Summary Background Thromboelastography is widely used as a tool to assess the coagulation status of surgical patients. It allows observation of changes in material properties of whole blood, beginning with early stages of clot formation and ending with clot lysis. However, the contact activation of the coagulation cascade at surfaces of thromboelastographic systems leads to inherent variability and unreliability in predicting bleeding or thrombosis risks. Objectives To develop acoustic tweezing thromboelastometry as a noncontact method for perioperative assessment of blood coagulation. Methods Acoustic tweezing is used to levitate microliter drops of biopolymer and human blood samples. By quasi-statically changing the acoustic pressure we control the sample drop location and deformation. Sample size, deformation and location are determined by digital imaging at each pressure. Results Simple Newtonian liquid solutions maintain a constant, reversible location vs deformation curve. In contrast, the deformation/location curves for gelatin, alginate, whole blood, and blood plasma uniquely change as the samples solidify. Increasing elasticity causes the sample to deform less, leading to steeper stress/strain curves. By extracting a linear regime slope, we show that whole blood or blood plasma exhibits a unique slope profile as it begins to clot. By exposing blood samples to pro- or anti-thrombotic agents, the slope profile changes, allowing detection of hyper- or hypo-coagulable states. Conclusions We demonstrate that quasi-static acoustic tweezing can yield information about clotting onset, maturation, and strength. The advantages of small sample size, non-contact and rapid measurement make this technique desirable for real-time monitoring of blood coagulation.

Current thromboelastography in the clinic requires contact between the measurement apparatus and the blood being studied. An alternative technique employs levitation of a small droplet to limit contact with the blood sample to air alone. As has been demonstrated for Newtonian liquid drops, the measurement of static spatial location and sample deformation can be used to infer sample surface tension. In the current study, ultrasonic acoustic levitation was used to levitate viscoelastic samples. Gelatin was used as a stand-in for blood to establish the validity of the ultrasonic levitation technique on viscoelastic materials. Liquid data was first taken to benchmark the apparatus, then deformation/location studies were performed on set and setting gelatin gels. Relationships between gelling time, gel concentration, and gel firmness were demonstrated. The elastic modulus of gels was inferred from the data using an idealized model.