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 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 Influence of Poly-(L-Lactic Acid) Nanofiber Functionalization on Maximum Load, Young's Modulus, and Strain of Nanofiber Scaffolds Before and After Cultivation of Osteoblasts: AnIn VitroStudy

2009 ◽  
Vol 9 ◽  
pp. 1382-1393 ◽  
Author(s):  
Jürgen Paletta ◽  
Karla Erffmeier ◽  
Christina Theisen ◽  
Daniel Hussain ◽  
Joachim H. Wendorff ◽  
...  
Keyword(s):  
Lactic Acid ◽  
Growth Factors ◽  
Young’S Modulus ◽  
Standardized Test ◽  
Mechanical Stability ◽  
Young's Modulus ◽  
Biological Effects ◽  
Maximum Load ◽  
Nanofiber Scaffolds ◽  
The Impact

The aim of this study was to characterize the influence of functionalization of synthetic poly-(L-lactic acid) (PLLA) nanofibers on mechanical properties such as maximum load, elongation, and Young's modulus. Furthermore, the impact of osteoblast growth on the various nanofiber scaffolds stability was determined. Nanofiber matrices composed of PLLA, PLLA-collagen, or BMP-2–incorporated PLLA were produced from different solvents by electrospinning. Standardized test samples of each nanofiber scaffold were subjected to failure protocol before or after incubation in the presence of osteoblasts over a period of 22 days under osteoinductive conditions. PLLA nanofibers electrospun from hexafluoroisopropanol (HFIP) showed a higher strain and tended to have increased maximum loads and Young's modulus compared to PLLA fibers spun from dichloromethane. In addition, they had a higher resistance during incubation in the presence of cells. Functionalization by incorporation of growth factors increased Young's modulus, independent of the solvent used. However, the incorporation of growth factors using the HFIP system resulted in a loss of strain. Similar results were observed when PLLA was blended with different ratios of collagen. Summarizing the results, this study indicates that different functionalization strategies influence the mechanical stability of PLLA nanofibers. Therefore, an optimization of nanofibers should not only account for the optimization of biological effects on cells, but also has to consider the stability of the scaffold.

scholarly journals Preparation and Evaluation of Bioactivity of Porous Bioglass Tablets for Bone Tissue Regeneration

2019 ◽  
Vol 1 (3) ◽  
pp. 112-123
Author(s):  
Rohith Kumar R. ◽  
Sangeetha Ashok Kumar ◽  
K. Periyasami Bhuvana
Keyword(s):  
Surface Characterization ◽  
Mechanical Stability ◽  
Average Pore Size ◽  
High Surface ◽  
Bone Tissue Regeneration ◽  
Average Pore ◽  
Hydroxy Apatite ◽  
Sbf Solution

The present study endeavors in the preparation and characterization of semi crystalline 45S5 bioglass (BG) (SiO2-CaO-P2O5) through sol gel process. Dry press mold technique was used in the preparation porous BG tablets to examine the bioactivity through invitro studies. The synthesized BG powder was subjected to structural, morphological and mechanical characterization and the bioactivity was examined in vitro by immersing the BG tablet in the Simulated Body Fluid (SBF) solution. XRD pattern and the SEM micrographs revealed the semi crystalline nature of BG with spherical morphology. The elemental analysis confirms the presence of vital constituents required for Bone regeneration (Calcium, Phosphorous, Silica, and Sodium). The surface characterization of BG tablet reveals the pores structure of average pore size of 240nm which contributed to the high surface activity resulting in formation of carbonated hydroxy apatite (HCAP) when immersed in SBF. The disintegration studies denoted the stabilization period was after 48 of immersion of BG tablets in SBF solution. The compressive strength measurement of the tablet also reveals the higher mechanical stability.

scholarly journals Carbon Dioxide Adsorption in Nanopores of Coconut Shell Chars for Pore Characterization and the Analysis of Adsorption Kinetics

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Chaiyot Tangsathitkulchai ◽  
Supunnee Junpirom ◽  
Juejun Katesa
Keyword(s):  
Pore Size ◽  
Adsorption Kinetics ◽  
Average Pore Size ◽  
Total Pore Volume ◽  
Carbonization Temperature ◽  
Coconut Shell ◽  
Average Pore ◽  
Porous Texture ◽  
Gcmc Simulation ◽  
Transient Measurement

The uptake data of CO2 adsorption at 273 K by coconut shell chars prepared at various carbonization temperatures from 250 to 550°C were used for characterizing pore texture of chars as well as the analysis of CO2 adsorption kinetics. The equilibrium isotherms were used to determine the porous texture of chars, employing the DR equation and GCMC simulation. It was found that all the test chars contain micropores of a size range from 0.8 to 2.2 nm with the pore size distribution becoming wider for char prepared at a higher carbonization temperature. Porous properties of chars, including surface area, total pore volume, and the average pore size, appear to increase with an increasing carbonization temperature. The analysis of CO2 uptake during the transient measurement of isotherms revealed that the kinetics of CO2 adsorption is governed by the internal diffusional transport of the adsorptive molecules. The effective pore diffusivity characterizing this transport process increases with increasing CO2 loading and passes through a maximum at a certain loading. This maximum pore diffusivity shifts to a higher value as the carbonization temperature is increased. A semiempirical equation was developed to correlate the effective pore diffusivity of CO2 with the equilibrium adsorption loading and its predictive capability is satisfactory.

scholarly journals Mechanical, Structural and Biological Properties of Chitosan/Hydroxyapatite/Silica Composites for Bone Tissue Engineering

Molecules ◽  
2021 ◽  
Vol 26 (7) ◽  
pp. 1976
Author(s):  
Robert Adamski ◽  
Dorota Siuta
Keyword(s):  
Tissue Engineering ◽  
Compressive Strength ◽  
Young’S Modulus ◽  
Hybrid Composites ◽  
Young's Modulus ◽  
Sol Gel ◽  
Biological Properties ◽  
Yield Strain ◽  
Developed Surface ◽  
Bioactive Composites

The aim of this work was to fabricate novel bioactive composites based on chitosan and non-organic silica, reinforced with calcium β-glycerophosphate (Ca-GP), sodium β-glycerophosphate pentahydrate (Na-GP), and hydroxyapatite powder (HAp) in a range of concentrations using the sol–gel method. The effect of HAp, Na-GP, and Ca-GP contents on the mechanical properties, i.e., Young’s modulus, compressive strength, and yield strain, of hybrid composites was analyzed. The microstructure of the materials obtained was visualized by SEM. Moreover, the molecular interactions according to FTIR analysis and biocompatibility of composites obtained were examined. The CS/Si/HAp/Ca-GP developed from all composites analyzed was characterized by the well-developed surface of pores of two sizes: large ones of 100 μm and many smaller pores below 10 µm, the behavior of which positively influenced cell proliferation and growth, as well as compressive strength in a range of 0.3 to 10 MPa, Young’s modulus from 5.2 to 100 MPa, and volumetric shrinkage below 60%. This proved to be a promising composite for applications in tissue engineering, e.g., filling small bone defects.

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.

What determines the bending strength of compact bone?

1999 ◽  
Vol 202 (18) ◽  
pp. 2495-2503 ◽  
Author(s):  
J.D. Currey
Keyword(s):  
Yield Stress ◽  
Young’S Modulus ◽  
Modulus Of Elasticity ◽  
Bending Strength ◽  
Young's Modulus ◽  
Bending Moment ◽  
Compact Bone ◽  
Yield Strain ◽  
Bone Material ◽  
Weak Part

The bending strength of a wide variety of bony types is shown to be nearly linearly proportional to Young's modulus of elasticity/100. A somewhat closer and more satisfactory fit is obtained if account is taken of the variation of yield strain with Young's modulus. This finding strongly suggests that bending strength is determined by the yield strain. The yield stress in tension, which might be expected to predict the bending strength, underestimates the true bending strength by approximately 40 %. This may be explained by two phenomena. (1) The post-yield deformation of the bone material allows a greater bending moment to be exerted after the yield point has been reached, thereby increasing the strength as calculated from beam formulae. (2) Loading in bending results in a much smaller proportion of the volume of the specimens being raised to high stresses than is the case in tension, and this reduces the likelihood of a weak part of the specimen being loaded to failure.

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 In Situ Evaluation of the Influence of Interstitial Oxygen on the Elastic Modulus of La2NiO4

Metals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1889
Author(s):  
Yuta Kimura ◽  
Takashi Nakamura ◽  
Koji Amezawa ◽  
Keiji Yashiro ◽  
Tatsuya Kawada
Keyword(s):  
Mechanical Properties ◽  
Young’S Modulus ◽  
Oxygen Concentration ◽  
Elastic Moduli ◽  
Mechanical Stability ◽  
Young's Modulus ◽  
Resonance Method ◽  
Lattice Defects ◽  
Interstitial Oxygen

Lattice defects significantly affect the mechanical properties of crystalline metal oxides. The materials for the components of solid oxide fuel cells (SOFCs) are no exception, and hence understanding of the interplay between lattice defects and the mechanical properties of components is important to ensure the mechanical stability of SOFCs. Herein, we performed an in situ evaluation of the temperature and P(O2) dependence of the elastic moduli of La2NiO4 (LN214), a candidate for the cathode material of SOFCs, using the resonance method to understand the influence of interstitial oxygen on its elastic properties. Above 873 K, both the Young’s and shear moduli of LN214 slightly decreased with increasing P(O2), suggesting that these elastic moduli are correlated with interstitial oxygen concentration and decreased with increasing interstitial oxygen. We analyzed the influence of interstitial oxygen on the Young’s modulus of LN214, based on numerically obtained lattice energy. The P(O2) dependence of the Young’s modulus of LN214 was found to be essentially explained by variation in the c-lattice constant, which was triggered by variation in interstitial oxygen concentration. These findings may contribute to a better understanding of the relationship between lattice defects and mechanical properties, and to the improvement of the mechanical stability of SOFCs.

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