Physico-chemical properties of human plasma fibronectin binding to well characterized titanium dioxide

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Biologically compatible implant materials are commonly used in medical applications. The physico-chemical nature of the implant surface influences macromolecular binding. In the case of titanium implants, these interactions are influenced by a thin titanium oxide layer (5–70 Å), the main oxide species is titanium dioxide (TiO 2). Shortly after implant insertion, a meshwork of fibrinogen and fibronectin forms between the soft tissue and the implant–oxide surface. Fibronectin is an important matrix glycoprotein that mediates the attachment of cells and proteins to each other or to the extra-cellular matrix. The objective of this study was to investigate the adsorption and desorption behavior of plasma fibronectin on titanium dioxide and measure the differences in the oxide particle surface potential caused by this binding. The surface of native titanium dioxide was characterized by X-ray diffraction, differential scanning calorimetry, and ESCA. Particle diameter was estimated by forward light scattering, and verified by scanning electron microscopy. Human plasma fibronectin radiolabeled with 125I was employed for adsorption and desorption studies on washed titanium dioxide samples. Electrokinetics were characterized by measuring the zeta potential (electrophoretic mobility) of titanium dioxide precoated with fibronectin. Titanium dioxide exhibited different isoelectric values ranging from 5.2 to 6.4 as a function of pretreatment. Adsorption of fibronectin on washed titanium dioxide occurred within 10 min, with 57% binding. Desorption studies showed that fibronectin was not completely desorbed after a series of buffer washes over 69 h at pH 7.4. The adsorption isotherm had a plateau value of 0.21 mg/m 2. Zeta potential measurements demonstrated that the fibronectin coating caused an increase in the negative zeta potential. These findings give an insight into how titanium oxides might be altered to provide improved matrix glycoprotein adsorption and increased host cellular binding for enhanced implant biointegration.