2025 SES William Prager Medal Plenary Lecture

Rupture of Vascular Blood Clots

The rupture of vascular blood clots is a cause of bleeding in traumatic injury and embolization of thrombi, which can lead to strokes and pulmonary embolisms, leading causes of death worldwide. Blood clots are poroelastic hydrogels with a fibrin network providing the primary resistance to rupture and with dissipative behavior arising from liquid diffusion. How to define fracture toughness of blood clots or thrombi is an open issue. The critical energy release rate associated with crack propagation is central in our work on fibrin hydrogels. We have carried out fracture experiments (both mode I and II) and investigated factors such as concentrations of fibrin, initiators of clotting such as tissue factor, and the crosslinking and stabilizing factor XIIIa, which are central in the blood coagulation process. Coupled with a large-deformation continuum model, the energy release rate is computed using a surface-independent integral that has two contributions – one from the stresses in the solid network, and another from the flow of liquid. The model is formulated for isotropic fibrous gels that exhibit a range of behaviors including volume decreasing under tensile deformations.  The latter directly affects liquid permeation (fluxes) around a crack tip. Importantly, our experiments have focused on clots made from pooled plasma, while our recent work is investigating the effects of platelets and blood cells. The contribution to the critical energy release rate from liquid permeation tends to be negative for tensile contracting gels, which can be interpreted as a crack shielding mechanism. From correlations with experiments, continuum simulations, and discrete network simulations, we show that a critical stretch fracture criterion can effectively predict the fracture toughness of fibrin gels. Some historical perspective on fracture toughness of dissipative solids will also be discussed.

(This is joint work with V. Barsegov, R. Litvinov, P. Purohit, V. Tutwiler, and J. Weisel).

Bio of the speaker: John L. Bassani is the Richard H. and S. L. Gabel Professor, Emeritus in the Department of Mechanical Engineering and Applied Mechanics (MEAM) and the Department of Materials Science and Engineering at the University of Pennsylvania (Penn). He received a B.S. in Mechanical Engineering from Lehigh University in 1973 and worked as a Structural Engineer at Fairchild-Republic Aviation in New York before beginning graduate studies. He received a M.S. in Applied Mechanics from Lehigh University in1975 on cracks in bimaterials and a Ph.D. in Engineering from Harvard University in 1978 on the mechanics of polycrystalline plasticity.  During the next two years, he was a post doc and lecturer and then an Assistant Professor of Mechanical Engineering at the Massachusetts Institute of Technology focusing on the mechanics of high-temperature crack growth. Since 1980 he has been on the faculty at Penn. He was Chair of MEAM from 1997-2005 and 2008-2011. He also has held appointments in Materials Science and Engineering, the Laboratory for Research on the Structure of Matter, and the Institute of Medicine and Engineering at Penn. He has held visiting professor positions at the University of California at Santa Barbara, Harvard University, and Brown University. He is the recipient of the Presidential Young Investigator Award, Life Fellow of the American Society of Mechanical Engineers, and recipient of the 2019 American Society of Mechanical Engineers Daniel C. Drucker Medal. Bassani has served on the Board of Directors of the Society of Engineering Science and its President in 2008. His research interests include: the relationship between properties of discrete and continuous media; interfacial mechanics; formation and properties of nanostructures; adhesion of shells, mechanics of living cells and tissue; plastic deformation of crystals and polycrystals; material stability and localized deformation; mechanics of fracture and fatigue; and material degradation under extreme environments.