title: Microfluidic assay of hemophilic blood clotting: distinct deficits in platelet and fibrin deposition at low factor levels.
abstract: BACKGROUND
  Coagulation factor deficiencies create a range of bleeding phenotypes. Microfluidic devices offer controlled hemodynamics and defined procoagulant triggers for measurement of clotting under flow.
  
  
  OBJECTIVE
  We tested a flow assay of contact pathway-triggered clotting to quantify platelet and fibrin deposition distal of dysfunctional thrombin production. Microfluidic metrics were then compared with PTT or % factor activity assays.
  
  
  METHODS
  Whole blood (WB) treated with low level corn trypsin inhibitor (4 μg mL⁻¹) from nine healthy donors and 27 patients (deficient in factor [F] VIII, 19 patients; FIX, one patient; FXI, one patient; VWF, six patients) was perfused over fibrillar collagen at wall shear rate = 100 s⁻¹.
  
  
  RESULTS
  Using healthy WB, platelets deposited within 30 s, while fibrin appeared within 6 min. Compared with healthy controls, WB from patients displayed a 50% reduction in platelet deposition only at < 1% factor activity. In contrast, striking defects in fibrin deposition occurred for patients with < 13% factor activity (or PTT > 40 s). Full occlusion of the 60-μm high channel was completely absent over the 15-min test in patients with < 1% factor activity, while an intermediate defect was present in patients with > 1% factor.
  
  
  CONCLUSIONS
  Spontaneous bleeding in patients with < 1% factor activity may be linked to deficits in both platelet and fibrin deposition, a risk known to be mitigated when factor levels are raised to > 1% activity (PTT of ~40-60 s), a level that does not necessarily rescue fibrin formation under flow.
authors.affiliation: Department of Chemical and Biomolecular Engineering, Institute for Medicine and Engineering, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: T V
authors.initials: TV
authors.lastname: Colace
authors.forename: P F
authors.initials: PF
authors.lastname: Fogarty
authors.forename: K A
authors.initials: KA
authors.lastname: Panckeri
authors.forename: R
authors.initials: R
authors.lastname: Li
authors.forename: S L
authors.initials: SL
authors.lastname: Diamond
mesh_terms: D001777:Blood Coagulation; D001792:Blood Platelets / Q000378:metabolism*; D005337:Fibrin / Q000378:metabolism*; D006467:Hemophilia A / Q000503:physiopathology*; D006801:Humans; D044085:Microfluidics / Q000379:methods*
chemical_list: D005337:Fibrin
keywords: blood coagulation; hemophilia; hemostasis; microfluidics; platelets