CH670380A5 - - Google Patents

Description

DESCRIPTION

The present invention relates to a synthetic vascular implant and, more particularly, to a drug-dispensing, blood-tight, collagen-coated and impregnated synthetic vascular implant which does not need to be pre-coagulated and which acts as a reservoir for the gradual release of a drug after implantation.

The replacement of segments of human blood vessels by synthetic vascular implants is widespread among experts. Synthetic vascular implants are available in a wide variety of configurations and are made from a large number of materials. Among the recognized and successful vascular implants are those that are made from a biologically compatible material that maintains an open lumen to allow blood to flow through the synthetic implant after use. The implants can be made from biologically compatible fibers such as "Dacron" and "Teflon", can be knitted or woven and can consist of a monofilament yarn, a multifilament yarn or a staple yarn.

An important factor when choosing a special implant underlay is the porosity of the fabric wall from which the implant is made. Porosity is important because it regulates the tendency to hemorrhage during and after implantation and regulates tissue ingrowth into the walls of the implant. It is desirable that the implant pad be sufficiently blood-tight to prevent blood loss during implantation, but the structure should be sufficiently porous to allow fibroblast and smooth muscle cell ingrowth to anchor the implant in host tissue. Synthetic vascular implants of the type described in U.S. Patents 3,805,301 and 4,047,252 are elongated flexible tubular bodies made from a yarn, e.g. B. «Dacron» are formed. In the first-mentioned patent, the implant is a knitted tube and in the second-mentioned patent, it is a double velor plastic, which is sold under the «Microvel» makre. These types of implants have enough porous structures to allow host tissue ingrowth.

The general procedure for implantation involves the pre-coagulation stage, in which the implant is immersed in the patient's blood and left to stand for a sufficient period of time to coagulate to impermeability. After pre-coagulation, hemorrhages no longer develop when the implant is inserted, and tissue growth is not affected. However, implant infection is one of the worst complications and occurs on average in 2% of prosthetic implant applications. It is associated with a high risk of limb loss and patient mortality increases to 75% depending on the location of the implant. While infection is generally noticeable soon after surgery, this time can also take longer, leading to even worse consequences.

An implant reinforced with absorbable collagen is known in the U.S. Patent 3,272,204, wherein the collagen is obtained from the deep flexor tendon of cattle. Another reinforced vascular graft is in U.S. Patent 3,479,670, which comprises an open-meshed cylindrical tube, which is wrapped with a spindle-shaped sheath made of molten polypropylene monofilament filled with collagen fibrils, whereby the implant is to be impermeable to bacteria and liquid. The collagen fibrils used are the same as in U.S. Patent 3,272,204.

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670 380

The synthetic vascular implants proposed in the prior art are described as being suitable for numerous applications. However, it is desirable to provide a flexible vascular implant that has zero porosity, that is accessible to host tissue ingrowth, and that serves as a reservoir for drugs that are to be slowly released from the surface of the implant after implantation.

The invention now relates to a collagen-coated and impregnated synthetic vascular implant, which provides a reservoir for the slow release of a drug material after implantation. The collagen fibrils in the coating are complexed with a drug such as antibacterial agents, antithrombotic agents and antivaral agents to protect against infection. The implant is defined in claim 1.

The porous implant underlay can be a tubular implant which is formed from a “Dacron” material and can be woven and knitted. The collagen source is an aqueous fibril dispersion of high purity, which contains a plasticizing agent, and is applied by massaging onto the plastic base to cover at least the entire inner surface in order to form a flexible implant of good handiness. After repeated coating and drying of the coating, the collagen is crosslinked, preferably by contacting it with formaldehyde vapor.

Another object of the invention is a method for producing the implant as defined in claim 8.

It should be noted that the terms «covering» and «impregnation», or «covering» and «impregnating» both always mean in the present text that the underlay covers the collagen material at least on the inner surface and in the spaces between the underlay material is, wherein the outer surface can be at least partially covered by material that passes through the spaces between the base.

The invention is described in more detail in the following description. For a better understanding, reference is made to the accompanying drawings, in which:

1 is a partial cross section of a collagen-coated synthetic vascular implant according to the present invention,

2 shows a partial cross section through a branched tubular implant of the type shown in FIG. 1,

3 is a graph showing the gradual release of tetracycline from a collagen slurry in rabbits.

4 is a graph illustrating the gradual release of tetracycline at various collagen gel concentrations, and

Figure 5 is a graph illustrating the gradual release of tetracycline in a collagen gel at various concentrations and dosages.

A synthetic vascular implant 10, constructed and assembled according to an embodiment of the invention, is shown in FIG. 1. The implant 10 comprises a tubular support part 12, which is formed from a biologically compatible filament-shaped synthetic material, preferably a polyethylene terephthalate, such as. B. «Dacron». The backing 12 is a porous "Dacron" knitwear which has an inner and outer velor surface of the U.S. Patent 4,047,252 described type. While the tubular portion 12 is made of "Dacron", any biocompatible filament-shaped material can be used for the base, provided that it can be processed into a porous structure that allows the tissue to grow in and an open lumen for the passage. ensures the flow of blood.

The inner surface of the tubular part is provided with a collagen coating designated as 16. The collagen coating 16 consists of a series of at least three layers of applied collagen fibrils. FIG. 2 shows a branched implant 20 covered with collagen. The implant 20 comprises a tubular main part 22 and two branches 24. The main part 22 and the branched parts 24 consist of a “Dacron” knitted fabric 26. The inner surface of this base 26 is covered with a collagen coating 28 coated, which also consists of three layers of collagen fibrils.

Porous supports for vascular implants suitable for the present invention are preferably produced from “Dacron” multifilament yarns by knitting or weaving processes which are usually used for the production of such products. In general, the porosity of the «Dacron» base is between approximately 2000 to 3000 ml / min-cm2 (purified water at approximately 15 999 Pa = 120 mm Hg). The inner coating of cross-linked collagen is applied by filling a tubular base with a slurry of collagen fibrils and plasticizers and massaging in by hand, removing the excess and allowing the deposited dispersion to dry. This process can be repeated any number of times. After the last application, the collagen material, e.g. B. crosslinked by exposure to formaldehyde vapor, air dried and then vacuum dried to remove excess moisture and excess formaldehyde. The treated implant according to the present invention has essentially zero porosity.

The present preparations and examples are intended to illustrate the method for the production of cleaned collagen from cowhides and of implants according to the present invention. The examples are for illustration purposes only and are not restrictive in any way.

preparation

Fresh calf skins were mechanically peeled from young calves, fetuses or stillbirths and washed in a rotating kettle with cold running water until the water was free of surface dirt, blood and / or tissues. The subcutis was mechanically cleaned to remove adherent tissues such as fat and blood vessels. The skins were then cut lengthwise into strips about 12 cm wide and placed in a wood or plastic kettle, as is usually used in the leather industry.

The skins were depilated using a solution of 1 M Ca (OH) 2 for 25 hours. The skin can also be depilated by mechanical means or by a combination of chemical and mechanical means. After depilation, the skins were cut into small pieces about 2.5 x 2.5 cm (1 "x 1") and washed in cold water.

After washing, 120 kg of the beef skin was placed in a kettle containing 160 liters of water, 2 liters of NaOH (50%) and 0.4 liters of H2O2 (35%). The components were mixed slowly at 4 C for 12 to 15 hours and washed with excess tap water for 30 minutes to give partially cleaned skins. The partially cleaned skins were in a solution of 260 liters of water, 1.2 liters of NaOH (50%) and 1.4 kg of CaO for 5 minutes with slow Ver5

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mix treated. This treatment was repeated twice a day for 25 days. After this treatment, the solution was decanted and discarded, and the skins were washed with excess tap water for 90 minutes with constant stirring.

The skins were then acidified by treatment with 14 kg NC1 (35%) and 70 liters of water while the skins were stirred vigorously. The acid was allowed to enter the skins for about 6 hours. After 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 adjusted to 3.3-3.4 using acetic acid with 0.5% preservative. The cleaned skin was then passed through a meat grinder and extruded under pressure through a series of filter screens of uniformly decreasing mesh size. The end product was a white, homogeneous, soft paste made from pure collagen from bovine skin.

In order to give the implants adequate flexibility in the dry state, plasticizers are added to the collagen slurry before it is applied. Suitable plasticizers include glycerin, sorbitol, or other biologically acceptable plasticizers. In a collagen slurry containing about 0.5 to 5.0 weight percent collagen, the plasticizer is present in an amount between about 4 and 12 weight percent.

Among the most important properties which are obtained when a synthetic vascular implant is covered with collagen fibrils according to the invention is the reduction of the porosity of the porous support to approximately zero. The porosity of twenty arbitrarily selected non-coated «Microvel-Dacron» synthetic vascular implants had an average value for purified water of 1796 ml / min.-cm2 at approx. 15 999 Pa (120 mm Hg) with a standard deviation of 130. After applying several collagen coatings, the porosity was reduced to zero. The following example illustrates the method for treating the implant pad.

example 1

A 50 cc syringe was filled with an aqueous slurry of 2% purified cow skin collagen made according to the preparation. The collagen slurry contained 8% glycerin, 17% ethanol and the rest water and had a viscosity of 30 Pa · s (30,000 cps). The tip was inserted into one end of a Meadox Medicai “Microvel-Dacron” implant, 8 mm in diameter and about 12 cm in length. The slurry was injected into the cavity of the "Microvel" implant and was massaged in by hand to impregnate the entire pad with the collagen slurry. Excess collagen slurry was removed through one of the open ends. The implant was then allowed to dry at room temperature for about half an hour. The impregnation and drying were repeated three more times.

After the fourth application of the coating, the collagen coating was crosslinked by exposure to formaldehyde for 5 minutes. The cross-linked implant was then air dried for 15 minutes and then vacuum dried for 24 hours to remove moisture and any excessive formaldehyde.

Example 2

The blood tightness of a vascular plastic made according to Example 1 and impregnated with collagen was examined as follows. A "Microvel" implant of 8 mm x 12 cm was attached to a blood reservoir at a pressure of approx. 15 999 Pa (120 mm Hg) due to the height of the reservoir. Blood stabilized with heparin was passed through the implant and the collected blood passed through the implant was measured and expressed in milliliters per minute-cm2. The porosity over five runs was found to be 0.04, 0.0, 0.0, 0.04 and 0.03. This results in an average porosity of 0.022 ml / min.-cm2, which was considered to be tantamount to zero, since the value lies within the experimental error limits of the investigation.

In order to compare this result with the blood loss occurring in the case of non-coated “mi-crovel” implants, the experiment was repeated using a non-coated implant. The average porosity was 36 ml / min.-cm2.

The antimicrobial activity of a collagen-coated implant made according to the invention was shown as follows:

Example 3

The porosity of an implant material coated with collagen is reduced to less than about 1% compared to the 25 non-coated implant after three coatings. A standard water porosity test, which is used to measure the water permeability of an implant, is carried out as follows: A water column corresponding to 15 999 Pa (120 mm Hg) pressure is flown through a 30 0.5 cm2 opening, which is a sample of the Contains implant over the opening for 1 minute. The amount of water collected was measured. The milliliters of water collected per minute per cm2 area was calculated. Different readings were taken for each sample. The porosity is expressed as follows:

Porosity = ml / min. / Cm2

The water permeability of a “Microvel” implant 40 material was approximately 1900 ml / min. / Cm2. The porosity after coating was as follows:

Number of porosity coatings

«0 1900

1 266

2 146

3 14

4 5

50 5 2.2

6 0

In each case, the collagen coating was a slurry made according to the composition described in Example 1, derived from bovine skin and plasticizer. Based on these results, it is preferable to use a collagen coating of at least three or four layers of fibrils, and particularly preferably four or five layers with drying after each application and cross-linking to fix the coating to the backing.

In accordance with the invention, each layer of the collagen coating and at least the last two layers applied to a porous support are chemically modified to contain a drug or diluent (antithrombic agent) such as Heprin to prevent infection and agglutinate along the inner top

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to prevent the area of the implant. As mentioned, the collagen can be complexed with a variety of drugs, such as antibacterial, antimicrobial or fungal agents, to prevent implant infection. Typical antibacterial agents that can be used include oxacillin, gentamicin, tetracycline, cephalosporin and the like, which can be complexed with the collagen fibrils before they are applied to the plastic support.

In addition to the reduced porosity, according to the present invention, vascular implants treated with collagen have reduced thrombogenicity compared to untreated implants.

Example 4

A homogeneous slurry of bovine skin-derived collagen prepared according to the preparation was prepared, the slurry containing 1% bovine skin-derived collagen, 8% glycerol, 17% ethanol and the balance water. "Ceclor", a cephalosporin antibiotic from Eli Lilly & Company, which inhibits the growth of Staphylococcus aureus and Escherichia coli, was mixed into the slurry at a concentration of 20 mg per ml. The collagen slurry containing the "Ceclor" was massaged in a double velor "Dacron" fabric on both sides, drying for half an hour after each application. The coating resulted in an addition of 3.1 mg collagen per cm 2.

As a control, “Dacron” double velor fabric was also impregnated with the same collagen slurry but without the “Ce-clor” antibiotic additive. This control had a coating of 4.1 mg collagen per cm 2.

Both samples of the coated fabric were immersed in 4% formaldehyde, 10% glycerol solution for 1 minute, dried in vacuo for 64 hours and sterilized using gamma rays.

The antimicrobial activity of the collagen-coated «Dacron» vascular implant substance, which was impregnated with «Ceclor», was determined in an agar diffusion test. 1 cm2 swatches were placed on inoculated agar surfaces, resulting in growth inhibition zones which indicated that the antibiotic was active against S. aureau (34 mm inhibition zone) and E. coli (29 mm inhibition zone). The untreated, i.e. H. only control substances impregnated with collagen without medication showed no antimicrobial effect. The results are summarized in Tables I and II below.

Table I

Fabric impregnated with antibiotics and collagen

Plate 1 Plate 2 Plate 3 X3

S. aureus 36 mm 31mm 35 mm 34 mm E. coli 33 mm 28 mm 27 mm 29 mm

Table II

Fabric impregnated with collagen without antibiotics

Plate 1 Plate 2 Plate 3 X3

S. aureus 0 0 0 0

E. coli 0 0 0 0

Example 5

A collagen slurry prepared according to the preparation and containing 13.2% collagen protein (determined by its hydroxyproline content) was mixed in a ratio of 1: 3 with water (W) to make a 3.3% collagen gel (G) to build. The pH of the collagen gel was adjusted to 3.8 and 20 mg of tetracycline (TC) were added per millimeter of gel. Immediately before injection into two rabbits, the collagen-gel-tetracycline complex was mixed with glutaraldehyde (0.3 ml of 3% glutaraldehyde per ml of the gel) and injected into the subcutis by 18 Gage needles. Two rabbits as controls were injected with a similar dose of tetracycline and water, 20 mg TC / ml water / kg body weight.

To study the rate at which tetracycline is released from the injected site, blood was drawn from the rabbit ear veins at various time intervals. The level of TC in the blood was determined by the method of Wilson et al. (Clin. Chem. Acta., 36; 260, 1972). The results of the TC analysis in the blood of all four rabbits collected within 2 hours to 7 days after the injection are shown in FIG. 3.

Figure 3 shows that after TC injection in water the drug reaches its maximum in serum within 2 hours as shown by curve A. The TC is no longer detectable after 11 hours. When tetracycline was administered in a collagen gel crosslinked with glutaraldehyde (10G + 30W), the level of the serum TC remained stable for about 6 days, as can be seen from curve B. The administration of TC in collagen gel thus extended the effective release of the drug twenty-five times compared to injection in an aqueous medium alone.

Example 6

The test described in Example 4 was repeated using collagen gel of two different concentrations for the final injection. In addition, the tetracycline content was 30 mg of oxytetracycline (OTC) per milliliter of gel per kilogram of body weight at a dose of 1 ml / kg of body weight, or 50% more tetracycline per dose than in Example 4. The results, which can be seen in FIG. 4, show that the concentration of collagen in the gel influences the rate of OTC release from the collagen matrix. The denser the collagen gel, the slower the release of the drug. In this example, the kinetic properties of the OTC release were examined over a total of 124 hours after the injection of the examined complex into the subcutis of a total of 6 rabbits.

In FIG. 4, curve A shows that the OTC in water reaches its maximum in the serum shortly after the injection and is no longer detectable after 18 or 20 hours. Curve B shows OTC serum concentrations for OTC, which is complex-bound with a collagen matrix in a weight ratio of gel complex to water of 1: 2, and curve C at a ratio of 3: 20. The OTC is released faster for the less concentrated gel of curve B.

Example 7

Collagen gel containing 3% collagen, measured as a dry substance, was mixed with tetracycline to form two concentrations, of which (A) contained 50 mg TC / ml and (B) 100 mg TC / ml gel . After mixing with 0.3 ml of 3% glutaraldehyde (Gl) per ml of gel (G), complex A was injected with a dosage of 2 ml / kg body weight and complex B with a dosage of 1 ml / kg body weight. The plasma concentrations of TC in mg / ml are in curves A and B of FIG. 5

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shown. Complex A was also injected at a dose of 1 ml / kg and this is shown by curve C in FIG. 5. The actual plasma levels of tetracycline up to 5 days after the injection are shown in FIG. 5.

The data of FIG. 5 show that both the actual concentration of tetracycline and the surface geometry of the implant influence the amount of drug release from the gel and the content of tetracycline in the plasma.

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Claims (10)

670 380 PATENT CLAIMS 1. Synthetic vascular implant, characterized by a tubular, flexible, porous, synthetic implant base with a porosity of not more than 3000 ml / min / cm2 [purified water at approx. 16,000 Pa (120 mm Hg)], which is at least on its inner surface carries a cross-linked coating of collagen fibrils which are complexed with an effective amount of a drug and mixed with a plasticizer, and which is impregnated with this collagen material in order to make the implant blood-tight and flexible and a gradual release of the drug portion of the complex after implantation. 2. Vascular implant according to claim 1, characterized in that the pharmaceutical portion of the complex is a pharmaceutical agent selected from the group consisting of antimicrobial agents, antibacterial agents, antifungal agents, antithrombogenic agents, cell proliferation-promoting agents and mixtures thereof. 3. Vascular implant according to claim 1, characterized in that both the inner and the outer surface of the base is coated with the collagen-fibril-drug complex. 4. Vascular implant according to claim 1, characterized in that the porous base consists of polyethylene terephthalate and is preferably knitted or woven. 5. Vascular implant according to claim 4, characterized in that the inner and the outer surface of the base have a velor surface. 6. vascular implant according to claim 1, characterized in that the plasticizing agent is a biologically compatible material with several hydroxyl groups, for. B. sorbitol or glycerin. 7. vascular implant according to claim 1, characterized by a tubular, flexible, porous Polyäthy-lenterephthalat-implant base, the inner surface of a coating of at least three and preferably at least five layers of cross-linked collagen fibrils, which are complexed with a drug and with a plasticizer are mixed. 8. A method for producing a drug-dispensing synthetic vascular implant according to one of claims 1 to 7, characterized in that a porous, tubular, flexible, synthetic implant pad with a porosity of not more than 3000 ml / min / cm2 [purified water at approx. 16,000 Pa (120 mm Hg)], an aqueous slurry of collagen fibrils complexed with a drug and applied by a plasticizer to at least the inner surface of the pad, massaged the slurry into the pad to intimately mix the colla -Genfibrillen complexes ensure in the porous structure of the base, the collagen material dries and the collagen material crosslinked and dried in a vacuum. 9. The method according to claim 8, characterized in that the succession of the steps of applying the aqueous slurry of collagen fibrils to the base, massaging and drying is repeated at least three times. 10. The method according to claim 8, characterized in that the aqueous slurry of collagen fibrils from 0.5 to 5.9% from collagen fibrils, which are complexed with an effective amount of a drug, from 4.0 to 12.0% from plasticizers and the rest consists of water.