Early-Stage Protein Adsorption Sequence on Blood-Contacting Surfaces: Answer to Vroman's Question

Plasma protein adsorption on blood-contacting surfaces is the initiating significant event and modulates the subsequent coagulation response. Despite decades of research in this area, Vroman's questions in 1986 "Who gets there first?" and "When does the next protein arrive?" remain unanswered due to the lack of detection techniques with sufficient temporal resolution. In this work, we develop a droplet microfluidic technology to detect protein adsorption sequences on six typical blood-contacting surfaces in milliseconds. Apolipoproteins (Apo) are found to be the first proteins to adsorb onto the surfaces in a plasma droplet, and the specific type of apolipoprotein depends on the surface. Apo CI is the first protein adsorbed on gold, platinum, graphene, stainless steel, and polyvinyl chloride with the adsorption time varying from 0.01 to 1 s, while Apo CIII preferentially reaches the titanium alloy surface within 1 s. Subsequent to the initial adsorption, Apo AI, AII, and other proteins continue to adsorb until albumin arrives. Thus, the adsorption sequence is revealed, and Vroman's questions are answered. Moreover, this finding demonstrates the influence of the initial protein adsorption on subsequent coagulation at the surface, and it offers new insights into the development of anticoagulant surfaces.