No abstract

The functionalization of chitosan with carboxymethyl groups allows zwitterionic or anionic chitosan derivatives to be obtained as a function of the degree of substitution. Here, we show that polyelectrolyte multilayers of chitosan and carboxymethylchitosan can be assembled by “dipping” or “spraying” to form strongly hydrated films in which both the polyanion and polycation possess the same polymer backbone (“matched chemistries”). Such films grow rapidly to fairly large thickness in very few assembly steps, especially in the case of “matched” charge densities, and atomic force microscopy reveals the formation of surface patterns that are dependent on the deposition conditions and on the number of layers. Interestingly, the influence of the molar masses of the polyelectrolyte pairs on the complex formation is somewhat counterintuitive, the stronger complexation occurring between polyanions and polycations of different (“non-matching”) lengths.

The immobilization of the glucose/mannose-binding lectin from Concanavalia ensiformis seeds (ConA) onto a monolayer made of a galactomannan extracted from Leucaena leucocephala seeds (GML), which was adsorbed onto - amino-terminated surfaces, was investigated by means of ellipsometry and atomic force microscopy. The mean thickness of GML monolayer, which polysaccharide consists of linear 1→4-linked β-D-mannopyranosil units partially substituted at C-6 by α-D-galactopyranosyl units, amounted to (1.5±0.2) nm. ConA molecules adsorbed onto GML surfaces forming (2.0±0.5) nm thick layers. However, in the presence of mannose the adsorption failed, indicating that ConA binding sites were blocked by mannose and were no longer available for mannose units present in the GML backbone. The GML film was also used as support for the adsorption of three serotypes of dengue virus particles (DENV-1, DENV-2 and DENV-3), where DENV-2 formed the thickest film (4±2) nm. The adsorbed layer of DENV-2 onto ConA-covered GML surfaces presented mean thickness values similar to that determined for DENV-2 onto bare GML surfaces. The addition of free mannose units prevented DENV-2 adsorption onto ConA-covered GML films by ~50%, suggesting competition between virus and mannose for ConA binding sites. This finding suggests that if ConA is also adsorbed to GML surface and its binding site is blocked by free mannose, virus particles are able to recognized GML mannose unities substituted by galactose. Interactions between polysaccharides thin films, proteins, and viruses are of great relevance since they can provide basis for the development of biotechnological devices. These results indicate that GML is a potential polysaccharide for biomaterials development, as those could involve interactions between ConA in immune system and viruses.

Summary: In this work, the rheological properties of the partial replacement of sodium alginate (AL) by galactomannan extracted from the seeds of L. leucocephala (GML), with or without the presence of calcium ions, were evaluated. The viscoelastic behaviour of polysaccharide blends at 15 gÁL À1 showed an increase in viscosity when AL was 50% (w/w) replaced by GML. The addition of calcium ions (45 mmol) increased the apparent viscosity of the blend more than 17 times, at a shear rate of 4 s À1 .Micrographs of [GML/AL/ALB] Ca 2þ crosslinked particles obtained by a spraying process were analysed by AFM and revealed spherical forms with diameters in the range of 518 nm, instead of 58.4 nm in the system without albumin. The results of ALB encapsulation (97% w/w) showed that the synergistic mixture GML/AL could be used, in the future, as a new carrier system.