# Angioplasty Using 4-Hexylresorcinol-Incorporated Silk Vascular Patch in Rat Carotid Defect Model
## 4 Discussion  
Silk derived from silkworms was used in various tissue engineering fields as a natural biopolymer scaffold [26; 36] owing to its excellent biological properties, such as biocompatibility, biodegradability, and tissue affinity [37]. Other reasons for choosing to employ silk as a vascular tissue engineering scaffolding biomaterial are its low thrombotic and immunologic properties and ease of clinical handling [37; 38]. In consideration of these properties, silk was processed into various forms of vascular scaffolds, such as tubes, films, and patches [39; 40; 41]. Specifically, studies that employed SF as an artificial vessel confirmed it to have excellent hemocompatibility, cell viability, tissue integrity, and mechanical strength [42; 43; 44]. SF was also incorporated into cardiovascular patches purposed for vascular surgery [45; 41]. Additionally, an in vivo study confirmed SF to have favorable biological and physical properties, and that it can be effectively used in vessel reconstruction surgery [41]. Silk mat from silk cocoons has various biological and mechanical properties that make it suitable for use as a vascular patch [24]. As an example, silk mat can be easily and economically manufactured by merely peeling the silk cocoon [24], thus making its manufacturing process simpler than that of the SF vascular patch [40]. Furthermore, vascular patch material should have enough mechanical strength to resist suture retention [41]. Thus, in a previous study, silk mat was evaluated as a patch material against collagen and PTFE membranes; the results revealed silk mat to have the highest tensile strength under wet conditions [27]. In addition, silk mat was demonstrated to have excellent suture-retention strength as compared to collagen [24]. In our study, a 4-HR-incorporated silk patch was manufactured by peeling a silk cocoon. This 4-HR silk patch was applied to a carotid artery defect by suturing it to the arterial wall; consequently, no tearing was observed under the wet conditions (Figure 4c). Silk derived from silkworms consists of fibroin and sericin [17]. Fiborin constitutes the core of the silk filament [46], while sericin is attached to the fibroin fibers and acts to bind them together [47]. During patch angioplasty, there was no excessive blood leakage in any group, and artery patency was confirmed via angiography (Figures 4 and 5). However, some blood leakage was observed around the patch in the PTFE group after the operation (Figures 4 and 5). As compared to the PTFE patch group, the 4-HR silk patch group had less blood leakage and good adhesion to the arterial wall (Figure 4b). As sericin is a bonding protein [47], it may have enhanced the attachment of the silk patch to the vessel. Patch angioplasty was reported to reduce the risk of stroke and restenosis more effectively than the primary closure method in a carotid stenosis patient [8]. This is likely due to the fact that primary closure of the small-diameter carotid artery following endarterectomy affects the blood flow in the narrow artery, and can increase the risk of postoperative restenosis [48; 49]. In our study, the angiography results showed that, in the control group, the diameter of the artery was substantially reduced after direct closure. In contrast, the arterial diameter of the animals in the 4-HR silk and PTFE groups tended to be stably maintained, with no significant reduction. Additionally, an acceptable rate of blood flow was observed in the 4-HR silk and PTFE groups using ultrasonography (Figure 6). The PSV of the 4-HR silk group significantly differed from that of the control group at one week and three weeks after the angioplasty operation (\(p\) = 0.005 and 0.024, respectively). Significant differences between the one- and three-week PSVs of the PTFE group and those of the control group were also determined (\(p\) = 0.005 and 0.020, respectively).