Gelation Speed Research Articles

Effects of salt concentrations of the aqueous peptide-amphiphile solutions on the sol-gel transitions, the gelation speed, and the gel characteristics.

Hydrogels made of peptide amphiphiles (PA) have attracted a lot of interest in biomedical fields. Considering the applications of PA hydrogels, the control of the gelation speed and the gel characteristics is essential to predominantly determine the usefulness and practicability of the hydrogels. In this work, the effects of the salt concentrations using sodium dihydrogenorthophosphate (NaH2PO4) on the sol-gel transition behaviors, especially the gelation speed and the gel characteristics of the designed PA (C16-W3K) hydrogels in aqueous solution were discussed. It was found that the original solution state before rheological testing was independent of the salt concentration, which was confirmed by observing the self-assembly structures and the peptide secondary structures of PA through transmission electron microscopy (TEM) and circular dichroism spectroscopy (CD). The PA solutions with different salt concentrations, however, presented a profound difference in the gelation speed and the gel characteristics: the solution exhibited higher gelation speeds and higher mechanical properties at higher salt concentrations. Concurrently, the density, the length of wormlike micelles, and the conformational ratio of β-sheets to α-helices in the equilibrium PA solutions all increased with the increase in the salt concentrations.

Enrichment of chitosan hydrogels with perfluorodecalin promotes gelation and stem cell vitality

Thermosensitive injectable hydrogels for bone regeneration consisting of chitosan, sodium beta-glycerophosphate (Na-β-GP) and alkaline phosphatase (ALP) were enriched with oxygenated perfluorodecalin (PFD), a liquid hydrophobic perfluorochemical with high oxygen affinity, in order to improve cell growth on the hydrogels. Furthermore, influence of PFD concentration on hydrogel physicochemical properties relevant for bone regeneration, namely gelation speed, radiopacity and homogenicity, was investigated. Addtionally, ALP-mediated and non-ALP-mediated mineralization were evaluated by incubation in 0.1M calcium glycerophosphate and simulated body fluid. 2% (w/v) chitosan hydrogels containing 2.5mg/ml ALP were enriched with PFD at five concentrations, namely 0 (control), 0.069, 0.138, 0.207 and 0.276ml/ml hydrogel, denoted A, B, C, D and E, respectively. Rheometrical investigations revealed that gelation speed increased with increasing PFD concentration. Micro-CT analysis revealed homogenicity of all sample groups except E and that radiopacity increased in the order B>C>A>D>E. ALP-mediated and non-ALP-mediated mineralization were not affected adversely by PFD. Growth of human adipose tissue-derived mesenchymal stem cells (ADSC) encapsulated in hydrogels was markedly higher in sample groups containing PFD, i.e. B–E. Hence, incorporation of oxygenated PFD can improve the suitability of hydrogels as bone regeneration materials.

Solvent‐Driven Chiral‐Interaction Reversion for Organogel Formation

AbstractFor chiral gels and related applications, one of the critical issues is how to modulate the stereoselective interaction between the gel and the chiral guest precisely, as well as how to translate this information into the macroscopic properties of materials. Herein, we report that this process can also be modulated by nonchiral solvents, which can induce a chiral‐interaction reversion for organogel formation. This process could be observed through the clear difference in gelation speed and the morphology of the resulting self‐assembly. This chiral effect was successfully applied in the selective separation of quinine enantiomers and imparts “smart” merits to the gel materials.

Thiolated hyaluronan-based hydrogels crosslinked using oxidized glutathione: An injectable matrix designed for ophthalmic applications

Future ophthalmic therapeutics will require the sustained delivery of bioactive proteins and nucleic acid-based macromolecules and/or provide a suitable microenvironment for the localization and sustenance of reparative progenitor cells after transplantation into or onto the eye. Water-rich hydrogels are ideal vehicles for such cargo, but few have all the qualities desired for novel ophthalmic use, namely in situ gelation speed, cytocompatibility, biocompatibility and capacity to functionalize. We describe here the development of an ophthalmic-compatible crosslinking system using oxidized glutathione (GSSG), a physiologically relevant molecule with a history of safe use in humans. When GSSG is used in conjunction with an existing hyaluronate-based, in situ crosslinkable hydrogel platform, gels form in less than 5min using the thiol–disulfide exchange reaction. This GSSG hydrogel supports the 3-D culture of adipose-derived stem cells in vitro and shows biocompatibility in preliminary intracutaneous and subconjunctival experiments in vivo. In addition, the thiol–disulfide exchange reaction can also be used in conjunction with other thiol-compatible chemistries to covalently link peptides for more complex formulations. These data suggest that this hydrogel could be well suited for local ocular delivery, focusing initially on front of the eye therapies. Subsequent uses of the hydrogel include delivery of back of the eye treatments and eventually into other soft, hyaluronan-rich tissues such as those from the liver and brain.

Effect of calcium source and exposure-time on basic caviar spherification using sodium alginate

Gelation speed is directly proportional to the concentration of calcium. Although the kinetics of gelation are altered by the source of calcium, the final alginate gel strength nor the resistance to calcium diffusion are altered. Calcium chloride reaches a gel strength plateau fastest (~100s), followed by calcium lactate (~500s) and calcium gluconoate (~2000s). Calcium chloride is the best option when the bitter taste can be masked and a fast throughput is required, while calcium gluconoate may have an advantage when the membrane thickness/hardness needs to be manipulated.

Microfluidic synthesis of chemically and physically anisotropic hydrogel microfibers for guided cell growth and networking

Hydrogel materials with microscale heterogeneity are of great interest in the effort to spatially control cellular microenvironments in tissue engineering applications. Here we present a microfluidic system to continuously synthesize chemically and physically anisotropic Ca–alginate hydrogel microfibers enabling the guidance of cell proliferation to form linear cell colonies and intracellular networks. The microfluidic gelation process involves 2 critical steps to obtain alginate microfibers using axisymmetric microchannels with uniform depth: introduction of a buffer solution between the sodium alginate (NaA) and CaCl2 solutions to modulate the gelation speed, and use of a thickener to balance the viscosities of the solutions. We synthesized hydrogel fibers with diameters of ∼7 to 200 μm, maintaining the anisotropy in the cross-section, and examined factors affecting the fiber diameter and uniformity. Moreover, parallel alginate flows with and without propylene glycol alginate (PGA) enabled the formation of sandwich-type solid-soft-solid hydrogel fibers, which were used to guide the direction of growth of cells inoculated in the soft-core, with the help of outer polycation membranes made of poly-L-lysine. We demonstrated the formation of linear colonies of 3T3 and HeLa cells inside the anisotropic fiber and observed elongated nuclei along the fiber direction. In addition, the heterogeneous morphology of the fiber was utilized to guide neurite elongation and generate cellular networks by using neuron-like PC12 cells. The hydrogel fibers reported here can be used as an innovative tool for investigating cell and tissue morphogenesis in heterogeneous microenvironments, and for creating tissue models with precise control of cellular alignment and elongation.

Synthesis of enzymatically-gellable carboxymethylcellulose for biomedical applications

We synthesized a carboxymethylcellulose with phenol moieties by covalently incorporating tyramine into carboxymethylcellulose using aqueous-phase carbodiimide activation chemistry. The resulting hydrogel was obtained from an aqueous solution of the conjugate via the horseradish peroxidase-catalyzed oxidation reaction of phenols by consuming H(2)O(2), where the gelation speed depended on the concentrations of enzyme and H(2)O(2). The viability of the mammalian cells enclosed within the hydrogel prepared from 1.5% (w/v) conjugate solution containing 5 units/ml horseradish peroxidase and 1 mM H(2)O(2), was 80% after 24 h. These results demonstrate that this carboxymethylcellulose with phenol moieties has potential for biomedical applications including tissue-engineering.

Effect of thermal history on kappa-carrageenan hydrogelation by differential scanning calorimetry

The effect of thermal history on gel–sol transition was investigated by highly sensitive differential scanning calorimetry (DSC) in order to clarify the non-equilibrium state of κ-carrageenan hydrogels. κ-Carrageenan with a concentration from 0.5% to 5.0% was used. When concentration of solution was lower than 2.0%, homogeneous κ-carrageenan gel was formed when aqueous solution was fully equilibrated. When concentration exceeded 3.0%, a sub-peak could be observed at the low temperature side of the main peak. It was indicated that helices having various sizes and different kinds of defects are present in the junction zone. Thermal histories, such as cooling rate from the sol state or annealing at around gel–sol transition temperature, markedly affect the junction zone formation. A large junction zone is formed at a slow gelation rate, and also that many small junction zones form at a fast gelation speed.

Viscoelasticity of Dental Tissue Conditioners during the Sol-gel Transition

Formation of tissue conditioners is a process of polymer chain entanglements. This study evaluated the influence of composition and structure on dynamic viscoelasticity of concentrated polymer solutions based on poly(ethyl methacrylate) (PEMA) used as tissue conditioners through the sol-gel transition. The hypothesis was that the ethanol content is the most influential factor in determining gelation speed. Rheological parameters were determined with the use of a controlled-stress rheometer. Analysis of variance by orthogonal array L(16)(4(5)) indicated that the strong polar bonding of ethanol (contribution ratio rho = 53.8%; confirming the hypothesis) and molecular weight of polymer powders (rho = 26.7%) had a greater influence on the gelation times of PEMA-based systems than did the molar volume of plasticizers (rho = 9.0%) and concentration of polymers (i.e., powder/liquid ratio) (rho = 4.5%). The results suggest that the gelation of tissue conditioners based on PEMA can be controlled over a wide range by varying the polymer molecular weight, and especially ethanol content.

Formulation of tissue conditioners

Dental tissue conditioners are compliant gels, formed in situ under a denture from a polymer powder and a plasticizer system. Hitherto, the powder has been poly(ethyl methacrylate) and the liquid a phthalate/ ethanol mixture. These materials are temporary, because they harden from plasticizer leaching. The current work has been aimed at producing material with extended oral lifetimes. A range of n-butyl/ethyl methacrylate copolymers have been studied, together with various ester-ethanol liquid systems, with respect to gelation behaviour with various alcohols and esters, viscoelastic behaviour of the set gels, and water extraction. Materials based on poly(ethyl methacrylate) show that gelation speed depends upon particle size, and the degree of ball milling of the powder, and the molar volume of the plasticizer. Systems based on n-butyl/ethyl methacrylate copolymers need less or no ethanol in the liquid system, although gelation speed is very temperature dependent. The gels from these last materials are more compliant, and retain their compliance longer in aqueous media than those based on poly(ethy) methacrylate).

Chemical Modification of Proteins Part 6. Further Studies on Gelation of Casein after Modification by Dialdehyde Starch

AbstractThe physical and chemical changes in casein during the gelation owing to the chemical modification by dialdehyde starch (DAS) in 8–10% solution were studied using electron‐microscopy, measuring the mechanical properties (shear deformation), turbidimetric titration, and determination of amino groups.The gelation which proceeds during a storage time of 2 weeks is accomplished by the formation of a super‐molecular network structure. Depending on the conditions of modification (pH, percentage of DAS, protein concentration) a more or less dense network is formed. An increase of pH (in the range of pH 6,3–9,7) leads to an increase of gelation speed, which favours the formation of irregular network structures. The denser the network formed the smaller is the shear deformation measured by the device of Tolstoi. During the storage of the gels the plastic component of compliance decreases to a greater amount than the elastic one. Therefore the relative amount of elastic component increases.During the reaction with DAS the maximum of turbidity of the protein (solubility minimum) shifted to lower pH owing to a blockage of positively charged groups. On the contrary to the changes measured by physical methods, this shift is complete soon after a 1 day storage. Similarly the blockage of amino groups is finished in the most cases this time too.

Photoréticulation de Polyacroléines et de Copolymères Greffés d'Acroléine Préparés par Voie Anionique

AbstractThe polyacroleins were prepared anionically in the presence of a sensitizor containing carbonyl groups and irradiated in solution with a mercury vapor lamp. The polymers obtained after various polymerizing times were completely insoluble in organic solvents. Different factors affecting gelation speed were studied. New acrolein graft copolymers prepared from a polycarbanionic polymer are also described. These new copolymers are also crosslinked by light and their use as a photosensitive layer is described.