Hydroxyapatite (HA) is a well‐established graft material used in bone repair. Silicon‐substituted hydroxyapatite (SA; 0.8 wt% Si) has shown greater bone ingrowth and bone coverage than phase pure HA. To assess the effect of microporosity on sensitivity of cell attachment to surface physiochemistry, microporous SA and HA discs, and control Thermanox (TMX) discs were incubated with osteoblast‐like cells (5 × 10⁴ HOS‐TE85 cells) under differing tissue culture conditions. To investigate early cellular attachment, organization, and differentiation, cells were also stained for integrin–α₅ β₁, actin, and runt‐related transcription factor (RUNX‐2), respectively, after incubation on HA, SA, and TMX discs for 3 days. No significant differences emerged between HA, SA, and TMX discs in mean numbers of cells attached in serum free medium (SFM) over 90 min incubation. In contrast, significantly more cells were attached to SA than HA after 180 min incubation in complete medium (C‐MEM) containing fetal calf serum (p < 0.05). Cell attachment to SA and HA discs pre‐conditioned in SFM supplemented with fibronectin (FN) was lower than discs pre‐conditioned in C‐MEM, suggesting sensitivity of an active FN conformation to the presence of co‐adsorbates. Confocal microscopy demonstrated significantly more co‐localization of integrin α₅ β₁ and actin on SA than HA. Translocalization of RUNX‐2 to the nucleus was stronger in cells incubated on SA. Microporosity did not diminish the effect of surface physiochemistry on cell adhesion, and enhanced cell attachment for SA appears to be mediated by differences in the quality of adsorbed protein rather than via direct effects of substrate chemistry.

Silicate‐Substitution, Early Development, Human Osteoblast‐Like