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Abstract
This paper describes a study of the ion exchange properties of alginate fibers. The release of calcium ions into the contacting solution is measured by an atomic absorption spectrometer. The calcium alginate fibers are placed in aqueous solutions of Na^sub 2^SO^sub 4^; with the formation of CaSO^sub 4^, these fibers can be converted into a mixed calcium/sodium alginate. Results show that the sodium ions in the fibers help increase their gel swelling ratio. Calcium alginate fibers can also be treated with aqueous solutions of ZnCl^sub 2^, producing mixed calcium/zinc alginate fibers. When put in contact with solutions containing sodium ions, the zinc in the fibers can be released into the solution.
Alginate is a natural polymer composed of two monomers, i.e., α-L-guluronic acid and β-D-mannuronic acid. Figure 1 shows the chemical structures of these two monomers and the GG, MM, and MG sequences in the polymer chain.
Alginate exists widely in brown seaweeds, acting as a reinforcing element for cell walls. It is extensively used in the textile, food, and chemical industries for its gel forming abilities and as a thickening agent [7]. Alginate fibers were first reported in 1944 [10].
In the 1980s, alginate fibers began to be used in the manufacture of high tech wound dressings. These fibers have unique gel forming characteristics: upon contact with wound exudates, the sodium ions in the wound exudates can exchange with the calcium ions in the fibers, and as more and more sodium ions enter the fiber structure, the fibers absorb more and more water and form a gel [8]. The gelled structure helps keep a moist interface between the dressing and the wound surface, which can assist the healing process [2, 4, 6, 9, 12].
In this paper, we report on the ion-exchange properties of alginate fibers. We attempt to quantify the ion exchange process between alginate fibers and the contacting solutions, and we study the properties of the resulting fibrous gels.
Experimental
We used two kinds of commercially available alginate wound dressings in this study, Sorbsan(TM) from Maersk Medical and Algosteril(TM) from Laboratory Brothier. The Sorbsan sample is made of calcium alginate fibers in a loose nonwoven format, and the Algosteril sample is a needled felt of calcium alginate.
For the alginate...