The characterisation of alginate systems for biomedical applications
This research project focused on a range of polysaccharides, including sodium alginates (with varying mannuronic (M)/guluronic (G) acid ratio), pectin and sodium carboxymethylcellulose (CMC), for wound dressing applications. The samples were prepared as mixed salts such as sodium/calcium salts as Ca2+ ions are known to promote faster healing. The aims of this research were: 1- to provide a greater insight into the nature of binding between various ions (NaT, Ca2+ as well as Zn2+ and Ag+) and the polysaccharide molecules. Interactions between alginate/pectin and alginate/CMC molecules were also studied. This was achieved using a range of analytical techniques such as Fourier transform infrared spectroscopy, Raman spectroscopy and neutron spectroscopy, thermogravimetric analysis, microprobe analysis, X-ray diffraction and atomic absorption spectroscopy. It was found that sodium ions were bound to the carboxyl groups of the alginate molecules, whilst calcium ions attached themselves onto COO- as well as onto the alginate backbone, leading to crosslinked structures. Appearance of OH ... -OOC to the detriment of OH ... OH bonding was also observed. Addition of zinc ions involved greater constraint in the alginate network and the silver ions were believed to produce insoluble alginate salts, due to their larger ionic radius; furthermore hydroxyl-hydroxyl interactions in the silver alginate were rather between the polymer molecules than with the water. The addition of pectin to alginate led to partial binding between the two polysaccharides via hydrogen bonds. By contrast, carboxymethylcellulose molecules were found to act as independent entities in contact with alginate, and therefore suggested incompatibility. 2- to determine the performance of sodium/calcium alginate systems as well as Na/Ca alginate/pectin and Na/Ca alginate/CMC systems, in order to improve properties such as absorbency, gel strength and calcium release (to assess the haemocompatibility) in a simulated serum solution. A greater calcium and guluronic acid content was found to improve the gel strength of alginate samples, but decrease the swelling ability. Calcium release was favoured with a low G and a high calcium content. Addition of a second polysaccharide enhanced these gel properties. For example, the gel strength could be significantly increased with a 25 % pectin addition, while addition of CMC up to 50 % increased both the swelling and the calcium release. 3- to develop a new model of the ion release process for a polysaccharide system brought into contact with a simulated serum solution. It was based on a "hoppingtrapping" mechanism for the calcium ions, whereby different release rates are due to different affinities with the polysaccharide blocks.