Emulsan-alginate microspheres

Emulsan-Alginate Microspheres as a New Vehicle for Protein Delivery... 

Gelation and characterization of alginate microspheres mixed with other polymers are well described previously in the literature (7,2). However, no references for the interaction of emulsan and other polymers were found. Comparative optical microscopy of alginate and emulsan-alginate microspheres showed different surface morphologies (Figure 3). The results were confirmed by SEM (Figure 4). 

Figure 5. Release of blue dextran from Alginate ( ), and emulsan-alginate microspheres (O) incubated at 200 rpm at 37 C.

Figure 7. Effect of emulsan concentration on BSA adsorption by emulsan-alginate microspheres incubated at 37°C for 25 minutes.

Table I. Enzymatic release of azo-BSA from emulsan-alginate microspheres incubated 20 minutes at 37 C.

Another question to be addressed is the status of the protein structure after release from the microspheres. Secondary structure cmi provide a qualitative estimate of function and reflects to some extent biological activity. Protein inactivation by unfolding is one of the major obstacles in drug delivery. For this purpose, analysis of BSA structure by circular dichroism before and after the release from the microspheres was assessed. After release from the emulsan-alginate microspheres, BSA showed some loss in helix content based on the decrease of negative elipcticity at 222 run typical of a-helix (Figure 10). 

In the experimental conditions utilized, native BSA dissolved in phosphate buffer at pH 7.4 had 56.0 1.4% a-helix content and 43.9 3.2% for the desorbed-filtered BSA without any other excipient. In previous work with poly(lactic-co-glycolic acid) microspheres the BSA a-helix content was 21% without any excipient and the a-helix value reported was 39.0% in the presence of additives 13). These values are between 27 to 60 % loss of the total a-helix content for PLGA microspheres compared to roughly 22% a-helix loss using the emulsan-alginate microspheres. 

Microscopy studies revealed the presence of emulsan likely on the surface of the emulsan-alginate microspheres. The presence of emulsan on the microsphere surface increased the stability of the gels in comparison to alginate alone based on the release of blue dextran, the amount of protein adsorbed and the delayed time of about two fold for the release of the carbohydrate to... 

Figure 10. Circular dichroism spectra ofBSA after adsorption (continuous line), and before release (dashed line) from emulsan-alginate microspheres.

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