Galloyl groups-regulated fibrinogen conformation: Understanding antiplatelet adhesion on tannic acid coating

Fibrinogen (Fgn) has been identified as the key protein in the process of biomaterial-induced platelet adhesion. We have recently reported a facile and effective method for constructing platelet-repellent surface using a natural polyphenol component tannic acid (TA). However, the mechanism by which the TA surface repels platelets was not fully understood. To address this issue, we investigated the adsorption of Fgn (amount and conformation) on four TA-functionalized surfaces with different amounts of galloyl groups and the potential for platelet adherence on these surfaces. The experimental results indicated that the four TA-functionalized surfaces adsorbed a similar amount of Fgn, but the conformation and bioactivity of the adsorbed Fgn and the subsequent platelet adherence were quite different among the surfaces. The TA surface with the most galloyl groups induced minimal changes in the conformation of Fgn, a result of the α and γ chains of the adsorbed Fgn being highly inactive on the surface, thus leading to an outstanding antiplatelet adhesion performance. With a decreased amount of galloyl groups, the activity of the α chain in the adsorbed Fgn remained unchanged, but the activity of the γ chain and the extent of platelet adhesion gradually increased. This work provided a new concept for controlling platelet adhesion on solid materials, and we envision that the TA film could have potential applications in the development of new blood-contacting biomaterials in the future. Statement of significance Reducing platelet adhesion on material surfaces is of tremendous scientific interest in the field of blood-contacting biomaterials, but it remains a big challenge due to the highly adhesive nature of the platelets. In this study, we demonstrated for the first time that tannic acid surface with abundant galloyl groups could induce minimal conformational changes of fibrinogen, eventually leading to an outstanding antiplatelet adhesion effect. In addition, the platelet adhesion response could be easily controlled through regulating the amount of galloyl groups on the surface. This work provided a new strategy for controlling platelet adhesion on solid materials, which was totally different from existing methods such as construction of physically patterned surfaces, modification of inert hydrophilic polymers or appending bioactive moieties to target surfaces.