FR2558720A1 - SYNTHETIC VASCULAR GRAFT, PROCESS FOR PREPARING SUCH A DISTRIBUTION GRAFT OF A MEDICAMENT COATED WITH COLLAGEN AND THINNING FOR FORMING THE SAME - Google Patents

Abstract

THE INVENTION RELATES TO A SYNTHETIC VASCULAR GRAFTING. ACCORDING TO THE INVENTION, IT INCLUDES A FLEXIBLE POROUS TUBULAR SUBSTRATE 12, WHICH SUBSTRATE HAS AT LEAST ON ITS INTERNAL SURFACE, A RETICULATED COATING 16 OF COLLAGEN FIBRILLES IN MIXED WITH AN EFFECTIVE AMOUNT OF A MEDICINAL PRODUCT AND BY MIXING WITH A TO MAKE THE GRAFT BLOOD-TIGHT AND FLEXIBLE AND TO ALLOW PROLONGED RELEASE OF THE MEDICINAL PORTION FROM THE COMPLEX AFTER IMPLANTATION. THE INVENTION APPLIES IN PARTICULAR TO BLOOD VESSEL GRAFTS.

Description

The present invention relates to a vascular graft

  synthetic, and more particularly to a collagen-coated and blood-tight synthetic vascular graft for delivery of a drug, which does not require precoagulation and which serves as a reservoir for sustained release of a drug

after implantation.

  The replacement of segments of human blood vessels by synthetic vascular grafts is well

  accepted in practice. Synthetic vascular grafts

  They have taken a wide variety of configurations and are made of a wide variety of materials. Among the successful and accepted vascular graft implants are those formed of a biologically compatible material that maintains an open port to allow blood to flow.

  to flow through the synthetic graft after

  tation. Grafts can be made of organic fibers

  compatible, such as Dacron and Teflon, can be knitted or woven and can be in a monofilament yarn,

  a multifilament yarn or a discontinuous yarn.

  An important factor in selecting a substrate for a particular graft is the porosity of the wall of the fabric of which the graft is formed. Porosity is

  important because it controls the tendency to haemorrhage

  during and after implantation and control of tissue growth in the graft wall. It is desirable that the vascular graft substrate be sufficiently blood tight to prevent loss of blood during implantation, and yet the structure must be sufficiently porous to allow growth of fibroblasts and smooth muscle cells to attach.

  the graft to the host tissue. Synthetic vascular grafts

  The type described in US Pat. Nos. 3,805,301 and 4,047,252, assigned to the Applicant of the present invention, are elongated and flexible tubular bodies formed of a wire such as Dacron Street. In the first patent, the graft is a knitted tube in a peel and in the

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  last published patent is a synthetic graft

  double velvet marketed under the trade name

  Microvel. These types of grafts have sufficiently porous structures to allow growth of the host tissue. The general process for implantation involves the step of precoagulation, where the graft is immersed in the patient's blood and left to rest for a period of time.

  sufficient for coagulation to occur. After

  coagulation, haemorrhage does not occur when the graft is implanted and tissue growth is not impaired. Infection of the graft is a very serious complication and occurs in an average of 2% of prosthetic graft placement. It is associated with a high risk of limb loss and mortality

  of the patient reaches 75% depending on the location of the transplant.

  While the infection usually becomes evident shortly after the surgery, the time can be extended

  which leads to more serious consequences.

  An absorbable collagen reinforced graft is proposed in US Pat. No. 3,272,204 where the collagen is obtained from the deep flexor tendon of cattle. Another reinforced vascular prosthesis is described in US Pat. No. 3,479,670 which comprises a cylindrical mesh tube. open surrounded by an outer helical wrapping of a molten polypropylene monofilament loaded with collagen fibrils which are claimed to render the prosthesis impervious to bacteria and fluids. The collagen fibrils used are the

  same as those described in US Pat. No. 3,272,204.

  Suggested synthetic vascular grafts

  prior art are claimed to be appropriate

  required for many applications. However, it is desirable to produce a flexible vascular graft having zero porosity, one that is receptive to growth of the host tissue and that serves as a reservoir for slowly releasing drug materials from the medium.

  surface of the graft following implantation.

  A collagen-coated synthetic vascular graft that provides a reservoir for the slow release of a drug after implantation is produced. The collagen fibrils in the coating are mixed

  to a drug material such as anti-

  bacterial agents, antithrombosis agents and anti-

  viriens to insure against infection of the graft.

  The porous substrate of the graft may be a tubular vascular graft formed of a Dacron material and may be woven or knitted. The collagen source is an aqueous dispersion of high purity fibrils comprising a plasticizer and is applied to the graft substrate by massage to cover at least the entire inner surface to produce a flexible graft with a good feel. After repeated application of coating and drying, collagen is

  cross-linked by exposure to formaldehyde vapor.

  Accordingly, the present invention

  subject an advanced synthetic vascular graft.

  Another object of the present invention is an improved synthetic vascular graft coated with collagen. Another object of the present invention is an improved synthetic vascular graft coated with collagen where the collagen serves as a reservoir for the slow

  release of a drug after implantation.

  It is another object of the present invention to provide an improved method for coating a synthetic collagen D0 vascular graft to make the graft blood-tight and serve as a reservoir for the collagen.

  slow release of a drug after implantation.

  The invention will be better understood, and other purposes, features, details and advantages thereof

  will become clearer during the description

  explanatory document which will follow made with reference to the attached schematic drawings of unés only as an example

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  illustrating several embodiments of the invention and in which: - Figure 1 is a partial cross sectional view of a synthetic vascular graft coated collagen according to the invention; FIG. 2 is a partial cross-sectional view of a branched tubular graft of the type illustrated in FIG. 1; FIG. 3 is a graph illustrating the prolonged release of tetracycline by a collagen slurry in rabbits; - Figure 4 is a graph illustrating the

  sustained release of tetracycline at various concentrations

  trations of collagen gel; and FIG. 5 is a graph illustrating the prolonged release of tetracycline in a gel of

  collagen at different concentrations and dosage.

  A synthetic vascular graft 10 constructed

  and arranged according to the invention is shown in FIG.

  The graft 10 comprises a tubular substrate portion 12 which is formed of a biologically compatible filamentary synthetic material, preferably a polyethylene terephthalate, such as Dacron. Substrate 12 is a knitted Dacron knitted porous fabric having an inner and outer pile surface of the type disclosed in US Pat. No. 4,047,252.

  tubular 12 is made of Dacron, any filamentary material

  biocompatible can be used for the substrate provided that it can be made into a porous structure allowing the growth of the tissue and now

  an open hole for the flow of blood.

  The inner surface of the tubular portion 12

  is coated with a collagen coating shown at 16.

  The collagen coating 16 is formed from a series of

  minus three layers of applied fibrils of collagen.

  Figure 2 shows a bifurcated graft coated with collagen. The graft 20 comprises a main tubular portion 22 and branches 24. The main tubular portion 22 and the bifurcated portions 24 are formed of a Dacron knitted fabric 26. The resin is This internie of the substrate 26 is coated with a coating of collagen 28 also formed from

  less -iroxis fibril layers of collagen.

  Suitable porous graft substrates for use according to the invention are preferably produced from Dacron multifilament yarns by knitting or weaving processes which are commonly used in the manufacture of these products. the porosity of the Dacron substrate is between about 2,000 and 3,000 ml / min-cm 2 (purified water at 160 mbar). The internal coating of cross-linked collagen is applied by filling an internal substrate with a slurry of collagen fibrils

  and plasticizer and massaging by hand, removing

  excess and allowing the deposited dispersion to dry. After the final application, the collagen coating is crosslinked by exposure to formaldehyde vapor, and air-dried and then dried under vacuum for

  remove excess moisture and excess formaldehyde.

  The grafts coated according to the invention have essentially

zero porosity.

  The following examples are given to illustrate the process for preparing collagen purified from bovine skin and coated grafts according to the invention. Examples are given to illustrate

  the invention without in any way limiting the frame.

EXAMPLE 1

  Young veautx, fetuses or dead animals were mechanically stripped from fresh calf skin, and these skins were washed in a rotating container with cold running water until

  water is free of surface dirt, blood and / or tissue.

  The dermis has been mechanically cleaned to remove contaminating tissues such as fat and vessels

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  blood. Subsequently, the skins were cut longitudinally into strips about 12 cm wide and placed in a wooden or plastic container as commonly used in the leather industry. The skins were depilated using a

  I M scanning solution of Ca (OH) 2 for 25 hours.

  Alternatively, the skins can be depilated by mechanical means or by a combination of mechanical and chemical means. Following unstacking, the skins were cut into small pieces of about 2.54 x 2.54 cm and washed with cold water. Following washing, 120 kg of cowhide were placed in a vessel with 260 L of water, 2 L of NaOH (50%) and 0.41 H 2 O 2 (35%). The components were slowly mixed for 12 to 15 hours at 4 ° C and washed with excess tap water for 30 minutes to produce partially purified skins. The partially purified skins were treated in a solution of 260 l of water, 1.21 of NaOH (50%) and 1.4 kg of CaO for 5 minutes with slow mixing. We have

  continued this treatment twice a day for 25 days.

  Following this treatment, the solution was decanted and discarded and the skins were washed with excess water

  of the tap for 90 minutes with constant stirring.

  The skins were acidified by treatment with 14 kg of HCl (35%) and 70 liters of water while subjecting the skins to vigorous agitation. The acid was allowed to penetrate the skins for about 6 hours. Following acidification, the skins were washed in excess tap water for about 4 hours or until a pH of 5.0 was reached. The pH of the skins was readjusted to 3.3-3.4 using acetic acid with 0.5% preservative. The purified skin was then passed through a meat grinder and extruded under pressure through a series of filter screens.

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  a mesh size decreasing constantly. The final product was a smooth, white, smooth paste

  of pure collagen derived from bovine skin.

  In order to impart adequate pliability to grafts in the dry state, plasticizers are added to the collagen slurry before application. Suitable plasticizers include glycerin, sorbitol or other polyhydric plastic-biologically compatible plasticizers. In a collagen slurry containing between about 0.5 and 5.0% collagen by weight, the plasticizer is present in a between

about 4 and 12%.

  Among the most important properties obtained when coating a synthetic vascular graft of collagen fibrils according to the invention include reducing the porosity of the porous substrate to about zero. The porosity of twenty random and randomly selected Dacron Microvel synthetic vascular grafts has a mean value compared to purified water of 1.796 ml / min-cm2 at 160 millibars with a standard deviation of 130. After application of several coatings collagen, the porosity is reduced to zero. The following example illustrates the method of coating the substrate of

the transplant.

EXAMPLE 2

  A 50 c syringe is filled with an aqueous slurry of 2% cow skin purified collagen prepared according to Example 1. The collagen slurry contains 8% glycerol 17% ethanol and the remainder is of water and it has a viscosity of 30,000 cps. The syringe is placed at one end of a Meadox Dacron Microvel Medica graft 8 mm in diameter and about 12 cm long. The slurry is injected into the orifice of the Microvel graft and massaged by hand to cover any inner surface of the collagen slurry. Any excess collagen slurry is removed through one of the open ends. We leave the

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  Graft dry for about half an hour at room temperature. The steps of coating and

  drying were repeated three times.

  Following the fourth coating application, the collagen coating was crosslinked by exposure to formaldehyde vapor for minutes. The crosslinked graft was then air-dried for 15 minutes and then dried under vacuum for 24 hours.

  to remove moisture and any excess formaldehyde.

EXAMPLE 3

  The blood tightness of a collagen-coated vascular graft prepared according to Example 2 was tested as follows. An 8 × 12 cm Microvel graft was attached to a blood reservoir at a pressure of 160 mbar due to the height of the reservoir. Stabilized blood was passed to heprin through the graft and the blood collected through the grafts was determined and expressed in ml per mm-cm 2. The porosity over five runs was determined to be 0.04, 0.0, 0.0, 0.04 and 0.03. This represents an average porosity of 0.022 ml / min-cm 2 which is considered as zero because the value is within the limits of the experimental error

of the study.

  To compare these results with blood loss for an uncoated Microvel graft, the experiment was repeated using an uncoated graft. The average porosity was 36 ml / min-cm. The antimicrobial activity of a collagen-coated fabric graft prepared according to the invention was

demonstrated as follows.

EXAMPLE 4

  The porosity of a collagen coated tissue graft is reduced to less than about 1% of an uncoated graft after three coats. A standard water porosity test used to measure the water porosity of a graft is as follows. A column of water equal to 160 mbar of pressure is allowed to flow to a port of half a square centimeter with a sample of water at the orifice for one minute. The same is true of the milliliters of water collected. The surface area of each surface was calculated. Several samples were prepared for each sample. The porosity was then equal to -orozite = / min / cm2a. The water porosity of a 2- Mizcovel graft fabric was 1.900 ml / min / cm. The porosity after evaporation was maintained. as follows Number of coatings Porosity

C 1900

I 266

2,146

3 14

4 5

2.2

6 0

  In each case, the collagen coating was a slurry of a plasticizer derived from bovine skin prepared according to the composition described in Example 2. Based on these results, it is preferable to provide a collagen coating of at least three or four layers of fibrils and better

  four or five layers with drying between

  and crosslinking to attach the coating to the substrate.

  According to the invention, each layer of collagen coating and at least the last two layers 0 applied to a porous substrate are chemically

  modified to incorporate a drug or anti-

  such as heprin, to prevent infection and to inhibit coagulation along the inner surface of the prosthesis. As noted, collagen may be great variety of drugs, such as ant agents. bacterial antimicrobial agents or antifungal agents to prevent the infection of the

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  graft. Typical antibacterial agents that can be used include oxacillin, gentamicin, tetracycline, cephalosporin and the like which can be mixed with collagen fibrils before application.

in the supratrate of the graft.

  In addition to the reduced porosity, the collagen-coated vascular grafts according to the invention have a reduced thrombogenicity in comparison

uncoated grafts.

EXAMPLE 5

  A homogeneous slurry of collagen derived from bovine skin prepared according to Example 1 was prepared, containing 1% collagen derived from bovine skin, 8%

  glycerol, 17% ethanol, the balance being water.

  Ceclor, an antibiotic cephalosporin from Eli Lilly and Co that inhibits the growth of Staphylococcus aureus and Escherichia coli, was mixed with the slurry at a concentration of 20 mg per ml. The collagen slurry containing Ceclor was massage-coated on double velvet Dacron cloth with both sides

  drying periods of half an hour between the layers.

  The coating resulted in the addition of 3.1 mg

of collagen per cm2.

  As a control, a double velvet fabric of Dacron was also impregnated with the same collagen slurry by omitting the Ceclor antibiotic. This witness had a

  coating of 4.1 mg collagen per cm2.

  The two pieces of coated fabric were immersed for 1 minute in 4% formaldehyde, 10% glycerol solution, dried under vacuum during

  64 hours and sterilized using gamma radiation.

  The antimicrobial activity of the Dacron Vascular Graft Tissue coated with coliagene, impregnated with

  Ceclor, was determined in a determination of -

  j5 diffusion of agar. 1 cm 2 fabric pieces were placed on inoculated agar surfaces resulting in growth inhibition zones indicating

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  that the antibiotic was active against S. aureus (34 mm zone of inhibition) and E. coli (29 mm of zone of inhibition). The collagen-coated vascular graft material as an untreated control showed no antimicrobial effect. The results are given to

Tables I and II below.

TABLE I

COLLAGEN COATED TREATED ETOFF

  Plate 1 Plaque 2_ Plate 3 X3 S.aureus 36 mm 31 mm 35 mm 34 mm E. coli 33 mm 28 mm 27 mm 29 mm

TABLE II

  UNCOATED ETOFF COATED WITH COLLAGEN

  Plate 1 Plate 2 Plate 3 3 S. aureus O O O O E. coli O O O O

EXAMPLE 6

  A slurry of collagen prepared according to

  Example 1 containing 13.2% O collagen protein (determined

  from the hydroxyproline content) was mixed at a ratio of 1: 3 with water (W) to form a homogeneous collagen gel at 3.3% by weight (G). The pH of the collagen gel was adjusted to 3.8 and 20 mg of teracin (TC) per millimeter of gel was added. At once

  before injection with two rabbits, the collagen gel complex

  Tetracycline was mixed with glutaraldehyde (0.5 ml of 3% glutaraldehyde per ml of the gel) and injected through 18 gauge needles into the dermis. Two rabbits as controls were injected with a similar dose of tetracycline and water, 20 mg TC / ml water /

kg body weight.

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  In order to study the rate of tetracycline released

  injected site, the blood was collected at various intervals

  Time lapse of the rabbit's auricular vein. TC content in the blood was measured according to the Wilson process, et al (Clin Chem Acta, 36, 260, 1972). The results of the TC analysis in the blood of the total

  of four rabbits collected in 2 hours to 7 days post-

  injection are given in Figure 3, in which: A = 20 mg TC / ml water / kg body weight, B = 10 G + 30 W (0.3 ml 3% glutaraldehyde / mlB 20 ml TC / mlB / kg body weight ), C = hours, D = days and E indicates TC serum

  and the release time of the tetracycline.

  Figure 3 shows that after injection of TC in water the drug reached its maximum in serum in 2 hours as shown in curve A. At 11 hours, TC is no longer detectable. When tetracycline was administered. in a collagen gel cross-linked with glutaraldehyde (10 G + 30 W), the level of TC serum remained stable for about 6 days as shown in curve B. Thus, the administration of TC in an aprolonged collagen gel effective release of the drug 25-fold compared to injection into a medium

aqueous only.

EXAMPLE 7

  The test described in Example 5 was repeated using the collagen gel at two different concentrations for the final injection. In addition, the tetracycline content was 30 mg oxytetracycline (OTC) / ml gel / kg body weight at a dose of 1 ml / kg body weight, or 50% more tetracycline per dose than the example 5. The results illustrated in Figure 4 show that the concentration of collagen in the gel affects the OTC release rate of the collagen matrix. The stronger the collagen gel, the slower the release of the drug. In this example, the kinetics of OTC release was studied for a total of 124 hours after injection of the test complex

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  dai, _s the dermis of so- - apins in total. In this figure Aip molter 3) mg 0TC / ml water / kg body weight and B shows rv dz; VG 'ó (' i 20) ('shows TC in Gr (3:20).), D shows the': The temperature of the plasma and the temperature of the cyclosporine, shown in FIG. 2, show that the OTC is not present. After a short time in the serum shortly afterwards, it is not detectable after 18 or so hours, and the concentration of OTC in h! 0 z, óórcm: ocur 'i; OTCmlairg -te - collagen trice at rs ppout-a complex gel at water of 1:20 and the court-be C at 3 = 20f The release of OTC is faster for the less co-eI.enitré gel of the Bo curve

EXPLE 8

  A collagen gel containing 3% collagen, by measuring under a dry substance, has been

  mixed with tetracycline to form two concentra-

  containing (A) 50 mg TC / ml and (B) 100 mg TC / ml gel.

  After mixing with 0.3 ml of 3% glutaraldehyde (G1) per ml of gel (G), complex A was injected at a dose of 2 ml / kg body weight and complex B was injected at a dose of I ml / kg. TC plasma level concentrations in mg / ml are shown by curves A and B in Figure 5. Complex A was also injected at a dose of I ml / kg and is shown by curve C in the figure. 5. Actual plasma levels

  tetracycline for the period up to 5 days post-

  The injections are shown in FIG. 5A indicates mg TC / ml 2 ml / kg B = 100 mg TC / ml I ml / kg and C = 50 mg TC / ml I ml / g, D shows the number of days after injection, E the plasma level and F the time of

  released: rat-ion of tetracycline (G-GI-TC).

  The data in FIG. 5 show that the actual concentration of tetracycline as well as the surface geometry of the implant affect the level of release of the drug by the gel and

  level of tetracyclia in the plasma.

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Claims (16)

R E V E N D I C A T I 0 NS   1.- A synthetic vascular graft characterized in that it comprises: a tubular flexible and porous graft substrate (12); the substrate having on at least its inner surface a crosslinked coating (16) of collagen fibrils mixed with an effective amount of a drug and mixed with a plasticizer to make the graft tight and flexible and allow for release prolonged the drug portion of the complex after implantation.   2. The graft according to claim 1, characterized in that the drug portion of the complex is a pharmaceutical agent selected from the group consisting of antimicrobial agents, antibacterial agents, agents   antifungal agents, antithrombogenic agents,   the proliferation of cells and their mixtures.   3.- graft according to claim 1, characterized in that the inner and outer surfaces of the graft   are coated with the collagen fibrils complex   drug. 4.- graft according to claim 1, characterized   in that the coating of the collagen fibrils complex   drug is in at least three layers formed by depositing an aqueous slurry of collagen fibrils which have been dried before application and crosslinked   after applying the last layer.   5.- graft according to claim 1, characterized in that the porous substrate is polyethylene terephthalate. 6. The graft according to claim 5, characterized   in that the porous substrate is knitted.   7.- graft according to claim 5, characterized   in that the porous substrate is woven. 2558720   8. The graft according to claim 5, characterized in that the inner and outer surfaces   of the substrate have a velvet surface.   9. The graft according to claim 1, characterized in that the complex collagen-drug fibrils is crosslinked by exposure to formaldehyde vapor. 10. The graft according to claim 1, characterized in that the plasticizing agent is a   biologically compatible polyhydric material.   11. The graft according to claim 10,   characterized in that the plasticizer is sorbitol.   12. The graft according to claim 10, characterized in that the plasticizer is from the glycerin.   13.- Process for preparing a vascular graft   A collagen-coated, medicament-distributing synthetic film characterized in that it comprises: forming a synthetic porous flexible tubular graft substrate; placing an aqueous slurry of a complex of collagen fibrils in admixture with a drug on the surface of the substrate; massaging the slurry in the substrate to ensure intimate mixing of the collagen fibril complex in the porous structure of the substrate; dry the collagen coating; crosslink the collagen coating by exposure to formaldehyde vapor; and vacuum dry to remove formaldehyde in excess.   14. The process as claimed in claim 13, characterized in that the steps of placing an aqueous slurry of collagen fibrils on the substrate,   massage and dry are repeated at least three times.   15.- Boiled to form a blood-tight synthetic vascular graft delivering a drug, : 16 2558720   characterized in that it comprises about 0.5 to 5.0% collagen fibrils in admixture with at least one effective amount of a medicament material, 4.0 to   12.0% of a plasticizer, the balance being water.   16.- A synthetic vascular graft characterized in that it comprises: a porous flexible tubular substrate graft polyethylene terephthalate; the inner surface having a coating of at least five layers of cross-linked collagen fibrils mixed with a drug and mixed with a plasticizer; each layer being formed of an aqueous slurry containing between about 1.5 and 4.0% by weight of collagen fibrils and between about 6 and about % by weight of the plasticizer.