Osteoblasts adhesion

Kessler and coworkers immobilized RGD peptides to a PMMA surface via a spacer incorporating an azobenzene unit [ 187]. The molecules were arranged in such a way that the RGD motifs were accessible to cells approaching the surface when the azo unit was in the E-form, and were hidden from the cells when the azo unit was in the Z-form. This enabled the reversible modulation of mouse osteoblast adhesion by irradiation with visible or UV light. However, the difference between on and off states is not very pronounced. Possibly, the accessibility of the RGD motif is not... 

Taubenberger A, Woodruff MA, Bai H F et al (2010) The effect of unlocking RGD-motifs in collagen I on pre-osteoblast adhesion and differentiation. Biomaterials 31 2827-2835... 

Kantlehner M, Schaffner P, Finsinger D et al (2000) Surface coating with cyclic RGD peptides stimulates osteoblast adhesion and proliferation as well as bone formation. Chembiochem... 

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. 

Reports found in the literature suggested that the peptide sequence lysine-arginine-serine-arginine (KRSR) selectively enhanced osteoblast adhesion by possibly binding to heparan sulfate on the membranes of osteoblasts (Dee et al, 1996). Compared to unmodified glass, Dee (1996) demonstrated enhanced osteoblast, fibroblast, and endothelial cell adhesion... 

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.,... 

Fig. 11. Unfolding of vitronectin exposes epitopes for osteoblast adhesion on nanophase ceramics. Schematic representation (not in scale) of a possible mechanism for enhanced osteoblast adhesion on (a) nanophase, compared to (b) conventional, ceramics, which involves unfolding of the vitronectin macromolecule to expose select cell-adhesive epitopes (such as arginine-glycine-aspartic acid) for osteoblast adhesion. Increased exposure of cell-adhesive epitopes of vitronectin for enhanced osteoblast adhesion on nanophase ceramics may be due to nanometer surface topography and/or increased wettability due to the greater number of grain boundaries at the surface.

Webster, T. J., Siegel, R. W., and Bizios, R., Osteoblast adhesion on nanophase ceramics. Biomaterials 20,1221-1227 (1999b). 

Tyrosine-arginine-serine-arginine (KRSR), enhancing osteoblast adhesion, 144-145... 

Webster, T.J., Ergun, C., Doremus, R.H., and Lanford, W.A. (2003) Increased osteoblast adhesion on titanium-coated hydroxylap-atite that forms CaTiOs. /. Biomed. Mater. Res. A, 67 (3), 975-980. 

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