Kurt Ingar Draget

Alginic acid gels: the effect of alginate chemical composition and molecular weight

Abstract The effect of chemical composition and sequence and molecular weight of different alginate samples on the final properties of alginic acid gels have been studied. It is shown that alginates with a high content of guluronic acid blocks give gels of a considerably higher strength compared to alginates rich in mannuronate. A high fraction of homopolymeric blocks seems to favour the formation of junction zones. Compared to Ca-alginate gels, a more extended molecular weight dependent regime is observed. Kinetic measurements show an initially rapid (∼30 min) sol-gel transition with an apparent equilibrium in the dynamic storage moduli gradually obtained within 24–48 h, depending on the chemical composition of the alginate sample used. Mechanical spectroscopy reveals gels with a high degree of solid-like nature, with an increasing frequency dependence with decreasing molecular weight.

Chitosan cross-linked with Mo(VI) polyoxyanions : a new gelling system

A procedure for preparing homogeneous chitosan gels by in situ molybdate cross-linking is described. The gels are obtained by dispersing solid MoO3 in a buffered chitosan solution and the polymer is cross-linked by formation of heavily negatively charged molybdate polyoxyanions. The resulting ionic gels are very transparent, thermoirreversible and can be made at low polymer concentrations. Depending on the ionic strength, these gels are able to swell several times their original size in aqueous solutions. Estimates of the degree of cross-linking reveal a very open pore structure which is confirmed by electron micrographs of the gel.

Temperature dependence of the elastic modulus of alginate gels

Abstract The temperature dependence of the elastic modulus for alginate gels was studied using two different gel systems: covalently crosslinked Na-alginate gels and in-situ prepared Ca-alginate gels. The modulus of physically crosslinked gels showed a complex behaviour. The temperature coefficient of the modulus of covalently crosslink gels changed from positive for the lowest crosslinked gels to negative for the highest crosslinked gels. This suggests a change from rubberlike to enthalpy-driven elasticity with an increasing degree of crosslinking for these gel networks.

Investigation of Physico-Chemical Properties of Gelatin Matrices in Correlation with Dissolution Studies

Gelatin is a versatile biopolymer obtained from a partial hydrolysis of collagen. Gelatin is commonly used in formulation of pharmaceuticals and nutraceuticals, encapsulating the active ingredient. For these applications the dissolution profile of the matrix in the gastrointestinal tract (GIT) is of crucial importance. The dissolution of a gelatin matrix in the GIT may be seen as a two-step procedure: gel-sol transition of the gelatin network, followed by diffusion of the peptide strands from the concentrated matrix to the bulk liquid. Thus, it is clear that the melting temperature is important in gelatin gel dissolution investigations. Depending on the raw material (bovine or porcine sources) and extraction conditions, gelatins with wide variations in molecular size distribution – and therefore varying rheological properties/melting temperatures – may be obtained. Dissolution studies are generally time consuming and therefore it would be advantageous to predict the dissolution profile without performing in vitro measurements. The scope of this work was to evaluate if any of the physico-chemical properties of the gelatin matrices can be used to predict the dissolution profiles of the gelatin gels.

Chapter 7:Alginates: Existing and Potential Biotechnological and Medical Applications

The present chapter on alginates in biotechnology and medicine comprises a description of traditional uses where alginates have been used as devices in e.g. wound dressings, as well as an in-depth introduction to possible future applications. The latter area is based on new scientific information on the immunostimulating properties of certain alginate sequences, as well as on the popularity gained by the alginate as immobilization matrix for cells. The latter opens up the use of alginate encapsulated cells for specific cell transplantation provided that the properties of the capsules are properly understood and controlled.

Gelatins – Physicochemical Properties, Source Dependence and Applications

With an estimated annual world-wide production of more than 300xa0000 metric tonnes, gelatin is one of the most abundant commercial biopolymers, and also one of the most versatile with several hundred different applications, from technical to pharmaceutical. Production of gelatin is based on a partial hydrolysis of the mother structural molecule collagen. Mammalian (homoeothermic) sources of gelatin have basically identical amino acid composition and physical properties, although gelatins (and collagens) from poikilothermic animals may vary considerably.