Calcium alginate dressings--I. Physico-chemical characterization and effect of sterilization.

In order to analyze the alginate components of alginate dressings and the fractions which are released when the dressing is in contact with model biological fluids, the use of various analytical methods was considered. The first step was the conversion of a calcium alginate batch to pure sodium alginate. The recovery of the latter from either insoluble or soluble mixed sodium/calcium alginates was performed by complexation of calcium ions with sodium citrate followed by ultrafiltration. Comparisons were made between sugar analysis, 1H NMR and circular dichroism (CD) data to determinate the contents in guluronic and mannuronic acids of sodium alginate chains. It was shown that CD measurements afford a rapid and nondestructive method for determination of %G when one takes the ratio theta200/theta220 into account. Fractionation of crude alginate (generally ranging from 30 to 70% G) was achieved by the triangle dissolution/precipitation method in order to increase the range of alginate in sugar composition. The various validated procedures were applied to investigate the effects of irradiation sterilization on alginate dressings. It was shown that sugar composition is retained whereas molecular weight decreased dramatically due to chain scission.

Hydrolytic degradation of devices based on poly(DL-lactic acid) size-dependence.

The hydrolytic degradation of aliphatic polyesters derived from lactic and glycolic acids (PLA/GA polymers) has been previously shown to proceed heterogeneously in the case of large size devices, the rate of degradation being greater inside than at the surface. A qualitative model based on diffusion-reaction phenomena was proposed which accounts for the formation of the more stable outer layer. However, this model also suggested that devices with dimensions smaller than the thickness of the outer layer should degrade less rapidly than larger ones. In an attempt to check this hypothesis, 15 x 10 x 2 mm compression moulded plates, millimetric beads and submillimetric microspheres and cast films, derived from the same batch of poly (DL-lactic acid) polymer were allowed to age comparatively in isoosmolar 0.13 M phosphate buffer, pH 7.4, at 37 degrees C. Ageing of the various devices was monitored by measuring water absorption, weight loss, L-lactic acid formation, pH and molar mass changes. As expected, large size plates and millimetric beads degraded heterogeneously and much faster than homogeneously degraded submillimetric films and particles.