Despite significant progress, stenosis is still a critical issue in vein grafting. Lipid-lowering drugs are still considered as a therapeutic winner, and the degree of vascular occlusion increases progressively over the years following surgical treatment. s a key foundation of stenosis in the context, formation of disturbed blood flow triggers pathological vascular remodeling. This phenomenon indicates that the progression from endothelial dysfunction to foam cell formation further induces aggressive SMC migration/proliferation, in turn leading to occlusive lesion formation. Hence, this study suggests an unprecedented solution to prevent vascular stenosis in vein to artery grafting by approaching the out-wall side of vessel instead of the intravascular side using a well-justified design of the external wrapping device (INNOSELF-V).

To fabricate external self-enclosable wrapping device (INNOSELF-V), a type of shape memory polymer (SMP; INNOSELF) was used with photo-initiator as crosslinker. The SMP solution was poured to fill the gap between molds. Then, polymer crosslinking (original shape) was processed by exposing the samples to ultraviolet irradiation. And it was programmed in an unfolded shape (temporary shape) that is easy to wrap. In rabbit vein graft model(end-to-end) and canine vein graft model(side-to-side), vein grafts and anastomosis sites were automatically wrapped with INNOSELF -V (recovery shape; original shape) in response to body temperature. After day 28 post surgery, the vein grafts were harvested and analyzed by a series of tissue staining to determine vein diameter, neo-intima formation, and vasa vasorum formation.

The properties of INNOSELFTM-V were computer-calculated to reach an arterial level of stiffness, and thus, wrapping a vein grafts in the rabbit and canine models controlled the volumetric expansion enough to prevent neo-intima formation by mechanical support. INNOSELF-V was designed to induce regenerative inflammatory activation by the porous structure with a consequent decrease in device stiffness. The collaborative effects among regenerative inflammation, vasa vasorum regeneration, and porosity appeared to rescue the ischemic disorders and induce migration of healthy SMCs towards adventitia instead of the intima side. Lastly, surgeon-friendly deployment processes were enabled by temperature-responsive, automatic wrapping to the vessel.

The results were promising enough to suggest this approach as a new solution for treatment of occlusive vascular remodeling in vein-artery grafting. Since the back and forth flow was not completely minimized in the current design, the U-shape grafting geometry and further advanced material properties will be applied to the next design so that the disturbed flow formation can be minimized, and the therapeutic effect can be promoted enough to move from bench to clinic. Moreover, a further study is required to maximize the benefits of self-wrapping (e.g. significant reduction of surgery time and risk of infection) in collaboration with surgeons and clinicians. Based on these results, products related to arteriovenous fistula surgery and coronary artery bypass graft surgery(CABG) are under commercialization and development respectively.