Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1998-10-26
2001-03-06
Ball, Michael W. (Department: 3738)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C600S036000, C623S901000, C623S910000
Reexamination Certificate
active
06197143
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of making conduits for use as bioprosthetic replacement, or by-pass, cardiac valve conduits.
BACKGROUND OF THE INVENTION
Extracardiac conduits in the form of biological or synthetic tubes are known to be used in cardiac surgery, primarily for the correction of ventricular outflow abnormalities in patients. It is also known in the literature that aorta or pulmonary valves, of human or animal origin, can be used for the replacement of defective cardiac valves. Replacement valves have also been made from pericardium.
For example in Ann. Thorac. Surg. 1995, 60, S200, there is described a method of making a valved conduit from pericardium tissue. The tissue is moulded by folding it over a template, and partially fixing it with glutaraldehyde. The template contains raised areas on both surfaces, which during fixation of the tissue, form protuberances on the outer surface of the tissue, so that when the folded tissue is sutured together, these protuberances form sinuses and cusps. The template is removed and the folded tissue sutured together in such a manner as to form cusps on one side of the tissue layer and sinuses on the other. The tissue is then rolled around an axis perpendicular to the fold line and sutured together to form a tubular structure, so that the cusps are on the inside and form a valve. The conduit is finally fixed with glutaraldehyde. However, since the tissue is sewn together to form the cusps after the template is removed, the cusps and sinuses may be irregular in size and shape. Thus may result in the valve not closing completely when the conduit is formed.
Another method of forming sinuses on a conduit, is by applying pressure to the inside of a conduit, which is surrounded by an external stent, so as to stretch the walls radially outwards through the stent, thus generating protuberances in the walls of the conduit. However, this is not a favourable method of forming sinuses, as the walls of the sinuses tend to be thinner and thus weaker than the main wall of the conduit.
It is believed that the exact shape and configuration of the cusps is important to guard against unnatural distortion of the valve in use, which would impair proper sealing of the valve cusps.
DESCRIPTION OF THE INVENTION
According to the present invention there is provided a method of making a bioprosthetic conduit, comprising the steps of:
(a) taking a cylindrical mould, having circumferentially spaced protuberances which extend radially from the axis;
(b) curving a layer of a biocompatible sheet material around the cylindrical mould, and joining the opposed edges of the layer together along a longitudinal axis, parallel to the axis of the mould to form a tubular layer, and
(c) removing the tubular layer from the mould and turning it inside out to form a cylindrical conduit with sinuses, the conduit being fully fixed by a chemical means; after removal or while still on the mould.
Where the conduit is required to be valved, in an additional step (d) an outer biocompatible layer is overlaid on the underlying tubular layer to form a superimposed layer, so that the superimposed layer partially covers the protuberances, the superimposed layer is held in place and sealed onto the underlying tubular layer around the protuberances, to form sinuses and cusps or valve flaps, the layers being partially fixed on the mould by a chemical means.
Preferably, the mould is radially collapsible like, for example, a chuck, an angioplasty balloon, or an apparatus similar to that used to make Chinese paper lanterns. The mould can, for example, be made of wood, rubber, plastic or metal e.g. stainless steel.
Alternatively, the cylindrical mould is made from soluble material that will quickly dissolve when placed in a solvent, leaving the tubular layer of biocompatible material intact.
The biocompatible layer can be made of biological tissue e.g. pericardium, or biocompatible synthetic material e.g. photo-fixable material.
Most preferably, the biocompatible layers are joined with sutures. Where appropriate, the layers can also be joined by heat sealing, whereby by the means for sealing can be automated and pre-programmed, so as to guide the heat sealer along an exact path. Alternatively, the layers are joined together with a fixing glue or staples.
Preferably, the conduit contains valves which are formed by joining an underlying layer with a superimposed layer, along a fixed pattern, and then turning the tubular structure inside out. Alternatively, the conduit is formed without valves, and a separate valve unit is inserted inside the conduit after assembly. Thus, in the step (d), the outer layer can comprise a second piece of biocompatible sheet material which is held in place on the underlying layer while it is sealed in place by suturing or welding around the periphery of that part of each protuberance which overlaid by the outer layer. Most conveniently however, the outer layer may simply be formed by peeling back one end of the tubular layer until it reaches the required position on the mould. In a particular preferred embodiment of the invention, the end of the tube formed by the two layers of material can be reinforced and cushioned by inclusion of an O-shaped ring. The O-shaped ring further facilitates secure attachment of the conduit to the patient's vascular system by padding the area that is being joined, so as to make suturing easier. The ring is conveniently made of synthetic material, for example a biocompatible rubber.
Preferably the tubular layer is slid off the mould and then turned inside out. Alternatively, the layer can be peeled off the mould so that the tubular layer turns inside out whilst being removed off the mould.
REFERENCES:
patent: 14114643 (1992-04-01), None
Ball Michael W.
Gottlieb Rackman & Reisman P.C.
Musser Barbara J.
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