Mechanisms of external and internal gelation and their impact on the functions of alginate as a coat and delivery system

The mechanisms of internal and external gelation and their impact on alginate in its use as a coat and as a delivery system for drugs and living cells were investigated. Surface topography, thickness, mechanical and permeation properties, drug encapsulation efficiency and drug release profiles of alginate matrices were evaluated. Comparable extent of cross-linkages was produced by the two gelation methods as indicated by comparable Ca2+ contents between externally and internally cross-linked films but the distributions of cross-linkages were different. External cross-linking produced thinner films with smoother surface, greater matrix strength, stiffness and permeability than internally cross-linked films. Externally cross-linked micropellets were also capable of greater drug encapsulation efficiency and slower drug release rate. The differences in the properties observed were due to the different gelation mechanisms involved and the physical form of the matrix produced. External gelation is the preferred method in producing cross-linked alginate for coating and encapsulation purposes.