Samples were chemically stabilized by immersion in 2.5% glutar-
aldehyde in 0.05 sodiumcacodylate buffer, pH 7.4 for 2 h at 4 C and
were postfixed with 1.0% osmium tetroxide for 1 h at room tem-
perature. Samples were then dehydrated with series of 50%e70%
ethanol concentrations, and critical point dried with carbon diox-
ide, using a Polaron CPD 7501. Dried samples were frozen in liquid
nitrogen and fractured. Samples were mounted on a carbon ad-
hesive to the sample holders and were coated with gold. This
method allowed the visualization of whole and fracture alginate
microparticles, as well as details about the entrapped bacteria.