Subsequent Gelation Research Articles

Decoupling the dependence of rheological/mechanical properties of hydrogels from solids concentration

Hydrogels are being increasingly used in medicine due to their potential to be delivered into the body in a minimally invasive manner (e.g. injection in solution form) for subsequent gelation at the site of introduction. Both the flow properties of the solution and mechanical properties of the gels are critical to their applications. However, both properties depend on the concentration of polymer, and simply increasing the concentration to improve the gel properties often leads to unacceptably high fluid viscosities. Thus, we hypothesized that hydrogels with a bimodal molecular weight distribution (MWD) (i.e. a mixture of high MW polymer and polymer tailored to have a lower MW but still able to participate in gel formation) would allow one to readily decouple the dependence of the two properties from the overall concentration. This hypothesis was investigated using alginate hydrogels, and we found that increasing the concentration of alginate ( C alginate) with high MW alginate from 2 to 5% raised the viscosity ( η) of solution from 0.7 to 20 Pa s, while enhancing the shear modulus ( G) from 25 to 50 kPa. In contrast, increasing C alginate of binary solutions at a weight fraction of high MW alginate of 0.50 raised η from 0.2 to only 3.6 Pa s, while enhancing G from 15 to 52 kPa. Strikingly, the low η of binary solutions can be attributed to a significant decrease in physical interactions between the chains, while strong gel strength could be attributed to an increased fraction of intermolecular cross-links and stiffened molecules as compared to gels comprised of high MW alginates. This approach of adjusting the MWD of gel forming solutions to control the fluid and solid properties in an independent manner may be broadly utilized in designing other hydrogels and materials for a variety of applications.

A DSC study on the gel-sol transition of a starch and hsian-tsao leaf gum mixed system.

Differential scanning calorimetric analysis was performed on the admixture of 4% hsian-tsao leaf gum and 8% wheat starch as a function of salt types and concentrations. The salt concentrations (C(s)) studied were 5-100 mM for sodium and potassium chloride, and 3.4-34 mM for calcium and magnesium chloride. It was found that hsian-tsao leaf gum or starch alone did not present a readily recognizable exothermic peak or endothermic peak during cooling or heating in DSC. However, mixing these two polymers promoted the intermolecular binding and subsequent gelation of the mixtures as evidenced by the DSC exothermic and endothermic peaks during cooling and heating, respectively. The setting and melting temperatures of such a mixed system shifted progressively to higher temperatures with increasing concentrations of added salts. It was considered that the aggregated mixed polymers formed thermally stable junction zones with higher binding energies. The thermal behavior change was more remarkable by the addition of K(+) than by Na(+), and by Ca(2+) than by Mg(2+). For monovalent cations, the DSC heating and cooling curves showed a single endothermic and exothermic peak. For divalent cations at low concentration, the DSC curves showed a single peak. However, with sufficient divalent cations, the DSC curves eventually developed a bimodal character. A mixed system with sufficient Ca(2+) could form firm gel that was difficult to remelt completely upon heating to 130 degrees C, indicating the possibility of the formation of ionic bonds through cross-links with the carboxyl groups in hsian-tsao leaf gum.

Whey Protein-based Microcapsules Prepared by Double Emulsification and Heat Gelation

Whey protein-based microcapsules containing a model apolar core, anhydrous milkfat, were prepared using a process consisting of double emulsification and subsequent heat gelation. Wall solids concentration and core load ranged from 15 to 30 g/100 g and from 25 to 50 g/100 g (on dry basis), respectively. In all cases, spherical microcapsules, 10–100μ m in diameter, were obtained and their outer topography and inner structure was affected by the pH of the core-in-wall emulsion. Microcapsules prepared from pH 7.2 core-in-wall emulsions exhibited smooth, dent-free surfaces. Surface porosity of microcapsules prepared from pH 4.5, 5.5 and 5.5 core-in-wall emulsions was inversely related to pH. Core retention during microencapsulation was higher than 90% and core losses could be attributed mainly to removal of core droplets from the outer surface and to some core extraction from inner parts of microcapsules by the solvents used to wash the microcapsules. Water solubility of microcapsules prepared from pH 4.5 or pH 7.2 core-in-wall emulsions was very limited and ranged from 0.2 to 6.3%, was inversely related to the pH of core-in-wall emulsion and was affected by incubation conditions. Results suggested that the microencapsulation process might be used to prepare whey protein-based microcapsules for controlled core-release applications in food systems.

Novel Electrode Materials for Thin‐Film Ultracapacitors: Comparison of Electrochemical Properties of Sol‐Gel‐Derived and Electrodeposited Manganese Dioxide

Thin films of manganese dioxide were formed on nickel foils by electrodeposition and by both dip‐coating and drop‐coating with manganese dioxide suspensions (sols) and their subsequent gelation and calcination. The performance of these films as ultracapacitors was studied by cyclic voltammetry in the range 0.0–0.9 V (SCE) and by chronopotentiometry in unbuffered solution. The cyclic voltammograms of ultrathin, dip‐coated sol‐gel‐derived films indicated better capacitive behavior and gave differential specific capacitance values as high as 698 F/g compared to values half to two‐thirds as great for the electrodeposited films. Multilayer drop‐coated sol‐gel films were prepared to attain film thicknesses comparable to the electrodeposited films, and these were found to provide charge‐storage capacity as high as , more than three times greater than that of the electrodeposited films. All films, except electrodeposited films that were not thermally cured, exhibited good cycling stability, losing not much more than 10% of capacity after 1500 cycles. © 2000 The Electrochemical Society. All rights reserved.

Fabrication of branched hybrid vascular prostheses.

We devised a branched, or bifurcated, hybrid vascular prosthesis that was mainly composed of bovine smooth muscle cells (SMCs) and type I collagen with minimal reinforcement by a knitted fabric mesh made of segmented polyester. The tubular hybrid medial tissue with small (3 mm) or large (6 mm) inner diameter was prepared by pouring a cold mixed solution of SMCs and collagen into a corresponding tubular mold and by subsequent thermal gelation, followed by 7-day culturing. A branched hybrid medial tissue was prepared by an end-to-side anastomosis between these tubes of different sizes. Two-week culture of the branched tissue resulted in continuous tissue formation at the anastomotic site. Upon seeding and culture of bovine endothelial cells (ECs), a fully endothelialized branched hybrid vessel was prepared. Under a continuous pulsatile flow condition, morphological alterations of ECs, responding to local flow dynamics generated by the branched configuration, were seen. Reinforcement with an elastomeric mesh improved mechanical strength of the hybrid tissue and created compliance matching with native arteries. A branched hybrid graft with mesh reinforcement is expected to be applicable to arterial replacement in a branching region.

Fabrication of compliant hybrid grafts supported with elastomeric meshes.

We devised tubular hybrid medial tissues with mechanical properties similar to those of native arteries, which were composed of bovine smooth muscle cells (SMCs) and type I collagen with minimal reinforcement with knitted fabric meshes made of synthetic elastomers. Three hybrid medial tissue models that incorporated segmented polyester (mesh A) or polyurethane-nylon (mesh B) meshes were designed: the inner, sandwich, and wrapping models. Hybrid medial tissues were prepared by pouring a cold mixed solution of SMCs and collagen into a tubular glass mold consisting of an inner mandrel and an outer sheath and subsequent thermal gelation, followed by further culture for 7 days. For the inner model, the mandrel was wrapped with a mesh. For the sandwich model, a cylindrically shaped mesh was incorporated into a space between the mandrel and the sheath. The wrapping model was prepared by wrapping a 7-day-incubated nonmesh gel with a mesh. The inner diameter was 3 mm, irrespective of the model, and the length was 2.5-4.0 cm, depending on the model. The intraluminal pressure-external diameter relationship showed that nonmesh and inner models had a very low burst strength below 50 mmHg, while the sandwich model ruptured at around 110-120 mmHg; no rupturing below 240 mmHg was observed for the wrapping model, regardless of the type of mesh used. Compliance values of wrapping and sandwich models were close to those of native arteries. Pressure-dependent distensibility characteristics similar to native arteries were observed for a mesh A wrapping model, whereas a mesh B wrapping model expanded almost linearly as intraluminal pressure increased, which appeared to be due to elasticity of the incorporated mesh. Thus, design criteria for hybrid vascular grafts with appropriate biomechanical matching with host arteries were established. Such hybrid grafts may be mechanically adapted in an arterial system.

Effect of light and temperature on zeta potential and physical stability in solid lipid nanoparticle (SLN™) dispersions

Aqueous dispersions of solid lipid nanoparticles (SLN™) are basically stable for up to 3 years, however some systems show particle growth followed by gelation. To assess the destabilizing factors, a poloxamer 188 stabilized Compritol SLN formulation was prepared. Its stability was investigated as a function of storage temperature, light exposure and packing material (untreated and siliconized vials of glass quality I). In general, introduction of energy to the system (temperature, light) led to particle growth and subsequent gelation. This process was accompanied by a decrease in zeta potential from approximately −25 mV to −15 mV. The effect of the packing material was less pronounced. However, siliconization of the vials almost eliminated particle growth. By optimization of the storage conditions (8°C, in the dark, siliconized vials), a stability of the less stable aqueous Compritol SLN over 3 years was achieved.

Silicic Acid Polymerization Catalyzed by Amines and Polyamines

Abstract Polymerization and subsequent gelation of silicic acid in water were catalyzed by amines and polyamines. Particularly effective were poly(allylamine), poly(lysine), and poly(arginine), which promoted spontaneous gelation. The resultant silica gel contained a sizable portion of amines, which altered the surface properties of silica gel.

Tissue Engineered Skeletal Muscle: Preparation of Highly Dense, Highly Oriented Hybrid Muscular Tissues

We prepared highly dense, highly oriented hybrid muscular tissues that are composed of C2C12 cells (skeletal muscle myoblast cell line) and type I collagen. A cold mixture of C2C12 cells suspended in DMEM and type I collagen solution was poured into capillary tube molds of two different sizes (inner diameters; 0.90 and 0.53 mm, respectively). One end of each mold was sealed. Upon centrifugation (1000 rpm, 5 min) and subsequent thermal gelation, a rod-shaped gel was obtained. It was cultured in an agarose gel-coated dish for 7 days (first for 3 days in a growth medium and then for 4 days in a differentiation medium), during which time it shrank to become a highly dense tissue. Small-diameter rod-shaped, highly dense cellular assemblages with multinucleated myotubes were formed and only few necrotic cells at the core of the tissue were observed. On the other hand, a ring-shaped tissue prepared using a specially devised agarose gel mold was subjected to cyclic stretching at 60 rpm, resulting in the formation of a highly dense, highly oriented hybrid muscular tissue in which both densely accumulated cells and collagen fiber bundles tended to be aligned in the direction of stretching. The hybrid muscular tissues that were prepared using via sequential procedures of a centrifugal cell packing method and a mechanical stress-loading method became closer to native muscular tissues in terms of cell density and orientation.

Tissue Engineered Skeletal Muscle: Preparation of Highly Dense, Highly Oriented Hybrid Muscular Tissues

We prepared highly dense, highly oriented hybrid muscular tissues that are composed of C2C12 cells (skeletal muscle myoblast cell line) and type I collagen. A cold mixture of C2C12 cells suspended in DMEM and type I collagen solution was poured into capillary tube molds of two different sizes (inner diameters; 0.90 and 0.53 mm, respectively). One end of each mold was sealed. Upon centrifugation (1000 rpm, 5 min) and subsequent thermal gelation, a rod-shaped gel was obtained. It was cultured in an agarose gel-coated dish for 7 days (first for 3 days in a growth medium and then for 4 days in a differentiation medium), during which time it shrank to become a highly dense tissue. Small-diameter rod-shaped, highly dense cellular assemblages with multinucleated myotubes were formed and only few necrotic cells at the core of the tissue were observed. On the other hand, a ring-shaped tissue prepared using a specially devised agarose gel mold was subjected to cyclic stretching at 60 rpm, resulting in the formation of a highly dense, highly oriented hybrid muscular tissue in which both densely accumulated cells and collagen fiber bundles tended to be aligned in the direction of stretching. The hybrid muscular tissues that were prepared using via sequential procedures of a centrifugal cell packing method and a mechanical stress-loading method became closer to native muscular tissues in terms of cell density and orientation.

Tissue Engineering of Skeletal Muscle Highly Dense, Highly Oriented Hybrid Muscular Tissues Biomimicking Native Tissues

A highly dense, highly oriented hybrid muscular tissue was devised using C2C12 cells (skeletal muscle myoblast cell line) and Type I collagen. A cold mixture of C2C12 cells suspended in DMEM (Dulbecco's modified Eagle's medium; Gibco Lab Inc., Grand Island, NY) and Type I collagen solution was poured into capillary tube molds of two different sizes (inner diameters: 0.90 mm and 0.53 mm, respectively) sealed at each end. After centrifugation (1000 RPM, 5 min) and subsequent thermal gelation, a rod shaped gel was formed. The resultant gel shrank to become a highly dense tissue after incubation on an agarose gel coated dish. Small diameter rod shaped tissues were composed of numerous multi-nucleated myotubes and a few necrotic cells. On the other hand, a ring shaped tissue fabricated by centrifugation with a specially devised agarose gel mold was subjected to cyclic stretching at 60 RPM. The resultant highly dense, highly oriented hybrid muscular tissue involved both densely accumulated cells and collagen fiber bundles, which tended to be aligned in the direction of stretching. Sequential procedures of a centrifugal cell packing method and a mechanical stress loading method facilitated fabrication of hybrid muscular tissues similar to native muscular tissues in terms of cell density and orientation. ASAIO Journal 1997; 43:M749-M753.

Tissue Engineering of Skeletal Muscle

A highly dense, highly oriented hybrid muscular tissue was devised using C2C12 cells (skeletal muscle myoblast cell line) and Type I collagen. A cold mixture of C2C12 cells suspended in DMEM (Dulbecco's modified Eagle's medium; Gibco Lab Inc., Grand Island, NY) and Type I collagen solution was poured into capillary tube molds of two different sizes (inner diameters: 0.90 mm and 0.53 mm, respectively) sealed at each end. After centrifugation (1000 RPM, 5 min) and subsequent thermal gelation, a rod shaped gel was formed. The resultant gel shrank to become a highly dense tissue after incubation on an agarose gel coated dish. Small diameter rod shaped tissues were composed of numerous multi-nucleated myotubes and a few necrotic cells. On the other hand, a ring shaped tissue fabricated by centrifugation with a specially devised agarose gel mold was subjected to cyclic stretching at 60 RPM. The resultant highly dense, highly oriented hybrid muscular tissue involved both densely accumulated cells and collagen fiber bundles, which tended to be aligned in the direction of stretching. Sequential procedures of a centrifugal cell packing method and a mechanical stress loading method facilitated fabrication of hybrid muscular tissues similar to native muscular tissues in terms of cell density and orientation.

In vitro release kinetics of biologically active transforming growth factor-β1 from a novel porous glass carrier

Sol-gel silica-based porous glass (xerogel) was used as a novel carrier material for recombinant human transforming growth factor-β1 (TGF-β1). Room temperature synthesis procedures included sol preparation, the addition of TGF-β1 solution to the sol, subsequent gelation and drying. After determination of optimal synthesis parameters, the material was assayed in vitro for its ability to release biologically active TGF-β1 in a controlled manner. Sustained release of TGF-β1 over a 7-day period was demonstrated. On the basis of published TGF-β1 potency, the amount released is capable of eliciting bone tissue reactivity. These findings suggest that this novel glass-growth factor composite may serve as an effective bone graft material for the repair of osseous defects.

Gelation properties of deamidated soluble wheat proteins

Compared with native wheat gluten proteins, chemically modified deamidated gluten proteins are more readily dispersed in aqueous solution. In this paper the gelation behaviour of commercial deamidated gluten, commonly referred to as soluble wheat protein (SWP) on heating as well as its interaction with calcium and basic proteins was investigated. Soluble wheat protein decreased in viscosity on heating at 60°C due to the breakdown of protein aggregates which was observed by phase contrast microscopy. Heating to 60°C was accompanied by an increase in hydrophobicity without conformational transitions as observed by differential scanning calorimetry. In aqueous solutions at concentrations greater than 17% wlw and after autoclaving at 120°C, SWP produced firm gels which were examined by large deformation testing. In the presence of calcium strong but coarse gels were formed which exhibited syneresis. The addition of 0.1–0.5% wlw of basic lysozyme or clupeine to the highly negatively charged SWP induced gelation at the lower temperature of 80°C which was detected by small deformation rheological testing and microscopy using basic and acidic stains. The structure and mechanism of lysozyme-induced gelation of SWP is different from the high thermal (>100°C) gelation of SWP alone. In the lysozyme-induced gelation non-covalent mainly electrostatic interactions occur between the positively charged lysozyme and the negatively charged soluble wheat proteins with the absence of conformational changes in the SWP. In contrast, in the heat gelation of SWP proteins at 120°C it is proposed that the intra-disulphide bonds are broken leading to conformational changes and subsequent association and gelation. This mechanism is supported by the fact that gelation occurred spontaneously in the presence of urea and β-mercaptoethanol indicating that in SWP the disulphide bonds normally prevent gelation unless exposed to very high heat (120°C) or disulphide reducing reagents.

Laser Light Scattering Study on the Heat-Induced Ovalbumin Aggregates Related to Its Gelling Property

A Multiangle laser photometer and a dynamic light scattering spectrophotometer were used to characterize the aggregation behavior and gel network structure of elastic and less elastic gels of ovalbumin. Ovalbumin formed opaque and less elastic gels in 50 mM phosphate buffer (pH 7.0). However, succinylated ovalbumin formed transparent and elastic gels. Heat-induced ovalbumin protein formed high molecular weight and polydisperse aggregates. Succinylation of the protein contributed to formation of lower molecular weight polymers with a narrow molecular size distribution during subsequent heat gelation. The root mean square and hydrodynamic radii of the protein polymers indicated that the elastic gel consisted of a more extended protein polymer network compared to that of the less elastic gel. The aggregation behavior of denatured ovalbumin appeared to play a crucial role in the subsequent gelling process of the proteins.

Staged curing of composite materials

In this paper the composites processing technique stage curing is developed. Stage curing is especially suited for the fabrication of thick composites in which thermal spiking and non-uniform consolidation are problematic. It is also useful for assessing the effects of lengthy lay-up times on mechanical integrity for large, complex composite structures. The effects of stage curing on the mode I interlaminar fracture toughness and interlaminar shear strength were investigated by double cantilever beam and interlaminar shear strength testing. From the results of these tests, no degradation was found for the staged cure cycles investigated. Additionally, the feasibility of reducing void content by stage curing was demonstrated. The interruption of the cure cycle with an intermediate cooldown under pressure before gelation results in shrinkage and collapse of voids. Subsequent gelation of the resin can give materials with reduced void content compared with conventional curing.

A Recent Advance In The Application of Blending Laws in Mixed Biopolymer Systems

Abstract A survey of the literature clearly indicates the potential of steric exclusion phenomena between proteins and polysaccharides in enhancing the functional properties of food/non-food products. However, in spite of the range and depth of research over the last fifty years, even the most recent reviewers accept that there are still very significant areas of obscurity in our understanding of how phase-separated proteins and polysaccharides contribute to the texture of industrial products. Recently, some progress has been made in the understanding of how biphasic gels behave in terms of phase continuity, phase inversion and, above all, solvent distribution between the two phases. It is based on the assumption that either bulk phase separation to equilibrium takes place first with gelation then occurring subsequently and independently in each phase or the fastest gelling component does so prior to the establishment of a true thermodynamic equilibrium with subsequent gelation of the second, slower gelli...

Fibrinogenemia Tampere — A dysfibrinogenemia with defective gelation and thromboembolic disease

Fibrinogen Tampere was found in a woman with a severe thromboembolic disease. The thrombin induced clotting time of her plasma and purified fibrinogen was slightly prolonged. The activation of fibrinogen Tampere appeared to be normal but subsequent gelation was defective. We studied fibrin gels formed at different ionic strengths and at different fibrinogen and calcium concentrations by liquid permeation, turbidity, and 3D laser microscopy. Crosslinking was studied by SDS-gel electrophoresis. The gels formed from fibrinogen Tampere were at inoic strength above 0.2 much tighter and had lower fiber mass-length ratios than normal gels as judged by permeability and turbidity data. At ionic strength 0.15 and at different calcium concentrations analysis by permeability showed the same results for fibrinogen Tampere as for normal gels. Analysis by turbidity at ionic strength 0.15 suggested swelling of the fibers at low calcium concentrations. 3D microscopy revealed perturbed clot architecture under all conditions. In fibrin gels from fibrinogen Tampere, the γ-chain crosslinking was normal but the crosslinking of α-chains was delayed at ionic strength 0.2 and also at lower ionic strengths on lowering the calcium concentration. The abnormal gelation may be due to a mutation in the fibrinogen molecule. Tendency to form tight fibrin gels and/or insufficient cross-linked fibrin matrix may be pathogenetic in this thrombotic disease.

Sustained-release interleukin-2 following intramuscular injection in rats

A potential sustained-release recombinant interleukin-2 (rIL-2) formulation was evaluated following intramuscular (i.m.) injection in rats. Poloxamer 407 (Pluronic® F-127) is a block copolymer comprised of polyoxyethylene and polyoxypropylene segments which exhibits the property of reverse thermal gelation. Thus, an rIL-2/poloxamer 407 preparation was injected i.m. in rats as a viscous mobile solution with subsequent gelation in vivo. Resultant plasma rIL-2 concentration-time data indicated absorption rate-limited disposition of rIL-2 following i.m. injection. The mean values of the absorption rate constant ( k clim were 0.64 ± 0.073 and 0.21 ± 0.019 h −1 following i.m. injection of an rIL-2 aqueous solution and the HL-2 gel formulation, respectively. The mean values of the elimination rate constant (k elim) were 1.76 ± 0.22 and 1.21 ±0.079 h −1 following administration of rIL-2 as an aqueous solution or gel formulation, respectively. The blood sampling time point at which the greatest plasma rIL-2 concentration (C max .) was observed was 2 h for rats injected i.m. with rIL-2 formulated in poloxamer 407 compared to 1 h for rats injected i.m. with an rIL-2 aqueous solution. The mean value of the C max. was significantly ( p < 0.05) less in rats injected i.m. with the rIL-2 gel formulation ( C max= 12500 ± 1450 pg/ml) compared to rats injected i.m. with an aqueous solution of rIL-2 ( C max = 19 600 ± 2650 pg/ml). The bioavailability of rIL-2 when injected i.m. as an rIL-2/poloxamer gel formulation relative to an i.m. injection of an rIL-2 aqueous solution was approx. 1.0. Cumulative amounts of rIL-2 recovered in the urine 48 h after an i.m. injection of either an rIL-2 aqueous solution or rIL-2 gel formulation were less than 1 percent of the administered dose. Since the rIL-2/poloxamer formulation evaluated in this study resulted in a decrease in the maximum blood concentration of rIL-2 achieved and an increase in the time required to reach a maximum blood concentration, without a reduction in the bioavailability of the protein, the rIL-2 gel formulation may represent an alternative, sustained-release mode of rIL-2 administration.

Carboxylation of scleroglucan for controlled crosslinking by heavy metal ions

Samples of carboxylated scleroglucan, sclerox, with a degree of carboxylation in the side-chains varying from 10 to 50% were made in order to investigate the potential of using carboxylation as a means to control subsequent gelation by heavy metal ions. The storage and loss moduli of aqueous solutions of sclerox samples as a function of time were determined at T = 20 °C and 30 °C after addition of trivalent chromium ions. The rheological characterization showed a transition from a viscoelastic liquid to a gel with a characteristic time depending on the chromium concentration and the degree of carboxylation. For 20% carboxylation, the rate of change in the storage modulus could be controlled within nearly three orders of magnitude from 10 −3 to 1 Pa min −1, using total chromium concentrations ranging from 0.3 to 6 m m. This rate was decreased by a factor of 2–5 by reducing the degree of carboxylation to 10%. The present study indicates that carboxylation of scleroglucan can be used to control the rate of gelation mediated by heavy metal ion complexation. This finding suggests that extension of the application range of this polysaccharide from an efficient viscosifer for polymer flooding to profile modification of high temperature oil reservoirs is attainable.