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Description  |
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The present invention concerns a process for forming a piece surgically
implantable in an organism and the piece thus obtained.
It is known that if a foreign body is introduced into an organism, a
natural defense mechanism thereof causes its cells to isolate said foreign
body. For example, if a splinter is lodged in the skin, the cells of the
epiderm surround it with a sealed envelope and work round it so as to try
to reject it outwardly. In addition, if a foreign body of great length,
such as thread or a tube, passes through the skin, this latter over the
whole of its thickness covers said body with a non adherent sheath of
epithelial cells. In this case, it is obvious that microbes may be
permanently introduced between the foreign body and said sheath, so that a
center of infection results therefrom.
The present invention has an object to overcome these drawbacks and to
allow a surgically implantable biocompatible piece to be formed capable
not only of not being rejected by said organism but further of being
integrally joined with the tissues in which it is implanted.
To this end, in accordance with the invention, the process for forming a
carbon fiber based piece surgically implantable in an organism is
remarkable in that
a bed is formed of carbon fiber sections whose length is at most equal to
30 mm, said sections resting freely on each other with random
orientations;
said bed is subjected to compressions so that its specific mass is between
0.05 and 0.3 g/cm.sup.2 ;
said bed thus compressed is introduced into an enclosure containing a
hydrocarbonated gas and said gas is subjected to the conditions of its
cracking, so that pyrocarbon is deposited on the fiber sections forming
said bed; and
cracking of said hydrocarbonated gas is continued until said bed of carbon
fiber sections reaches a specific mass between 0.5 and 1.6 g/cm.sup.3.
Thus a biocompatible porous composite structure is obtained formed of a
carbon frame whose fiber sections are coated with a pyrocarbon matrix.
Tests have shown that the cells of the tissues surrounding an implanted
piece having such a structure presented such an affinity with said piece
that they are firmly fixed thereto before the rejection phenomenon can
begin to appear. Consequently, an implantable piece in accordance with the
invention, is not only not rejected by the organism but is further firmly
fixed to the living tissues which surround it, since the cells of said
tissues (fibroblasts) colonise it over the whole of its thickness.
It will be noted that the patents U.S. Pat. No. 3,992,725 and U.S. Pat. No.
4,129,470 described a surgically implantable piece having a carbon fiber
basis. However, in this case, the carbon fibers are joined together by
polytetrafluoroethylene, so that the pores of the structure are sealed in
their large majority. The result is that the anchorage positions of the
living tissues on the piece are not as numerous as they could be and the
rapidity and the quality of the connection between the piece and the
tissues are not optimum.
In the present invention, on the contrary, during cracking of the
hydrocarbonated gas, the pyrocarbon is deposited solely on the fiber
sections while enlarging the diameter thereof, and such a deposit is
formed practically uniformly over the whole length of said sections, since
the hydrocarbonated gas passes freely between the carbon sections forming
the compressed bed.
Consequently, although the pyrocarbon deposit reduces the dimensions of the
pores existing between the fiber sections of the compressed bed, the
number of said pores remains the same so that the piece obtained is
particularly porous and has communicating pores.
It will be readily understood that by controlling the cracking of the
hydrocarbonated gas, the best possible compromise may be obtained between
the dimensions of the pores of the piece and the solidity thereof, given
by the pyrocarbon matrix.
When it is desired to confer on the piece obtained by the process of the
invention mechanical properties reinforced in a direction perpendicular to
said bed, for example for providing wear surfaces or holes orientated in
this way, it is advantageous to subject said bed of carbon fiber sections,
preferably after compression, to tufting in a direction orthogonal to the
multiple coplanar directions of said sections. Thus a sort of tufted felt
of carbon fibers is obtained which is then possibly compressed and
receives the pyrocarbon matrix.
To give its final form to the piece obtained by using the process of the
invention, it may be necessary to machine it. In this case, so as to
prevent the machining cuttings on the one hand from remaining fixed to the
machined piece and from spreading consequently into the organism and on
the other hand for preventing fragile surface particles from being
detached after implantation, said machined piece is subjected to very
active cleaning which comprises not only a thorough removal of dust, but
also the application of ultrasounds for eliminating said particles weakly
adhering to the rest of said piece.
Such cleaning may also comprise oxidization of the machined piece at a high
temperature (for example a 1000.degree. C.), for a few seconds in an
oxygen atmosphere. Such oxidization allows not only the combustion and
elimination of free particles due to machining as well as the rounding off
of the fragile micro roughnesses but also the formation of oxygenated
groups, for example of the carboxyl type, which are fixed on the piece.
Subsequently, if said piece is heated (for example at 1500.degree. C.)
under a vacuum (10.sup.-3 torrs), the oxygen of these oxygenated groups is
released so that free radicals appear allowing the grafting of atoms or
molecules (lactide, muco-polysaccharide, halogen, . . . ) capable of
promoting the fixation of living cells. In this case, the fixation of the
living cells on the piece is therefore not only physical (engagement of
the cells in the pores of the piece), but also chemical.
It is in addition, advantageous, before implantation of the piece in the
organism, to impregnate it with a nutritive serum for the cells. Thus the
life of the cells is promoted during their initial growth inside the pores
of the piece. Such a nutritive serum may be of the type used for the in
vitro culture of similar cells.
Thus a piece surgically implantable in an organism is remarkable in that it
has a composite structure comprising a framework of carbon fiber sections
whose length is at most equal to 30 mm and which form a bed in which said
sections are coated with pyrocarbon joining them to each other, the
specific mass of this composite structure being between 0.5 and 1.6 g/cm.
Preferably, said framework forms a tufted felt of carbon fiber sections and
a diameter of said fibers is of the order of 8 to 12 microns.
Although not exclusively, the implantable piece of the invention is
particularly well adapted to the construction of a percutaneous passage
device, such for example as described in patent U.S. Pat. No. 3,663,965,
U.S. Pat. No. 3,783,868, U.S. Pat. No. 4,321,914, U.S. Pat. No. 4,344,435
and GB-A-2 056 282, comprising a tubular part integral with a collar at
one of its ends.
Preferably, according to a feature of the invention, the outer wall of the
tubular part has the form of a coaxial cone at said tubular part and is
joined to said collar, on the same side as its base. The slant of the
generatrices of the cone with respect to said collar is advantageously
between 30.degree. and 60.degree..
So as to further increase the solidness of the connection between the piece
and the living tissue, at least one annular groove with rounded edges and
concentric with said tubular part is provided in the face of the collar
directed there towards. Thus, the cells of said living tissues may
populate the groove and be fixed therein.
Such a groove may have a depth and a width of the order of a millimeter.
In order to hold said implantable piece firmly in position before and
during development of the cells in said piece, it is advantageous for this
latter to comprise a removable cap, disposed on the outside of the skin
and having points directed thereto, as well as clamping means for pressing
the points of said cap against the skin. After complete cicatrisation,
such a cap may be removed and replaced by a plug or similar.
The Figures of the accompanying drawing show how the invention may be
implemented. In these Figures, identical references designate similar
elements.
FIG. 1 shows, in a schematical axial section, a percutaneous passage device
in accordance with the invention.
FIG. 2 shows, in a view similar to FIG. 1, a variant of the percutaneous
passage device of the invention.
FIG. 3 illustrates, in axial section, another variant of the composite
carbon piece of the percutaneous passage device of the invention.
As shown in FIGS. 1 and 2, the skin, through which the embodiment described
of the device of the invention is to allow a passage, comprises several
superimposed layers which, from the outside towards the inside are the
epiderm 1, the derm 2, a first layer of adipous tissue 3, the surface
fascia 4 and a second layer of adipous tissue 5.
The percutaneous passage device of the invention comprises an implantable
piece 6, formed of a tubular part 6a integral with a collar 6b at one of
its ends. The thickness of the collar 6b may be of the order of 2 mm.
The implantable piece 6 is positioned by surgery so that its collar 6b is
situated just below the derm 2, inside the first layer of adipous tissue 3
and above the surface fascia 4, and so that the tubular part 6a passes
through the epiderm 1 and the derm 2.
Inside the tubular part 6a of the implantable piece 6 is disposed a liner
7, made from titanium or stainless steel for example, said liner 7 being
firmly fixed to the piece 6, for example by bonding. The bottom of liner 7
is pierced so as to allow an element 8 to pass therethrough, such as a
cable, pipe, etc . . . connecting the inside of a patient to the outside.
A sealing mass 9, made for example from a quick setting epoxy resin,
provides the sealing between element 8 and liner 7.
So that the skin is held correctly in position after implantation and
during the whole of the cicatrisation time, a washer 10 is provided having
pointed pins 11 on its face intended to be directed towards the epiderm 1.
These pins 11, for example, are spaced apart every 2 or 3 mm and have a
diameter of 0.2 mm. Washer 10 is held in position by a screw 12
cooperating with an inner thread of the liner 7.
Pins 11 penetrate into the epiderm 1 which allows the skin to be
efficiently held in position and applied against collar 16. In addition,
the space formed between washer 11 and epiderm 1 promotes ventilation of
the wound and so the cicatrisation.
After final cicatrisation, washer 10 and screw 12 are replaced by a
protective plug (not shown), screwed into liner 7 and bearing against the
free end of the tubular part 6a of the piece 6. Such a plug is readily
removable for allowing the necessary checks.
In FIG. 1, the outer wall of the tubular part 6a is cylindrical. On the
other hand, in the variants shown in FIGS. 2 and 3, the outer wall 6c of
the tubular part 6a is conical, the base of this conical part being joined
to the collar 6b. Such an embodiment is preferable for avoiding possible
pockets in which the epithelial cells might form a sheath rejecting the
implantable piece 6. The angle A of the cone may be between 30.degree. and
60.degree..
Furthermore, as shown in FIG. 3, an annular cavity 6d may be provided in
the face of collar 6b directed towards a tubular part 6a. Such an annular
cavity 6d, preferably with rounded edges, may have a depth and a width of
the order of 1 mm. It increases the tear strength, as soon as it is
populated by the cells of the derm. Its inner edge may be situated at
about 1 mm from the base of the cone 6c.
In accordance with the invention, so as to obtain the implantable piece 6
of FIGS. 1 to 3, a bed of carbon fiber sections of about 8 microns in
diameter and a few millimeters in length is formed, for example by pouring
these carbon fiber sections on a horizontal support. In this bed, the
carbon fiber sections occupy more or less horizontal positions with random
direction and freely rest on each other. Then, said bed is subjected to
compression and vertical tufting, so that a felt of carbon fiber sections
is obtained. This felt is then possibly subjected to an additional
vertical compression for adjusting its specific mass to 0.25 g/cm.sup.3.
The compressed felt is introduced into an enclosure containing town gas at
a pressure of 15 torrs and cracking of said gas is carried out at
1000.degree. C. Cracking of the gas is stopped when the specific mass of
the felt reaches 1 g/cm.sup.3.
Then a very porous material is obtained, with open pores. These pores have
outside cross dimensions of about 0.2 mm to 0.005 mm.
In this material thus obtained, piece 6 is machined so that the tubular
part 6a is parallel to the vertically tufted fibers and so that collar 6b
is parallel to the initial horizontal fibers.
The machined base 6 is subjected to dust removal, to the action of an
ultrasonic generator and to oxidization at a high temperature and for a
few seconds.
After possible grafting of atoms and molecules promoting the fixing speed
and/or adhesion of the cells of the derm (as mentioned above) and
impregnation with nutritive serum, piece 6 is positioned in the above
described way.
During cicatrisation, the implantable piece 6 will be integrated with the
skin, mainly through the penetration of the fibroblasts of the derm into
the whole thickness of collar 6b.
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