<title>Structural characterization of pharmaceutical fibers of alginate salts by confocal Raman spectral imaging</title>

Alginates are biological polymers extracted from brown algae and well known for their gelling and viscosifying properties and biodegradability. Calcium-alginate gels are used for spinning fibers which are particularly interesting as wound dressings since exhibit antihemorrhagic and healing effects. Alginates are copolymers of (alpha) -guluronate (G) and (beta) -D-mannuronate (M). The M/G ratio and the monomer sequence are determinant for their physico-chemical properties but are difficult to control since they are variable depending on algae family, region of origin and season of their harvesting. For rapid and non-destructive structural characterization of single fibers of alginates we used confocal Raman spectral imaging with a micron-scale spatial resolution. The characteristic Raman features were assigned as correlated with the M/G ratio. For the fibers with a determined average M/G ratio, the spectral images appeared rather homogeneous. On the other hand, the Raman relative intensities were found to be dependent on relative orientation of the fiber and laser polarization. We concluded that, with a micron-scale resolution, the fiber samples are well homogeneous and the polymer chains are highly ordered with domination of parallel stacking of the M-M blocks. The approach is actually being applied to study the alginate fibers at the tissular level.