scholarly journals Production of Porous Agarose-Based Structures: Freeze-Drying vs. Supercritical CO2 Drying

Gels ◽  
2021 ◽  
Vol 7 (4) ◽  
pp. 198
Author(s):  
Mariangela Guastaferro ◽  
Lucia Baldino ◽  
Ernesto Reverchon ◽  
Stefano Cardea
Keyword(s):  
Cooling Rate ◽  
Supercritical Co2 ◽  
Freeze Drying ◽  
Average Pore Size ◽  
Mesoporous Structure ◽  
Porous Structures ◽  
Average Pore ◽  
Thermal Changes ◽  
Supercritical Co2 Drying ◽  
Fast Cooling

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.

scholarly journals Recent Progress in Polysaccharide Aerogels: Their Synthesis, Application, and Future Outlook

Polymers ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1347
Author(s):  
Arbanah Muhammad ◽  
Dabin Lee ◽  
Yonghun Shin ◽  
Juhyun Park
Keyword(s):  
Drug Delivery ◽  
Supercritical Co2 ◽  
Wound Dressing ◽  
Freeze Drying ◽  
Recent Progress ◽  
Present Review ◽  
Porous Structures ◽  
Air Filtration ◽  
Future Outlook ◽  
Synthetic Process

Porous polysaccharides have recently attracted attention due to their porosity, abundance, and excellent properties such as sustainability and biocompatibility, thereby resulting in their numerous applications. Recent years have seen a rise in the number of studies on the utilization of polysaccharides such as cellulose, chitosan, chitin, and starch as aerogels due to their unique performance for the fabrication of porous structures. The present review explores recent progress in porous polysaccharides, particularly cellulose and chitosan, including their synthesis, application, and future outlook. Since the synthetic process is an important aspect of aerogel formation, particularly during the drying step, the process is reviewed in some detail, and a comparison is drawn between the supercritical CO2 and freeze drying processes in order to understand the aerogel formation of porous polysaccharides. Finally, the current applications of polysaccharide aerogels in drug delivery, wastewater, wound dressing, and air filtration are explored, and the limitations and outlook of the porous aerogels are discussed with respect to their future commercialization.

Preparation and Characterization of Chitosan-Based Scaffolds for Biomedical Applications

2006 ◽  
Vol 514-516 ◽  
pp. 1005-1009 ◽  
Author(s):  
José V. Araújo ◽  
J.A. Lopes da Silva ◽  
Margarida M. Almeida ◽  
Maria Elisabete V. Costa
Keyword(s):  
Biomedical Applications ◽  
Freeze Drying ◽  
Average Pore Size ◽  
Composite Scaffolds ◽  
Average Pore ◽  
Chitosan Matrix ◽  
Freeze Dried ◽  
Porous Chitosan ◽  
Interconnected Structure

Porous chitosan/brushite composite scaffolds were prepared by a freeze-drying technique, starting from brushite suspensions in chitosan solutions. The obtained scaffolds showed a regular macroporous and interconnected structure with brushite particles uniformly distributed in the chitosan matrix. The variation of the brushite concentration affected the microstructure of the final freeze-dried scaffold, in particular, its porosity and its average pore size. The yield strengths of the composite scaffolds could also be improved by the increase of the brushite content.

scholarly journals Comparison of Supercritical CO2-Drying, Freeze-Drying and Frying on Sensory Properties of Beetroot

Foods ◽  
2020 ◽  
Vol 9 (9) ◽  
pp. 1201
Author(s):  
Nikola Tomic ◽  
Ilija Djekic ◽  
Gerard Hofland ◽  
Nada Smigic ◽  
Bozidar Udovicki ◽  
...  
Keyword(s):  
Supercritical Co2 ◽  
Freeze Drying ◽  
Sensory Quality ◽  
Quality Parameters ◽  
Acceptance Testing ◽  
Drying Methods ◽  
Promising Alternative ◽  
Supercritical Co2 Drying ◽  
Negative Effect ◽  
Drying Technology

The aim of this study was to compare the sensory quality and acceptance of dried ready-to-eat beetroot snacks as a result of different drying methods applied: supercritical CO2-drying (scCO2-drying), frying, and freeze-drying. Descriptive sensory analysis, quality rating (10 assessors), and consumer acceptance testing (n = 102) were performed. Mean overall quality scores within the range of “very good” quality were found only in non-precooked scCO2-dried samples which were characterized by typical magenta color, low level of shape and surface deformations, pronounced brittleness and crispiness, and good rehydration during mastication. The other samples were in the range of “good” quality. The pre-cooking step before scCO2-drying negatively influenced the sensory quality parameters, particularly appearance. Around 60% of tested consumers showed a preference for the fried and non-precooked scCO2-dried samples. The drivers of liking were mostly related to the characteristics of the product, which was salted, fried, and crispy, with an oily and overburnt flavor, i.e., the product most similar to commercial potato chips products. Freeze-drying had a negative effect primarily on appearance and flavor. According to the sensory evaluation conducted, direct scCO2-drying without a pre-cooking step showed itself as a promising alternative drying technology in the production of dried beetroot snacks.

scholarly journals Fabrication and Characterization of Strontium-Substituted Hydroxyapatite-CaO-CaCO3 Nanofibers with a Mesoporous Structure as Drug Delivery Carriers

Pharmaceutics ◽  
2018 ◽  
Vol 10 (4) ◽  
pp. 179 ◽  
Author(s):  
Shiao-Wen Tsai ◽  
Wen-Xin Yu ◽  
Pai-An Hwang ◽  
Sheng-Siang Huang ◽  
Hsiu-Mei Lin ◽  
...  
Keyword(s):  
Drug Carrier ◽  
Drug Loading ◽  
Average Pore Size ◽  
Sol Gel ◽  
Mesoporous Structure ◽  
Drug Carriers ◽  
Burst Release ◽  
Doping Amount ◽  
Sem Images ◽  
Average Pore

Hydroxyapatite (HAp) is the main inorganic component and an essential part of hard bone and teeth. Due to its excellent biocompatibility, bioactivity, and osteoconductivity, synthetic HAp has been widely used as a bone substitute, cell carrier, and therapeutic gene or drug carrier. Recently, numerous studies have demonstrated that strontium-substituted hydroxyapatite (SrHAp) not only enhances osteogenesis but also inhibits adipogenesis in mesenchymal stem cells. Mesoporous SrHAp has been successfully synthesized via a traditional template-based process and has been found to possess better drug loading and release efficiencies than SrHAp. In this study, strontium-substituted hydroxyapatite-CaO-CaCO3 nanofibers with a mesoporous structure (mSrHANFs) were fabricated using a sol–gel method followed by electrospinning. X-ray diffraction analysis revealed that the contents of CaO and CaCO3 in the mSrHANFs decreased as the doping amount of Sr increased. Scanning electron microscopy (SEM) images showed that the average diameter of the mSrHANFs was approximately 200~300 nm. The N2 adsorption–desorption isotherms demonstrated that the mSrHANFs possessed a mesoporous structure and that the average pore size was approximately 20~25 nm. Moreover, the mSrHANFs had excellent drug- loading efficiency and could retard the burst release of tetracycline (TC) to maintain antibacterial activity for over 3 weeks. Hence, mSrHANFs have the potential to be used as drug carriers in bone tissue engineering.

scholarly journals Fabrication and Characterization of Cellulose Nanofiber Aerogels Prepared via Two Different Drying Techniques

Polymers ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 2583 ◽  
Author(s):  
Zhe Wang ◽  
Wenkai Zhu ◽  
Runzhou Huang ◽  
Yang Zhang ◽  
Chong Jia ◽  
...  
Keyword(s):  
Specific Surface ◽  
Surface Area ◽  
Liquid Nitrogen ◽  
Compression Strength ◽  
Pore Volume ◽  
Supercritical Co2 ◽  
Freeze Drying ◽  
Drying Method ◽  
Drying Techniques ◽  
Supercritical Co2 Drying

Studies on the influence of drying processes on cellulose nanofiber (CNF) aerogel performance has always been a great challenge. In this study, CNF aerogels were prepared via two different drying techniques. The CNF solution was prepared via existing chemical methods, and the resultant aerogel was fabricated through supercritical CO2 drying and liquid nitrogen freeze-drying techniques. The microstructure, shrinkage, specific surface area, pore volume, density, compression strength, and isothermal desorption curves of CNF aerogel were characterized. The aerogel obtained from the liquid nitrogen freeze-drying method showed a relatively higher shrinkage, higher compression strength, lower specific surface area, higher pore volume, and higher density. The N2 adsorption capacity and pore diameter of the aerogel obtained via the liquid nitrogen freeze-drying method were lower than the aerogel that underwent supercritical CO2 drying. However, the structures of CNF aerogels obtained from these two drying methods were extremely similar.

Cellulosic aerogels as ultra-lightweight materials. Part 2: Synthesis and properties 2nd ICC 2007, Tokyo, Japan, October 25–29, 2007

Holzforschung ◽  
2009 ◽  
Vol 63 (1) ◽  
Author(s):  
Falk Liebner ◽  
Emmerich Haimer ◽  
Antje Potthast ◽  
Dieter Loidl ◽  
Stefanie Tschegg ◽  
...  
Keyword(s):  
Young’S Modulus ◽  
Mechanical Stability ◽  
Young's Modulus ◽  
Average Pore Size ◽  
Mesoporous Structure ◽  
Cellulose Content ◽  
Cellulose Solution ◽  
Yield Strain ◽  
Average Pore ◽  
Porous Texture

Abstract Ultra-lightweight cellulose aerogels can be obtained in three steps: (1) preparation of a cellulose solution in molten N-methylmorpholine-N-oxide monohydrate (NMMO·H2O) at 110–120°C and casting of the viscous mass into moulds; (2) extraction of the solidified castings with ethanol to initiate cellulose aggregation and to remove NMMO·H2O so that the fragile, fine-porous texture of cellulose II is largely retained; and (3) drying of the lyogel using supercritical carbon dioxide (scCO2). According to this approach, cellulosic aerogels were prepared from eight commercial cellulosic materials and pulps and analysed for selected chemical, physicochemical and mechanical parameters. The results reveal that all aerogels obtained from 3% cellulose containing NMMO·H2O melts had a largely uniform mesoporous structure with an average pore size of ∼9–12 nm, surface area of 190–310 m2 g-1, and specific density of 0.046–0.069 g cm-3, but rather low mechanical stability expressed as compressive yield strain of 2.9–5.5%. All samples showed viscoelastic behaviour, with Young's modulus ranging from ∼5 to 10 N mm-2. Doubling the cellulose content in the NMMO·H2O melt from 3% to 6% increased Young's modulus by one order of magnitude. Shrinkage of the fragile cellulose bodies during scCO2 drying was still considerable and is subject to further investigations. Influencing parameters such as scCO2 pressure, cellulose content, regenerating solvent and the number of regenerating baths were optimised.

scholarly journals Application of Ultrasound and Curing Agent during Osmotic Dehydration to Improve the Quality Properties of Freeze-Dried Yellow Peach (Amygdalus persica) Slices

Agriculture ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1069
Author(s):  
Yuanming Chu ◽  
Saichao Wei ◽  
Zhaoyang Ding ◽  
Jun Mei ◽  
Jing Xie
Keyword(s):  
Freeze Drying ◽  
Osmotic Dehydration ◽  
Average Pore Size ◽  
Nutrient Loss ◽  
Ultrasonic Power ◽  
Curing Agent ◽  
Average Pore ◽  
Quality Properties ◽  
Freeze Dried

This study aimed to improve the quality of freeze-dried yellow peaches (Amygdalus persica). Yellow peaches were pretreated with osmotic dehydration for 15 min prior to vacuum-freeze drying and supplemented with different ultrasonic power levels (180 W, 240 W, 300 W) and a curing agent (calcium lactobionate, CaLa) to investigate the effects on the quality of freeze-dried yellow peach slices. After vacuum freeze-drying the yellow peach slices for 48 h, their moisture, color, texture, microstructure, total phenol (TP) content and oligomeric proantho-cyanidin (OPC) content were determined. It was found that the auxiliary ultrasonic power with various levels, especially powered at 240 W, produced very favorable effects on the quality characteristics of freeze-dried yellow peaches. The average pore size of USOD-240 W samples was reduced by 57.07% compared with that of the FD samples. In terms of nutrient maintenance, USOD-240 W can also prevent nutrient loss to the greatest extent. The TP content (5.40 mg/g) and OPC content (14.42 mg/g) were always highest in each pretreatment. The addition of CaLa can further improve the quality of yellow peach slices. Overall, the application of ultrasound and CaLa to improve the quality of freeze-dried yellow peach slices along with osmotic dehydration before freeze-drying is a method worth considering.

Synthesis and Characterization of the Y/MCM-41 Composite Molecular Sieves

2011 ◽  
Vol 480-481 ◽  
pp. 159-164 ◽  
Author(s):  
Li Qin Wang ◽  
Xiang Ni Yang ◽  
Yang Han ◽  
Ning Yu ◽  
Xiu Li Zhao
Keyword(s):  
Pore Size ◽  
Molecular Sieves ◽  
Average Pore Size ◽  
Nitrogen Adsorption ◽  
Mesoporous Structure ◽  
Decomposition Temperature ◽  
Average Pore ◽  
Y Zeolites ◽  
Ft Ir ◽  
Mcm 41

The Y/MCM-41 composite molecular sieves were synthesized in the method of hydrothermal crystallization with cetyltrimethylammonium bromide (CTMABr) as the template agent. The as-prepared composite molecular sieves were characterized by the means of X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), the thermogravimetric and differential thermal analysis (TG-DTA) and the nitrogen adsorption test. The experimental results were shown as follows: the Y/MCM-41 composite molecular sieves kept properties of Y-zeolites and MCM-41 molecular sieves. In the XRD and FT-IR spectra, it can be found both characteristic peaks of Y-zeolites and MCM-41 molecular sieves. The pore size distribution plot indicated that the Y/MCM-41composite molecular sieves had micro-mesoporous structure, and the average pore size were about 1.5 nm and 15 nm. The decomposition temperature of the template agent was at 320 °C, and the calcined temperature of Y-zeolites was at about 560 °C. There showed an endothermic process constantly in the DTA curve, and there was little mass loss in the TG curve, indicating the obtained Y/MCM-41 composite molecular sieves had higher thermal stability.

Novel Technique of Polymer Composite Preparation for Bone Implants

2012 ◽  
Vol 488-489 ◽  
pp. 681-685 ◽  
Author(s):  
Maria Mucha ◽  
Michał Tylman
Keyword(s):  
Freeze Drying ◽  
Average Pore Size ◽  
Bactericidal Effect ◽  
High Porosity ◽  
Natural Polymers ◽  
Average Pore ◽  
Novel Technique ◽  
Chitosan Scaffolds ◽  
Formed Structure ◽  
Porous Hydrogel

Extensive interest in bone tissue engineering focuses on bio-degradable materials based on natural polymers. One of these polymers is chitosan which is deacetylated derivative of chitin. The paper presents preparation of chitosan scaffolds containing collagen and hydroxyapatite by electrolytic method. Chitosan dissolved in acetic acid forms chitosan acetate which is polyelectrolyte (protonated group NH3+). The flow of current through a solution of chitosan acetate causes its reduction and accumulation of chitosan on cathode. Formed structure is highly hydrated porous hydrogel. Hydrogel structure can be coated (in the process of electrodeposition) by nano-silver having a bactericidal effect. Subsequently hydrogel was frozen at -37°C for 24h and freeze-drying. Obtained scaffold has a high porosity (more than 88%) with average pore size of about 0.1-3 μm (micropores) and 0,1- few millimeters (macropores).

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