A non-porous coated PTFE graft includes a PTFE tube having a conventional porous inner cylindrical wall and a non-porous elastomeric coating applied over at least a portion of the outer cylindrical wall of the PTFE tube to render such portion of the outer cylindrical wall non-porous. The elastomeric coating is made of polyurethane or another biocompatible non-porous elastomer and precludes tissue ingrowth into the outer cylindrical wall, minimizes suture hole bleeding, and increases suture retention strength, while reducing the incidence of serous weepage. The elastomeric coating is preferably applied by mounting the PTFE tube upon a mandrel of like diameter and either dip coating or spray coating all, or selected portions, of the PTFE tube with liquified polyurethane. After the polyurethane coating is completely dried, the non-porous vascular graft is removed form the mandrel and is ready for use.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
1. "BLOOD VESSEL PATCH", Ser. No. 07/358,785, filed concurrently herewith, 
naming Berguer et al. as inventors, and assigned to the assignee of the 
present invention. 
2. "LONGITUDINALLY COMPLIANT PTFE GRAFT", Ser. No. 07/358,011, filed 
concurrently herewith, naming Della Corna et al. as inventors, and 
assigned to the assignee of the present invention, now issued as U.S. Pat. 
No. 4,955,899. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to prosthetic vascular grafts for 
implantation within the vascular system of a patient, and more 
particularly, to a prosthetic vascular graft made from expanded, porous 
polytetrafluoroethylene (PTFE) tubing that is fabricated to retain the 
porous inner cylindrical wall of conventional PTFE vascular grafts, but 
wherein the outer cylindrical wall of the PTFE tube is rendered non-porous 
over at least a portion of its length. 
2. Description of the Prior Art 
The use of implantable prosthetic vascular grafts made of expanded, porous 
PTFE is well known in the art. Such vascular grafts are often implanted 
just below the skin to provide blood access for long term hemodialysis. 
Such PTFE vascular grafts are also used to replace or bypass occluded or 
damaged natural blood vessels. Such prosthetic vascular grafts, and 
methods of implanting the same, are generally described in Bennion et al., 
"Hemodialysis and Vascular Access", Vascular Surgery, pp. 625-662, 1983. 
Methods of forming expanded, porous PTFE tubing are well known in the art. 
For example, U.S. Pat. No. 4,187,390 issued to Gore discloses one such 
process which may be used to produce highly porous, expanded PTFE 
structures. 
Expanded, porous PTFE material offers a number of advantages when used as a 
prosthetic vascular graft. PTFE is highly biocompatible, has excellent 
mechanical and handling characteristics, does not require preclotting with 
the patient's blood, heals relatively quickly following implantation, and 
is thromboresistent. Notwithstanding its many advantages, certain problems 
may arise with the use of PTFE vascular grafts. For example, PTFE material 
is not very elastic, and the suture holes formed in the ends of the graft 
when the graft is sutured to a blood vessel during implantation often leak 
blood until clotting occurs within the suture holes. Moreover, while 
porous PTFE vascular grafts are generally impermeable to blood, instances 
have arisen wherein serous weepage has occurred; serous weepage arises 
when the watery portion of the blood passes through the wall of the PTFE 
vascular graft and forms a collection of fluid, known as a seroma, 
adjacent the outer wall of the vascular graft. Additionally, instances 
have arisen wherein sutures used to secure the ends of PTFE vascular 
grafts to blood vessels within the body have torn the wall of the PTFE 
vascular graft, causing failure thereof. 
Conventional PTFE vascular grafts have a porous outer cylindrical wall 
which facilitates tissue ingrowth into the outer cylindrical wall of the 
vascular graft, thus helping to heal and stabilize the graft. Nonetheless, 
there are instances wherein it is desired to preclude such tissue 
ingrowth. For example, should it later become necessary to perform a 
thrombectomy to remove a blood clot within the graft, the wall of the 
graft must be exposed in order to permit the formation of an incision 
therein. Exposure of the vascular graft is made more difficult if 
significant tissue ingrowth has taken place. Similarly, there are 
instances wherein it is desired to implant a jump graft onto a previously 
existing vascular graft. Once again, the outer cylindrical wall of the 
original graft must be exposed in order to implant the jump graft. 
However, the significant tissue ingrowth fostered by conventional PTFE 
vascular grafts make such exposure more difficult. 
Accordingly, it is an object of the present invention to provide a PTFE 
vascular graft having a porous inner cylindrical wall and including an 
outer cylindrical wall, at least a portion of which is rendered non-porous 
for preventing tissue ingrowth and facilitating later exposure of the 
vascular graft. 
It is another object of the present invention to provide such a PTFE 
vascular graft which eliminates or minimizes suture hole bleeding when the 
graft is implanted. 
It is still another object of the present invention to provide such a PTFE 
vascular graft which significantly reduces the incidence of serous 
weepage. 
It is a further object of the present invention to provide such a PTFE 
vascular graft with increased suture retention strength to avoid tearing 
of the walls of the graft. 
These and other objects of the present invention will become more apparent 
to those skilled in the art as the description thereof proceeds. 
SUMMARY OF THE INVENTION 
Briefly described, and in accordance with the preferred embodiments 
thereof, the present invention relates to a PTFE vascular graft having a 
porous inner cylindrical wall and having an opposing outer cylindrical 
wall, wherein at least a portion of the outer cylindrical wall is rendered 
non-porous through the application of a non-porous elastomeric coating 
thereto. The vascular graft includes an expanded, porous PTFE tube, and a 
coating of a non-porous elastomer coated to at least a portion of the 
outer cylindrical wall of the PTFE tube. The coated portion of the PTFE 
tube precludes tissue ingrowth into the outer cylindrical wall thereof, 
minimizes blood leakage through any suture holes formed therein, increases 
suture retention strength, while reducing the incidence of serous weepage. 
Non-porous polyurethane is preferably used to form the non-porous 
elastomeric coating upon the outer cylindrical wall of the PTFE tube. 
Other biocompatible elastomers which may be used to form such coating 
include medical-grade silicone rubber elastomers, segmented polyurethanes, 
polyurethane-ureas, and silicone-polyurethane copolymers. 
PTFE vascular grafts can be formed with the above-described non-porous 
elastomeric coating applied over the entire length of the underlying PTFE 
tube. Alternatively, the non-porous elastomeric coating may be applied 
over the outer cylindrical wall of the PTFE tube only along the first and 
second opposing end portions of the PTFE tube, and not along the central 
portion thereof. Such end-coated PTFE vascular grafts provide the 
aforementioned advantages of minimizing suture hole bleeding, increased 
suture retention strength, and preclude tissue ingrowth near the points of 
anastomosis, while permitting tissue ingrowth in the central portion of 
the vascular graft to help stabilize the same. 
The present invention also relates to the method by which such implantable 
vascular grafts may be produced. The porous PTFE tube starting material is 
coated with a liquified elastomer upon at least a portion of the outer 
cylindrical wall thereof, and the liquified elastomeric coating is then 
dried to form the non-porous coating upon the outer cylindrical wall of 
the PTFE tube. As used herein, the term liquified elastomer should be 
understood to refer to an elastomer dissolved in a liquid solvent. 
Preferably, the PTFE tube starting material is pulled over a cylindrical 
mandrel having an outer diameter commensurate with the internal diameter 
of the PTFE tube, before the liquified elastomeric coating is applied. The 
liquified elastomer is preferably applied by either dip coating or spray 
coating the liquified elastomer upon the PTFE tube while the PTFE tube is 
supported upon the mandrel. Those portions, if any, of the outer 
cylindrical wall of the PTFE tube which are to remain porous are not 
coated with the liquified elastomer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1, a PTFE vascular graft having a non-porous outer cylindrical wall 
is designated generally by reference numeral 20. As shown, vascular graft 
20 is in tubular form and may be made to have any desired length and 
internal diameter. Within FIG. 1, dashed lines 22 indicate the central 
longitudinal axis of vascular graft 20. Vascular graft 20 includes a first 
end 24 and an opposing second end 26. 
Within FIG. 2, a cross section of vascular graft 20 is shown. Vascular 
graft 20 includes an inner expanded, porous PTFE tube 32 having a 
micro-structure characterized by nodes interconnected by fibrils. PTFE 
tube 32 includes an inner cylindrical wall 34 and an opposing outer 
cylindrical wall 36. As shown in FIG. 2, outer cylindrical wall 36 is 
coated entirely around its circumference by a uniformly thick coating 38 
of a biocompatible elastomer. 
The preferred starting material used to form PTFE tube 32 is expanded 
porous PTFE material of the type generally described within U.S. Pat. No. 
4,187,390 to Gore. Such expanded, porous PTFE material is commonly used to 
form prosthetic vascular grafts. The preferred wall thickness of PTFE tube 
32 ranges from 0.1 millimeter to 1.0 millimeters; the preferred internoda 
distance within such expanded PTFE material ranges from 10 micrometers to 
60 micrometers. The longitudinal tensile strength of such PTFE material is 
preferably equal to or greater than 1500 psi, and the radial tensile 
strength of such PTFE material is preferably equal to or greater than 400 
psi. The suture retention strength of such PTFE starting material is 
preferably equal to or greater than 300 grams. 
In regard to elastomeric coating 38 shown in FIG. 2, such elastomeric 
coating is selected to be a biocompatible elastomer and may be selected 
from the group consisting of medical-grade silicone rubber elastomers, 
segmented polyurethanes, polyurethane-ureas, and silicone-polyurethane 
copolymers. Suitable candidates for use as elastomeric coating 38 
typically have a hardness rating between 50A-100A and 55D-60D. Most of the 
above-mentioned elastomers can be chemically or biologically modified to 
improve biocompatability; such modified compounds are also candidates for 
use in forming elastomeric coating 38 shown in FIG. 2. 
Apart from biocompatability, other requirements of an elastomer to be a 
suitable candidate for use as elastomeric coating 38 are that the 
elastomer be sufficiently elastic to effect instantaneous closure of 
suture holes formed by a suture needle. Elasticity should be balanced 
against the thickness of elastomeric coating 38, the objective being to 
select the minimum coating thickness necessary to prevent significant 
blood leakage through the suture hole locations without significantly 
impeding suture needle penetration. The elastomeric coating should also be 
sufficiently non-porous to preclude serous weepage and inhibit tissue 
ingrowth therethrough. Yet another requirement of such elastomers is that 
they be easily dissolvable in low boiling point organic solvents such as 
tetrahydrofuran, methylene chloride, trichloromethane, dioxane, and 
dimethylflormamide, by way of example. Finally, suitable elastomers should 
lend themselves to application to PTFE tube 32 by either the dip coating 
or spray coating methods described in greater detail below. 
The presently preferred elastomer used to form elastomeric coating 38 is a 
polyurethane formulation grade SG-80 sold under the trademark "TECOFLEX" 
by Thermedics, Inc. of Woburn, Mass. Such formulations are considered 
medical grade aliphatic polyurethanes resins of solution processible 
grades. Such formulations are designed to be dissolved in various solvents 
for use in solution casting or for coating of medical products. The 
polyurethane formulation is preferably dissolved in the solvent known as 
Tetrahydrofuran (THF), a solvent commercially available from Mallinckrodt, 
Inc. through the Scientific Products Division of Baxter Corp., of Irvine, 
Calif. 
Further details concerning the preferred construction of vascular graft 20 
shown in FIGS. 1 and 2 can more readily be understood in conjunction with 
the preferred method by which vascular graft 20 is produced. It has 
already been noted above that PTFE tube 32 is formed of expanded, porous 
PTFE material of a type often used to form vascular prostheses. In 
practicing the preferred method, the PTFE starting material is initially 
in the form of a cylindrical tube having an inside diameter ranging from 
1.0 millimeters to 30 millimeters, and ranging in length up to 100 
centimeters. 
Prior to applying the non-porous elastomeric coating to the outer 
cylindrical walls of the PTFE tube, the PTFE tube is preferably pulled 
onto a supporting mandrel, as shown in FIG. 6. Within FIG. 6, the PTFE 
tube starting material is designated by reference numeral 66. As shown in 
FIG. 6, PTFE tube 66 is pulled over a cylindrical supporting mandrel 68 
which has an outer diameter that is equal to or slightly larger than the 
internal diameter of PTFE tube 66. Preferably, mandrel 68 should be 
approximately 0.2-0.4 millimeters larger than the inside diameter of PTFE 
tube 66 to prevent PTFE tube 66 from sliding upon the mandrel during 
coating. 
After mounting PTFE tube 66 upon mandrel 68, the above-described 
elastomeric coating may then be applied to the outer cylindrical wall of 
PTFE tube 66. As mentioned above, the two preferred methods of applying 
the elastomeric coating are dip coating and spraying. Regardless of which 
application method is used, the preferred method of formulating the 
liquified elastomer is the same. As has been described, the preferred 
liquified elastomer is formed by preparing a solution of "Tecoflex" 
polyurethane grade SG-80A. This solution is prepared by dissolving 
polyurethane pellets in the above-described terahydrofuran solvent in a 
heated glass reactor equipped with a cold water condenser held at 
60.degree. C. Such polyurethane pellets may also be dissolved in the 
solvent at room temperature through continuous stirring. The use of the 
heated reactor is preferred, as it dissolves the polyurethane pellets in a 
few hours, whereas the method of stirring the solution at room temperature 
takes approximately two days. 
The preferred solids content for "Tecoflex" grade SG-80A is 2-4 percent by 
weight; however, the solids content may range up to 15 percent by weight, 
depending upon the specific polymer composition, the dip coating 
parameters, and the intended end uses. Where multiple coatings are 
employed, the composition of the polyurethane solution may be varied 
between coating layers. For example, it might be advantageous to apply 
progressively more dilute polyurethane solutions to the underlying PTFE 
tube. 
Following preparation of the liquified polyurethane solution as described 
above, the next step is to apply the polyurethane solution as a coating 
upon the outer wall of PTFE tube 66. The method of dip coating the PTFE 
tube will now be described in conjunction with FIG. 4, which illustrates a 
dip coating machine. 
FIG. 4 illustrates a dip coating machine designated generally by reference 
numeral 65. As mentioned above, mandrel 68 is preferably selected to have 
a diameter that is approximately 0.2-0.4 millimeters larger than the 
inside diameter of PTFE tube 66 to prevent PTFE tube 66 from sliding upon 
mandrel 68 during the coating process. Preferably, the length of PTFE tube 
66 is approximately 25-30 centimeters. Lengths in excess of 30 centimeters 
are not preferred due to the effects of gravity pulling upon the 
polyurethane coating during the coating process; attempts to process PTFE 
tube sections much in excess of 25-30 centimeters in length can result in 
uneven coating thicknesses as measured between the top and bottom of 
mandrel 68. 
As shown in FIG. 4, mandrel 68 extends vertically downward from a motor 70 
which continuously rotates mandrel 68 and PTFE tube 66 secured thereto. 
Motor 70 is, in turn, supported by a bracket 72 adapted to travel 
vertically upward and downward. Bracket 72 includes a smooth bushing 74 
through which a smooth vertical support rod 76 passes. Bushing 74 is 
adapted to slide upwardly and downwardly along support rod 76. Bracket 72 
further includes a threaded collar 78 through which a threaded rotatable 
drive rod 80 passes. The lowermost end of drive rod 80 is secured to the 
drive shaft of a second motor 82 which rotates in a first rotational 
direction to raise mandrel 68 and which rotates in an opposing rotational 
direction to lower mandrel 68. Both motor 82 and support rod 76 are 
supported at their lower ends by a base 84. The upper end of support rod 
76 is fixedly secured to bracket 86 which rotatably supports the upper end 
of drive rod 80. 
Motor 82 of dip coating machine 65 is initially operated to raise mandrel 
68 to its uppermost position. A tall, slender container 88 containing the 
above-described polyurethane solution 90 is placed upon base 84 
immediately below mandrel 68. Motor 82 may then be operated in the reverse 
rotational direction to lower mandrel 68, and PTFE tube section 66 secured 
thereto, into polyurethane solution 90. 
The variables controlled by dip coating machine 65 include the speed at 
which mandrel 68 is immersed and withdrawn, the rotational speed of 
mandrel 68, and the drying time between successive coatings. These 
parameters are controlled to ensure that the polymer coating penetration 
is restricted to the outer layers of the PTFE tube section 66. 
The preferred number of polyurethane solution coatings applied to PTFE tube 
66 is eight, but may range between one and twenty coatings, depending upon 
the concentration of the elastomer solution used in the dipping process, 
and depending upon the intended use of the end product. The preferred 
coating thickness at the completion of the dip coating process is between 
0.06-0.08 millimeters, but may vary up to two millimeters, depending upon 
the dimensions of the coated tube and the elastomer solution 
concentration. 
The dip coating procedure of immersing and then withdrawing PTFE tube 66 is 
a continuous process, and PTFE tube 66 is continuously in motion at any 
given time during the procedure. Drying intervals between successive 
polyurethane coatings can vary up to a few hours depending upon the type 
of solvent used and the drying conditions. PTFE tube 66 is dried in 
ambient air, preferably in an inert atmosphere, but may also be dried at 
elevated temperatures of 40.degree.-100.degree. C. PTFE tube 66 remains 
secured to mandrel 68 until the coating and drying process described above 
is completed. When the last of the eight coatings has substantially dried, 
PTFE tube 66 is further dried under vacuum at 50.degree. C. at 10-15 mmHg 
vacuum for 10-24 hours to completely remove any remaining solvents. The 
polyurethane coated PTFE tube is then removed from mandrel 68. 
A second method for applying the polyurethane coating to the PTFE tube 
involves the use of spraying and will now be described in conjunction with 
the spray coating machine shown in FIG. 5. The polyurethane solution to be 
sprayed is first prepared in the same manner as described above for the 
dip coating process. The polyurethane solution is inserted within cylinder 
92 of a pump 94 for delivery through a plastic tube 96 to a spray nozzle 
98. An inert gas, such as nitrogen, is also supplied to spray nozzle 98 
through connecting tube 100 from supply tank 102. An inert gas is 
preferably used to minimize reactions which polyurethane can undergo upon 
exposure to air and oxygen. 
Still referring to FIG. 5, PTFE tube 66' is again stretched over a mandrel 
68'. Once again, mandrel 68' is preferably of a diameter slightly larger 
than the inner diameter of PTFE tube 66' to prevent PTFE tube 66' from 
sliding thereupon. Mandrel 68' is supported for rotation about a 
horizontal axis. One end of mandrel 68' is coupled to the drive shaft of a 
first motor (not shown) within motor housing 104, while the opposite end 
of mandrel 68 is rotatably supported by bracket 106. Both motor housing 
104 and bracket 106 are supported upon base 108. The aforementioned first 
motor continuously rotates mandrel 68' at speeds of up to 500 rotations 
per minute. 
Spray nozzle 98 is supported for reciprocal movement above and along 
mandrel 68'. As shown in FIG. 8, spray nozzle 98 is secured to support rod 
110 which includes at its lowermost end a carriage 112. A threaded drive 
rod 114 is coupled at a first end to the drive shaft of a second motor 
(not shown) within motor housing 104 for being rotated thereby. The 
opposite end of threaded drive rod 114 is supported by and freely rotates 
within bracket 106. Threaded drive rod 114 threadedly engages a threaded 
collar (not shown) within carriage 112. Accordingly, rotation of drive rod 
114 causes carriage 112, and hence spray nozzle 98, to move in the 
directions designated by dual headed arrow 116, depending upon the 
direction of rotation of drive rod 114. Also shown in FIG. 5 are a pair of 
microswitches 118 and 120 which are periodically engaged by carriage 112 
and which, when actuated, reverse the direction of rotation of threaded 
drive rod 114 in a manner which causes spray nozzle 98 to reciprocate back 
and forth along mandrel 68'. 
As shown in FIG. 5, spray nozzle 98 makes several passes along mandrel 68', 
repetitively spraying PTFE tube 66' as it rotates. Spray nozzle 98 is 
caused to travel at a linear speed of up to 50 centimeters per minute. The 
polyurethane coating thickness which results from this spraying process is 
determined by the speed of rotation of mandrel 68', the linear speed of 
spray nozzle 98, as well as the rates of delivery of both the polyurethane 
solution by pump 94 and the rate of delivery of inert gas. These rates of 
delivery may range up to 5 milliliters per minute for the polyurethane 
solution, and up to 5 liters per minute for the nitrogen gas. After an 
appropriate number of spray cycles, PTFE tube 66' is vacuum dried and 
pulled from mandrel 68', in the same manner as described above. 
While the dip coating and spray coating methods described above in 
conjunction with FIGS. 4 and 5 are directed to the process of coating the 
entire outer cylindrical wall of the PTFE tube 66, those skilled in the 
art will appreciate that such dip coating and spray coating methods may be 
used to form a non-porous elastomeric coating upon only portions of the 
PTFE tube. For example, it may be desired to provide a PTFE vascular graft 
40 like that shown in FIG. 3 wherein only the opposing end portions 42 and 
44 of vascular graft 40 are to have a non-porous outer cylindrical wall. 
Accordingly, the dip coating process illustrated in FIG. 4 may be 
practiced by dipping only one end of PTFE tube 66 (corresponding to first 
end 42 of graft 40 in FIG. 3) into the liquified polyurethane solution 90; 
after the desired number of coatings have been applied to the lower end of 
PTFE tube 66, mandrel 68 may be inverted to cause the opposite end of PTFE 
tube 66 (corresponding to second end 44 of graft 40 in FIG. 3) to be 
immersed within polyurethane solution 90. Similarly, in FIG. 5, spray 
nozzle 98 may be maintained away from the central region of PTFE tube 66' 
to avoid spraying such central region with the liquified elastomer. 
Alternatively, a cylindrical shield (not shown) may be extended around the 
central portion of PTFE tube 66' within the spray coating apparatus of 
FIG. 5 to prevent the liquified polyurethane spray from contacting the 
central region of PTFE tube 66'. 
With respect to the end-coated PTFE vascular graft described above in 
conjunction with FIG. 3, a cross section taken through either of end 
portions 42 or 44 would resemble the cross-sectional drawing shown in FIG. 
2. The central portion of graft 40 in FIG. 3 extending between end 
portions 42 and 44 would have a cross section as shown in FIG. 2, but 
without the elastomeric coating 38. Within FIG. 3, the central portion of 
graft 40 has been shown as being of reduced outer diameter in comparison 
with the outer diameters of end portions 42 and 44, for purposes of 
illustration. In most instances, the actual variation in wall thickness 
along the length of graft 40 would be difficult to detect visibly. The 
preferred dimensions of the end-coated sections 42 and 44 may range up to 
40 percent of the overall length of the graft. The extent of the coating 
will depend upon the specific application and surgeon preference. A short 
coated length may be preferred when only the advantages of reduced suture 
hole bleeding and increased suture retention strength are sought. A longer 
coated length may be desired to allow for more trimming of the ends of the 
graft, and/or to reduce tissue ingrowth to a greater extent at the ends of 
the graft. Briefly referring to FIG. 4, the lengths of the end portions of 
the graft shown in FIG. 3 are easily adjusted by controlling the depth of 
immersion of PTFE tube 66 into polyurethane solution 90. 
Apart from the fully-coated and end-coated vascular grafts shown in FIGS. 1 
and 3, respectively, other configurations of non-porous coated PTFE grafts 
may also be constructed. For example, it might be desired to provide a 
PTFE graft wherein only the central portion of the graft is coated with 
polyurethane or another biocompatible elastomer. 
A laboratory simulation was conducted in a manner described below to 
determine the susceptibility of non-porous coated PTFE vascular grafts to 
suture hole bleeding. Test segments were taken from two PTFE tube 
sections, each measuring 19 millimeters in internal diameter, one of such 
tube sections being pure PTFE having a wall thickness of 0.774 millimeters 
and the second PTFE tube section having a wall thickness of 0.594 
millimeters and having a polyurethane coating thickness of 0.088 
millimeters applied to it in the manner described above. Thus, the overall 
wall thickness of the coated test segments was less than that of the 
uncoated test segments. A two inch length from each of the aforementioned 
tube sections was clamped between two hemostats, and ten 6-0 polypropylene 
sutures were placed in a continuous fashion in the middle of each tube. 
The test sections were then each pressurized to 2 psi with water, and 
water loss through the suture holes was measured for a one minute period. 
Similar measurements were also made with the water pressure being raised 
to 4 psi. Leak rate measurements obtained by the procedure described above 
are set forth below. 
______________________________________ 
Leak Rate 
Water (ml/min) 
Pressure Non-coated Coated 
(Psi) PTFE Tube PTFE Tube 
______________________________________ 
2 psi 11.04 3.44 
4 psi 19.96 8.3 
______________________________________ 
By way of comparison, normal blood pressures within the human body 
typically range from 1.8 to 2.3 psi. Thus, the formation of the 
polyurethane coating upon the PTFE tube significantly reduces the suture 
hole leakage rate. 
The aforementioned laboratory simulation was also used to compare suture 
retention strength of such non-porous coated PTFE vascular grafts to 
conventional uncoated PTFE vascular grafts. Both axial suture retention 
strength and radial suture retention strength were tested. Axial suture 
retention strength was tested by sewing a 6-0 polypropylene suture through 
the wall of the graft two millimeters from the end and applying a load to 
the suture along the longitudinal axis of the tubular graft. Peak loads at 
failure of the graft or breaking of the suture itself were noted. Radial 
suture retention strength was tested by first slitting the tubular test 
segment, opening the test segment to form a relatively flat sheet, sewing 
6-0 polypropylene suture into the test segment, and applying a load to the 
suture in a direction perpendicular to what would have been the 
longitudinal axis of the tubular graft before it was slit open. Again, 
peak loads at failure of the graft or breaking of the suture itself were 
noted. The results of this comparison are set forth below: 
______________________________________ 
Axial and Radial Suture Retention Strength 
Non-coated 
Coated 
PTFE Tube 
PTFE Tube 
______________________________________ 
Axial suture retention 
321.4 .+-. 63.4 
747.1 .+-. 169.3 
strength (grams) 
Radial suture retention 
782.2 .+-. 74.3 
743.9 .+-. 80.3 
strength (grams) 
______________________________________ 
Thus, the polyurethane coating significantly increases axial suture 
retention strength without adversely impacting upon radial suture 
retention strength. 
The aforementioned laboratory simulation also included a comparative 
investigation of the respective water entry pressures for the uncoated and 
coated PTFE test segments described above. Water entry pressure is a test 
of the pressure at which water applied to the inner passageway of the 
graft leaks through the outer porous wall of the PTFE tube, and thereby 
serves as a measure of the tendency for such a vascular graft to exhibit 
serous weepage when implanted in the body. The respective water entry 
pressures noted for the test segments described above are as follows. 
______________________________________ 
Water Entry Pressure 
Non-coated 
Coated 
PTFE Tube 
PTFE Tube 
______________________________________ 
Water entry pressure (psi) 
7.4 .+-. 0.76 
&gt;15 psi 
______________________________________ 
Thus, the polyurethane coating significantly increases water entry pressure 
and lessens the tendency of a graft to exhibit serous weepage. 
Those skilled in the art will now appreciate that an improved PTFE vascular 
graft has been described which has a cylindrical outer wall that is 
non-porous over at least a portion of its length and which may be used 
wherever prosthetic vascular grafts are currently used today, including 
various applications in both peripheral vascular and vascular access uses. 
The above-described graft may be implanted in the same manner as is 
currently used to implant porous PTFE vascular grafts. Moreover, the 
elastomeric coating minimizes suture hole bleeding at the time of 
implantation, increases suture retention strength, reduces serous weepage, 
and selectively precludes tissue ingrowth at the coated sections. While 
the invention has been described with reference to preferred embodiments 
thereof, the description is for illustrative purposes only and is not to 
be construed as limiting the scope of the invention. Various modifications 
and changes may be made by those skilled in the art without departing from 
the true spirit and scope of the invention as defined by the appended 
claims.