Application of Alginate Gels to the Study of Mammalian Development

Alginic acid is a linear polysaccharide of approx 240 kDa present in the cell walls of the fronds of various seaweeds, including the giant brown kelp (Macrocystis pyrifera ), horsetail kelp (Laminaria digitalis ), and sugar kelp (L. saccharina ). It is a hydrophilic colloidal polyuronic acid consisting of β-(1 →4)-d -mannuronic acid and α-(1→4)-l -guluronic acid residues with composition varying according to both the age and species of alga. It is capable of absorbing 200–300 times its weight of water in which it has only very limited solubility. The sodium salt of alginic acid, referred to as sodium alginate, is a cream-colored powder that dissolves in aqueous media to form a viscous colloidal solution. Upon addition of calcium, the saccharide chains of sodium alginate crosslink to form a stable gel through the displacement of two monovalent sodium ions by this divalent cation. Aside from its many industrial applications, including giving ice cream a creamy texture and preventing crystalization, it has also been employed widely both clinically in the dressing and repair of wounds, and in basic biomedical research. Encapsulation of cells or tissue for transplantation and achieving controlled release of drugs, growth factors, and other molecules are prominent among the ways it has been exploited in these latter contexts.