Droplet Microfluidics with Reagent Micromixing for Investigating Intrinsic Platelet Functionality

Precision mapping of the functional structure of platelet populations holds great promise for the identification of hyper-reactive subtypes that are likely to be disease drivers, having value in prognostics and as therapeutic targets. However, the ability to measure the intrinsic functional capacity of individual platelets is confounded by potent paracrine cross-talk, resulting in phenotypic remodeling of the entire platelet population, and in doing so obscuring the identity of hyper-reactive platelets. To address this we have developed a droplet microfluidics strategy for single platelet confinement to exclude paracrine signaling. Consideration of the Poisson distribution was used for high throughput single platelet encapsulation and the preparation of minimal platelet collectives serving as digital models for understanding the role of hyper-reactive platelets coordinating system-level behavior by paracrine signaling. Platelets are retrieved from the droplets for phenotyping using standard flow cytometry. In addition, we have incorporated a staggered herringbone micromixing element for accurate agonist and antibody dispensing in droplets. The methodology was used for characterizing sensitivity distributions from healthy blood donors in response to convulxin (agonist of the GPVI receptor, the major platelet receptor for collagen). P-selectin exposure and αIIbβ3 integrin activation were used as analytical end-points to demonstrate the existence of hyper-reactive platelets that direct 20-fold gains in system level sensitivity. The analytical workflow represents an enabling tool for the accurate classification of platelet subtypes and description of their underlying biology.