Abstract
In situ vascular tissue engineering aims to regenerate vessels “at the target site” using synthetic scaffolds that are capable of inducing endogenous regeneration. Critical to the success of this approach is a fine balance between functional neo-tissue formation and scaffold degradation. Circulating immune cells are important regulators of this process as they drive the host response to the scaffold and they play a central role in scaffold resorption. Despite the progress made with synthetic scaffolds, little is known about the host response and neo-tissue development during and after scaffold resorption. In this study, we designed a fast-degrading biodegradable supramolecular scaffold for arterial applications and evaluated this development in vivo. Bisurea-modified polycaprolactone (PCL2000-U4U) was electrospun in tubular scaffolds and shielded by non-degradable expanded polytetrafluoroethylene in order to restrict transmural and transanastomotic cell ingrowth. In addition, this shield prevented graft failure, permitting the study of neo-tissue and host response development after degradation. Scaffolds were implanted in 60 healthy male Lewis rats as an interposition graft into the abdominal aorta and explanted at different time points up to 56 days after implantation to monitor sequential cell infiltration, differentiation, and tissue formation in the scaffold. Endogenous tissue formation started with an acute immune response, followed by a dominant presence of pro-inflammatory macrophages during the first 28 days. Next, a shift towards tissue-producing cells was observed, with a striking increase in α-Smooth Muscle Actin-positive cells and extracellular matrix by day 56. At that time, the scaffold was resorbed and immune markers were low. These results suggest that neo-tissue formation was still in progress, while the host response became quiescent, favoring a regenerative tissue outcome. Future studies should confirm long-term tissue homeostasis, but require the strengthening of the supramolecular scaffold if a non-shielded model will be used.
Highlights
Recent developments in vascular tissue engineering strategies show a shift towards in situ vascular tissue engineering while using cell-free synthetic scaffolds that promote tissue regeneration inside the human body [1,2]
Based on a previous study by Talacua et al [6], we hypothesize that these infiltrating immune cells are endogenous circulating monocytes and macrophages, which initiate an inflammatory response by secreting cytokines and growth factors that subsequently attract progenitor cells that are capable of matrix formation
scanning electron microscopy (SEM) analysis confirmed that electrospinning resulted in isotropic fibrous tubular PCL2000-U4U scaffolds that consisted of non-fused, micrometer thick fibers (fiber diameter distribution of 3.5 ± 0.2 μm) (Figure 1E)
Summary
Recent developments in vascular tissue engineering strategies show a shift towards in situ vascular tissue engineering while using cell-free synthetic scaffolds that promote tissue regeneration inside the human body [1,2]. Based on a previous study by Talacua et al [6], we hypothesize that these infiltrating immune cells are endogenous circulating monocytes and macrophages, which initiate an inflammatory response by secreting cytokines and growth factors that subsequently attract progenitor cells that are capable of matrix formation. The source of these progenitor cells remains to be further elucidated. In order to specify which changes in biomaterial design are needed to direct these cells towards tissue regeneration and to prevent adverse remodeling, it is of great importance to fully understand their interaction with the biomaterial during scaffold remodeling
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