Improvement of Anselme's adhesion model for evaluating human osteoblast response to peptide-grafted titanium surfaces.

Investigations on the relationships between the properties of biomaterial surfaces and cell adhesion/proliferation processes have recently gained increasing interest. To describe the behaviour of cells adhering and proliferating over different types of (and/or differently treated) substrates, some mathematical models have been also suggested in literature; these models consider both the dependence of cell adhesion/proliferation over time, and the influence of substrate morphology in allowing (or even hampering) cell attachment. Major developments in the biochemical functionalization of the materials used for the production of endosseous devices have been achieved; the ability of the so-called "biomimetic" surfaces to promote cell adhesion, thus favoring the osseointegration process, is already well acknowledged. The aim of this study was to formulate a mathematical model for osteoblast adhesion, mediated by an adhesion peptide (sequence 351-359 mapped on the Human Vitronectin Protein) covalently grafted to a titanium-based surface. To assure a highly homogenous orientation of the peptide to cells, the "specific functionalization" strategy was properly designed. Enzymatic detachment assays allowed comparing osteoblast behaviour over three differently treated titanium substrates (i.e., oxidized, silanized, and peptide-grafted), thus determining how and how much the bioactive peptide can improve the strength of cell adhesion. The results confirmed the capacity of the peptide to increase cell adhesion and adhesion strength; moreover, the role of the peptide was described by a mathematical equation characterizing cells behaviour.

Human osteoblast-like cell adhesion on titanium substrates covalently functionalized with synthetic peptides.

Biomaterials to be used for the production of endosseous devices in dental, orthopedic and maxillo-facial applications, might be designed to support, guide and enhance osteoblast adhesion. Cell recruitment onto biomaterial surface is a fundamental step within the complex process responsible for implant osseointegration; this process involves several proteins from the extra cellular matrix (ECM), cytoskeleton and cell membrane. A new strategy to improve endosseous implant integration is based on preparing biomimetic surfaces able to present adhesive factors to cells. Osteoblast adhesion takes place by at least two different mechanisms: the most investigated one implies the interaction with RGD sequences via cell-membrane integrin receptors; a further mechanism concerns the interaction between cell-membrane heparan sulfate proteoglycans and heparin-binding sites of ECM proteins. In the present study two different biomimetic surfaces were obtained by covalently grafting two adhesive peptides on oxidized titanium substrates after silanization: an RGD-containing peptide and a peptide mapped on human vitronectin. The two sequences are known to act via different adhesive mechanisms. The amount of human osteoblasts adhered onto peptide-enriched or not enriched titanium oxidized surfaces and the strength of cell binding were estimated, thus comparing the capacity of the bioactive substrates in promoting cell adhesion.