Factors influencing the mechanical stability of alginate beads applicable for immunoisolation of mammalian cells

• Mechanical stability of alginate capsules dominates the success encapsulated cells.
• Mechanical stability is dependent on the force and time required for compression.
• Force determines the strength, and time determines the elasticity of microcapsules.

Transplantation of microencapsulated cells has been proposed as a cure for many types of endocrine disorders. Alginate-based microcapsules have been used in many of the feasibility studied addressing cure of the endocrine disorders, and different cancer types. Despite years of intensive research it is still not completely understood which factors have to be controlled and documented for achieving adequate mechanical stability. Here we studied the strength and elasticity of microcapsules of different composition with and without cell load. We compared strength (force) versus elasticity (time) required to compress individual microcapsule to 60% deformation. It is demonstrated that the alginate viscosity, the size of the beads, the alginate type, the gelling time, the storage solution and the cell load are dominant factors in determining the final strength of alginate-based microcapsules while the type of gelling ion, the polyamino acid incubation time, the type of polyamino acid and the culturing time determines the elasticity of the alginate-based microcapsules.Our data underpin the essence of documenting the above mentioned factors in studies on encapsulated cells as mechanical stability is an essential factor in the success and failure of encapsulated grafts.

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