Network Pore Size Research Articles

Rupture mechanics of blood clots: Influence of fibrin network structure on the rupture resistance

Embolization is a leading cause of mortality, yet we know little about clot rupture mechanics. Fibrin provides the main structural and mechanical stability to blood clots. Previous studies have shown that altering the concentration of coagulation activators (thrombin or tissue factor (TF)) has a significant impact on fibrin structure and viscoelastic properties, but their effects on rupture properties are mostly unknown. Toughness, which corresponds to the ability to resist rupture, is independent of viscoelastic properties. We used varying TF concentrations to alter the structure and toughness of human plasma clots. We performed single-edge notch rupture tests to examine fibrin toughness under a constant strain rate and we assessed viscoelastic mechanics using rheology. We utilized fluorescent confocal and scanning electron microscopy (SEM) to quantify the fibrin network structure under varying TF concentrations. Our results revealed that increased TF concentration resulted in increased number of fibrin fibers with a reduction in network pore size, thinner and shorter fibrin fibers. Increasing TF concentration yielded a maximum toughness at mid-TF concentration, such that fibrin diameter and number of fibers underlie a complex role in influencing the rupture resistance of blood clots, resulting in a nonmonotonic relationship between TF and toughness. A simple mechanical model, built on our findings from our Fluctuating Spring (FS) computational model, adopted to estimate the fracture toughness (critical energy release rate) as a function of TF predicts trends that are in good agreement with experiments. The differences in mechanical responses point to the importance of studying the structure-function relationships of fibrin networks, which may be predictive of the tendency for embolization. Statement of significanceFibrin, a naturally occurring biomaterial, is the main mechanical and structural scaffold of blood clots that provides the necessary strength and stability to the clot, ensuring effective stemming of bleeding. The rupture of blood clots can result in the blockage of downstream vessels thereby blocking blood flow and oxygen supply. The fibrin network structure has been shown to influence the viscoelastic mechanical properties of clots, but has not been explored for fracture mechanics. Here, we modulate the fibrin network structure by varying the concentration of Tissue Factor (TF). Interestingly, the association between TF concentration and maximum toughness of the clots is non-monotonic. The variations in mechanical responses highlight the importance of studying the structure-function relationships of fibrin networks, as these may predict the tendency for embolization.

Evolution of microstructure and CO2 diffusion coefficient of compacted recycled aggregates during carbonation investigated by X-ray tomography

Recycled aggregates compacted in road layers are made of a majority of concrete aggregates which can mineralize atmospheric CO2. Previous studies showed that carbonation modifies the microstructure of recycled concrete aggregates, but little information is available in the case of compacted recycled aggregates. Furthermore, carbonation kinetics depends on CO2 diffusion through the compacted material, which is linked its microstructure. This paper presents an investigation of the evolution of both microstructure and CO2 diffusion coefficient of compacted recycled aggregates during carbonation in two different environments by X-ray tomography. Segmented 3D images were analyzed to fully extract resolved pore structures. In addition, the CO2 diffusion coefficient variations were investigated by calculating the macroscopic diffusivity tensor in the segmented 3D images. We show that the numerical results are very similar to previous experimental results from gas diffusion tests and that the diffusivity coefficients can be estimated by using only the larger pore network (pore size > 5.5 µm). These findings suggest that nondestructive imaging approaches, such as micro-Computed Tomography (µCT), are a relevant alternative to experimental characterization methods.

Airway mucus in pulmonary diseases: Muco-adhesive and muco-penetrating particles to overcome the airway mucus barriers

Airway mucus is a complex viscoelastic gel that provides a defensive physical barrier and shields the airway epithelium by trapping inhaled foreign pathogens and facilitating their removal via mucociliary clearance (MCC). In patients with respiratory diseases, such as chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF), non-CF bronchiectasis, and asthma, an increase in crosslinking and physical entanglement of mucin polymers as well as mucus dehydration often alters and typically reduces mucus mesh network pore size, which reduces neutrophil migration, decreases pathogen capture, sustains bacterial infection, and accelerates lung function decline. Conventional aerosol particles containing hydrophobic drugs are rapidly captured and removed by MCC. Therefore, it is critical to design aerosol delivery systems with the appropriate size and surface chemistry that can improve drug retention and absorption with the goal of increased efficacy. Biodegradable muco-adhesive particles (MAPs) and muco-penetrating particles (MPPs) have been engineered to achieve effective pulmonary delivery and extend drug residence time in the lungs. MAPs can be used to target mucus as they get trapped in airway mucus by steric obstruction and/or adhesion. MPPs avoid muco-adhesion and are designed to have a particle size smaller than the mucus network, enhancing lung retention of particles as well as transport to the respiratory epithelial layer and drug absorption. In this review, we aim to provide insight into the composition of airway mucus, rheological characteristics of airway mucus in healthy and diseased subjects, the most recent techniques to study the flow dynamics and particle diffusion in airway mucus (in particular, multiple particle tracking, MPT), and the advancements in engineering MPPs that have contributed to improved airway mucus penetration, lung distribution, and retention.

The Effect of C/Si Ratio and Fluorine Doping on the Gas Permeation Properties of Pendant-Type and Bridged-Type Organosilica Membranes.

A series of pendant–type alkoxysilane structures with various carbon numbers (C1–C8) were used to fabricate sol–gel derived organosilica membranes to evaluate the effects of the C/Si ratio and fluorine doping. Initially, this investigation was focused on the effect that carbon-linking (pendant–type) units exert on a microporous structure and how this affects the gas-permeation properties of pendant–type organosilica membranes. Gas permeation results were compared with those of bridged–type organosilica membranes (C1–C8). Network pore size evaluation was conducted based on the selectivity of H2/N2 and the activation energy (Ep) of H2 permeation. Consequently, Ep (H2) was increased as the C/Si ratio increased from C1 to C8, which could have been due to the aggregation of pendant side chains that occupied the available micropore channel space and resulted in the reduced pore size. By comparison, these permeation results indicate that pendant–type organosilica membranes showed a somewhat loose network structure in comparison with bridged–type organosilica membranes by following the lower values of activation energies (Ep). Subsequently, we also evaluated the effect that fluorine doping (NH4F) exerts on pendant−type [methytriethoxysilane (MTES), propyltrimethoxysilane (PTMS)] and bridged-type [1,2–bis(triethoxysilyl)methane (BTESM) bis(triethoxysilyl)propane (BTESP)] organosilica structures with similar carbon numbers (C1 and C3). The gas-permeation properties of F–doped pendant network structures revealed values for pore size, H2/N2 selectivity, and Ep (H2) that were comparable to those of pristine organosilica membranes. This could be ascribed to the pendant side chains, which might have hindered the effectiveness of fluorine in pendant–type organosilica structures. The F–doped bridged–type organosilica (BTESM and BTESP) membranes, on the other hand, exhibited a looser network formation as the fluorine concentration increased.

Tailoring the structure of a sub-nano silica network via fluorine doping to enhance CO2 separation and evaluating CO2 separation performance under dry or wet conditions

The amorphous nature of a silica network structure offers an attractive opportunity for excellent separation of small molecules such as He and H2. CO2 separation systems are restricted, however, by the density of amorphous silica structures. Hence, the objective of this work was to tailor the network pore size of conventional tetraethoxysilane (TEOS)-derived silica membranes via fluorine (NH4F) doping. Fluorine doping can precisely enlarge the network pore size in a subnano range by reducing the Si–OH groups in the network structure, while CO2 adsorption properties are decreased as doped fluorine concentration increases. A fluorine-doped silica membrane (F/Si=0.1/9.9) showed a CO2/N2 permeance ratio that reached as high as 50 with CO2 permeance of 1.6 × 10−7 mol m−2 s−1 Pa−1 at 50 ⁰C. In a wet system (200–300 oC, H2O partial pressure of 3 kPa), fluorine-doped silica membranes were quite stable, irrespective of the doped fluorine concentration, but a blocking effect at around 100–150 ⁰C was observed and gas permeance (He, CO2, N2) was apparently lower than that in a dry system. Under steam with a high partial pressure (300 ⁰C, H2O partial pressure of 30 kPa), the hydrothermal stability of silica membranes was increased with increases in the fluorine concentration.

In situ PEGylation of polyamide network of thin film composite membrane by inter-polymer H-bond complex formation

Fouling propensity of membranes is a bottleneck problem. PEGylation is an effective approach to improve the antifouling property of a polyamide (PA) thin film composite (TFC) membrane. However, reactive PEG involves in the covalent network formation with PA leading to the increase of network pore size and lowers the rejection efficiency of the membranes. Post-surface modification by reactive PEG leads to lowering of permeates flux. End-functional (reactive) PEG samples are costly and prepared by multi-step process. Herein, the high pKa value of the fraction of –COOH groups of PA network is utilized for the formation of stable complex with PEG. Addition of linear PEG into the aqueous solution of m-phenylenediamine during interfacial polymerization leads to grafting of polyamide network by PEG through the formation of interpolymer H-bond complex of ether oxygen of PEG and –COOH groups of cross-linked PA network. PEG in the PA network increases the hydrophilicity, permeate flux, rejection efficacy and antifouling property of the membranes. The PEG chains remain stable in the PA network in the pH window of acidic to ≤8 as confirmed by the ATR-IR, wetting behavior, model spectroscopic experiments and X-Ray photoelectron spectroscopy. A PEGylated membrane prepared by the in situ addition of PEG (molecular weight 2000 g mol−1, 1% w v−1) into the MPD solution shows 20–30% higher permeate water flux, superior salt rejection efficiency and fouling resistant property than that of a pristine membrane. This approach is simple, cost-effective and easy to implicate.

Defect size and cross-linker properties controlled fracture of biopolymer networks

Damage in cytoskeleton can occur frequently during processes like cell migration and division. However, the question of how the presence of micro-cracks affects the deformation and fracture response of such bio-filament networks remains unclear. Here, we report a computational study to address this unsettling issue where large deformation and thermal fluctuations of individual biopolymers, as well as the forced breaking of crosslinks between them, have all been taken into account. It was found that the introduction of micro-cracks could alter the fracture path inside the network, change its ductility and actually result in an increased fracture energy of the material. More interestingly, we showed that on average the maximum fracture resistance will be achieved when the crack length is a few times of the network pore size, highlighting the flaw insensitive nature of such materials. Finally, the network fracture energy was observed to increase with the linear stiffness of crosslinking molecules monotonically but reach its minimum at an intermediate rotational stiffness value. In addition to enhancing our understanding of how cytoskeleton performs different cellular duties, findings here could also provide useful information for the development of high performance biological materials in the future.

Effect of fluorine doping on the network pore structure of non-porous organosilica bis(triethoxysilyl)propane (BTESP) membranes for use in molecular separation

Long-chain organosilica bis(triethoxysilyl)propane (BTESP) membranes typically have a flexible non-porous structure. Fluorine was used to tune the network pore structure of BTESP membranes in an effort to improve the gas permeation properties. The network pore size was enlarged and the effect of calcination temperature on the network structure was evaluated based on gel and membrane characterizations. Fluorine-doped BTESP membranes calcined at 350 °C and 650 °C have shown H2 permeance on the orders of 1.2 × 10−6 mol m−2 s−1 Pa−1 and 1.5 × 10−6 mol m−2 s−1 Pa−1 with H2/N2 selectivities of 8 and 6, respectively, which indicates similar pore sizes with lower condensation effect at high temperature of 650 °C, that was suppressed due to the presence of Si–F and C–F bonds. Undoped BTESP membranes, on the other hand, showed H2/N2 selectivity that was significantly lower—from 24 to 11 at 650 °C. FT-IR and N2 adsorption isotherms clearly indicated that fluorine significantly decreased the Si–OH density and increased the surface area and micropore volume. Further water adsorption analysis revealed that fluorine significantly increased the hydrophobicity of the BTESP network structure. Overall, the results of this study endorse the effectiveness of fluorine to control the network pore structure in both wet and dry molecular separation systems.

Cancer cell migration in collagen-hyaluronan composite extracellular matrices

Hyaluronan (HA) is a key component in the tumor microenvironment (TME) that participates in cancer growth and invasiveness. While the molecular weight (MW) dependent properties of HA can cause tumor-promoting and -repressing effects, the elevated levels of HA in the TME impedes drug delivery. The degradation of HA using hyaluronidases (HYALs), resulting in fragments of HA, is a way to overcome this, but the consequences of changes in HA molecular weight and concentration is currently unknown. Therefore, it is critical to understand the MW-dependent biological effects of HA. Here we examine the influence of HA molecular weight on biophysical properties that regulate cell migration and extracellular matrix (ECM) remodeling. In our study, we used vLMW, LMW and HMW HA at different physiologically relevant concentrations, with a particular interest in correlating the mechanical and structural properties to different cell functions. The elastic modulus, collagen network pore size and collagen fiber diameter increased with increasing HA concentration. Although the collagen network pore size increased, these pores were filled with the bulky HA molecules. Consequently, cell migration decreased with increase in HA concentration due to multiple, long-lived and unproductive protrusions, suggesting the influence of steric factors. Surprisingly, even though elastic modulus increased with HA molecular weight and concentration, gel compaction assays showed an increased degree of ECM compaction among HMW HA gels at high concentrations (2 and 4 mg mL−1 [0.2 and 0.4%]). These results were not seen in collagen gels that lacked HA, but had similar stiffness. HA appears to have the effect of decreasing migration and increasing collagen network contraction, but only at high HA molecular weight. Consequently, changes in HA molecular weight can have relatively large effects on cancer cell behavior. Statement of significanceHyaluronan (HA) is a critical component of the tumor microenvironment (TME). Overproduction of HA in the TME results in poor prognosis and collapse of blood vessels, inhibiting drug delivery. Hyaluronidases have been used to enhance drug delivery. However, they lead to low molecular weight (MW) HA, altering the mechanical and structural properties of the TME and cancer cell behavior. Understanding how HA degradation affects cancer cell behavior is critical for uncovering detrimental effects of this therapy. Very little is known about how HA MW affects cancer cell behavior in tumor-mimicking collagen-HA composite networks. Here we examine how MW and HA content in collagen-HA networks alter structural and mechanical properties to regulate cell migration and matrix remodeling in 3D TME-mimicking environments.

Hydrothermal stability of fluorine‐induced microporous silica membranes: Effect of steam treatment conditions

AbstractA fluorine‐SiO2 membrane was prepared using triethoxyfluorosilane (TEFS) as a Si precursor, and its hydrothermal stability was evaluated. The TEFS membrane calcined at 750°C had fewer Si‐OH and Si‐F groups in its network structure and showed H2 permeance that was greater than 10−6 mol m−2 s−1 Pa−1 with H2/N2 and N2/SF6 permeance ratios of 10 and 210, respectively. This membrane performance was relatively stable under the temperature (< 500°C) used for steam treatment, regardless of the steam partial pressure (30, 90 kPa). On the other hand, when the steam treatment temperature was increased beyond 500°C, gas permeance decreased significantly and the membrane became highly selective for He and H2 over smaller molecules (He/N2: > 600, H2/N2: > 100). The relationship between the activation energy of H2 and the permeance ratios (He/H2, He/H2O, H2/H2O) of a TEFS‐derived membrane under steam treatment higher than 600°C resulted in a network pore size that approximated in conventional microporous SiO2 membranes.

3D porous Ti6Al4V-beta-tricalcium phosphate scaffolds directly fabricated by additive manufacturing

3D Ti6Al4V-beta-tricalcium phosphate (TCP) hybrid scaffolds with interconnected porous network and controllable porosity and pore size were successfully produced by three-dimensional fiber deposition (3DF). The macrostructure of scaffolds was determined by the 3D design, whereas the micro- and submicron structure were derived from the Ti6Al4V powder sintering and the crystalline TCP powder, respectively.Ti6Al4V-TCP slurry was developed for 3DF by optimizing the TCP powder size, Ti6Al4V-to-TCP powder ratio and Ti6Al4V-TCP powder content. Moreover, the air pressure and fiber deposition rate were optimized. A maximum achievable ceramic content in the Ti6Al4V-TCP slurry that enables 3DF manufacturing was 10 wt%. The chemical analysis showed that limited contamination occurred during sintering. The compressive strength and Young's modulus of the scaffolds exhibited values between those of cancellous and cortical bone. The 3D Ti6Al4V-TCP scaffolds with 10 wt% TCP allowed deposition of a calcium phosphate layer on the surface in a simulated body fluid. Cumulative release of calcium and phosphate ions from the scaffolds was observed in a simulated physiological solution, in contrast to a cell culture medium. A pilot in vivo study, in which the scaffolds were implanted intramuscularly in dogs showed ectopic bone formation in the Ti6Al4V-TCP scaffolds with 10 wt% TCP, showing their osteoinductive potential. The porous 3D Ti6Al4V-TCP scaffolds developed here combine the mechanical properties of the metal with the bioactivity of the ceramic and are therefore likely to yield more effective strategies to control the implant-bone interface and thereby improve long-term clinical results in orthopaedics and craniomaxillofacial surgery. Statement of significanceIn this work, 3D porous hybrid scaffolds made of a titanium alloy and a beta-tricalcium phosphate ceramic (Ti6Al4V-TCP) were developed using the direct additive manufacturing technique 3D fiber deposition. Upon optimization of the powders and slurry, scaffolds with up to 10 wt.% TCP with good mechanical properties and controllable porous structure at different length scales were successfully manufactured. A preliminary in vivo study in an intramuscular model demonstrated that the addition of TCP to the metal alloy improved its bioactivity. The combination of the two materials and the use of a direct additive manufacturing technique resulted in scaffolds that may lead to more effective strategies to control the implant-bone interface and thereby improve long-term clinical results in orthopaedics and craniomaxillofacial surgery.

Design of a SiOC network structure with oxidation stability and application to hydrogen separation membranes at high temperatures

SiOC membranes were fabricated by a sol-gel method using three types of silica precursors: vinyltrimethoxysilane (VTMS), triethoxysilane (TRIES), and 1,1,3,3-tetramethyldisiloxane (TMDSO). The timing of the addition of TMDSO was evaluated via single-gas permeation for its effect on formation of the SiOC structure and on membrane performance. The effect that VTMS compounding exerted on membrane performance and on oxidation stability was also evaluated. The network size of SiOC membranes was precisely tailored by controlling the timing of the addition of TMDSO during the sol preparation process. There was no significant change in the network pore size either before or after thermally induced hydrosilylation (Si–C=C + Si–H → Si–CH2–CH2–Si) and the cross-linking of Si–CH3 groups (Si–CH3 + Si–CH3 → Si–CH2–Si + CH4). These SiOC membranes were highly selective of H2 over larger molecules such as CF4 and SF6. The effect of VTMS compounding on network pore size was small, but the oxidation stability of the SiOC structure at 500 °C was dramatically enhanced.

Relationship between gel properties and water holding of ovalbumin-carboxymethylcellulose electrostatic complex hydrogels

The relationship between the water holding (WH) and gel properties of protein-based hydrogels is important for designing and regulating the texture and sensory properties of foods. Herein, the relation among WH and heat-set gel properties of ovalbumin (OVA)-carboxymethylcellulose (CMC) electrostatic complexes was explored. The results showed that the gels exhibited homogeneous and dense structure and good WH compared with pure OVA at pH 4.6, while Young's modulus decreased significantly (P < 0.05). This was closely related to the inhibition of the electrostatic interaction on the formation of large protein aggregates during heat treatment (90 °C, 30 min). Specially, the CMC1.2 (the degree of substitution was 1.2) with higher charge density showed stronger interference than CMC0.7 (the degree of substitution was 0.7) for the gel network structure and properties. Moreover, the addition of salt ions could enhance the gel strength. Meanwhile, the coarseness and microstructure pore size were also increased with enhancing of ionic strength, resulting in a significant decrease in the WH. The effective permeability coefficient (k1) and water flux coefficient (k2) of gels have a significant positive correlation with their network pore size, indicated that the regulation of WH of hydrogel mainly depended on controlling the pore size of its microstructure.

Pore size tuning of bis(triethoxysilyl)propane (BTESP)-derived membrane for gas separation: Effects of the acid molar ratio in the sol and of the calcination temperature

Bis(triethoxysilyl)propane (BTESP) is a bridged-type organoalkoxysilane with a Si-C3H6-Si bond. It was utilized for membrane fabrication via a sol-gel method to achieve high permselectivity for large molecules. Membrane fabrication parameters such as the acid molar ratio (AR) in the sol and calcination temperature were evaluated for their effect on the network pore size and on gas permeation properties, as evaluated by the molecular size dependence (0.26–0.55 nm) and temperature dependence (50–200 °C) of gas permeance. BTESP membranes with different ARs (10−1, 100, and 10) showed H2/N2 and H2/CF4 selectivities of 20–30 and 640–32,000, respectively. As AR was increased, each gas permeance also increased, but H2 selectivity that corresponds to network pore size was decreased. FT-IR analysis indicated that the density of the Si-OH groups (Si-OH/Si-O-Si) of unfired gels was decreased with a higher AR, so that condensation of the Si-OH groups during the calcination process formed a dense network structure in the case of BTESP membranes with a low AR (10−1). Calcination temperature also affected the network structure of BTESP membranes. BTESP membranes calcined at different temperatures (350, 450, and 600 °C) showed H2/N2 and H2/CF4 selectivities of 10–30 and 410–32,000, respectively. A BTESP membrane calcined at high temperature (600 °C) showed loose networks since the linking units derived from BTESP were decomposed at temperatures above 500 °C, which resulted in the formation of methyl groups. In conclusion, the AR in a sol is suitable for tuning small pore sizes, while calcination temperature as a membrane fabrication parameter offers the advantage of controllability for loose network structures.

Particle diffusion in extracellular hydrogels.

Hyaluronic acid is an abundant polyelectrolyte in the human body that forms extracellular hydrogels in connective tissues. It is essential for regulating tissue biomechanics and cell-cell communication, yet hyaluronan overexpression is associated with pathological situations such as cancer and multiple sclerosis. Due to its enormous molecular weight (in the range of millions of Daltons), accumulation of hyaluronan hinders transport of macromolecules including nutrients and growth factors through tissues and also hampers drug delivery. However, the exact contribution of hyaluronan to tissue penetrability is poorly understood due to the complex structure and molecular composition of tissues. Here we reconstitute biomimetic hyaluronan gels and systematically investigate the effects of gel composition and crosslinking on the diffusion of microscopic tracer particles. We combine ensemble-averaged measurements via differential dynamic microscopy with single-particle tracking. We show that the particle diffusivity depends on the particle size relative to the network pore size and also on the stress relaxation dynamics of the network. We furthermore show that addition of collagen, the other major biopolymer in tissues, causes the emergence of caged particle dynamics. Our findings are useful for understanding macromolecular transport in tissues and for designing biomimetic extracellular matrix hydrogels for drug delivery and tissue regeneration.

Interconnected macropores cryogel with nano-thin crosslinked network regenerated cellulose

Dissolved oil palm empty fruit bunch cellulose (EFBC) and sodium carboxymethylcellulose (NaCMC) were chemically crosslinked with epichlorohydrin (ECH) to generate designated hydrogel. After swelling process in distilled water, the swollen hydrogel was frozen and freeze-dried to form cryogel. The swelling phenomenon of hydrogel during the absorption process gave substantial effects on thinning of crosslinked network wall, pore size and volume, steadiness of cryogel skeletal structure, and re-swelling of cryogel. The swelling effects on hydrogel were confirmed via microscopic study using variable pressure scanning electron microscope (VPSEM). From the retrieved VPSEM images, nano-thin crosslinked network wall of 24.31 ± 1.97 nm and interconnected pores were observed. As a result, the amount of water, the swelling degree, and the freeze-drying process indirectly affected the VPSEM images that indicated pore size and volume, formation of interconnected pores, and re-swelling of cryogel. This study determined the intertwined factors that affected both hydrogel and cryogel properties by investigating the swelling phenomenon and its ensuing effects.

Structural and mechanical characterization of crosslinked and sterilised nanocellulose-based hydrogels for cartilage tissue engineering

Nanocellulose is a natural biopolymer derived from cellulose. Combined with sodium alginate, it is used to 3D print hydrogels for articular and nasal cartilage engineering and shows good integration, promising cartilage regeneration and mechanical stability over 60 days of implantation in mice. Yet, little is known about their structural and mechanical properties, particularly the impact of crosslinking and sterilisation methods. This study investigates the impact of different calcium chloride crosslinker concentrations and sterilization methods on the structural and mechanical properties of nanocellulose-based hydrogels containing plant-derived cellulose nanofibrils, cellulose nanocrystals or a blend of the two. Crosslinking significantly alters the overall network distribution, surface morphology, pore size and porosity of the hydrogels. Sterilisation has a striking effect on pore size and affects swelling depending on the sterilisation method. The effect of crosslinker and sterilisation on the overall properties of the hydrogels was reliant on the form of nanocellulose that comprised them.

Nanocellulose for gel electrophoresis

HypothesisCellulose nanofibres produced by TEMPO-mediated oxidation can form gels. This study presents a proof-of-concept for gel electrophoresis with nanocellulose (NC). ExperimentsTEMPO-oxidised cellulose nanofibre dispersion is chemically cross-linked by inducing amide linkages to produce gel slabs for electrophoretic separation. Nanocellulose gel slabs 1 cm thick containing Tris/Borate/EDTA (TBE) buffer were casted. Different cross-linker types and ratios are investigated to assess the migration of conventional electrophoresis tracking dyes. FindingsTracking dyes (bromophenol blue and orange G) can diffuse within the gel at different rates and therefore separate. Changing the cross-linker length from EDA to HMDA (C2- to C6-chain) increases the overall network pore size resulting in a faster migration rate for both bromophenol blue and orange G. Increasing the cross-linker concentration stabilises the HMDA-NC gel (no extension) during the electrophoresis run without any effect on the dye migration rate. Increasing the voltage increases the migration rates for both orange G and bromophenol blue. Further development is required to cast the gels evenly and to prevent bubble formation during the cross-linking process. This will enable to effectively separate mixtures of proteins. Nanocellulose gels can become a novel substrate for sustainable biomedical separation and diagnostics by electrophoresis.

On the permeability of colloidal gels

We reexamine and refine analytical theories for permeability in colloidal networks, with particular focus on constants and identification of approximations. The new theories are compared against numerical simulations of Stokes flow through the networks and reveal nearly quantitative power-law predictions for both pore size and permeability at low volume fractions, with systematic deviations observed only at high volume fractions. Comparison with two previously published experimental data sets yields mixed results: in one case, very good agreement is found, while in the other, only the scaling is correctly predicted. In fractal gel networks, the permeability is commonly modeled as a power-law function of volume fraction, with the fractal dimension of the network determining the power-law exponent. To quantitatively probe the influence of gel structure on permeability, we investigate this relation in structures generated by diffusion-limited cluster aggregation (DLCA) and reaction-limited cluster aggregation (RLCA) and, for contrast, non-overlapping uniform random dispersions of particles. Geometric analyses are used to determine network pore size distributions, fractal dimensions, and percolation characteristics. High-fidelity simulations of the slow viscous flow of Newtonian fluids are used to obtain first-principles-based velocity and fields and hence network permeabilities. Interestingly, the effective pore size that determines permeability is found to be somewhat larger than that measured by a method based on the insertion of spherical probes. Empirical inclusion of a fractal dimension dependence on volume fraction is found to yield quantitative results for permeabilities over the entire volume fraction range studied, in both DLCA and RLCA materials.

Fluorine Doping of Microporous Organosilica Membranes for Pore Size Control and Enhanced Hydrophobic Properties.

Fluorine-doped organosilica membranes for gas and pervaporation (PV) separation were fabricated using a sol–gel method. NH4F and bis(triethoxysilyl)methane (BTESM) were selected as the dopant and Si precursor, respectively, for the fabrication of fluorine-doped organosilica membranes. Doping with fluorine was evaluated for its effect on the physicochemical properties of organosilica (hydrophobicity/hydrophilicity and network size). Fluorine doping dramatically eliminated the formation of Si–OH groups in the sol, so that the condensation of Si–OH groups during the calcination process was suppressed. It is possible that fluorine doping enlarged the network pore sizes in organosilica, because the F-BTESM (F/Si = 1/9) membrane showed superior He and H2 permeance with a low H2/N2 permeance ratio that corresponded to the network pore size by comparison with an undoped BTESM membrane. The F-BTESM (F/Si = 1/9) membranes clearly showed a high level of C3H6 permeance (>3.0 × 10–7 mol m–2 s–1 Pa–1) with a high C3H6/SF6 permeance ratio (∼250), which suggests that the network pore size of F-BTESM is suitable for the separation of large molecules such as hydrocarbon gases (C3/C4, C4 isomer, etc.). Organosilica membranes both with and without fluorine doping showed stable PV performance because of the fact that H2O permeance and each permeance ratio under different separation systems was approximately constant over 10 h at 70 °C. Fluorine doping enhanced the hydrophobic nature of the organosilica, which was confirmed by the H2O adsorption and PV properties.