Title:  Tetracarbon

United States Patent:  6,454,797

Issued:  September 24, 2002

Inventors:  Guseva; Malvina B. (Moscow, RU); Novikov; Nikolay D. (Moscow, RU); Babaev; Vladimir G. (Moscow, RU); Adamyan; Arnold A. (Moscow, RU); Lavygin; Igor A. (Moscow, RU)

Assignee:  Tetra Consult Limited (Moscow, RU)

Appl. No.:  929968

Filed:  August 14, 2001

A synthetic polymeric form of carbon (Tetracarbon.TM.) which exhibits some properties similar to biological tissues. Tetracarbon is highly biocompatible and may have application in medicines and microelectronics. Tetracarbon is a biocompatible substrate coating made by depositing short linear chains of carbon stores upon the surface of the substrate. The carbon chains are non-turbostratic and oriented perpendicular to the substrate surface and are densely packed parallel to one another in hexagonal structures with the distance between the carbon chains being between 4.8-5.03 ANG.. A layer of Tetracarbon is identical to an adjacent layer and randomly shifted laterally relative to each other.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a biocompatible coating for a surgically implantable article.

It is a further object of this invention to provide a non-turbostratic carbon film adapted for coating a substrate surface.

It is a further object of the invention to provide a method for making a prosthesis or similar surgically implantable device which has a biocompatible tissue-contacting coating on the outer surface.

It is yet a further feature of the invention to provide an apparatus which is operable for depositing a non-turbostratic biocompatible polymeric coating upon the surface of a substrate.

A further objective of the invention is to provide a coating for a surgically implantable medical device wherein the coating is adapted to permit self-reassembly in order to accommodate tissue ingrowth.

Tetracarbon is a polymeric carbon film having a non-turbostratic 2-dimensional planar structure. In Tetracarbon films the short, straight linear carbon chains that form the layer are organized into densely packed hexagonal structures with the distance between chains being 4.8-5.03 .ANG.. Unlike turbostratic carbon films, in Tetracarbon film the long axis of the linear carbon chains comprising the film ares oriented perpendicular to the plane of the film. A Tetracarbon film may be a single layer or many layers which overlie one another. If the number of layers in a Tetracarbon film exceeds one, the layers are identical and randomly shifted relative to each other. In Tetracarbon, the interaction between the linear carbon chains in the film is due to van der Waals forces which set the distance between the chains in the range 4.8-5.03 .ANG.. As is true with carbyne, a carbon chain is the main structural element of Tetracarbon. The Tetracarbon chain consists substantially entirely of carbon atoms, each carbon atom having two 1.19-1.38 .ANG.-long valence bonds with a 180^o angle between them. The introduction of hetero atoms into a carbon chain under the influence of ion irradiation and alloying can modify the structure of Tetracarbon be to adapted to particular applications. The morphological features characterizing a Tetracarbon coating can be modified, for example by:

(a) regular joining of chains within adjacent layers;

(b) splitting of a chain into linear fragments; and/or

(c) formation of bends within a carbon chain; and/or

(d) changing the distance between carbon chains.

The length of linear carbon chain fragments and the number of bends effect the morphology of Tetracarbon. Thus, the morphology may be varied by the choice of gas used for ion irradiation, the composition using an admixture of gases and varying the proportions of the admixture and the temperature of deposition. Tetracarbon structure may "self-organized" in vivo; structurally readjusting to adapt itself to the structure of a protein molecule growing on and intimately into the Tetracarbon due to the interaction between the film and the protein penetration of endogenous ions into the Tetracarbon layer.

The above objectives are met with a polymeric carbon film referred to herein as Tetracarbon. Tetracarbon refers to a carbonaceous polymeric film, the surface of the film defining a plane. The film may be either a single layer or a superimposition of multiple layers wherein each layer within the film consists essentially of a plurality of linear chains of covalently bonded carbon atoms. The linear (end to end) axis of each linear carbon chain in a layer is perpendicular to the plane of the film surface. Thus, Tetracarbon is a non-turbostratic material. Only one end of the carbon chains comprising the innermost layer of Tetracarbon may be bonded to the surface of the substrate upon which the Tetracarbon layer is deposited. The opposing end of the carbon chains project away from the substrate surface in a substantially vertical direction.

An apparatus operable for depositing a Tetracarbon coating upon a substrate surface comprises essentially a vacuum chamber inside which are disposed in combination: a graphite cathode of main discharge, an anode of main discharge; an ignition electrode, a cathode of auxiliary discharge separated from the ignition electrode by a dielectric spacer; and a power supply. The vacuum chamber has two side compartments, each of which are in gaseous communication with the interior of the vacuum chamber by means of apertures therebetween. One of the two side compartments contains the cylindrical graphite cathode of main discharge and the anode of auxiliary discharge, surrounding the cathode of main discharge with a gap therebetween. The end of the cylindrical anode of auxiliary discharge closest to the substrate has a conic shear directed axially inward and facing the cathode of main discharge. The anode of the main discharge comprises two or more electrically conductive parallel rings which are rigidly connected to one another by metal rods. The ignition electrode, dielectric spacer, and the cathode of the auxiliary discharge are fabricated as a laminated ring, each of the elements being rigidly affixed to each other and interposed between the anodes of the main and auxiliary discharges. The anode of auxiliary discharge, cathode of main discharge, ignition electrode, cathode of auxiliary discharge, dielectric spacer and anode of main discharge are coaxially disposed with respect to each other.

A substrate holder, placed inside the vacuum chamber behind the anode is adapted to support a substrate and permit planetary rotation of the substrate around two axes and is connected electrically to the chassis ground of the vacuum chamber. The axis around which the substrate holder revolves is tilted or inclined with respect to the orbital axis. An aperture in the wall of the second side compartment of the vacuum chamber permits entry of an ion beam into the vacuum chamber. The ion and plasma beams intersect at the substrate surface. The apparatus also includes a capacitor and an inductance, one pole of the inductance being connected to the cathode of main discharge and the other pole being connected to a negatively charged plate of the capacitor, the positively charged plate of which is connected to the anode of main discharge. The poles of the power supply are attached to the corresponding plates of the capacitor. The cathode of main discharge is made of graphite having high purity. For medical applications, a purity of 99.99% or better is preferred.

Claim 1 of 7 Claims

What we claim is:

1. A medical implant adapted for implantation within a mammal and having a tissue facing surface wherein at least a portion of said tissue facing surface has a non-turbostratic, two-dimensionally ordered, densely packed, linear chain carbon coating affixed thereto comprising a plurality of linear carbon chains, each said carbon chain having an inner end adjacent to said tissue facing surface and an outer end in opposition thereto and a carbon chain axis therebetween wherein said carbon chain axis is defined as being line connecting said inner end and said outer end and wherein said carbon chain axis is oriented substantially perpendicular to a plane tangent to said tissue facing surface at a point on said surface immediately adjacent to said inner end and wherein said inner end of a portion of said plurality of linear carbon chains is chemically bonded to said tissue facing surface of said medical implant.
 

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