Rheological Study on Gelatin Gelation

Crosslinked gelatin matrices: release of a random coil macromolecular solute

The purpose of this investigation was to evaluate the effect of matrix crosslinking and solute size on release of a random coil macromolecular solute from crosslinked gelatin matrices. Gelatin hydrogel matrices crosslinked with different molar ratios of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC):epsilon-amino groups on gelatin (1:1, 4:1, and 10:1) were prepared containing dextran of molecular weights 12, 20, and 77 kDa, and hydrodynamic diameters 54, 74, and 133 A, respectively. The extent of matrix crosslinking was determined quantitatively and used to calculate the molecular weight between crosslinks (Mc). The Mc parameter and equilibrium swelling ratio (Qm) were used to calculate an estimated matrix mesh size (xi). The in vitro release of incorporated dextran was evaluated at 37 degrees C in PBS at pH 7.4 for approximately 80 h. The one-, four- and 10-fold molar ratios of crosslinking agent EDC yielded 24, 41, and 78% of gelatin matrix crosslinking, respectively. The calculated average matrix mesh size ranged from 338 to 90 A. The effect of matrix crosslinking varied with solute size, from retarding diffusional release of the dextran to completely entrapping it inside the crosslinked matrices. These results support the threshold concept of solute size relative to matrix mesh size for release of a flexible, random coil macromolecular solute from a hydrogel.

Physical properties of shark gelatin compared with pig gelatin

Physical properties of shark gelatin were examined during gel formation and postgelation in comparison with pig gelatin. Samples with various concentrations and pH values were evaluated by breaking strength, dynamic viscoelasticity, and dynamic light scattering. Sol-gel and gel-sol transition temperatures for shark gelatin were remarkably lower than those for pig gelatin. Shark gelatin gel shows a narrower pH range to form a stable gel compared with pig gelatin. Melting enthalpy of shark gelatin gel was greater than that of pig gelatin gel, and G' of shark gelatin gel changed more extensively with rising temperature in comparison with pig gelatin gel. It is concluded that shark gelatin has different characteristics from pig gelatin not only for gel characteristics but also for the solution property.

Swelling behavior and mechanical properties of chemically cross-linked gelatin gels for biomedical use

Cross-linked gelatin gels are used as biomaterials in living tissues, either as bioadhesives or as devices for sustained drug release. As these applications involve surgical insertion of gels, the effect of cross-linking on mechanical properties is relevant. The effect of cross-linking on the gel water uptake is also relevant for the kinetics of drug release. Equally important is the influence of initial amounts of gelatin in the gelling solutions. We investigated the influence of cross-linking (with glutaraldehyde) and of gelatin content upon the equilibrium water content and tensile properties of resulting gels. A range of gels was prepared with gelatin contents of 10 to 40% wt, and cross-linked with 2.5 to 50% wt glutaraldehyde. The increase in gelatin content and degree of cross-linking reduced the water uptake of gels from about 60-65% wt to about 50% wt. The tensile characteristics were differentially affected. While the increase of cross-linking induced a decrease of toughness and elasticity and an increase of stiffness, it did not affect the ultimate strength of gels. On the contrary, the increase of gelatin content induced a definite increase of the ultimate strength but did not significantly affect the other properties.