Alginates in Tissue Engineering

Alginate is a polysaccharide derived from brown seaweed, which has the unique property of being able to form a gel in the presence of certain divalent cations (e.g., calcium, strontium, or barium). Alginate has been of commercial interest in the food industry since the 1930s, when its properties as an emulsifier, thickener, and stabilizer were recognized. Alginate has also long been used for biomedical purposes, particularly in the manufacture of surgical dressings for exuding wounds (1 ). However, the explosive increase in medical applications for alginate, began with the recognition of its use as a scaffold for the encapsulation and immunoprotection of transplanted cells. The encapsulation of non-autologous islet cells in alginate for the treatment of diabetes is based on the concept that nutrients can diffuse in and insulin out of the alginate construct without triggering an immune response (2 –3 ). Similarly, alginate has been used to immunoprotect recombinant cells delivering tumor-suppressing agents (4 –5 ) and growth hormone (6 ). Stable cultures in alginate beads have been achieved with a number of cell types including chondrocytes, bone-marrow stromal cells, islets, myoblasts, fibroblasts, Schwann cells, kidney cells, epithelial cells, and hepatocytes. For orthopedic purposes, encapsulated bone-marrow stromal cells and chondrocytes have been proposed for the healing bone and cartilage defects (7 –9 ). As a bulking agent, alginate has gained attention as a space-filling material for treating pediatric urinary reflex (10 –12 ).