The influence of surface patterning and/or sterilization on the haemocompatibility of polycaprolactones M. Stavridi, M. Katsikogianni, Y.F. Missirlis * Biomedical Engineering Laboratory, Department of Mechanical Engineering, University of Patras, Patras, Achaia 26500, Greece Abstract Platelet adhesion, coagulation and complement activation of flowing human blood over flat, nanostructured, sterilized or not sterilized surfaces of polycaprolactones (PCL) has been attempted. Two PCL samples were secured in place forming a parallel plate flow chamber. Platelet-poor plasma (PPP) or platelet-rich plasma (PRP) circulated for 30 min with a flow rate of 22 ml/min. The PPP was then collected to determine the nAPTT and the coagulation time as well as the amount of SC5b-9 and iC3b present. PRP was also collected under the same flow conditions and platelet counting was performed. Contact of blood with all PCL surfaces resulted in platelet adhesion with the phenomenon becoming more pronounced in the case of patterned surfaces. The coagulation time was affected by the nanopatterning. EB sterilization diminished platelet adhesion without significantly affecting the coagulation time. SC5b-9 complex activation increased with nanopatterning while iC3b activation was not affected by surface treatment. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Polycaprolactones; Nanopatterning; Blood compatibility 1. Introduction When flowing blood enters into contact with an artificial surface, a series of events is initiated: rapid adsorption of a layer of plasma proteins at the interface, platelet adhesion to the protein layer and activation of the coagulation system to form thrombin and fibrin [1]. The nature of the adsorbed protein layer, which depends on the relative concentrations and mobilities of the proteins in plasma and on their affinity for the surface, will condition the subsequent platelet – sur- face interaction [2]. The physicochemical nature of the biomaterial at the interface (hydrophobic or hydrophilic, charged or neutral, polar or nonpolar), its smoothness and its degree of heterogeneity in the distribution of reactive chemical groups are responsible, in part, for the selectivity of composition of the adsorbed plasma proteins. The expo- sure of blood to biomaterials may lead to clinical and biological consequences that depend essentially on the nature and area of the artificial surface and hemodynamic conditions [3]. Thrombosis is the most frequent complica- tion. In areas of high flow, the thrombous is mainly composed of platelets and fibrin. In areas of stasis, the thrombus is red and composed of red cells enmeshed in fibrin strands. The thrombus may embolize to the distal microcirculation, causing organ damage. Biologically active products released from these platelets may in turn have systemic effects. The exposure of an artificial surface to blood, for example, in cardiovascular implants, extracorporeal circu- lation systems, blood filters and blood storage containers, leads to protein adsorption followed by platelet adhesion and activation [3]. Discoid platelets will make contact, change shape, adhere to and spread on the surface. This is followed by the release of the contents of dense ADP, ATP, serotonin and alpha-granules and the formation of throm- boxane (TXA 2 ). Released ADP and TXA 2 induce circulat- ing platelets to change shape and to aggregate with the platelets adhering to the artificial surface, thus promoting the growth of a platelet thrombus. The surface of the platelet thrombus localizes and catalyzes the formation of Xa, which forms increased platelet aggregation and promotes fibrin formation which stabilizes the thrombus. Hemodynamic forces, which promote platelet interactions with the surface, also tend to break the platelet – fibrin thrombus into smaller 0928-4931/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0928-4931(02)00287-4 * Corresponding author. Tel.: +30-61997-232. E-mail address: misirlis@mech.upatras.gr (Y.F. Missirlis). www.elsevier.com/locate/msec Materials Science and Engineering C 23 (2003) 359 – 365