93 research outputs found
Reentrant phase diagram and pH effects in cross-linked gelatin gels
Experimental results have shown that the kinetics of bond formation in
chemical crosslinking of gelatin solutions is strongly affected not only by
gelatin and reactant concentrations but also by the solution pH. We present an
extended numerical investigation of the phase diagram and of the kinetics of
bond formation as a function of the pH, via Monte Carlo simulations of a
lattice model for gelatin chains and reactant agent in solution. We find a
reentrant phase diagram, namely gelation can be hindered either by loop
formation, at low reactant concentrations, or by saturation of active sites of
the chains via formation of single bonds with crosslinkers, at high reactant
concentrations. The ratio of the characteristic times for the formation of the
first and of the second bond between the crosslinker and an active site of a
chain is found to depend on the reactant reactivity, in good agreement with
experimental data.Comment: 8 pages, 8 figure
Kinetics of bond formation in crosslinked gelatin gels
In chemical crosslinking of gelatin solutions, two different time scales
affect the kinetics of the gel formation in the experiments. We complement the
experimental study with Monte Carlo numerical simulations of a lattice model.
This approach shows that the two characteristic time scales are related to the
formation of single bonds crosslinker-chain and of bridges between chains. In
particular their ratio turns out to control the kinetics of the gel formation.
We discuss the effect of the concentration of chains. Finally our results
suggest that, by varying the probability of forming bridges as an independent
parameter, one can finely tune the kinetics of the gelation via the ratio of
the two characteristic times.Comment: 8 pages, 9 figures, revised versio
Mechanically induced helix-coil transition in biopolymer networks
The quasi-equilibrium evolution of the helical fraction occurring in a
biopolymer network (gelatin gel) under an applied stress has been investigated
by observing modulation in its optical activity. Its variation with the imposed
chain extension is distinctly non-monotonic and corresponds to the transition
of initially coiled strands to induced left-handed helices. The experimental
results are in qualitative agreement with theoretical predictions of helices
induced on chain extension. This new effect of mechanically stimulated
helix-coil transition has been studied further as a function of the elastic
properties of the polymer network: crosslink density and network aging
Controlled antibody release from gelatin for on-chip sample preparation
A practical way to realize on-chip sample preparation for point-of-care diagnostics is to store the required reagents on a microfluidic device and release them in a controlled manner upon contact with the sample. For the development of such diagnostic devices, a fundamental understanding of the release kinetics of reagents from suitable materials in microfluidic chips is therefore essential. Here, we study the release kinetics of fluorophore-conjugated antibodies from (sub-) µm thick gelatin layers and several ways to control the release time. The observed antibody release is well-described by a diffusion model. Release times ranging from ~20 s to ~650 s were determined for layers with thicknesses (in the dry state) between 0.25 µm and 1.5 µm, corresponding to a diffusivity of 0.65 µm2/s (in the swollen state) for our standard layer preparation conditions. By modifying the preparation conditions, we can influence the properties of gelatin to realize faster or slower release. Faster drying at increased temperatures leads to shorter release times, whereas slower drying at increased humidity yields slower release. As expected in a diffusive process, the release time increases with the size of the antibody. Moreover, the ionic strength of the release medium has a significant impact on the release kinetics. Applying these findings to cell counting chambers with on-chip sample preparation, we can tune the release to control the antibody distribution after inflow of blood in order to achieve homogeneous cell staining
Effects of sulfate starvation on agar polysaccharides of Gracilaria species (Gracilariaceae, Rhodophyta) from Morib, Malaysia
The effects of sulfate starvation on the agar characteristics of Gracilaria species was investigated by culturing two red algae from Morib, Malaysia, Gracilaria changii and Gracilaria salicornia in sulfate-free artificial seawater for 5 days. The seaweed samples were collected in October 2012 and March 2013, periods which have significant variation in the amount of rainfall. The agar yields were shown to be independent of sulfate availability, with only 0.60–1.20 % increment in treated G. changii and 0.31–1.40 % increment in treated G. salicornia while their gel strengths did not increase significantly (approximately 5–7 %) after sulfate starvation for both species. The gelling and melting temperatures did not vary between control and treated samples from both species, except for the treated G. changii collected in March 2013. The gel syneresis index of G. salicornia collected in March 2013 increased significantly after sulfate deprivation. Sulfate starvation introduced some variations in the content of 3, 6-anhydrogalactose and total sulfate esters, but the changes did not have a pronounced effect on the physical properties of agar
New insight into kinetics behavor of the structural formation process in Agar gelation
A time-resolved experimental study on the kinetics and relaxation of the
structural formation process in gelling Agar-water solutions was carried out
using our custom-built torsion resonator. The study was based on measurements
of three naturally cooled solutions with agar concentrations of 0.75%, 1.0% and
2.0% w/w. It was found that the natural-cooling agar gelation process could be
divided into three stages, sol stage (Stage I), gelation zone (Stage II) and
gel stage (Stage III), based on the time/temperature evolutions of the
structural development rate (SDR). An interesting fluctuant decaying behavior
of SDR was observed in Stage II and III, indicative of a sum of multiple
relaxation processes and well described by a multiple-order Gaussisn-like
equation: . More interestingly, the temperature dependences of the fitted
values of Wn in Stage II and Stage III were found to follow the different
Arrhenius laws, with different activation energies of EaII= 39-74 KJ/mol and
EaIII~7.0 KJ/mol. The two different Arrhenius-like behaviors respectively
suggest that dispersions in Stage II be attributed to the relaxation of the
self-assembly of agar molecules or the growth of junction zones en route to
gelation, in which the formation or fission of hydrogen bonding interactions
plays an important role; and that dispersions in Stage III be attributed to the
relaxation dynamics of water released from various size domains close to the
domain of the viscous flow of water during the syneresis process.Comment: 24 pages, 4 figures, 1 tabl
Recent approaches in designing bioadhesive materials inspired by mussel adhesive protein
Marine mussels secret protein-based adhesives, which enable them to anchor to various surfaces in a saline, intertidal zone. Mussel foot proteins (Mfps) contain a large abundance of a unique, catecholic amino acid, Dopa, in their protein sequences. Catechol offers robust and durable adhe-sion to various substrate surfaces and contributes to the curing of the adhesive plaques. In this article, we review the unique features and the key functionalities of Mfps, catechol chemistry, and strategies for preparing catechol-functionalized poly- mers. Specifically, we reviewed recent findings on the contributions of various features of Mfps on interfacial binding, which include coacervate formation, surface drying properties, control of the oxidation state of catechol, among other features. We also summarized recent developments in designing advanced biomimetic materials including coacervate-forming adhesives, mechanically improved nano- and micro-composite adhesive hydrogels, as well as smart and self-healing materials. Finally, we review the applications of catechol-functionalized materials for the use as biomedical adhesives, therapeutic applications, and antifouling coatings
Physical gelation of crystallizing metallocene and Ziegler-Natta ethylene–hexene copolymers
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