Carotid Artery Bypass Surgery of In-Body Tissue Architecture-Induced Small-Diameter Biotube in a Goat Model: A Pilot Study

Abstract

Biotubes are autologous tubular tissues developed within a patient’s body through in-body tissue architecture, and they demonstrate high potential for early clinical application as a vascular replacement. In this pilot study, we used large animals to perform implantation experiments in preparation for preclinical testing of Biotube. The biological response after Biotube implantation was histologically evaluated. The designed Biotubes (length: 50 cm, internal diameter: 4 mm, and wall thickness: 0.85 mm) were obtained by embedding molds on the backs of six goats for a predetermined period (1–5 months). The same goats underwent bypass surgery on the carotid arteries using Biotubes (average length: 12 cm). After implantation, echocardiography was used to periodically monitor patency and blood flow velocity. The maximum observation period was 6 months, and tissue analysis was conducted after graft removal, including the anastomosis. All molds generated Biotubes that exceeded the tensile strength of normal goat carotid arteries, and eight randomly selected Biotubes were implanted. Thrombotic occlusion occurred immediately postoperatively (1 tube) if anticoagulation was insufficient, and two tubes, with insufficient Biotube strength (<5 N), were ruptured within a week. Five tubes maintained patency for >2 months without aneurysm formation. The spots far from the anastomosis became stenosed within 3 months (3 tubes) when Biotubes had a wide intensity distribution, but the shape of the remaining two tubes remained unchanged for 6 months. The entire length of the bypass region was walled with an αSMA-positive cell layer, and an endothelial cell layer covered most of the lumen at 2 months. Complete endothelial laying of the luminal surface was obtained at 3 months after implantation, and a vascular wall structure similar to that of native blood vessels was formed, which was maintained even at 6 months. The stenosis was indicated to be caused by fibrin adhesion on the luminal surface, migration of repair macrophages, and granulation formation due to the overproliferation of αSMA-positive fibroblasts. We revealed the importance of Biotubes that are homogeneous, demonstrate a tensile strength > 5 N, and are implanted under appropriate antithrombotic conditions to achieve long-term patency of Biotube. Further, we clarified the Biotube regeneration process and the mechanism of stenosis. Finally, we obtained the necessary conditions for a confirmatory implant study planned shortly.

Diverse Shape Design and Physical Property Evaluation of In-Body Tissue Architecture-Induced Tissues

“…The basic structure of the moulds for fabricating iBTA-induced tissues is shown below. The moulds primarily consisted of outer cases with micropores and inner cores of several geometries [ 8 , 9 , 13 , 30 , 34 ]. Figure 1 shows a typical example of a mould (Biotube maker).…”

“…Therefore, these results will be reported in a separate study in the future. However, few histological images showed that the harvested connective tissues mainly comprised collagen produced by fibroblasts [ 3 , 4 , 7 , 9 ] and that the compact layers of collagen in the tissue were likely located in the vicinity of the surface [ 8 ]. These were not different from those of previous studies.…”

“…We employed porous outer cases with sufficiently large aperture areas. However, if the micropores are occluded by the collagen produced before a sufficient amount of subcutaneous tissue migrates through the micropores into the cavities, the cavities would not be filled with connective tissue [ 9 ]. Therefore, the maximum thickness of the tissue that could be fabricated by iBTA was approximately 5–6 mm, depending on the inner core material.…”

“…We have previously applied iBTA to fabricate 2D and 3D structures such as tubular or membranous tissues and their combination, not only autologously but also allogeneically or xenogeneically without donor sacrifice. These tissues were subjected to the following applications: vascular grafts (Biotubes) for the carotid or aortic artery with a diameter of 0.6–5.0 mm [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ] or shunt grafts for dialysis [ 15 ], aortic stent grafts [ 16 , 17 ], and aortic, pulmonary, or mitral heart valves (Biovalves) [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. Patches for the peritoneum [ 30 ], dura mater [ 31 ], trachea [ 32 , 33 ], and skin grafts [ 31 ] have also been developed.…”