Fabrication of heparinized small diameter TPU/PCL bi-layered artificial blood vessels and in vivo assessment in a rabbit carotid artery replacement model

Increasingly growing problems in vascular access for long-term hemodialysis lead to a considerable demand for synthetic small diameter vascular prostheses, which usually suffer from some drawbacks and are associated to high failure rates. Incorporating the concept of in situ tissue engineering (TE) into synthetic small diameter blood vessels, for example, thermoplastic poly(ether urethane) (TPU) ones, could provide an alternative approach for vascular access that profits from the advantages of excellent mechanical properties of synthetic polymer materials (early cannulation) and unique biointegration regeneration of autologous neovascular tissues (long-term fistulae). In this study, a kind of heparinized small diameter (d = 2.5 mm) TPU/poly(ε-caprolactone) (TPU/PCL-Hep) bi-layered blood vessels was electrospun with an inner layer of PCL and an outer layer of TPU. Afterward, the inner surface heparinization was conducted by coupling H₂N-PEG-NH₂ to the corroded PCL layer and then heparin to the attached H₂N-PEG-NH₂ via the EDCI/NHS chemistry. Herein a heparinized PCL inner layer could not only inhibit thrombosis, but also provide sufficient space for the neotissue regeneration via biodegradation with time. Meanwhile, a TPU outer layer could confer the vascular access the good mechanical properties, such as flexibility, viability and fitness of elasticity between the grafts and host blood vessels as evidenced by the adequate mechanical properties, such as compliance (4.43 ± 0.07%/ 100 mmHg), burst pressure (1447 ± 127 mmHg) and suture retention strength (1.26 ± 0.07 N) without blood seepage after implantation. Furthermore, a rabbit carotid aortic replacement model for 5 months was demonstrated 100% animal survival and 86% graft patency. Puncture assay also revealed the puncture resistance and self-sealing (hemostatic time < 2 min). Histological analysis highlighted neotissue regeneration, host cell infiltration and graft remodeling in terms of extracellular matrix turnover. Altogether, these results showed promising aspects of small diameter TPU/PCL-Hep bi-layered grafts for hemodialytic vascular access applications.