Modeling the transmural stress distribution during healing of bioresorbable vascular prostheses

Little attention has been given to the stresses within the wall of bioresorbable vascular prostheses and how they might affect the resorption process. We modeled the graft "complex" (inner tissue capsule, residual graft, and outer tissue capsule) as a three-layered compound tube under internal pressure. Using this biomechanical model, we studied the effects of alterations in the geometry (i.e., radius and thickness) and mechanical properties of each stratum on the overall transmural stress distribution. Hypothetical simulations were performed to investigate the possible sequence of and alterations in the radial and circumferential stresses during the resorption process. Our results suggest that early in the resorption phase, the inner tissue capsule is subjected to compressive hoop stresses and concentrated, large-magnitude compressive radial stresses. This distribution gives way to the more typical distribution for a thick-walled tube when equilibration (i.e., complete resorption) is approached. The prediction of the compressive stresses in the pseudo-intima during early resorption parallels findings of an elevated mitotic index in that region at that time. This leads to a new hypothesis, namely, that compressive stresses, both in-plane and out-of-plane with respect to the regenerated vascular cells, participate in the resorption process of bioresorbable vascular grafts by modulating elevated cellular proliferative activity and may play an important role in other aspects of vascular cell biology. Results of recent experimentation support this hypothesis.