CULTURE OF CHONDROCYTES IN ALGINATE GEL - VARIATIONS IN CONDITIONS OFGELATION INFLUENCE THE STRUCTURE OF THE ALGINATE GEL, AND THE ARRANGEMENT AND MORPHOLOGY OF PROLIFERATING CHONDROCYTES

Sodium alginate, which gels in the presence of calcium ions, is common ly used for culture of anchorage-independent cells, such as chondrocyt es. Normally, the gel appears microscopically homogeneous but, dependi ng on the conditions of gelation, it map contain a varying number of s mall channels that extend inward from the surface. We have examined th e influence of these channels on the morphology of cultured chondrocyt es entrapped in alginate beads. Growth-plate or articular chondrocytes cultured in alginate normally proliferate and farm rounded cell clust ers but, in alginate beads containing numerous channels, many chondroc ytes become aligned and form columns similar to those in the growth pl ate in vivo. As the pattern of cellular growth and morphology in algin ate is profoundly influenced by the presence of channels in the gel, f urther studies were conducted to determine what specific conditions of gelation affect their formation. The channels are especially numerous when both the alginate and the gelling solutions lack sodium ions or other monovalent cations. The channels are cavities in the gel formed by particulate blocking of the rapid diffusion of calcium ions from th e gelling solution into the boundary of the calcium alginate solution, and hence they extend inward from cells at the surface of the alginat e gel. An understanding of the conditions under which these channels d evelop makes it possible either to avoid their formation or, alternati vely, to enhance the number of channels in order to encourage prolifer ating cells to grow in radial columns, rather than in a less organized pattern characteristic of most culture systems.