Osteoblasts protein-mediated cell adhesion

Fig. 8. Schematic representation of protein-mediated cell adhesion on biomaterial surfaces. Biomaterial surface properties (such as hydrophilicity/hydrophobicity, topography, energy, and charge) affect subsequent interactions of adsorbed proteins these interactions include but are not limited to adsorbed protein type, concentration, and conformation. Changes in protein-surface interactions may alter accessibility of adhesive domains (such as the peptide sequence arginine-glycine-aspartic acid) to cells (such as osteoblasts, fibroblasts, or endothelial cells) and thus modulate cellular adhesion. (Adapted and redrawn from Schakenraad, 1996.)...

Kennedy et al. found similar osteoblast adhesion along the entire wettability gradient, although more pronounced proliferation was observed at the hydrophobic end. Finally, Lee et al. reported increased pheochromocytoma cell (PC-12) adhesion to an intermediate surface wettability, whereas neurite growth was enhanced at the hydrophilic end. The results of all these studies, however, are influenced by the presence of proteins and other components in the cell media, which may pre-adsorb onto the wettability gradient and mediate cell adhesion, especially in those cases where enhanced cell adhesion corresponds to an enhanced protein adsorption. ... 

Bone sialoprotein, osteopontin, and osteocalcin are synthesized and deposited as the mineralization process begins and mineral nodules form (Stein and Lian, 1993). Bone sialoprotein contains the cell-adhesive arginine-glycine-aspartic acid peptide sequence and may thus mediate osteoblast adhesion on the extracellular matrix (Gehron-Robey, 1989). Osteocalcin, a calcium-binding protein, interacts with hydroxyapatite and is thought to mediate coupling of bone resorption (by osteoclasts) and bone formation (by osteoblasts and/or osteocytes) (Stein and Lian, 1993). 

Select proteins that mediate adhesion of specific anchorage-dependent cells (such as osteoblasts, fibroblasts, and endothelial cells) on substrate surfaces have been identified (Underwood and Bennett, 1989 Thomas et al., 1997 Ayad et al, 1994). For example, adsorption of fibronectin and vitronectin on tissue-culture polystryene subsequently enhanced osteoblast, fibroblast, and endothelial cell adhesion (Underwood and Bennett, 1989). More importantly, fibronectin and vitronectin adsorption on borosilicate glass, in a competitive environment, maximized fibroblast and osteoblast adhesion, respectively (Thomas et al., 1997). Ayad et al. (1994) reported that enhanced adsorption of laminin on tissue-culture polystyrene promoted subsequent endothelial cell adhesion. These studies provided evidence that adsorption of specific protein(s) can, subsequently, control select cell adhesion on material surfaces. 

Investigations of the underlying mechanism(s) revealed that the concentration, conformation, and bioactivity of vitronectin (a protein contained in serum that is known to mediate osteoblast adhesion ((Thomas et al., 1997) see the section Vitronectin ) was responsible for the select, enhanced adhesion (a crucial prerequisite for subsequent, anchorage-dependent-cell function) of osteoblasts on these novel nanoceramic formulations. Specifically, of the proteins (such as albumin, laminin, fibronectin, collagen, and vitronectin) tested, vitronectin adsorbed in the highest concentration on nanophase alumina after 4 hr moreover, competitive adsorption of vitronectin was 10% greater on nanophase compared to conventional alumina (Webster et al.,... 

---