Comparison of the mechanical properties of bypass grafts: Experimental assays.

OBJECTIVE: One prevalent therapeutic strategy for addressing atherosclerosis is using an alternative blood supply route to the heart, referred to as bypass surgery. In these surgeries, the saphenous vein, radial artery, and internal mammary artery are commonly used to create this bypass route. Unfortunately, due to negligence regarding the compatibility of the graft with the host tissue, reoperation is often required after several years. One method that can aid in selecting a suitable vein for bypass is simulating the solid-fluid interaction, and performing such simulations requires knowledge of the mechanical properties of bypass grafts. Therefore, extracting the mechanical properties of bypass grafts is essential. METHODS: In this study, human bypass grafts were subjected to uniaxial tensile testing, and their elastic modulus was extracted and compared. Additionally, the hyperelastic properties of these grafts were extracted using the Mooney-Rivlin model for use in numerical software. RESULTS: The average elastic modulus in the circumferential direction for radial artery, mammary artery, and saphenous vein samples were determined to be 1.384 ± 0.268 MPa, 3.108 ± 1.652 MPa, and 7.912 ± 2.509 MPa, respectively. Based on the results of uniaxial tests, the saphenous vein exhibited the highest stiffness among the three vascular tissues. CONCLUSION: The mechanical characterization results of the bypass vessels can be applied to the clinical studies of heart diseases. They may help develop an appropriate treatment approach.

Carbon monoxide release from ultrasound-sensitive microbubbles improves endothelial cell growth.

Carbon monoxide is a gasotransmitter that may be beneficial for vascular tissue engineering and regenerative medicine strategies because it can promote endothelial cell (EC) proliferation and migration by binding to heme-containing compounds within cells. For example, CO may be beneficial for vascular cognitive impairment and dementia because many patients' disrupted blood-brain barriers do not heal naturally. However, control of the CO dose is critical, and new controlled delivery methods need to be developed. This study developed ultrasound-sensitive microbubbles with a carefully controlled precipitation technique, loaded them with CO, and assessed their ability to promote EC proliferation and function. Microbubbles fabricated with perfluoropentane exhibited good stability at room temperature, but they could still be ruptured and release CO in culture with application of ultrasound. Microbubbles synthesized from the higher boiling point compound, perfluorohexane, were too stable at physiological temperature. The lower-boiling point perfluoropentane microbubbles had good biocompatibility and appeared to improve VE-cadherin expression when CO was loaded in the bubbles. Finally, tissue phantoms were used to show that an imaging ultrasound probe can efficiently rupture the microbubbles and that the CO-loaded microbubbles can improve EC spreading and proliferation compared to control conditions without microbubbles as well as microbubbles without application of ultrasound. Overall, this study demonstrated the potential for use of these ultrasound-sensitive microbubbles for improving blood vessel endothelialization.

Epsin Mimetic UPI Peptide Delivery Strategies to Improve Endothelization of Vascular Grafts.

Endothelialization of engineered vascular grafts for replacement of small-diameter coronary arteries remains a critical challenge. The ability for an acellular vascular graft to promote endothelial cell (EC) recruitment in the body would be very beneficial. This study investigated epsins as a target since they are involved in internalization of vascular endothelial growth factor receptor 2. Specifically, epsin-mimetic UPI peptides are delivered locally from vascular grafts to block epsin activity and promote endothelialization. The peptide delivery from fibrin coatings allowed for controlled loading and provided a significant improvement in EC attachment, migration, and growth in vitro. The peptides have even more important impacts after grafting into rat abdominal aortae. The peptides prevented graft thrombosis and failure that is observed with a fibrin coating alone. They also modulated the in vivo remodeling. The grafts are able to remodel without the formation of a thick fibrous capsule on the adventitia with the 100 µg mL-1 peptide-loaded condition, and this condition enabled the formation of a functional EC monolayer in the graft lumen after only 1 week. Overall, this study demonstrated that the local delivery of UPI peptides is a promising strategy to improve the performance of vascular grafts.