Patchwise character of fibronectin films adsorbed on biomaterials with different surface free energies; the influence of protein concentration, adsorption time, shear rate and pH

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Abstract
It is the aim of this study to determine the influence of substratum surface free energy, protein concentration, adsorption time, shear rate and pH on the distribution patterns of adsorbed fibronectin films on FEP‐Teflon, PMMA and glass. Replicas of the adsorbed protein surface were made and examined by transmission electron microscopy. On high energy substrata, adsorption occurred in a grained reticulated manner, whereas on low energy substrata adsorption occurred in a patchy way. At low shear rates, fibronectin distribution patterns became more irregular at higher protein concentrations and complete surface coverage occurred on FEP‐Teflon, whereas at a higher shear rate, an inverse effect of protein concentration was seen. At pH 4–8, a pH close to the iso‐electric point of fibronectin, the fine reticulated structures on glass and PMMA, observed at pH 70, turned into more coarsely knotted structures, whereas on FEP‐Teflon structures became more patchy, indicative of a more extensive unfolding of the protein. Longer adsorption times resulted in more blotchy patterns, which can be associated with higher amounts adsorbed. Fibronectin adsorbs to a certain degree, non‐homogeneously to all substrata. However, there is as yet no comprehensive picture of the interrelationship between all the mechanisms involved.