Calcium alginate beads coated with chitosan: Effect of the structure of encapsulated materials on their release

Bovine serum albumin, human haemoglobin and dextran (with different molecular weights) were encapsulated in calcium alginate beads coated with chitosan. Their release from these modified alginate beads was studied to determine what parameters related to the encapsulated materials govern their release during bead formation and storage. By comparing release of albumin (BSA) and haemoglobin (Hb) that have about the same molecular weight (67000 for BSA and 64500 for Hb), it was found that pH played an important role during both bead formation and storage. pH influences the degree of ionisation of proteins and thus the interactions between proteins and alginate; it also has an influence on the Ca²⁺-alginate and alginate-chitosan interactions. With neutral molecules such as dextran, release is directly connected to the chain molecular weights, although the flexibility of the encapsulated molecules favours their diffusion through the bead alginate-Ca²⁺ core and through the polyelectrolyte chitosan-alginate membrane.