In this work, a steroidal gelator containing an imine bond was synthesized, and its gelation behavior as well as a sensitivity of its gels towards acids was investigated. It was shown that the gels were acid-responsive, and that the gelator molecules could be prepared either by a conventional synthesis or directly in situ during the gel forming process. The gels prepared by both methods were studied and it was found that they had very similar macro- and microscopic properties. Furthermore, the possibility to use the gels as carriers for aromatic drugs such as 5-chloro-8-hydroxyquinoline, pyrazinecarboxamide, and antipyrine was investigated and the prepared two-component gels were studied with regard to their potential applications in drug delivery, particularly in a pH-controlled drug release.
Many biological materials exist in non-equilibrium states driven by the irreversible consumption of high-energy molecules like ATP or GTP. These energy-dissipating structures are governed by kinetics and are thus endowed with unique properties including spatiotemporal control over their presence. Here we show man-made equivalents of materials driven by the consumption of high-energy molecules and explore their unique properties. A chemical reaction network converts dicarboxylates into metastable anhydrides driven by the irreversible consumption of carbodiimide fuels. The anhydrides hydrolyse rapidly to the original dicarboxylates and are designed to assemble into hydrophobic colloids, hydrogels or inks. The spatiotemporal control over the formation and degradation of materials allows for the development of colloids that release hydrophobic contents in a predictable fashion, temporary self-erasing inks and transient hydrogels. Moreover, we show that each material can be re-used for several cycles.
- Journal of the mechanical behavior of biomedical materials
- Published over 7 years ago
Orientated focal cross-linking can be used to generate surface anisotropy, improve material stiffness and layer integration for the production of a stable 3D construct. Riboflavin (0.25mM) diffusion into plastically compressed (PC) collagen gel was assessed by measuring the diffusion depth of riboflavin with time. The dynamic force analyser was used for peel force testing for interlayer cross-linking and material stiffness in perpendicular axis after orientated/topical cross-linking. One minute riboflavin diffusion time on either surface will saturate >12% of the collagen gel. Bonding strength doubled between PC collagen gel layers with a 5min increase in cross-linking time (between 4 and 9min) and break stress was increased significantly after cross-linking. Importantly, mechanical anisotropy was introduced in the break stress using orientated stripes of riboflavin in cross-linking, almost doubling the break stress parallel to the stripes. Limited riboflavin penetration in 1min means that surface photo-dynamic cross-linking will enhance deep cell survival within the gel. Riboflavin mediated focal/orientated cross-linking generated new predictable anisotropy at the construct. The increase in bonding strength between layers after cross-linking enhances layer integration and graded surface stiffness will impact on cellular/mechanical properties of compressed gels.
Cumin (Cuminum cyminum L.), Fennel (Foeniculum vulgare L.) and Longleaf (Falcaria vulgaris Bernh) that all belong to Apiaceae family as medicinal plants are very important in many countries. Study of genetic diversity for medicinal plant is important for researches in future. One of the methods to evaluate plant genetic diversity and classification of them is the electrophoresis of seed storage proteins. This research was conducted in order to evaluate seed protein variability in different Iranian Cumin, Fennel and Longleaf accessions and grouping them based on these proteins as a biochemical marker. For this purpose, the samples were first powdered in liquid nitrogen and seed protein was extracted with extraction buffer. Then total soluble proteins were resolved on 12.5 % sodium dodecyl sulphate polyacrylamide gel electrophoresis gels. The electrophoretic protein pattern showed 38 bands that were low polymorphism among the accessions. The result of cluster analysis showed that the accessions were classified in three groups (all 29 Cumin accessions in the first group, three Fennel ecotypes in second group and three Longleaf accessions in the last one).
The use of ethylcellulose (EC) polymers as a means to structure edible oils for fat replacement is beginning to show great promise and the use of these ‘oleogels’ has recently been shown to be feasible in food products. These gels are very versatile, as the mechanical properties can be tailored by altering either the fatty acid profile of the oil component, or the viscosity or concentration of the polymer component. Here we report the observation that certain formulation of EC oleogels tend to separate into two distinct phases; a soft interior core surrounded by a firm exterior sheath. It was found that the extent of this effect depends on EC viscosity, and can also be induced through the addition of certain surfactants, such as sorbitan monostearate and sorbitan monooleate, though not by glycerol monooleate. Although the two visually distinct regions were shown to be chemically indistinct, the cooling rate during gel setting was found to play a large role; rapid setting of the gels reduces the fractionation effect, while slow cooling produced a completely homogeneous structure. In addition, by reheating only the soft region of the gel, a firm and soft fractionated gel could again be produced. Finally, it was observed that oleogels prepared with castor oil or mineral oil have the ability to remove or induce the gel separation, respectively. Taken together, these results indicate chemical interactions may incite the separation into two distinct phases, but the process also seems to be driven by the cooling conditions during gel setting. These findings lend insight into the EC-oleogel gelation process and should provide a stepping stone for future research into the manufacturing of these products.
The characterization of amyloid-beta peptide (Aβ) oligomer forms and structures is crucial to the advancement in the field of Alzheimer´s disease (AD). Here we report a critical evaluation of two methods used for this purpose, namely sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), extensively used in the field, and ion mobility coupled to electrospray ionization mass spectrometry (ESI-IM-MS), an emerging technique with great potential for oligomer characterization. To evaluate their performance, we first obtained pure cross-linked Aβ40 and Aβ42 oligomers of well-defined order. Analysis of these samples by SDS-PAGE revealed that SDS affects the oligomerization state of Aβ42 oligomers, thus providing flawed information on their order and distribution. In contrast, ESI-IM-MS provided accurate information, while also reported on the chemical nature and on the structure of the oligomers. Our findings have important implications as they challenge scientific paradigms in the AD field built upon SDS-PAGE characterization of Aβ oligomer samples.
A one-pot-two-step labeling of an oligonucleotide with an (18)F-ArBF3(-)(aryltrifluoroborate) radioprosthetic is reported herein. In order to characterize labeling in terms of radiochemistry, phosphorus-32 was also introduced to the 5'-terminus of the oligonucleotide via enzymatic phosphorylation. A pendant azide group was subsequently conjugated to the 5'-phosphate of the oligonucleotide. Copper(I) catalyzed [2+3] cycloaddition was undertaken to conjugate an alkyne-bearing(18)F-ArBF3(-) to the oligonucleotide. Following polyacrylamide gel electrophoresis, this doubly-labeled bioconjugate exhibited decay properties of both the phosphorus-32 and fluorine-18, that were confirmed by autoradiography at selected lengths of time, which in turn provided concrete evidence of successful conjugation. These results are corroborated by HPLC analysis of the labeled material. Taken together this work demonstrates viable use of (18)F-ArBF3(-) prosthetics for labeling oligonucleotides for use in PET imaging.
Polysaccharide hydrogels with tunable stiffness and provasculogenic properties via α-helix to β-sheet switch in secondary structure
- Proceedings of the National Academy of Sciences of the United States of America
- Published almost 7 years ago
Mechanical aspects of the cellular environment can influence cell function, and in this context hydrogels can serve as an instructive matrix. Here we report that physicochemical properties of hydrogels derived from polysaccharides (agarose, κ-carrageenan) having an α-helical backbone can be tailored by inducing a switch in the secondary structure from α-helix to β-sheet through carboxylation. This enables the gel modulus to be tuned over four orders of magnitude (G' 6 Pa-3.6 × 10(4) Pa) independently of polymer concentration and molecular weight. Using carboxylated agarose gels as a screening platform, we demonstrate that soft-carboxylated agarose provides a unique environment for the polarization of endothelial cells in the presence of soluble and bound signals, which notably does not occur in fibrin and collagen gels. Furthermore, endothelial cells organize into freestanding lumens over 100 μm in length. The finding that a biomaterial can modulate soluble and bound signals provides impetus for exploring mechanobiology paradigms in regenerative therapies.
In situ forming systems including thermoreversible hydrogels, which undergo sol-gel transition upon an increase in temperature have been used for various biomedical applications. Heparins are the standard of anticoagulation in the prophylaxis and treatment of deep vein thrombosis and pulmonary embolism. Both conditions require long-lasting treatment with frequent subcutaneous administrations of heparin. The objective of this study was to prepare and evaluate in situ forming gel systems designed by combination of two poloxamers (P407 and P188) and hydroxypropylmethylcellulose (HPMC) for prolonged release of heparin. Thermoreversible hydrogels were prepared with heparin solution and dispersion of heparin/chitosan nanocomplexes. Nanocomplexes formed by self-assembly of heparin with chitosan at various mass ratios were thoroughly characterized. A heparin/chitosan mass ratio of 1:1 with pH 5.20 was the most appropriate for preparation of small, homogenous and stable nanocomplexes (mean diameter 123 nm; polydispersity index 0.22 and zeta potential +35.5 mV). Thermoreversible hydrogels were evaluated by gelation temperature, viscosity over the temperature range 20 to 40°C, rate of hydrogel dissolution, and heparin release in vitro. The addition of P188 to P407 gel formulations resulted in an increase in gelation temperature, decrease in viscosity at room temperature and faster gel dissolution. The opposite effects were observed with formulations containing HPMC which demonstrated 18-day-long gel dissolution and complete heparin release in 9 days from gels containing heparin solution. Considerable prolongation of heparin release was achieved with incorporation of heparin/chitosan nanocomplexes into the gelling systems. It may be concluded that with poloxamer mixtures at specific concentrations, addition of HPMC and use of heparin/chitosan nanocomplexes dispersions, thermoreversible formulations for prolonged subcutaneous release of heparin are feasible.
Chitosan (CS) grafted with β-cyclodextrin (CD-g-CS) nanoparticles as a new carrier for poorly water-soluble drugs has been developed. The CD-g-CS polymer is readily synthesized from chitosan and mono-6-deoxy-6-(p-toluenesulfonyl)-β-cyclodextrin. Three different degrees of substitution (DS) of β-cyclodextrin (β-CD) on CD-g-CS (9.6%, 14.0% and 20.0%) are designed and evaluated by controlling the mole ratio of β-CD to chitosan. Then CD-g-CS nanoparticles are prepared by an ionic gelation method, with the controlled size of 202.0-589.0nm. Stable colloidal dispersion of the nanoparticales has been formed with the zeta potential of +23.0 to +43.0mV. In vitro stability test indicates that CD-g-CS nanoparticles are more stable in phosphate-buffered saline compared with CS nanoparticles. Finally, the poorly water-soluble drug, ketoprofen (KTP), is used as a model drug to evaluate the efficiency of the new drug delivery carrier. It is found that the encapsulation efficiency of KTP in the nanoparticles with 20% DS of CD is as high as 1.36-fold than that of CS nanoparticles. Moreover, notably KTP is released from the nanoparticles in a controlled-release manner and is pH-responsive on DS of CD. In summary, these results suggest that the CD-g-CS nanoparticles, as a general promising drug delivery system, can be used as a potential biodegradable nano-drug delivery system for controlled release of poorly water- soluble drugs with pH-responsive capability.