Bilayered Polymeric Micro- and Nanofiber Vascular Grafts as Abdominal Aorta Replacements: Long-Term in Vivo Studies in a Rat Model

In vivo long-term evaluation of degradable implants offers valuable information for the further design and optimization of biomaterials. In this study, we prepared one type of bilayer graft, which had an internal layer of oriented elastic degradable poly(l-lactide-ϵ-caprolactone) (PLCL) microfibers and an external layer of slowly degradable poly-ϵ-caprolactone (PCL) nanofiber. After in vivo implantation for 18 months, no aneurysm or graft rupture occurred, despite the finding that the mechanical properties of explanted PLCL grafts had decreased due to the degradation of PLCL materials. Explanted grafts maintained complete endothelialization and the degradation of PLCL improved vascular remodeling, which included the formation of a thicker media layer, denser extracellular matrix deposition, and obvious contractile and diastolic functions. Also, we found that the degradation products of PLCL tended to cause calcification, which may limit the return of vascular function to the natural artery level. Taken together, this bilayered graft showed a positive impact on vascular regeneration, while modification of bioactive or anticalcification factors should be considered for incorporation in future designs and the fabrication of small-diameter vascular grafts.