Biomedical subjects
Publications and source records attributed to V Ketharanathan.
Information obtained from physical and chemical characterization of vascular grafts can prove valuable in obtaining a preliminary assessment of potential in vivo performance. The data presented illustrate the concept and show that the new biological graft made from bovine ureters has adequate performance characteristics for use as a potentially successful vascular graft.
The organization of collagen in custom-built biosynthetic vascular prostheses (Omniflow Vascular Graft), which are suitable for peripheral revascularization, has been examined. The grafts were a glutaraldehyde-tanned ovine-collagen composite with a polymer mesh reinforcement. Comparisons were made between grafts using different mesh fiber polymers and knit patterns. There was a basic similarity in the arrangement of the tissue structure in all graft types. Scanning electron microscopy and light microscopy showed that the collagen formed a layered structure which fully encased the polymer mesh and held it firmly in position. Rather than polymer mesh, the inner surface of the graft was found to be collagen, and lined with a layer of flattened cells. Collagen formed a continuous layer surrounding the mesh, with no distinct boundary, membrane or structurally weak point being apparent. Immunohistology, using a monoclonal antibody specific for type III collagen, and chemical analysis, indicated that there was high proportion of type III collagen in the grafts, particularly in the region surrounding the mesh fibers.
Glutaraldehyde-tanned, mesh-reinforced, mandrel-grown ovine collagen conduits were compared with tanned human umbilical arteries and polytetrafluoroethylene (PTFE) grafts in the aorta of rat recipients. All grafts had 100% patency and became lined by a cellular neointima. The mean maximum thickness of the neointima of the tanned human umbilical artery, ovine collagen graft, and the PTFE grafts was 68, 57, and 13 micrometer, respectively. Neointimal proliferation was complete for the two biosynthetic grafts, but none was seen in the center of the PTFE grafts as late as ten weeks. The mean increase in lumen cross-sectional area was 49% for the umbilical artery grafts, 23% for ovine collagen conduits, and 4% for the PTFE grafts. Longer follow-up periods will be required before unqualified support can be given to clinical trials of these small-diameter prostheses; however, long-term patency for synthetic grafts of such a small caliber is encouraging for future microvascular applications and for study of host-prosthesis interactions.
Bovine ureters from healthy cattle were mounted on a glass rod, covered with a polyester mesh, then tanned in glutaraldehyde. Processed ureters 6 mm X 100 mm were inserted as an aortoiliac bypass around the ligated terminal aorta in seven dogs. All prostheses remained patent during an observation period of 3 to 17 months. No aneurysms, anastomotic aneurysms, or dystrophic changes occurred during this time. The epithelium lining the biological prosthesis became replaced by endothelila-like cells within 3 months, ureteric smooth muscle was replaced by host fibrous tissue within 17 months.
Collagen tubes with a polyester mesh endoskeleton were grown in sheep around silastic mandrils and were then tanned in alkaline glutaraldehyde. Tanned ovine collagen conduits and polytetrafluoroethylene conduits (Gore-Tex), each 10 cm long and 6 mm wide, were deployed in parallel as aorto-iliac bypass grafts in 10 dogs. The grafts remained patent for periods up to and exceeding 23 months. No grafts showed aneurysmal dilatation. All grafts formed a neointima lined with cells. In the Gore-Tex grafts there was fibrous tissue ingrowth through the wall which resulted in progressive and irregular luminal narrowing. This was not seen in the tanned ovine collagen grafts.
A new modification of the mandril-grown vascular prosthesis appears to combine the best features of presently available synthetic vascular replacement materials. Glutaraldehyde-tanned polyester mesh-supported conduits (diameters 4, 6, and 8 mm) grown in the subcutaneous tissue of sheep, maintain 100% patency in the aortic, aortoiliac, and common iliac positions of canine recipients for over 2 years. One-millimeter diameter grafts placed in the infrarenal abdominal aorta of rat recipients were patent in 72% for 6-month follow-up periods. The grafts maintained a modicum of antigenicity despite tanning, as evidenced by the slightly elevated hemagglutination (0 to 2 dilutions) titers against sheep red blood cells in ovine graft recipients and the accelerated rejection of the donor strain skin grafts in Fischer rats receiving Brown-Norway conduits. Finally, in a limited clinical study, 21 of 24 femoropopliteal and three of three femoroposterior tibial grafts remained patent in short follow-up periods (2 to 16 months). Two aortocoronary bypass grafts have continued to function in one patient for 19 months. Minimal inflammatory reaction and no aneurysmal degeneration were found in the material studied.
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To date no prosthetic vascular prosthesis performs as well as the autologous saphenous vein in diameters of 6 mm and less. The purpose of this study was to compare the in vitro and in vivo performance of a new glutaraldehyde stabilized, narrow diameter (4 mm), vascular prosthesis fashioned from bovine ureters (Flonova) with the saphenous vein and polytetrafluoroethylene (PTFE) prostheses. The methods used for the comparative in vitro analysis of the bovine ureter and saphenous vein were modifications of tests recommended by the American National Standards for Vascular Prostheses. Blood compatibility was evaluated by measuring platelet consumption in an artificial circulation, and heparin uptake was quantified using tritiated heparin. The results indicate that the bovine ureter grafts have an adequate degree of mural integrity and hemocompatible properties comparable to saphenous vein. The in vivo patency in a canine bilateral femoral interposition model was 62.5% (10/16) for the bovine ureters and 43.75% (7/16) for PTFE. Bovine ureter grafts appear to have an excellent potential for use in narrow diameter peripheral and coronary arterial bypass procedures and warrant further investigation.
Synthetic and biosynthetic conduits 6 mm in internal diameter and 3 cm long were implanted as aorto-pulmonary shunts in 4 week old piglets. The synthetic conduit was made of Polytetrafluoroethylene (P.T.F.E.) manufactured by Gore-Tex; the biosynthetic graft was prepared by tanning bovine ureters and covering it with a polyester mesh. Two groups of six animals for each conduit underwent operation. Following implantation, when the animals were physiologically stable, the pressure and blood flow were measured in the pulmonary artery, conduit and aorta, and at the same time blood gases were obtained. These measurements were repeated four weeks later, following which the grafts were excised and processed for histological studies. All the conduits were patent, 4 weeks after implantation, but whereas there was little difference in the flows through the bovine grafts (506 ml/min) there was a marked reduction in the flow through the Gore-Tex conduit (235 ml/min). These differences could be related to the changes seen histologically. No drugs were used to affect patency of the conduits in this study.