Effect of alginate composition and purity on alginate microspheres

Alginate is commonly used to microencapsulate islets in experiments with islet allografts and xenografts for the treatment of Type I diabetes. The purpose of the present study is to determine the effects of alginate composition and purity on the morphology and size of microspheres.

Microcapsules produced with the impure alginate types, medium-viscosity high-guluronic acid (IMVG), low-viscosity high-G (ILVG), low-viscosity high-mannuronic acid (ILVM) and medium-viscosity high-M (IMVM) were compared with one another and others generated with a highly purified LVM (HPLVM) alginate. Droplets of 1.5% alginate from an air-syringe pump were gelled in 1.1% CaCl2 solution. While leaving the alginate pressure and needle recess constant, the air-jacket pressure was varied between 9.5-10.5 PPSI to enhance stable microcapsule generation and different batches of microbeads were made from each alginate type.

The sizes of the high-guluronic acid alginate microbeads were consistently bigger than those of the corresponding high-mannuronic acid alginate beads at all air-jacket settings. At the optimal air-jacket pressure of 9.0 PPSI, the mean+SD diameter of the IMVG microbeads was 780 + 20 microm, while that of IMVM was 607 + 44 microm (p < 0.0001, n=30). Similarly, the mean ILVG microbead diameter was 816+28 microm compared to 656+26 microm for ILVM capsules (p<0.0001, n=30). Less polymorphism was found with the HPLVM microspheres than with the ILVM microbeads.

Highly purified high-mannuronic acid alginate will provide smaller, spherical microcapsules suitable for islet cell transplantation.