Investigation of the adsorption of tropocollagen type I on titanium and Ti6Al4V

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Abstract
The adsorption of tropocollagen type I on titanium and Ti6Al4V has been investigated using physicochemical (zeta potential measurements), biochemical (ELISA), and imaging methods (SEM, AFM). Zeta potential measurements on both materials showed isolectric points in the pHiep range 4.3-4.8 if the metal surfaces were covered with amorphous oxide layers. Adsorption of both collagen molecules and fibrillar collagen led to a shift of about 0.5 pH units towards the alkaline region. From ELISA-based results it can be concluded that in the investigated concentration range of 0.01-0.5 mg/ml, the adsorption of collagen molecules leads to the formation of a rather uniform covering. The influence of pH and ionic strength on the adsorption behavior has been investigated. A model of the competitive adsorption of both tropocollagen molecules and in vitro reconstituted fibrils is presented. Based on this model, two methods are proposed for the improved adsorption of collagen fibrils: (i) adsorption from solutions that are essentially free from tropocollagen and oligomeric species; and (ii) use of already adsorbed tropocollagen as nucleation sites for further fibrillar growth.