Alginate/silica composite hydrogel as a potential morphogenetically active scaffold for three-dimensional tissue engineering

Pursuing our aim to develop a biomimetic synthetic scaffold suitable for tissue engineering, we embedded bone cells, osteoblast-related SaOS-2 cells and osteoclast-like RAW 264.7 cells, into beads, formed of a Na-alginate-based or a silica-containing Na-alginate-based hydrogel matrix. The beads were incubated either separately (only one cell line in a culture dish) or co-incubated (SaOS-2-containing beads and RAW 264.7 beads). The alginate and alginate/silica hydrogel matrices were found not to impair the viability of the encapsulated cells. In these matrices the SaOS-2 cells retain their capacity to synthesize hydroxyapatite crystallites. The mechanical properties, including surface roughness and hardness, of the hydrogel were determined. If silica is included in the hydrogel matrix, the encapsulated SaOS-2 cells were found to increasingly express the gene encoding for osteoprotegerin in co-cultivation experiments with RAW 264.7 cell beads, suggesting that under the applied conditions the differentiation capacity of the RAW 264.7 cells is impaired. In continuation it was found that under these conditions (SaOS-2 cells cultured together with RAW 264.7 cells) the RAW 264.7 cells show a reduced capacity to express the gene for tartrate-resistant acid phosphatase. It is concluded that the applied bead-encapsulation of bone cells is a useful technique to produce bioactive programmable hydrogels.