Search

This review presents and critically evaluates recent advances in non-conventional gelation method of native alginate. A special focus is given to the following three methods: cryotropic gelation, non-solvent induced phase separation and carbon dioxide induced gelation. A few other gelation approaches are also briefly reviewed. Results are discussed in the context of subsequent freeze and supercritical drying. The methods are selected so as to provide the readers with a range of novel tools and tactics of pore engineering for alginate and other anionic polysaccharides., Competing Interests: The authors declare no conflict of interest.

Different plant raw materials (corn stalk, wheat straw, saw dust, corn cobs, broom grass and Sudan grass) were carbonized and secondary activated in the rotating kiln with the action of water vapor as activation agent under different temperatures and lasting times. Optimum carbonization parameters such as temperature and lasting time were found to be 750°C and 45 min, while optimal conditions for powdered activated carbon obtained by water vapor activation at a temperature of 1,000 C and contact time of 120 min were determined. All obtained activated carbons were distinctly macroporous with mercury intrusion total specific pore volume in the range from 2.04 to 4.86 cm 3 /g for activated carbons originating from sawdust and broom grass, respectively. Activated carbon prepared from broom grass had the largest specific surface area of 1,190 m 2 /g. Freundlich, Langmuir, Dubinin-Radushkevitch and Temkin adsorption isotherm models were applied for groundwater humic matter adsorption modeling. Broom grass-originated activated carbon was found to have excellent adsorption affinities toward natural organic matter with regard to the Langmuir model, with maximum adsorption capacity of 90.1 mg TOC/g. The Freundlich isotherm was best fitted with the obtained experimental data. Adsorption experiment followed a physical process as can be seen from heat of sorption of 118.82 J/mol estimated by the Temkin isotherm model, and mean free energy of 0.158 kJ/mol estimated by the Dubinin-Radushkevitch isotherm model.

Generally, metal-organic frameworks (MOFs) are made up from kinds of repeating microporous structure. Here, a series of Eu 3+ ions activated terephthalate-based lanthanum-organic frameworks (La-MOFs) was synthesized by a hydrothermal reaction. By controlling the reaction time, we obtained some unique brick-shaped La-MOFs in a micron scale size range, and these La-MOFs showed tunable mesoporous and macroporous architectures. It is speculated that the change in the composition and structure of building units results in the formation of this mesoporous and macroporous heterogeneous architectures. Powder X-ray diffraction patterns and Eu 3+ luminescence behavior support the speculation., (Copyright © 2017 John Wiley & Sons, Ltd.)

Petrophysical analysis using X-ray microtomography provides key textural and compositional information, useful to investigate porous media characteristics of hydrocarbon and geothermal reservoirs. Several approaches, used for rock porosity estimation from tomography data, rely mainly on visual or mathematical segmentation algorithms that attempt to obtain thresholding values to segment a phase solved by pixel analysis resolution. Therefore, porosity is evaluated using only pores above pixel resolution (macroporosity), and dismiss pores sized less than the pixel resolution (microporosity) that can be essential to characterize permeability conditions of geothermal reservoirs. Here we propose an improved method to calculate the total effective porosity and simulate the absolute permeability of rock samples. This method combines the analysis of X-ray computed microtomography (μCT) with the interpretation of data using a powerful thresholding method that is based on the greyscale interclass variance. The 3D volume is segmented into three domains: solid, pores above resolution and, an intermediate region where each pore below resolution is linearly combined with solid matrix resulting in a grey scaled pixel equal to this combination. For the intermediate region, the microporosity was calculated employing a Matlab code that provides a new thresholding value containing pores, both above and below resolution (total porosity). Finally, by using this new calculated thresholding value the total effective porosity was obtained and an absolute permeability simulation was implemented only to the connected pores. Our results show that micropores contribute for nearly 50 percent of the total porosity and that microporosity plays a key role in estimating effective porosity, and assessing the geothermal potential of a rock reservoir., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Influence of more than 20 years (1988-2010) of reduced tillage (RT) practices on water and pesticide balances and dynamics is analyzed and compared to results from a conventional tillage plot (CT). The field study soils are described as silty clay stagnic luvisol, developed on a low permeable schist layer. A drainage network was set up according to French criteria (0.9 m deep, 10 m space) to avoid soil winter waterlogging. Climate is temperate oceanic and drainage generally occurs from November to March. Data were analyzed at yearly, weekly (pesticides) and hourly (water) time steps. Over the long term, cumulated drainage decreases significantly on RT (3999 mm) compared to CT (5100 mm). This differentiation becomes significant from 1999, 10 years after plowing was stopped. Strikingly, hourly drainage peak flows are higher under RT, especially during the second period (2000-2010), associated with low or no base flow. These results suggest a strong influence of the macropore network under RT practice. In particular, drainage peaks are higher at the beginning of the drainage season (mid-October to December). Consistently, pesticides applied in late autumn, which are the most quantified on this site, are often significantly more exported under RT. For atrazine, applied in spring, fluxes are linked to cumulative flow and are de facto higher under CT. For others pesticides, losses appear to be heterogeneous, with generally low or null export rates for spring application. Generally speaking, higher concentrations are measured on RT plot and explain observed exportation rate differences. Finally, there is no clear evidence of correlation between pesticide losses and long-term impacts of RT on hydrodynamics, pointing the importance of studying the short-term effect of tillage on water and especially solute flow.

In recent years, there has been a great interest in using natural polymers in the composition of calcium phosphate bone cements to enhance their physical, mechanical, and biological performance. Gelatin is a partially hydrolyzed form of collagen, a natural component of bone matrix. In this study, the effect of blooming gelatin on the nanohydroxyapatite precipitation, physical and mechanical properties, and cellular responses of a calcium phosphate bone cement (CPC) was investigated. Various concentrations of blooming gelatin (2, 5, and 8 wt.%) were used as the cement liquid and an equimolar mixture of tetracalcium phosphate and dicalcium phosphate was used as solid phase. The CPC without any gelatin additive was also evaluated as a control group. The results showed that gelatin accelerated hydraulic reactions of the cement paste, in which the reactants were immediately converted into nanostructured apatite precipitates after hardening. Gelatin molecules induced 4%-10% macropores (10-300 μm) into the cement structure, decreased initial setting time by ~190%, and improved mechanical strength of the as-set cement. Variation in the above-mentioned properties was influenced by the gelatin concentration and progressed with increasing the gelatin content. The numbers of the G-292 osteoblastic cells on gelatin-containing CPCs were higher than the control group at entire culture times (1-14 days), meanwhile better alkaline phosphatase (ALP) activity was determined using blooming gelatin additive. The observation of cell morphologies on the cement surfaces revealed an appropriate cell attachment with extended cell membranes on the cements. Overall, adding gelatin to the composition of CPC improved the handling characteristics such as setting time and mechanical properties, enhanced nanoapatite precipitation, and augmented the early cell proliferation rate and ALP activity., Competing Interests: The authors report no conflicts of interest in this work.

Calcium phosphate cements (CPCs) have been extensively used in reconstructive dentistry and orthopedics, but it is only recently that CPCs have been combined with stem cells to engineer biological substitutes with enhanced healing potential. In the present study, macroporous CPC scaffolds with defined composition were fabricated using an easily reproduced synthesis method, with minimal fabrication and processing steps. Scaffold pore size and porosity, essential for cell infiltration and tissue ingrowth, were tuned by varying the content and size of polyethylene glycol (PEG) particles, resulting in 9 groups with different architectural features. The scaffolds were characterized for chemical composition, porosity and mechanical properties, then tested in vitro with human mesenchymal progenitors derived from induced pluripotent stem cells (iPSC-MPs). Biomimetic decellularized bone scaffolds were used as reference material in this study. Our manufacturing process resulted in the formation of macroporous monetite scaffolds with no residual traces of PEG. The size and content of PEG particles was found to affect scaffold porosity, and thus mechanical properties. Irrespective of pore size and porosity, the CPC scaffolds fabricated in this study supported adhesion and viability of human iPSC-MPs similarly to decellularized bone scaffolds. However, the architectural features of the scaffolds were found to affect the expression of bone specific genes, suggesting that specific scaffold groups could be more suitable to direct human iPSC-MPs in vitro toward an osteoblastic phenotype. Our simplistic fabrication method allows rapid, inexpensive and reproducible construction of macroporous CPC scaffolds with tunable architecture for potential use in dental and orthopedic applications., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Intrinsic material skills have a deep effect on the mechanical and biological performance of bone substitutes, as well as on its associated biodegradation properties. In this work we have manipulated the preparation of collagenous derived fiber mesh frameworks to display a specific composition, morphology, open macroporosity, surface roughness and permeability characteristics. Next, the effect of the induced physicochemical attributes on the scaffold's mechanical behavior, bone bonding potential and biodegradability were evaluated. It was found that the scaffold microstructure, their inherent surface roughness, and the compression strength of the gelatin scaffolds can be modulated by the effect of the cross-linking agent and, essentially, by mimicking the nano-scale size of hydroxyapatite in natural bone. A clear effect of bioactive hydroxyapatite nano-rods on the scaffolds skills can be appreciated and it is greater than the effect of the cross-linking agent, offering a huge perspective for the upcoming progress of bone implant technology., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The electrospinning technique is widely used for the fabrication of micro- and nanofibrous structures. Recent studies have focused on the use of less toxic and harmful solvents (benign solvents) for electrospinning, even if those solvents usually require an accurate and longer process of optimization. The aim of the present work is to demonstrate the versatility of the use of benign solvents, like acetic acid and formic acid, for the fabrication of microfibrous and nanofibrous electrospun poly(epsilon-caprolactone) mats. The solvent systems were also shown to be suitable for the fabrication of electrospun structures with macroporosity, as well as for the fabrication of composite electrospun mats, fabricated by the addition of bioactive glass (45S5 composition) particles in the polymeric solution.

Biomaterials in the form of scaffolds hold great promise in the regeneration of diseased tissues. The scaffolds stimulate cellular adhesion, proliferation and differentiation. While the scaffold composition will dictate their biocompatibility, their porosity plays a key role in allowing proper cell penetration, nutrient diffusion as well as bone ingrowth. Porous scaffolds are processed with the help of a wide variety of techniques. Designing scaffolds with the appropriate porosity is a complex issue since this may jeopardize other physico-chemical properties. From a macroscopic point of view, parameters such as the overall architecture, pore morphology, interconnectivity and pore size distribution, have unique roles in allowing bone ingrowth to take place. From a microscopic perspective, the adsorption and retention of proteins in the microporosities of the material will dictate the subsequent cell adhesion. Therefore, the microstructure of the substrate can determine cell proliferation as well as the expression of specific osteogenic genes. This review aims at discussing the effect of micro- and macroporosity on the physico-chemical and biological properties of scaffolds for musculo-skeletal tissue regeneration., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Fan Yang and co‐workers report on page 346 that microribbon‐like, photo‐crosslinkable elastomers form macroporous tissue engineering scaffolds, which facilitate cell encapsulation and cell proliferation in three dimensions. The unique geometry of microribbons leads to scaffolds with superior flexibility, which can sustain repetitive compression without failing. Such scaffolds could be particularly useful for engineering shock‐absorbing tissues such as articular cartilage and intervertebral discs. [ABSTRACT FROM AUTHOR]

Methods for evaluating soil conditions as influenced by tillage are often limited to analysis of bulk samples. The application of medicalcomputed tomography (CT) to the characterization of tillage effects on soil provides an alternative tool for measurement since it is at amore detailed scale. The objective of this study was to compare soils under conventional and no-tillage (NT) systems using X-ray CT. Chisel-disk-disk (CDD) conventional tillage and NT systems were compared for a Mexico silt loam (fine, smectitic, mesic Aeric Vertic Epiaqualfs) soil. Five replicate soil cores (75 mm long by 75 mm diameter) were collected from each treatment. Two CT systems were used in this study: a medical CT scanner (MCT, 1 mm thick scans) and an ultra-high resolution CT scanner (UHCT, 0.1 mm thick scans). Significantly higher soil density was found for the NT treatment using the MCT scanner (P=0.05). Data from the UHCT scanner were used to compare the effects ofscan thickness and to evaluate macropore characteristics. Macropore area was significantly higher (P<0.001) for CDD as compared to the NTtreatment: 11 versus 5%. The number of macropores in the CDD treatment were twice those in NT; their perimeter was 62% longer; and their circularity was 94% of that for pores from the NT tillage treatment. The macropore box-counting fractal dimension (D) was significantly greater (P<0.001) for CDD (D=1.44) as compared to the NT treatment (D=1.26), reflecting the greater space-filling behavior of the CDD treatment. This study shows that the UHCT scanner can characterize differences in soil macroporosity more precisely than standard MCT scanners. The use of ultra-high resolution tomography can aid in the discrimination of differences between seedbeds created by different tillage systems. [ABSTRACT FROM AUTHOR]

Little is known about the processes of infiltration and water movement in the upper layers of blanket peat. A tension infiltrometer was used to measure hydraulic conductivity in a blanket peat in the North Pennines, England. Measurements were taken from the surface down to 20 cm in depth for peat under four different vegetation covers. It wasfound that macropore flow is a significant pathway for water in the upper layers of this soil type. It was also found that peat depth andsurface vegetation cover were associated with macroporosity and saturated hydraulic conductivity. The proportion of macropore flow was found to be greater at 5 cm depth than at 0, 10 and 20 cm depth. Peat beneath a Sphagnum cover tends to be more permeable and a greater proportion of macropore flow can occur beneath this vegetation type. Functional macroporosity and matrix flow in the near-surface layers of bare peat appear to have been affected by weathering processes. Comparision of results with rainfall records demonstrates that infiltration-excess overland flow is unlikely to be a common runoff-generating mechanism on blanket peat; rather, a saturation-excess mechanism combined with percolation-excess above much less permeable layers dominates the runoff response. [ABSTRACT FROM AUTHOR]