Alginate−Oligochitosan Microcapsules: A Mechanistic Study Relating Membrane and Capsule Properties to Reaction Conditions

A new generation of microcapsules was prepared by utilizing a polyelectrolyte complexation reaction between two oppositely charged polysaccharides, one of which is oligomeric. This capsule combines extremely high deformability (>80%) and elasticity with permeability control and can be applied in various bioencapsulation technologies. The relative number of interchain ionic bonds, which determine the cross-linking density and membrane properties, can be controlled by either pH or ionic strength. Specific binding with respect to the molar mass of chitosan occurs during capsule formation. With increasing ionic strength and pH, a shift toward higher molar masses involved in membrane formation was observed. The preparation of capsules under physiological conditions (pH 7.0, 0.9% NaCl) was demonstrated, overcoming the limitation of all other microcapsules based on chitosan which must be prepared at pH below 6.5. It has been shown that the parameters such as reaction time, chitosan molar mass, and concentration primarily influence the mechanical properties, whereas alginate concentration effects both mechanical and porosity characteristic of the capsule membrane.