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Means for improving biocompatibility of implants, particularly of vascular grafts
| Details |
Inventors: Alonso, Manuel T.;
Assignee: Medtronic, Inc. (Minneapolis, MN)
Primary Examiner: Cannon; Alan
Assistant Examiner:
Attorney, Agent or Firm: Duthler; Reed A.
Implants containing a reasonably biocompatible fabric, which is to be exposed to blood flow after implantation, are rendered biocompatible and substantially impervious to blood, by applying a collagen composition containing soluble collagen, and preferably also collagen fibers, to the fabric in such a manner that the collagen composition penetrates into the interstitial spaces of the fabric. The fabric retaining collagen composition is then incubated at elevated temperature for sufficient time to form collagen fibers from the soluble collagen. Thereafter, the implant is dried. The steps of applying collagen composition, incubating and drying are repeated approximately two to four times. The implants, particularly when they comprise tubular vascular grafts, are tested for porosity by placing a pressurized column of aqueous solution, such as saline, into their interior. When the implant is sufficiently impervious to liquid, it is treated with a suitable cross-linking agent, such as glutaraldehyde solution, to bond adjacent collagen fibers to one another. When the implants are tubular vascular grafts, the treatment with glutaraldehyde is conducted in a longitudinally extended position of the graft, and with a pressurized column of glutaraldehyde placed within the interior of the tubular grafts. |
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DETAILED DESCRIPTION OF THE INVENTION Referring to FIG.
1, a section of a vascular graft shows the intertwining of the small diameter collagen strands 11 with the preformed cloth 10.
In the present embodiment, a microporous woven fabric, consisting of woven strands 12 and 13 of polyester or other biocompatible materials, forms the substrate.
However, any type of biocompatible mesh, including braided or knitted, may be used.
The intertwining is the result of natural growth processes of the collagen fibers when incubated.
In one preferred embodiment of the present invention, the fabric 10 comprises the structural material of a tubular, usually corrugated, vascular graft 12, schematically shown on FIG.
3.
Such vascular grafts are usually of approximately 4 to 30 millimeter internal diameter.
It should be noted that in another preferred embodiment of the present invention the fabric 10 can be formed integrally with structural members of a prosthesis, such as valve prosthesis (not shown) in which the fabric is attached at the time of the molding of a stent (not shown) and sewing ring (not shown).
The collagen is adhered to the polyester or other biocompatible fabric in accordance with the following procedure.
Bovine skin (not shown) is cleaned, trimmed, and flesh is removed from the skin.
The skin is cut into strips and immersed in acetic acid.
The saturated skin is homogenized in a homogenizer and then diluted in 0.
05 mol acetic acid and then centrifuged at low temperature.
The resulting slurry is then salt (NaCl) precipitated and re-centrifuged to obtain a collagen paste.
The paste is then diluted in buffer solution to adjust the pH factor to 7.
4.
The product obtained in this manner is called acidity adjusted soluble collagen, or simply soluble collagen.
Collagen fibers are obtained from soluble collagen by incubating (maintaining) soluble collagen at 37 degrees centigrade until the solution becomes a gel.
In accordance with one method of the invention, the fabric of the prosthesis is impregnated with soluble collagen
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