Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1055843
NON-ANTIGENIC, NON-THRO~BOGENIC INFECTION-RESISTANT
I~:RAFTS FROM U~IBILICAL CORD VESSELS AND PROCESS FOR
PREPARING AND USING SAME
A major problem in vascular reconstructive surgery is
the provision of blood to organs and tissues the blood vessels
of which are inade~uate either as the result of congenital
defects or acquired disorders such as trauma, arterial sclerosis
or other diseases. Initially, arterial homografts ~human
arteries) were used to restore continuity but lirnited supply,
inadequate size ranges, development of aneurysms and athero-
sclerosis necessitated the search ~or a bet~er substitute.
Artificial grafts of porous and pliable plastic cloth
have been made but these suffer from the following problems:
1. Infection in a foreign body graft is catastrophic,
often leading to hemorrhage, sepsis and death.
2. The inner lining is throm~ogenic, predispoæed to
clotting of the gra~ and distal embolism of the
clot.
3. The rigidity of cloth grafts may resul~ in twisting
and kinking, especially in areas of crossing a joint.
4. Because of clotting difficulties, smaller caliber
artificial grafts are frequently unsuccessful.
Other types o~ grafts which have been testedl with
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10 5 5 ~ ~ 3
grea~er or le~ser degrPes of success are bo~ine heterogra~s,
collagen tube~ created within the recipient patient, saphenous
veins both as autograf~s where the patilent i9 the dGnor and as
allografts or h~ografts where another human is the donor.
These variou~ substitutes also give ris~e to problems of unavail-
ability9 small size, non-uniform caliber, time required or
harve~ting, intraluminal valves, easy twisting leading to
occlu~ion and taper in the wrong direction. Thi3 las~ problem
is particularly acute where saphenous veins are used since the
veins must be reversed as to the direction of flow o~ blood .:
therethrough when substituted for arteries. In view of the
difficulties encountered, it is evident that there is pressing
need for ~ vascular prosthesis which is free of the problems
enumer.ated ab~ve. In addition, it would be highly desirable
that such prostheses could be stored and kept .at hand.in a ..
wide var~ety of size~ and shape~ immediately available for use.
SUMMARY OF THE INVENTION
_
TKe human umbilical cord contains structures which
may be use~ ~or grafts in the vascular system or other body
condults in ~ nals including man. The umbilical cord contains
a vein and t~ arteries surrounded by ~arton's Jelly. Both
arteries an~ the vein are suitable for use in surgery. Composite
1 0 5 5 ~ 4 3
grafts and patches can be made in various sizes and shapes.
Arteries and veins removed from umbilical cords
may be used fresh or as a stored homograft in elther frozen
or chemically preserved form. Treatment with antibiotics
~r other means for sterilization may be carried out. Although
the antigenicity of these members is low, treatment with enzymes
may be carried out to eliminate any antigenic substances.
In general, the cord is somewhat coiled and the
artèrles therein are twisted around the veln. Consequently,
mechanical or chemical techniques to stralghten out the vein
and arteries may be necessary.
In preparation or use of the vein and arteries,
Wharton's jelly may be removed either manually or by flushing
out wi~h saline solution. A mandrel, which may be shaped, a
preferred shape be~ng a taper, ~ay be inserted into the vein
after which the vein and the arteries may be dissected readily
out of the umbilical cord itself. As aforenoted, the vein
and the arteries may be used fresh or frozen. In addition,
a tanning treatment as with an aldehyde can be used to stifen
the material, one advantage of such tr~eatment being that the
tanned member will retain the shape of the mandrel. Glùtaraldehyc e
is a preferred tanning agent. Prior to use of the ~anned mem~er,
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1055~
residual traces of glutaraldehyde are removed by trea~ment wi~h
appropriate chemical reagents, a preferred reagent being
glutamic acid. It has been ound that such treatment with a
tanning agert and a reagent to remove residual traces of same
yield a product of low antigenicity and thrombogenicity.
The advantages of the umbilical vessels, whether
fresh or preserved, for use as a conduit or a patch or rein-
forclng member are as follows:
1, Ready availability.
2. High 1exibility with freedom from tendency to
kink.
3. Marked strength, particularly in the smaller
diameter vessels.
4. Highly smooth, natural inner lining with extremely
low clotting tendency.
- 5. Low tendency to become infected.
6. Low antigenicity.
7. Controllable diameter.
8. Size selec~ion available for bo~h large and
small vessels.
9, Sufficient length for virtually any use.
10, Adaptability to a wide variety of shapes including
both tapers and curves.
11. Compatability with an outer support in ~he form
of a mesh for reinforcement of larger vessels
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1055843
to be used under pulsatile condition
12. Use as a coating Eor promotlng ~he healing of sur~ace
trauma such as wounds and burns.
A~cordingly, an object of the present lnvention is an
improved material for use as a vascular prosthesis, a rein-
forcement for organs in the form of patches, for reinforcement .
of a~asto~ases, and for promoting the healing of surface trauma.
. kno~her object of the present invention is a method o~
emplo!ying the vein and arteries from an umbilical cord in
surg~cal procedures.
A.further ob~ect of the present inventioll i8 a method
of s~aping ve~ns and arteries rom an umbil~cal cord in
preparation for usa in surgical proceduresO ~.
An important object of the present invention is a method
of pr.eparing and preserving veins and arteries from umbilical
cords, so that they ~ay be stored in readiness for use in surgical
procedures.
~ .s~gnificant ob~ect o~ the present Lnvention is a
material in the shape of conduits or patches using veins and
. arteries fro~ umb~lical cords as the source of same, said
mater.~al ~aving low antigenicity. low thro~bogenicity and
being highly resistant to in~ection.
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Still other objects and advantages of ~he invention will
in par~ be obvious and will in part be aLpparent from ~he
specification.
~ he invention accordingly comprlses the scveral steps
and the relation of one or more of such steps with respect to
each of the others, and the article possessing the ~eatures,
properties, and the relat~on of elements, which are exemplified
in ~he following detailed disclosure, and the scope of thP
invention will be i~dicated in the claims.
BRIET oEsoRIPrloN OF THE DRAWINGS
For a fuller understanding of the invention, reference
is had to the following description taken in connection with the
accompanying drawings, in which:
Flg. 1 is a view in perspecti~e of an umbilical cord
prior to treatment;
Fig. 2 is a sectional view of an umbilical cord vessel
on a cylindrical mandrel;
Fig. 3 is a view in partial section of an umbilical cord
vessel pressed against the interior of a mold hydraulically;
Fig. 4 is a sec~ional view of an umbilical cord vessel
on a tapered mandrel;
Fig, 5 is a view in perspective of a segment o~ an
umbilical cord;
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l~S5~3
Fig. 6 is a side view of a vessel reinforced at a seam
by a segment in the shape of a patch;
Fig. 7 is a sectional view of an anastamosis reinfarced
by a segment in the form of a strip; and
Fig. 8 is a view in perspective of an eyeball wherein
the region of attachment of a retina to the interior of an eyeball
~8 reinforced by an eye sling, the sling being formed af an
umbiliral eord vessel in ac~ordance with ~he present invention,
DESCRIPTION OF THE PREFERRED EMBODIMENTS
. __
. The following example illustrates the t~chnique of
vascular surgical interposition of an u~bilical cord vessel
derived ~rom the human into the abdominal aorta of an animal.
The animal, in ~his case a baboon, was prepared under general
anesthesia and sterile conditions for making an abdominal incision
The baboon was prepared and shaved and a longitudinal incision
was made in the midline of the abdomen. The incision extended
ro~ the xythoid to the pubic area and was carried down through
the midline and into the peritoneal cavity, Bleeding vessels
were clamped and ligated with 3-0 polyglycollic acid sutures.
The peritoneal cavity was entered and the viscera and bowel were
explored for any other dis~ases. ~he animal was found to be
n 1. m e bowel and viscera were walled off with cloth pads
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and re~ra tors. The peritoneum overlying the aorta was inclsed
and the aorta immobilized by sharp and blunt dissectlon. Lumbar
arteries were individually clamped and liga~ed with 3-0 silk
suture so that the segment o abdomirlal ~orta extend~ng fro~
the infra-renal arteries to the bifurcat:ion of the aorta was
immobilized. The entire segmen~ of abdominal aorta was thus
made available for transplant of the umbilical cord. Dur~ng
preparation o~ the abdominal aorta of the baboon, another
investigator had taken the umbilical cord o an infant (human)
that had been born two hours prior to the 5urgical intervention
of the baboon. Th~ cord had been delivered and taken in it9
entirety and transported in sterile saline solution, packed in ice
The purpose of freezing the umbilical cord in ice was ~o prevent
any further decomposition of the cord structure. The cordg
prior to insertion, was washed and irrigated numerous times
with sterile Collins solutlon with antibiotics, in this particuLar
lnstance, 1% cephalosporln solution and 25,000 units of bacitracin
per liter of solution. The blood was thoroughly washed out from
within the vessels of the cord and the cord was also irrigated
wi~h a 1% heparin anticoagulant solution. Follow~ng this thorough
cleansing of ~he cord, one end of the um~ilical vein wi~in
the cord which was to be used as the transpl ~ was clamped
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lOS51~143
with a clamp and ~hrough the other end a red rubber catheter,
No~ 1~ French, was introduced and the vein was distended. At
this point a suitable segment of umbilical graft, approx~mately
5 centimeters in length, was selected for excision. A mandrel
was placed in the vein and the remainder of the cord was CUt away.
This segment o~ ~in was then s~erilely handled and placed into
the operating fiel~. At this point the animal was heparinized
with 2,500 units of aqueous heparin given in~ravenously. The
abdominal aorta was then clamped proximally and distally to
the segment to be resected. A segment o~ approximately 3
centimeters in ~ength was resected rom the abdominal aorta
and an end-to-end anastomosis was performed between host aorta
and donor umbilical vein, first using continuous 6-0 prolene
suture which is a nylon monof~lament suture. The distal
anasto~os~s was then performed following flushing of the aorta
to r~d it of any ~lot material and debris. Following completion
of anastomosis t~e distal and then the proximal clamps were
removed. It was noted that there was no bleeding between the
inte~stices of the sutures, which is unusual, and is ~elt ~o
be du~ to the streng~h and self-sealing gelatinous quali~ies
of t~e cord str~c~ure. Excellent pulses were noted to be
presen~ in the gr~ft as well as the distal iliac vessels. The
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~l~S5`~343
area was lavaged with saline and suctionecl. The retroperitoneum was
closed with interrupted 3-0 pol~cJlycollic acid sutures ancl the vis-
cera was replaced. The animal, -throughout the procedure thus far,
was stable; the respiration and vital SigtlS were normal. The ab-
dominal wall was then closed in layers using continuous 0 silk for j'
the posterior fascia and peritoneum and interrupted 2-0 silk sutures
for the anterior fascia. The skin was approxlmated with continuous
3-0 nylon suture. The anesthesia used in this procedure was nembu-
tal. The blood loss estimated during the procedure was approximate-
ly 50 to 75 cc. The animal tolerated the procedure well and awokewithin 30 minutes. Postoperatively on the following day the animal
was sitting and walking in its cage, and on the third postoperative
day was eating its regular diet and was allowed out of its cagé to
roam around and climb up and down the walls, and appeared to be in
excellent health. The legs were warm and pulses were intact in the
extremities.
A number of procedures will become apparent to those
s~illed in the art. If desired or necessary, the vein or artery of
the umbilical cord may be split longitudinally and formed into com-
posites of larger diameter. The umbilical cord vessel or a portionthereof whether tanned or fresh may be used to reinforce, support
or seal a weakened area or defect of any body structure, such as the
heart, the heart valves or urinary bladder, or to cover a surface
trauma to promote healing thereuncler. Such procedures are included
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within the scope of the claims.
Before removal ~rom the umbilical cord, the vessels,
especially the vein, appear to be almost closed and quite small as
can be seen in Fig. 1 which is a perspec-tive view in enlarged scale
of a portion of an umbilical cord. The umbilical cord vein carries
the reference numeral 11 and -the arteries the reference numeral 12.
These vessels are surrounded by Wharton's jel;Ly, as aforenoted.
Moreover, the arteries 12 are twis-ted and coiled about vein 11 and
also contain the valves of Hoboken. These are some of the factors
which have made it unobvious to use these vessels as tubular
grafts. Mention has already been made of the fact that the
insertion of a mandrel into the vein 11 facilitates the removal
of the remainder of the umbilical cord. However, arteries 12
can also be carefully ciissected from the umbilical cord and
mounted upon mandrels. When this is done and they are properly
tanned, the valves of Hoboken are eli.minated and vessels smaller
than 1 mm in inside diameter can readily be prepared and permanently
shaped by the use of appropriate tanni.ny solution. The umbilical
cord vein is substantially larger than the arteries and can be
stretched on a mandrel so that vessels as large as 1 cm in inside
diameter can be prepared. Such vessels can, of course, be cut
open and laid out flat in which condition they are suitable as
~L~S~i~343
patches for reinforcement of organs, for supplementation of
anastomoses and Eor coverings OVeL surface trauma.
After dissecting out the desired vessel or vessels
and clearing of resldual blood, they are irrigated for several
minutes with a hardening agent, preferably 3 - 10 minutes. This
step effects partial elimination of Hoboken's valves from the
arteries. The hardening agent found mos-t suitable is the class
of aldehydes. Examples are formaldehyde, glyoxal, dialdehyde
starch and glutaraldehyde, with glutaraldehyde being the best
from the standpoints of elimination of any traces of an-tigenicity
and thrombogenicity and convenience, with a solution of dialdehyde
starch being next best. The concentra-tion of the glutaraldehyde
solution should be between about 0.15~ and 0.7~. The concentration
of dialdehyde starch should be between about 0.5 and 2.0~ by
weight. At lower concentrations the glutaraldehyde solut:ion does
not render the material non-antigenic, while at higher concentra-
tions the reaction is too rapid and embrittles the wall of the
vessel.
After irrigating a vessel with a hardening solution,
the vessel is slipped onto a mandrel of appropriate shape. The
vessel on the mandrel is then placed in a tank (not shown) of
hardening solution for about 15 to ~5 minutes, during which time
the vessel conforms to the shape of the manclrel. A preferred
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solution for hardening the vessel is 0.5% glutaraldehyde
buffered with 1% sodium bicarbonate so lthat ~he pH of the
solution is between 7.5 and 8.5. The hardening agent causes
the vessel to conorm to the shapP of the mandrel and also
increases the strength of the vessel material, A vein 11
i8 shown on a cylindrical mandrel 15 in Fig. 2.
Another means of shaping a vessel is shown
in Fig. 3 in which a vein 11 is inserted in a tubular mold 18,
end 19 of vein 11 being closed with stopper 21. The other end
22 of vein 11 is connected to hose 23 ~or introduction of harden-
ing solution 16 under moderate pressure, The pres~ure o~ the
hardening solution 16 forces vein 11 against the interior
of mo~d 18 to con~orm to said interior. This process results
in a vessel having a smoothed exterior.
The practice of shrinking a vein or artery
onto a cylindrical mandrel 15 as in Fig. 2 or a tapered
mandrel 25 as in Fig. 4 has the advantage that any internal `
irregularities such as the valves of Hoboken are eliminated,
the reference numeral 24 indicating a vessel segment where
the vessel may be either a vein or an artery. Ar~eries of
11 diameter a e particula-ly valuable for replacement
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of ~lood vessels in the body. In this context, the umbilical
l~ cords of the larger mammals, while not so readily available as
those of humans, contain larger vessels so that larger and
thicker-walled vessels and patches become available throu~h use
~'of vessels from such sources. Also, the small mammals provide
vessels of smaller diameter, such vessels being needed for
~pecialized applications such as in fingers and toes.
It should be noted that for use o~ segments
treated in accordance with the present invention in pulsatile
blood vessels smaller than abou~ 2 mm internal diameter, rein-
~orcement with artiflcial mesh Ls unnecessary. This follows not
only from the fact that tubes of smaller diameter can wi~hstand
higher pressure, in genPral, but from the fact that in collapsing
the vessels, the wall thickness is increased. Soaking the vessel ¦
~in alcohol prior to the aldehyde treatmen~ results in a stiffer
~'vessel. ' j '
After hardening the vessel, it is rinsed to remove
most of the hardener. A 1% solution of NaHC03 may be used. It is
then desirable to tre~t the vessel or segment for a period of
30 - 45 minutes wi~h a reagent which reacts with residual aldehyde.
'Suitable materials are amino acids, alkali salts thereof and
oxidizing agents in dilute ~orm such as peroxides, peracids and
hypcchlorites. The amino acids as sodium salts, and preferably of
'L-sodium glutamate, L-sodium alanine 9 L-sodium phenylalanine
and L-cyst'eine are partîcularly sui~able for this purpose l ;
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~ 1055843
because they are antitllrombogenic, the best of the above being
the glutamate. The mechanism is believed to depend on
condensation of the amine group of the a~inoacid with the
carbonyl group of aldehydes. This leave~ the carboxyl group
of the condensate free to ionize and impart a negative charge
to the surface of the vessel. Negatively charged surfaces
are known to be antithrombogenic.
Although the preferred method of storage subsequent
to hardening and shaplng of the vessel is in a dllute solution of
aldehyde, it is advantageous to treat the vesseL with an
amino-acid ater hardening to eliminate aldehyde as lndicate~.
A suitable method of storage of tanned vessel
segments is in a dilute solution of aldehyde, 0,5% glutaraldehyde
being preferred. Some further hardening of the segment takes
place over a period of 4 - 6 days. However, the extent of
hardening during s~orage is small and can readily be compensated
for in the principal hardening stage.
In preparation or implantation, after storage, the
segmen~ is rinsed, as in sterile saline or 1% NaHC03 solution,
It is preferably treated again wi~h sodium L-glutamate or one
of the other aforenoted co~pounds to eliminate residual
aldehyde.
105584;3
An alterna~e method of storage is in a solution
of 40 - 50~/O aqueous alcohol containing about 1% of propylene oxide.
Treatment of segments stored by this method wIth reagent to
remove aldehyde is, of course, unnecessary.
As will be recognized, a substantlal number of
variations on the procedures outlined above are Eeasible
Thus, after flushing out the vein in the umbilical cord, a
mandrel, either tapered or straight, may be inserted into the
vein, the cord frozen, ~he mandrel placed in a chuck and all
elements other than the vein cut away on a lathe In the
process, the exterior of the vein may be cut 80 that the wall
thickness becomes uniform or, tapered, if so desired As
would be expected, the vessel or segment must be rendered
sterile after subjection to such manipulation. Conventional
non-destructive techniques such as radiation, antibio~ics
and elevated temperature are used. ~lso, elevation of the
temperature up to as high as 60C during ~he tanning reaction
increases the rate of tanning. The same technique can be used
¦for removal of residual traces of tannlng agent.
~ nother ~ariation ls to slit the vein open and
lay ~t out flat. The use of a flat mandrel facilitates the
formation Qf 1at segments. The vessel may then be cut into
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5S843
isegments ~0 of any desired size as shown in Fig. 5, such
~segments to be ysed as reinforcements or patches. One use of
such a patch is shown in Fig. 6 wherein a vessel 26, which may
llbe a portion of a bowel which has been sewn together to form
lla seam 27, using sutures 28. This repair of the vessel 26 can
,be reinforced by placing a segment 29 as a patch over seam 27
I!and suturing the patch over vessel 26.
li The function of such a patch is greater than
mere reinforcement. As is well known, in stitching together j
portions of walls of o~gans in the body, it is necessary that
'the sutures not be pulled too tight and ~hat the stitches not be
too close, else the blood supply to the wall of the organ may
be cut off in which case gangrene may supervene. As a result,
~using standard techniques, there may be leakage through the
, suture line in the wall. It is for this reason that drains
are so commonly used. Reinforcing the seam with a patch as
shown in Fig. 6, greatly decreases i~ not completely eliminates
this danger. -
- Another version o~ the use of a segment
prepared in accordance with the present invention is shown in
Fig. 7 which represents an anastamosis in a bowel 31. In
accordance with the usual surgical procedure, the two ends 32
and 33 of bowel 31 are turned inward and the ends are then
sewn together with suture 34. A segment 36 is then sèwn around
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105584;~
the join between bowel ends 32 and 33, thereby eliminating
or greatly reducing the danger of seepage of bowel contents
into the abdomen. Needless to say, although Fig. 7 shows
only a single turn of segment about the bowel, two or more
turns about the bowel could also be taken.
A plurality of segments may be used in certain
applications such as for lining the pericardium o~ ~he heart,
or a heart valve, or for covering an arti~icial implant such
as a pacemaker. Segments may also be used in plastic surgery
as an inert reconqtructive material,
Although the tensile strength of a hardened
vessel is only moderate, it has other characteristics which
make it highly desirable for use surgically. These are the
afdrenoted non-antigenicity and non-thron~ogenlcity as well
as characteristic flexibility, slipperyness and complete
compatibllity with body organs and ves~els.
There i8 a wide variety of surgical procedures
in wh~ch cord segments can be used to great advantage. It
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Ihas already been mentioned that a segment can be used to
reinforce a seam and an anastamosis.' ]:t can also be used to
reinforce a weak portion or a defect in the wall of an organ
¦suc~ as an urinary bladder. A segment can be shaped to form
an artificial conduit between the urinary,bladder and the skin.
A most important use is as a retinal eye sling, The need for a
sling arises in the surgical procedure for repairing a detached
!¦retina. The way in which an eye sling- is used is shown in Fig. 8¦
wherein the reference numeral 47 generally indicates an eyeball.
The pupil 48 of the'eyeball 47 i8 shown and the area where a
repair llas been e~fected surgically is shown at 49. Th~ region
of repair mus~ be held under pressure until the retLna attaches
itself permanently to the eyeball. For this purpose a sling 51
!
is wrapped around the eyeball so that the eyeball is compressed
aga~nst the retlna in the ;nterior thereof. This generally
requires that the internal pressure in the eyeball be increased
by about 30 mm of mercury.
Up to ~he present time retinal eye slings have
been made ~ silicone plastic or fascia lata. The Eormer
. . .
~' can erode the eyeball and precipitate infection. Consequently,
a certain fraction ,of such procedures fail andp in suc~ cases,
' blindness can result. Use of fascia lata, on the other hand,
I necessitates a prior operation in order to obtain the material.
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Substitution of a segment prepared in accordance with the
present invention eliminates these diE~iculties. The material
is completely compatiblP with the body and has no tendency to
erode the eyeball.
Another important use for patches derived
from umbilical cord vessels is in connection with skin grafting.
a patch can be placed in position ovar a burned or tra~atized
area, even in the presence o infection. In many cases even
a dressing is not needed. The patch "takes" quickly. Healing,
including clearing of underlying inection,proceeds rapidly
under the patch and with no need for the usual change oE
surgical dressings. The patch sloughs of~ when healing is
sufficiently advanced. Of major importance, these grafts -
will persist for several months while healing proceeds.
The use of umbilical cord vessels, whether
from humans or from other mammais, as can be seen from the
above, presents numerous advan~ages. The supply is virtually
unLimlted and the treatment needed for rendering the vessels
appropriate for use in surgery is simple. Also, many variations
are possible in order to meet specific and varied needs. As
a result, steriLe cord vessel segments can be produced in
unlimited supply and at relatively low cost. They can be stored
indefinitely and in a variety of shapes and ~hicknesses to meet
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1055843
virtu~lly any need. Assuming they are stored in dilute
glutaral~ehyde solution, they need only be rinsed ln sterile
water cr saline solution or dilute NaHC03 preparatory to u~e.
If desired, they can be further rinsed in sodium-L-glutamate
to eliminate any residual aldehyde.
In preparation for tanning and shaping, cleansing,
rinsing or irrigating solutions may be passed through the vein
and arteries of the umbilical cord, solutions which may be
employed including water, sterile saline solution, E~inger's
lactate solution, hydrogen peroxlde, sodium ~icarbonate solution,
alcohol, and transplantation perfusate solutions, Antithrombo-
genic agents which may be used to treat the graft include
L-sodium glu~amate, L-alanine, L-phenylalanine, L-cysteine
and L-lysine. These compounds are also suitable for treating
vessel segments after tanning in order to remove residues of
the tanning agent.
Wharton's ~elly may be removed mechanically
or chemically using hyaluronidase to dissolve the hyaluronic
acid which comprises the jelly. Moreover, saline solution
-ls also effecti~e for this purpose.
Mandrels used for shaping vessels may be of glass,
silicone plastic, stainless steel or any other material inert
to the graft vessel and the chemicals used in the process. The
mandrel may be straight or curved, solid or hollow, cylindrical
or tapered and smooth or rough on its surface, as desir~d.
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1 0 5 5~ 4 3
Among aldehydes suitable for tanning agents are
glutaraldehyde, dialdehyde starch and formaldehyde, as well
anhydrous alcohol, glyoxal and chromic oxide.
In addition to the am~no ~cids listed above for
rem~ing residues of aldehyde tanning agents, mild oxidizing
agents can also be effecti~e. Examples of such agents are
~ilute hypochlorite solution and dilute peroxide.
Particularly where the larger vessels are to be
used, especially those over about 5 mm in inside diameter,
it is desirable to reinforce the vessel. In general the vessels
are reinforced by the use of an exterior coating o~ a mesh
support,. Both polyesters and fluorocarbon plastics can be used,
with the polyesters being preferred. ~o~nercially available
Mers1ene m~sh having wide interstices (0.5 - 2.0 mm) may
be wound around the vessel in order to gi~e the grat added
streng~.h and support, the mesh actually embedding itself into
the outer watl of the graf~. A pre~erred form o the mesh
is a~ a preformed ~leeve. '',
&rafts reinforced by mesh can 'be tes~ed for leaks
and strength by attaching them to a pulsa~ing machine and passing
solu~ion therethrcugh at a pressure of 150 to 300 mm of mercury.
It will thus be seen that the objects set forth
above, among ~hose made apparent from the preceding descrip~'ion,
are efficiently attained and, since certain changes may be
made in carrying out the above process and in ~he article set
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orth without departing from the spirit: and scope of the
~nvention, it is intended that all matter contained in the
above description and shown in the accompanying drawlngs shall
be interpreted as illustrative and not in a limiting sense.
It is al80 to be understood that the following claims
are intended to cover all of the generic and specific features
of the invention herein described, and all statements of the
scope of the invention, which, as a matter of language, might
be said to fall therebetween.
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