Fundamentals
`of
`
`Vascular Grafting
`
`edited by
`
`SIGMUND A. WESOLOWSKI, M.D.
`Associate Professor of Surge>)'
`State Un iversity of New York
`Downstate ft1 edical Center
`H ead, Vascu lar Surgical Services
`Kings County Hosf1ital, B rooklyn
`
`and
`
`CLARENCE DENNIS, M.D., Ph.D.
`P rof essor and Chairman, Def1artm ent of Surge>)'
`State University of New York
`Down.~tate M edical Center
`Surgeon -in -Chief
`Kings County H osf1ital, Brooltlyn
`
`Th e Blakiston Division
`McGRAW-HILL BOOK COMPANY, INC.
`Toronto
`London
`New York
`
`TMT 2091
`Medtronic v. TMT
`IPR2021-01532
`
`

`

`FUNDAMENTALS OF VASCULAR GRAFTING
`
`Copyright © 1963 by the McGraw-Hill Book Com(cid:173)
`pany, Inc. All rights reserved. Printed in the United
`States of America. This book, or parts thereof, may
`not be reproduced in any form without permission
`of the publishers.
`
`Library of Congress Catalog Card Number: 63-15462
`
`69461
`
`

`

`6
`
`Designing Prosthetic Vascular Grafts
`
`Thomas Edman, Ph.D.
`
`Philadelphia College of Textiles and Science;
`Fashion Institute of Technology, New York; and
`College of Medicine, Baylor University, Houston
`
`It is gratifying to find extended uses for textile materials in medical
`and surgical applications. Unfortunately, we cannot seek out the problems
`where we can be of help to you, but we have to wait for you to initiate
`the possible approaches to using fabrics as reinforcements for surgical re(cid:173)
`placements. I am fully aware that no matter how perfect a prosthetic sub(cid:173)
`stitute is, it cannot approach Nature's own design in working harmony
`and functional suitability.
`A brief discussion of some developments in grafting during the last
`decade illustrates a significant progress in this field and an ever-contin(cid:173)
`uous effort toward further improvements. You recall the early stages of
`graft replacements, when surgeons had to rely on homografts for clinical
`repair of arterial defects. The procurement and preparation of homografts
`for storage were very expensive and inconvenient even in the artery bank
`of member hospitals. The supply was irregular and inadequate in the
`necessary sizes; the transplanted grafts often occluded; and gradually
`weakening areas were subject to rupture under arterial pressure.
`Voorhees at al.1 reported in 1952 the use of Vinyon-N cloth for the
`repair of arterial defects. In 1953, Vargas and Deterling2 discussed the use
`of nylon net for the support of grafts. During the 1954 meeting of the
`American College of Surgeons in Atlantic City, Wesolowski and Sauvage3
`evaluated Orlon mesh, and Seit et al., 4 braided plastic-coated nylon
`tubes, for arterial restitutions. The general method of preparing a tubular
`graft replacement from a tightly woven flat fabric was described by Poth
`et al." in 1955. This fabric performed as a graft, but the seam promoted
`occlusion.
`By 1955, there were several new approaches under development with
`Lhe assistance of research technologists from the textile, pharmaceutical,
`ll9
`
`

`

`120
`
`Z.ABRICllTIONS OF THE PROSTHETIC GRAFT
`
`chemical, and allied industries. The design of a suitable graft has to take
`into consideration several functional requirements and some easily man.
`ageable prerequisites. The graft has to be readily acceptable by the body;
`it must remain strong and durable for an infinite period of time; it must
`perform the functions of the removed or bypassed part of the arterial
`system; the fabric must be e2sy to cut and suture, and must not fray; it
`must have acceptable porosity that allows tissue growth without excessive
`loss of blood during the operation; and it has to be flexible and elastic
`to allow the continuous flow of blood under any physical movement of
`the body. Grafts in a great number of shapes and sizes, for the entire
`arterial system, have to be readily available in a standardized system for
`the convenience of surgeons and must be unaffected by repeated steriliza.
`tion.
`The design of the seamless straight or bifurcated arterial prosthesis has
`to incorporate into the synthetic graft the physical and chemical advan(cid:173)
`tages of three components: the fiber, the fabric construction, and the
`finishing of the material.
`A textile fiber can be defined as a thread-like structure that can be pro(cid:173)
`cessed into a fibrous material. Many fibers have been processed into grafts,
`but only a few deserve serious consideration. Listed in order of decreasing
`tissue reactivity, the fibers are nylon, Orlon, Dacron, and Teflon.* Teflon
`is the most chemically inert fiber used, and the newly formed tissue can
`not anchor itself within the fiber structure. The loosely held tissue can
`break away from the graft wall, forming a moving obstacle within the
`arterial system. Teflon is also difficult to process in the bleaching and
`heat-setting operations. Since Teflon has no capacity for moisture absorp•
`tion, it will leak blood more easily than Dacron. There are no final con(cid:173)
`clusions centered on one fiber; however, at present the production of
`grafts is divided approximately 60 per cent Dacron and 40 per cent
`Teflon, with a definite trend in favor of Dacron.
`Textile fibers are grown and produced in staple form (No. 5 and 8 in
`Fig. 73 show fibers of short lengths of definite dimensions), and in con(cid:173)
`tinuous filament form (No. 6 and 7 in Fig. 73 show fibers of infinite
`length). The staple fiber is not suitable because the fibers are held to•
`gether in the spinning process only by a twist in the yarn, and the indi(cid:173)
`vidual fiber can break away from the yarn and occlude the lumen of the
`graft. The filament yarn can be extruded either as a heavy single end,
`calle~ monofilament (No. 6 in Fig. 73), or as many parallel ends, called
`mu_lt1filament (No. 7 in Fig. 73). The monofilament yarn has less capillary
`act10n and does not bend easily. The design of synthetic grafts requires
`as many filaments as possible to achieve reduced porosity and ease of
`
`• Orlon is the registered trade name for the acrylic fiber manufactured by E. I. du Pont
`de Nemours & Company; Dacron is the Du Pont Company's trade name for its polyester
`fiber; Teflon is its trade name for its tetralluoroethylene fiber.
`
`

`

`DESIGNING PROSTHETIC GRAFTS
`
`121
`
`Fie. 73. Sec tex t.
`
`suLUriug. For example, Lhe older type of De Bakey Dacron bifurcated
`graft had 378 filaments in each thread. r\n additional process imparts
`bulkiness to filament yarns, known by their trade names. Fig. 73 illustrates
`some of the important bulking processes, such as No. I Flufion, No. 2
`Helenca, No. 3 Taslan, and No. 4 Banlon. Fluflon is the most widely used
`process of yarn modification because it reduces porosity and imparts
`elasticity to the graft.
`The next important step in graft design is fabric construction, using
`all three methods of manufacturing tubular fabrics : weaving, knitting,
`and braiding. The braided fabrics gained early recognition with the Tapp(cid:173)
`Erlwards nylon graft in 1954. ,-vhen the fabric is extended or contracted,
`its diameter changes, and it frays easily. Braided grafts have been entirely
`replaced by knitted and woven fabrics. The volume of knitted and woven
`fabrics sold is about equal, but there is a growing preference for knitted
`fabrics.
`In 1955, at the Textile School of the North Carolina State College, a
`tubular graft was knitted, which required three hand-stitched tubes to be
`_joined into one bifurcation. In 1956, at the Philadelphia College of Tex(cid:173)
`tiles and Science, I started the development of the De Bakey Dacron graft
`in cooperation with Dr. De Bakey and his staff at Baylor University. The
`construction design of this graft has been widely copied here and abroad .
`The woven constructions were originated using several differen t
`methods of manufacturing. The grafts made by John Sidebotham, Inc.,
`and United States Catheter & Instrument Corp. are products of narrow
`fabric looms, while the graft made by Meadox Medicals, Inc., is pro(cid:173)
`duced on a broad-width Jacquard loom.
`
`

`

`122
`
`FARR/CATION OF THE PROSTHETIC GRAFT
`
`Figure 74 shows the braided fabric. In this construction there is one
`system of threads twisting around each ot_her. The yarns a~e not sup(cid:173)
`porting each other sufficiently to avoid fraying. A hot needle 1s necessary
`to weld the free ends together.
`Figure 75 compares the knitted and woven fa~ric _forma~ions. K~itting
`is a construction of interlacing loops, and weaving 1s the intersection of
`two systems of straight threads. Owing to the bending of the yarn into a
`loop, there is a limit to the tightness of the knitted fabric, whereas the
`woven fabric can be made almost watertight. The bifurcated knitted
`graft has a ~oarser and stronger construction than the straight knitted
`graft in terms of the amount of pressure they have to withstand. If the
`fabrics are cut on the bias, the woven fabric will fray more easily than
`the knitted cloth. The straight yarn in the width and length of the woven
`fabric makes the fabric stable, while the loop construction of the knitted
`fabric is elastic enough to move with flexing of the living tissue.
`The last step in the design of the synthetic graft is the finishing, or
`aftertreatment. The fabric is thoroughly washed and tumble-dried; the
`bulkiness of the modified filament yarn is fully developed. Some grafts
`are used in the straight form, but experience has shown that the me(cid:173)
`chanical crimping operation, heat-set in the fabric, gives additional elas(cid:173)
`ticity; it makes the inside wall smoother and less porous and keeps the
`graft tubular all the time without collapsing it in a sharp bend. The
`grafts are individually crimped. The Edwards graft has a spiral ring; the
`Meadox graft has an irregular saw-tooth crimp; and the De Bakey graft
`has a double reverse spiral to eliminate narrowing of the inside diameter
`when the tube is fully extended. The aftertreatment is gaining additional
`importance owing to several new developments under study. The crimped
`graft can be coated with an absorbable chemical compound to eliminate
`
`F,c. 74. See text.
`
`

`

`DESIGN I NG PROSTHETIC GIUFTS
`
`the loss of blood entirely and to adjust the rate o[ absorption to the re(cid:173)
`placement growth of the new tissue.
`In conclusion, I want to recall the work of the last 7 years in the de(cid:173)
`velopment of the De Bakey Dacron graft. ' "'e cannot say that we have
`found a perfect synthetic vascular graft yet, but our efforts to find addi(cid:173)
`tional improvements never cease. The value of this approach is proved
`daily by surgeons who have learned the proper technique of vascular re(cid:173)
`placement with the De Bakey Dacron graft and have achieved a similarly
`high percentage of success in human patients. The design of the graft
`is only a small contribution toward a successful operation ; however, your
`skill and confidence in using the graft measures its value. J trust that the
`world-wide acceptance of the knitted graft made of Dacron Fluflon ya rn,
`double reverse crimped, and coated with an absorbable compo und will
`save the lives of countless people in addition lo the thousands already
`enjoying extended vitality.
`
`References
`
`1. Voorhees, A. B., Jr., Jaretzki, A. , III, and Blakemore, A. 1-1 .: The use of tubes
`constructed from Vinyon-N cloth in bridging arterial defects, Ann. Surg., 135,
`332, 1952.
`2. Vargas, L. L., a nd Deterling, R. A., Jr.: The use of n ylo n net for the externa l
`support of blood grafts and aneurysms, Surgery, 34, I 061 , 1953.
`3. Wesolowski, S. A., and Sauvage, L. R .: Comparison o[ fates of Orlo n 111e,lt
`prosthetic replacement of thoracic aorta and aortic bifurcation, S. f o rum . 5.
`16, 195,1.
`
`

`

`124
`
`FABRICATION OF THE PROSTHETIC GRAFT
`
`4. Self, M. M., Cooley, D. A., De Bakey, M. E., and Creech, 0 ., Jr.: Use o[
`braided plastic coated nylon tubes for arterial restitution by end to encl
`suture method, S. Forum, 5, 16, 1954.
`5. Poth, E. J., Johnson, J. IC, and Childers, J. H .: The use of plastic fabrics as
`arterial prostheses, Ann. Surg., 142, 624, 1955.
`
`