Development of a morphogenetically active scaffold for three‐dimensional growth of bone cells: biosilica–alginate hydrogel for SaOS‐2 cell cultivation

Polymeric silica is formed from ortho ‐silicate during a sol–gel formation process, while biosilica is the product of an enzymatically driven bio‐polycondensation reaction. Both polymers have recently been described as a template that induces an increased expression of the genes encoding bone morphogenetic protein 2 ( BMP‐2 ) and osteoprotegerin in osteoblast‐related SaOS‐2 cells; simultaneously or subsequently the cells respond with enhanced hydroxyapatite formation. In order to assess whether the biocompatible polymeric silica/biosilica can serve as a morphogenetically active matrix suitable for three‐dimensional (3D) cell growth, or even for 3D cell bioprinting, SaOS‐2 cells were embedded into a Na‐alginate‐based hydrogel. Four different gelatinous hydrogel matrices were used for suspending SaOS‐2 cells: (a) the hydrogel alone; (b) the hydrogel with 400 μ m ortho ‐silicate; (c) the hydrogel supplemented with 400 μ m ortho ‐silicate and recombinant silicatein to allow biosilica synthesis to occur; and (d) the hydrogel with ortho ‐silicate and BSA. The SaOS‐2 cells showed an increased growth if silica/biosilica components were present in the hydrogel. Likewise intensified was the formation of hydroxyapatite nodules in the silica‐containing hydrogels. After an incubation period of 2 weeks, cells present in silica‐containing hydrogels showed a significantly higher expression of the genes encoding the cytokine BMP‐2, the major fibrillar structural protein collagen 1 and likewise of carbonic anhydrase. It is concluded that silica, and to a larger extent biosilica, retains its morphogenetic/osteogenic potential after addition to Na‐alginate‐based hydrogels. This property might qualify silica hydrogels to be also used as a matrix for 3D cell printing. Copyright © 2013 John Wiley & Sons, Ltd.