activity of the extracts were strongly affected by the pre-treatment method. Intensive pre-treatment methods such as flaking and cutting + grinding caused a considerable comminution of the lichen thallus and enabled high extraction yields. On the other hand, mild pre-treatment of the lichen such as impact + shearing enabled isolation of extracts with lower MIC values. Experimental results indicated that extraction with liquid carbon dioxide at 30 MPa and 25 °C was the most favorable condition at which a satisfactory high extraction yield was obtained (2.08%). Extract isolated with liquid carbon dioxide had a high usnic acid content in the extract (632 g/kg) and a very strong antibacterial activity (average MIC of 19.11 μg/mL). Antibacterial activity of all the extracts against tested strains was comparable to the pure usnic acid or even stronger. This study indicated a potential use of the supercritical extracts of U. barbata in pharmaceutical formulations for treatment of infections caused by staphylococci. © 2013 Elsevier B.V.Publicationtype: Journal Article108