pH-dependent release of alginate beads coated with polylysine

Alginate beads were coated with basic proteinoid, polylysine (PL), by taking advantage of an electrostatic interaction in order to obtain a controlled release in response to change in pH. When the amount of PL adsorbed on the surface of alginate beads was 1.77 g PL/1.0 g alginate, the loading efficiency of FITC-dextran was about 82%. In the range of pH 5.0–9.0, the degrees of release in 240 min were relatively high, around 70%, and there was no significant effect of pH on the degree of release. At pH 3.5 and pH 4.0, the releases were markedly suppressed and the degrees of release were about 33% and 50%, respectively. At lower pHs, the amino groups of PL will be more protonated, so the coating layer would become compact due to a strong electrostatic interaction. In fact, the degrees of swelling of alginate beads at pH 3.5 and pH 4.0 were lower than the values at the other pHs.