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Abstract Vascular hypo‐fibrinolysis is a historically underappreciated and understudied aspect of venous thromboembolism (VTE). This paper describes the development of a micro‐clot dissolution assay for quantifying the fibrinolytic capacity of endothelial cells – a key driver of VTE development. This assay is enabled using aqueous two‐phase systems (ATPS) to bioprint microscale fibrin clots over human umbilical vein endothelial cells (HUVECs). Importantly, these micro‐clots are orders of magnitude smaller than conventional fibrin constructs and allow HUVEC‐produced plasminogen activators to mediate visually quantifiable fibrinolysis. Using live‐cell time‐lapse imaging, micro‐clot dissolution by HUVECs is tracked, and fibrinolysis kinetics are quantified. The sensitivity of cell‐driven fibrinolysis to various stimuli is rapidly tested. The physiological relevance of this convenient high‐throughput assay is illustrated through treatments with lipopolysaccharide (LPS) and rosuvastatin that elicit anti‐ and pro‐fibrinolytic responses, respectively. Furthermore, treatment with baricitinib, an anti‐inflammatory therapeutic found to increase cardiovascular risks after market approval, provokes an anti‐fibrinolytic response – which highlights the potential role of endothelial cells in increasing VTE risk for patients receiving this drug. This endothelial cell fibrinolysis assay provides a high‐throughput and versatile drug testing platform – potentially allowing for early preclinical identification of therapeutics that may beneficially enhance or adversely impair endothelial fibrinolysis. 

Aqueous two-phase systems (ATPSs) have long been used for the facile and rapid extraction of biomolecules of interest. Selective partitioning of DNA is useful for nucleic acid purification and in the design of novel sensing technologies. This paper investigates the partitioning of a plasmid within a poorly understood ATPS comprising the polymers poly(ethylene glycol) (PEG) 35 kDa and Ficoll 400 kDa. The focus is placed on dissecting the compositional effects of the ATPS—that is, whether set concentrations of physiological ions or the polymers themselves can tune DNA phase preference and strength of partitioning. The work here uncovers the antagonistic effects of magnesium and ammonium ions, as well as the role that phase-forming polymer partitioning plays in plasmid enrichment. Testing the ions in conjunction with different ATPS formulations highlights the complexity of the system at hand, prompting the exploration of DNA’s conformational changes in response to polymer and salt presence. The work presented here offers multiple optimization parameters for downstream applications of PEG–Ficoll ATPSs, such as in vitro transcription/translation-based biosensing, in which performance is heavily dependent upon nucleic acid partitioning.