hPF4 binds to elongated strings of VWF released from injured HUVECs in a microfluidic system. (A) Schematic of the endothelialized microfluidic system used to study the effect of photochemical injury to targeted regions of the endothelium. (B) Comparison of a representative area of uninjured endothelium and the immediate upstream hematoporphyrin-injured area showing pyknotic nuclei and VWF strings only released after injury. (C) Appearance at representative injured site within the microfluidic channel and at site DR, the first 250 µ downstream of the edge of the injured site. Direction of flow is indicated by arrows. Channels were stained for PF4 using a polyclonal anti-hPF4 antibody as well as staining for nuclei and VWF. (D) Relative binding of PF4 to either 250 µ of the upstream uninjured region (UUR), the injured region, or the downstream of injury region (DR). Results are expressed as the mean ± 1 standard error of the mean (SEM) from N ≥ 4 separate microfluidic channels. P values were determined using a 1-way ANOVA analysis to compare binding to the UUR of the channel. EC, endothelial cells.