CA1092303A - Flexible vascular graft of polymeric material with internal porous surface - Google Patents
Flexible vascular graft of polymeric material with internal porous surfaceInfo
- Publication number
- CA1092303A CA1092303A CA259,054A CA259054A CA1092303A CA 1092303 A CA1092303 A CA 1092303A CA 259054 A CA259054 A CA 259054A CA 1092303 A CA1092303 A CA 1092303A
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- Canada
- Prior art keywords
- vascular graft
- tube
- graft
- porous
- subsurface
- Prior art date
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Abstract
ABSTRACT OF THE DISCLOSURE
A novel vascular graft comprises a flexible elongate tube of polymeric material having an internal porous surface and a network of interconnected interstitial pores below the surface in fluid flow communication with the surface pores. Tissue forms a smooth thin adherent coating of self-determining thickness on the porous surface making it resistant to the formation of the blood clots normally associated with the presence of foreign bodies in the blood-stream.
A novel vascular graft comprises a flexible elongate tube of polymeric material having an internal porous surface and a network of interconnected interstitial pores below the surface in fluid flow communication with the surface pores. Tissue forms a smooth thin adherent coating of self-determining thickness on the porous surface making it resistant to the formation of the blood clots normally associated with the presence of foreign bodies in the blood-stream.
Description
~09'~3~3 This invention relates to novel vascular graf-ts.
It is well known that the introduction of foreign bodies into the blood stream, for example, the polished ; metal surfaces of artificial heart valves, tends to cause i ~ the formation of blood clots which may break loose and embolize to various parts of the body. Such thromboembolic ` problems have led to the administration of anticoagulants to patients with artificial heart valves. The effects of these anticoagulants on the blood clotting mechanism cause - 10 difficulties in stopping the flow of blood through even ` a minor flesh wound. In addition, flexible plastic conduits are used for vascular graft purposes and such surfaces also ` ~ are thrombogenic. ~ -.;, ` ~.
- Attempts have been made to overcome the thrombo-embolic problems of polished metal heart valves by providing a porous fabric covering over blood-engaging metal parts.
When such porous fabrics have been used for covering metal heart valve-parts, pores of typical size 500 to 700 ~- microns have been provided and some tissue ingrowth has been observed. While the fabric covering has resulted in a ~ ~ ;decreased incidence of thromboembolism, apparently due to the ~- observed tlssue ingrowth, such valves do suffer from other ~'J : defe~ts, notably wear of the fabric, causing cloth fragment embolism and chronic hemolytic anemia as a result of . f, . ~ turbulence oE the blood over disrupted fabric coverings.
To date, the prior art has been unable to provide 5~. ` a-heart valve which not only overcomes the thromboembolic fi ,I problems of a smooth metal surface but also does not exhibit the wear failure problem of the prior art fabric covered , 30 heart valves.
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. .
~Z303 .' Similarly, small vessel replacement by a graft ~- has not been entirely satisfactory, although many~ sugges-tions have been made, includlng fresh and preserved allografts, "DACRON" (Trademclrk~ and other ~abric `,t~ ~ prostheses and bovine heterografts.
The present invention provides a flexible cardio-vascular graft, preferably a graft having an inside diameter less than about 6 mm, consisting of an elongate tube of ~ ~ polymeric material inert to blood. At least the internal t ` . 10 surface, i.e., the blood stream engaging surface, is porous and in fluid flow communicakion with a network of ¦~
interconnected pores in the subsurface.
~, ~ Nucleated cells circulating in the bloodstream col-onize onto the blood-engaging surface and subsequently differentiate into other cell types to form a thin, smooth, ; generally uniformly-thick, firmly~attached tissue covering i on the s~urface. The tissue oovering is ~orned ra~ var about a._ ` ~ one month period, does not appear to increase significantly - "
; in thickness thereafter, and includes flattened endothelial~ e cells at the surface thereof. The tissue formation is not ~` accompanied by thrombosis or embolism owing to its blood-compatible nature, and once the maximum thickness has been attained, the tissue covering is self-regenerating The invention is described further, by way of illus- !
',".' ~' ~;: tration~ with reference to the accompanying drawings, in which: ' Figure 1 is a full scale photograph of a microporous . hydrophilic polyurethane vascular graft provided in accordance with the invention;
Figure 2 is a photograph of a cut section of the tube shown in Figure 1 at 16 times magnification;
Figure 3 is a photograph of a cut section of the ~, ~ , , .
j ~P~ tube shown in Figure 1 at 50 times magnification;
~ `~
~Z3U3 Figure 4 is a photograph of a cut section of the tube shown in Figure 1 at 1000 times magnification;
Figure 9 is a photograph of a cut section of a 5, ~ porous tube similar to that shown in Figure 1 having a woven fabric reinforcing core at 18 times magnification;
,~ Figure 6 is a photograph of the cut section of F~gure 5 at 200 times mag~ification; and igure 7 is a photograph of the cut section of Figure 5 at 1000 times magnification.
The microporous polymeric vascular graft of the . present invention may be formed by uniformly dispersing solvent-elutable particles in a first continuous or dis-` continuous polymer phase, forming a coherent shaped article from the dispersion having solvent-elutable particles substantially dispersed throughout a second continuous solid polymer phase, and eluting the solvent- -;, : . : , elutable particles from the article to provide a porous . . - .
` shaped polymer product having interconnected pores therein.
~; A specific procedure for the formation o~ the ,~ ~ 20 microporous polymeric vascular graft includes forming a -~ viscous casting solution of the polymer, dispersing solvent-elutable particles in the solution and placing the~viscous casting solution in a tube of inside diameter corresponding to the outside diameter of the desired tube. A plumb ball ; or other suitable device, such as a rod, of diameter corresponding to the inside diameter of the article desired is drawn through the column of viscous material, resulting in the casting of the polymer on the inside of the tube.
Following drying of the casting, the polymer tube is ;~
removed, and the particles eluted to provide the porous ` structure. Following the elution step, the structure of ;` the devicel including its porosity, may be modified by heat treatment, such as, in an autoclave. ~ ;~
lO9Z303 The latter procedure is particularly adapted for the formation of microporous, flexible pol~meric vascular . ~ grafts of narrow inside and c,utside diameters, for example, - ~ 4and 6 mm respectively. The dimensions may vary widely, ': however, depending on the desired use, with inside diameters :~ varying from about 2 mm to about 10 mm or more and wall thicknesses varying from about 0.1 mm to about 1 mm or more.
. The vascular grafts also may be in the form of large diameter -- grafts, for example, having diameters of 5 cm or more.
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~Z3~3 , Such grafts, o~ any desired len~th, have particular ; utility as aorto-coronary by pas~ grafts, and may be pro-- vided as a single linear tube or a branched tube by suitable adjustment of the procedure.
The grafts may be w,holly porous or laminated with a solid coherent polymer substrate as the outer wall or as a centre layer between two porous layers, as desired~ In a further modification, reinforcing material such as fibres, fabrics, platelets and fillers may be provided in association with the microporous polymer layer to enhance the strength and sewability of the graft.
The solvent-elutable particles and -the elution solvent used in the above described procedure should be non-toxic in nature so that any residual material in the porous structure is not harmful to body tissues or blood in , use. Typically, the solvent-elutable particles are water- ~
soluble, for example, sodium chloride or sodium carbonate particles, and solvent elution is achieved using watex.
The pàrticle size of the solvent-elutable particles ~ 20 to a large degree dictates~the pore size in the polymer ; body, a}though irregular pore shapes generally result. ~-Pore sizes from about 10 to over 100 microns are possible, using particles in the size range of abo~t -500 to ~100 1`
^ mesh. -~
The pore size, volume and shape,of the product may be controllecl by varying the size, shape and distribl~tion of the solvent-elutable particles and the weight ratio of the i~ - polymer to partic~es.
Another procedure for the formation of the vascular '~
- .:
graft porous polymeric material is to cast the polymer ~; around a latticework~which may then be rolled or formed into the desired shape.
,('' ' . ~,:
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lO9Z303 The invention is illustrated by the following Examples:
~ -, Exam~le 1 ,. , ~ ; A 30~ solution of a hydrophilic polyurethane ~
consisting of urea interlinked blocks of polyether and chain extended urethane in dimethyl formamide was mixed with sodium chloride crystals of average size 200 ~300 mesh in a 1:1 weight ratio of sodium chloride to polymer to form a viscous solution. The solution was positioned ~ 10 in a glass tube of inside diameter 6 mm and the tube was ; ~ allowed to pass a conically-shaped plumb ball of maximum diameter approximately 4 mm attached to the lower end of a string to cast a polymer tube inside the glass tube.
After drying under an infra-red heating lamp, the polymer tube was removed from the glass tube by immersion , :~
;~ in water and annealed by boiling in the water. The-operations of immersion and annealing also resulted in leaching o the sodium chloride from the tube to form a wholly porous microporous tube. Photographs of the tube ~ ;
, ,- . ~
~ 20 at various magnifications are shown in Figures 1 to 4~ ~
:
;- Example 2 T~e procedure of Example 1 was repeated with the ~ exception that a woven "DACRON" CTrademark) fabric was - posltioned in the polymer tube to provide reinforcement thereto. Photographs o~ the resulting tube at various magnifications are shown in Figures 5 to 7.
~ In summary of this disclosure, the present invention ; provides novel vascular grafts which have biocompatibility and hence auoid the prior art thrombogenic problems. Modi-~ications are possi~le within the scope of the invention.
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~ 9Z3~3 SUPPLEMENiT RY D.ISCLOSURE
~ In the principal disclosure, there is described a v flexible vascular gra~t structure comprised o~ polymeric :, material and having at least the internal surface thereof ~A, ~ porous and in fluid flow communication with a network o~
, ~ interconnected pores in the subsurface.
The grafts may be o~ the small bore category, i.e., '.', ' ~ .`' . , ~.: ..
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less than 6 mm inside diameter, or of large bore category, i.e., greater than 6 mm inside diameter. In accordance with this supplementary disclosure, the para~eters of the small -~ and large bore grafts are described in more detail.
:i .
1. SMALL BORE VASCULAR GRAFTS
- Smalll bore vascular grafts comprise an elongate tubular body having an inside diameter from about 2 to about - 6 mm, the diameter generally corresponding to the diameter of the vessel to which the tube is to be grafted. The wall ` 10 thickness of the graft may vary widely from about 0.2 mm to ,. .
about 1 mm or more.
The vascular grafts may be in the form of a single .
; tube length or may have one or more integral branches to conform with the anatomical requirements of the graft.
, The inner blood-engaging surface of the graft is porous and communicates with a network of interconnected pores in the subsurface region. The interconnected pores ~ preferably are substantially uniformly distributed throughout ;` the subsurface region. The pore size in the surfacP and the subsurface region is generally less than about 50 microns and preferably less than about 20 mlcrons.
~- ~ The internal porosity promotes the formation of tissue ;~
- on the surface, as described above in connection with the rigid ltems provided in accordance with this invention.
` The outer surface of the graft also is porous and communicates with a network of interconnected pores in the -;
~ subsurface region, permitting ingrowth of soft tissue from -~ the surrounding body tissue, to incorporate the graft permanently into the body.
The interstitial pore size of the outer porous region .
of the graft may be the same as that of the inner porous region, '. .
' ' ~ ~......................... ~ ~ . , ~i ... , - .: .
:..... .
~923~3~
but the pore sizes also may vary and in -the outer porous region, f, pore sizes of up to about 200 m:icrons may be used.
The porosity of the inner and outer porous regions of the graft may vary ~rom about 10 to about 70 vol.% con-sistent with the interconnected porosity requirement for the ; subsurface regions.
. .-~ .
~ The graft is required to have a minimum strength in :,- use consistent with the requirements that the graft may be sutured readily without tearing and that the graft have sufficient strength to prevent struc~ural b~eakdown at the ~` anas~omosis and along the length of the graft.
The actual minimum strength requirements will vary depending on the intended use of the gra~t, the strength -requirements for venous grafts being very much less than those for arterial grafts because o~ the lower venous blood pressures.
The grafts provided in accordance with this embodiment of the invention for venous use should be able to withstand venous ~` blood pressure of not less than 25 mm Hg for prolonged periods, generally greater than oné year, preferably greatér than 5 years, in a physiological environment. ~ ~ `
., : ' : ' The preferred aspect of this embodiment of the ~ ~;
invention is the provision of an arterial graft, which also may be used as a venous graft, if desired, and such an arterial graft should be able to withstand pulsatile arterial blood `~
pressure of greater than about 300 mm Hg, preferably greater than about 500 mm Hg, for a prolonged period of time, gene~ally ; , ~, greater than~one year, preferably greater than 5 years, in a physiological environment. ~ -Consistent with these minimum strength requirements~
the graft may have a wholly porous wall having a uniform pore d, ~, size throughout, or a wholly porous wall in which the pore ::'` . 9 . ~ , ~r p~
! i `- 10~;~303 size vari~s in the inner and ou-ter surface regions. Ar~sdition-~; ally, a dense coherent flexib:Le polymeric substrate layer i may be laminated between inner and outer porous layers.
In one preferred structure of the vascular graft, j~ reinforcing material is provicled in association with the porous wall, and such reinforcing material preferably takes the form of a fabric layer, such as a knitted Dacron fabric layer laminated between inner and outer porous layers, although fibres, platelets and fillers also may be used as ~` 10 reinforcing agents.
-~ 2 . LARGE BORE ASCULAR GRAE TS
Large bore ~ascular grafts differ from the small .. . .
bore vascular grafts described above in having an inside - diameter greater than ahout 6 mm up to about 10 cm, although . ::
'~ it is preferred for such grafts to have an inside diameter of less than about 5 cm.
The large bore vascular grafts also differ from the ~ ;~
i. , .
small bore grafts in that the pore size of blood engaging surface and associated subsurface region may vary up to about - 20 200 microns, if desired, although it is preferred to utilize the smaller pore size of less than 50 microns and more prefer-f. ;, ably less than 20 microns.
,,~ ; .
' - The porosity and strength requirements of the large bore graft are the same as those for the small bore graft referred to above. Additionally, in common with the small . :
~ ~bore grafts, the large bore grafts may be provided as a i ~ .
single tube or as a branched tube having one or more integral bra~ches. Further, large bore grafts may be provided with one or more integral small bore branches, if desired.
, ~ 3 0 ~ 'i;~ ~e ~, ~, ~
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.
It is well known that the introduction of foreign bodies into the blood stream, for example, the polished ; metal surfaces of artificial heart valves, tends to cause i ~ the formation of blood clots which may break loose and embolize to various parts of the body. Such thromboembolic ` problems have led to the administration of anticoagulants to patients with artificial heart valves. The effects of these anticoagulants on the blood clotting mechanism cause - 10 difficulties in stopping the flow of blood through even ` a minor flesh wound. In addition, flexible plastic conduits are used for vascular graft purposes and such surfaces also ` ~ are thrombogenic. ~ -.;, ` ~.
- Attempts have been made to overcome the thrombo-embolic problems of polished metal heart valves by providing a porous fabric covering over blood-engaging metal parts.
When such porous fabrics have been used for covering metal heart valve-parts, pores of typical size 500 to 700 ~- microns have been provided and some tissue ingrowth has been observed. While the fabric covering has resulted in a ~ ~ ;decreased incidence of thromboembolism, apparently due to the ~- observed tlssue ingrowth, such valves do suffer from other ~'J : defe~ts, notably wear of the fabric, causing cloth fragment embolism and chronic hemolytic anemia as a result of . f, . ~ turbulence oE the blood over disrupted fabric coverings.
To date, the prior art has been unable to provide 5~. ` a-heart valve which not only overcomes the thromboembolic fi ,I problems of a smooth metal surface but also does not exhibit the wear failure problem of the prior art fabric covered , 30 heart valves.
s, l , :
~ 2 - ~
. .
~Z303 .' Similarly, small vessel replacement by a graft ~- has not been entirely satisfactory, although many~ sugges-tions have been made, includlng fresh and preserved allografts, "DACRON" (Trademclrk~ and other ~abric `,t~ ~ prostheses and bovine heterografts.
The present invention provides a flexible cardio-vascular graft, preferably a graft having an inside diameter less than about 6 mm, consisting of an elongate tube of ~ ~ polymeric material inert to blood. At least the internal t ` . 10 surface, i.e., the blood stream engaging surface, is porous and in fluid flow communicakion with a network of ¦~
interconnected pores in the subsurface.
~, ~ Nucleated cells circulating in the bloodstream col-onize onto the blood-engaging surface and subsequently differentiate into other cell types to form a thin, smooth, ; generally uniformly-thick, firmly~attached tissue covering i on the s~urface. The tissue oovering is ~orned ra~ var about a._ ` ~ one month period, does not appear to increase significantly - "
; in thickness thereafter, and includes flattened endothelial~ e cells at the surface thereof. The tissue formation is not ~` accompanied by thrombosis or embolism owing to its blood-compatible nature, and once the maximum thickness has been attained, the tissue covering is self-regenerating The invention is described further, by way of illus- !
',".' ~' ~;: tration~ with reference to the accompanying drawings, in which: ' Figure 1 is a full scale photograph of a microporous . hydrophilic polyurethane vascular graft provided in accordance with the invention;
Figure 2 is a photograph of a cut section of the tube shown in Figure 1 at 16 times magnification;
Figure 3 is a photograph of a cut section of the ~, ~ , , .
j ~P~ tube shown in Figure 1 at 50 times magnification;
~ `~
~Z3U3 Figure 4 is a photograph of a cut section of the tube shown in Figure 1 at 1000 times magnification;
Figure 9 is a photograph of a cut section of a 5, ~ porous tube similar to that shown in Figure 1 having a woven fabric reinforcing core at 18 times magnification;
,~ Figure 6 is a photograph of the cut section of F~gure 5 at 200 times mag~ification; and igure 7 is a photograph of the cut section of Figure 5 at 1000 times magnification.
The microporous polymeric vascular graft of the . present invention may be formed by uniformly dispersing solvent-elutable particles in a first continuous or dis-` continuous polymer phase, forming a coherent shaped article from the dispersion having solvent-elutable particles substantially dispersed throughout a second continuous solid polymer phase, and eluting the solvent- -;, : . : , elutable particles from the article to provide a porous . . - .
` shaped polymer product having interconnected pores therein.
~; A specific procedure for the formation o~ the ,~ ~ 20 microporous polymeric vascular graft includes forming a -~ viscous casting solution of the polymer, dispersing solvent-elutable particles in the solution and placing the~viscous casting solution in a tube of inside diameter corresponding to the outside diameter of the desired tube. A plumb ball ; or other suitable device, such as a rod, of diameter corresponding to the inside diameter of the article desired is drawn through the column of viscous material, resulting in the casting of the polymer on the inside of the tube.
Following drying of the casting, the polymer tube is ;~
removed, and the particles eluted to provide the porous ` structure. Following the elution step, the structure of ;` the devicel including its porosity, may be modified by heat treatment, such as, in an autoclave. ~ ;~
lO9Z303 The latter procedure is particularly adapted for the formation of microporous, flexible pol~meric vascular . ~ grafts of narrow inside and c,utside diameters, for example, - ~ 4and 6 mm respectively. The dimensions may vary widely, ': however, depending on the desired use, with inside diameters :~ varying from about 2 mm to about 10 mm or more and wall thicknesses varying from about 0.1 mm to about 1 mm or more.
. The vascular grafts also may be in the form of large diameter -- grafts, for example, having diameters of 5 cm or more.
;,~ . .
i ~ ~ 10 . .: , .
:., , ~ :-., .
~''" ~.
., ", -.
, ,.~ :
~ q '' ~ ' :: ~
., . --. ~ :
~:` - ~ ' , .. i ~:
., ~ .
,~
~, `:` `.`. ' , ., ~ 4a -: ~ :
~Z3~3 , Such grafts, o~ any desired len~th, have particular ; utility as aorto-coronary by pas~ grafts, and may be pro-- vided as a single linear tube or a branched tube by suitable adjustment of the procedure.
The grafts may be w,holly porous or laminated with a solid coherent polymer substrate as the outer wall or as a centre layer between two porous layers, as desired~ In a further modification, reinforcing material such as fibres, fabrics, platelets and fillers may be provided in association with the microporous polymer layer to enhance the strength and sewability of the graft.
The solvent-elutable particles and -the elution solvent used in the above described procedure should be non-toxic in nature so that any residual material in the porous structure is not harmful to body tissues or blood in , use. Typically, the solvent-elutable particles are water- ~
soluble, for example, sodium chloride or sodium carbonate particles, and solvent elution is achieved using watex.
The pàrticle size of the solvent-elutable particles ~ 20 to a large degree dictates~the pore size in the polymer ; body, a}though irregular pore shapes generally result. ~-Pore sizes from about 10 to over 100 microns are possible, using particles in the size range of abo~t -500 to ~100 1`
^ mesh. -~
The pore size, volume and shape,of the product may be controllecl by varying the size, shape and distribl~tion of the solvent-elutable particles and the weight ratio of the i~ - polymer to partic~es.
Another procedure for the formation of the vascular '~
- .:
graft porous polymeric material is to cast the polymer ~; around a latticework~which may then be rolled or formed into the desired shape.
,('' ' . ~,:
5 _ "; . ., ~: t"
lO9Z303 The invention is illustrated by the following Examples:
~ -, Exam~le 1 ,. , ~ ; A 30~ solution of a hydrophilic polyurethane ~
consisting of urea interlinked blocks of polyether and chain extended urethane in dimethyl formamide was mixed with sodium chloride crystals of average size 200 ~300 mesh in a 1:1 weight ratio of sodium chloride to polymer to form a viscous solution. The solution was positioned ~ 10 in a glass tube of inside diameter 6 mm and the tube was ; ~ allowed to pass a conically-shaped plumb ball of maximum diameter approximately 4 mm attached to the lower end of a string to cast a polymer tube inside the glass tube.
After drying under an infra-red heating lamp, the polymer tube was removed from the glass tube by immersion , :~
;~ in water and annealed by boiling in the water. The-operations of immersion and annealing also resulted in leaching o the sodium chloride from the tube to form a wholly porous microporous tube. Photographs of the tube ~ ;
, ,- . ~
~ 20 at various magnifications are shown in Figures 1 to 4~ ~
:
;- Example 2 T~e procedure of Example 1 was repeated with the ~ exception that a woven "DACRON" CTrademark) fabric was - posltioned in the polymer tube to provide reinforcement thereto. Photographs o~ the resulting tube at various magnifications are shown in Figures 5 to 7.
~ In summary of this disclosure, the present invention ; provides novel vascular grafts which have biocompatibility and hence auoid the prior art thrombogenic problems. Modi-~ications are possi~le within the scope of the invention.
~'' . :.
'' ''' ` ' ' , ~
~,. . . . . .. . .. .. . .
- . ; i ~: . , , -:
~ 9Z3~3 SUPPLEMENiT RY D.ISCLOSURE
~ In the principal disclosure, there is described a v flexible vascular gra~t structure comprised o~ polymeric :, material and having at least the internal surface thereof ~A, ~ porous and in fluid flow communication with a network o~
, ~ interconnected pores in the subsurface.
The grafts may be o~ the small bore category, i.e., '.', ' ~ .`' . , ~.: ..
,,~, ' .
.
~ . . .
~, ,. , .
,:. . ~ ~
~, "
~ `, .
:` - - 1~
. . . .
. , ,.
,.~,, , . :
. . . ~, .
~ ` ~ .~
.' ! i '~ 1 ' ' ' '' ' . ~ ~' .
.~ ~
, ' . ` ' ''~'' ~ ' . ' ' .
. ~ - 7 - .
,3~3 .
less than 6 mm inside diameter, or of large bore category, i.e., greater than 6 mm inside diameter. In accordance with this supplementary disclosure, the para~eters of the small -~ and large bore grafts are described in more detail.
:i .
1. SMALL BORE VASCULAR GRAFTS
- Smalll bore vascular grafts comprise an elongate tubular body having an inside diameter from about 2 to about - 6 mm, the diameter generally corresponding to the diameter of the vessel to which the tube is to be grafted. The wall ` 10 thickness of the graft may vary widely from about 0.2 mm to ,. .
about 1 mm or more.
The vascular grafts may be in the form of a single .
; tube length or may have one or more integral branches to conform with the anatomical requirements of the graft.
, The inner blood-engaging surface of the graft is porous and communicates with a network of interconnected pores in the subsurface region. The interconnected pores ~ preferably are substantially uniformly distributed throughout ;` the subsurface region. The pore size in the surfacP and the subsurface region is generally less than about 50 microns and preferably less than about 20 mlcrons.
~- ~ The internal porosity promotes the formation of tissue ;~
- on the surface, as described above in connection with the rigid ltems provided in accordance with this invention.
` The outer surface of the graft also is porous and communicates with a network of interconnected pores in the -;
~ subsurface region, permitting ingrowth of soft tissue from -~ the surrounding body tissue, to incorporate the graft permanently into the body.
The interstitial pore size of the outer porous region .
of the graft may be the same as that of the inner porous region, '. .
' ' ~ ~......................... ~ ~ . , ~i ... , - .: .
:..... .
~923~3~
but the pore sizes also may vary and in -the outer porous region, f, pore sizes of up to about 200 m:icrons may be used.
The porosity of the inner and outer porous regions of the graft may vary ~rom about 10 to about 70 vol.% con-sistent with the interconnected porosity requirement for the ; subsurface regions.
. .-~ .
~ The graft is required to have a minimum strength in :,- use consistent with the requirements that the graft may be sutured readily without tearing and that the graft have sufficient strength to prevent struc~ural b~eakdown at the ~` anas~omosis and along the length of the graft.
The actual minimum strength requirements will vary depending on the intended use of the gra~t, the strength -requirements for venous grafts being very much less than those for arterial grafts because o~ the lower venous blood pressures.
The grafts provided in accordance with this embodiment of the invention for venous use should be able to withstand venous ~` blood pressure of not less than 25 mm Hg for prolonged periods, generally greater than oné year, preferably greatér than 5 years, in a physiological environment. ~ ~ `
., : ' : ' The preferred aspect of this embodiment of the ~ ~;
invention is the provision of an arterial graft, which also may be used as a venous graft, if desired, and such an arterial graft should be able to withstand pulsatile arterial blood `~
pressure of greater than about 300 mm Hg, preferably greater than about 500 mm Hg, for a prolonged period of time, gene~ally ; , ~, greater than~one year, preferably greater than 5 years, in a physiological environment. ~ -Consistent with these minimum strength requirements~
the graft may have a wholly porous wall having a uniform pore d, ~, size throughout, or a wholly porous wall in which the pore ::'` . 9 . ~ , ~r p~
! i `- 10~;~303 size vari~s in the inner and ou-ter surface regions. Ar~sdition-~; ally, a dense coherent flexib:Le polymeric substrate layer i may be laminated between inner and outer porous layers.
In one preferred structure of the vascular graft, j~ reinforcing material is provicled in association with the porous wall, and such reinforcing material preferably takes the form of a fabric layer, such as a knitted Dacron fabric layer laminated between inner and outer porous layers, although fibres, platelets and fillers also may be used as ~` 10 reinforcing agents.
-~ 2 . LARGE BORE ASCULAR GRAE TS
Large bore ~ascular grafts differ from the small .. . .
bore vascular grafts described above in having an inside - diameter greater than ahout 6 mm up to about 10 cm, although . ::
'~ it is preferred for such grafts to have an inside diameter of less than about 5 cm.
The large bore vascular grafts also differ from the ~ ;~
i. , .
small bore grafts in that the pore size of blood engaging surface and associated subsurface region may vary up to about - 20 200 microns, if desired, although it is preferred to utilize the smaller pore size of less than 50 microns and more prefer-f. ;, ably less than 20 microns.
,,~ ; .
' - The porosity and strength requirements of the large bore graft are the same as those for the small bore graft referred to above. Additionally, in common with the small . :
~ ~bore grafts, the large bore grafts may be provided as a i ~ .
single tube or as a branched tube having one or more integral bra~ches. Further, large bore grafts may be provided with one or more integral small bore branches, if desired.
, ~ 3 0 ~ 'i;~ ~e ~, ~, ~
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.
Claims (28)
1. A flexible vascular graft consisting of an elongate tube of polymeric material inert to blood, at least the internal surface of said tube being porous and in fluid flow communication with a network of interconnected pores in the subsurface.
2. The graft of claim 1 comprising a layer of dense coherent polymeric material and an inner layer of porous polymeric material adhered to said dense layer and including said surface and subsurface.
3. The graft of claim 2 further comprising an outer layer of porous polymeric material adhered to said dense layer and having a plurality of interconnected pores distributed therethrough.
4. The graft of claim 1 having an inside diameter of less than about 6 mm.
5. The graft of claim 1 which is wholly porous.
6. A process for the formation of a flexible vascular graft consisting of an elongate tube of polymeric material inert to blood, at least the internal surface of said tube being porous and in fluid flow communication with a network of interconnected pores in the subsurface, which comprises:
the procedure of uniformly dispersing solvent-elutable particles in a first continuous or discontinuous polymer phase, forming a coherent shaped article from the disper-sion having solvent-elutable particles substantially uniformly dispersed throughout a second continuous solid polymer phase, and eluting the solvent-elutable particles from the article to provide a porous shaped polymer product having interconnected pores therein.
the procedure of uniformly dispersing solvent-elutable particles in a first continuous or discontinuous polymer phase, forming a coherent shaped article from the disper-sion having solvent-elutable particles substantially uniformly dispersed throughout a second continuous solid polymer phase, and eluting the solvent-elutable particles from the article to provide a porous shaped polymer product having interconnected pores therein.
7. The process of claim 6 wherein said procedure includes forming a viscous casting solution of a polymer, dispersing the solvent-elutable particles in the viscous casting solution, casting the solution onto a casting surface in tubular form, removing the solvent phase, and eluting the solvent-elutable particles from the cast tube.
8. The process of claim 7 wherein said solvent-elutable particles are sodium chloride.
9. The graft of claim 1 including reinforcing material associated with said subsurface,
10. The process of claim 6 wherein said procedure includes heat treating the porous shaped polymer product.
CLAIMS SUPPORTED BY SUPPLEMENTARY DISCLOSURE
CLAIMS SUPPORTED BY SUPPLEMENTARY DISCLOSURE
11. A small bore flexible vascular graft constructed of flexible biocompatible polymeric material and comprising an elongate tube having an inside diameter of from about 2 to about 6 mm and a strength at least sufficient to withstand venous blood pressure of greater than 25 mm Hg in the physiological environment for at least one year, said tube having an inner porous surface in fluid flow communication with a network of interconnected pores in the adjacent subsur-face which has a pore size of less than about 50 microns and a porosity of about 10 to about 70% by volume, said tube having an outer porous surface in fluid flow communication with a network of interconnected pores in the adjacent subsurface which has a pore size of less than about 200 microns and a porosity of about 10 to about 70% by volume.
12. The vascular graft of claim 11 having a strength at least sufficient to withstand pulsatile arterial blood pressure of greater than about 300 mm Hg in its physiological environment for at least 1 year.
13. The vascular graft of claim 11 wherein said tube has a wall thickness of about 0.2 to about 1 mm.
14. The vascular graft of claim 11 which is wholly porous and said subsurface networks comprise a single integral network of interconnected pores communicating with both surfaces with said network of interconnected pores being substantially uniformly distributed through the tube wall.
15. The vascular graft of claim 11 wherein said respective adjacent subsurfaces are constituted by inner and outer porous layers laminated to a coherent flexible substrate polymeric layer.
16. The vascular graft of claim 11 which is reinforced to provide a strength at least sufficient to withstand pulsatile arterial blood pressure of greater than about 300 mm Hg in its physiological environment for at least 1 year.
17. The vascular graft of claim 16 wherein said rein-forcement is provided by a layer of fabric positioned in the tube wall.
18. The vascular graft of claim 17 wherein said respective adjacent subsurfaces are constituted by inner and outer porous layers laminated to a central layer of fabric.
19. The vascular graft of claim 11 wherein said inner porous surface and subsurface region has a pore size of less than about 20 microns.
20. The vascular graft of claim 11 in the form of a branched tube.
21. A large bore flexible vascular graft constructed of flexible biocompatible polymeric material and comprising an elongate tube having an inside diameter of greater than about 6 mm up to about 10 cm and a strength at least sufficient to permit suturing without tearing and to prevent structural breakdown at the anastomosis and along the length of the graft over prolonged periods of use, said tube having an inner porous surface in fluid flow communication with a network of interconnected pores in the adjacent subsurface which has a pore size of less than about 200 microns and a porosity of bout 10 to about 70% by volume, said tube having an outer porous surface in fluid flow communication with a network of interconnected pores in the adjacent subsurface which has a pore size of less than about 200 microns and a porosity of about 10 to about 70% by volume.
22. The vascular graft of claim 21 having a strength at least sufficient to withstand pulsatile arterial blood pressure of greater than about 300 mm Hg in its physiological environment for at least 1 year.
23. The vascular graft of claim 21 which is reinforced to provide a strength at least sufficient to withstand pulsatile arterial blood pressure of greater than about 300 mm Hg in its physiological environment for at least 1 year.
24. The vascular graft of claim 23 wherein said reinforcement is provided by a layer of fabric positioned in the tube wall.
25. The vascular graft of claim 24 wherein said respective adjacent subsurfaces are constituted by inner and outer porous layers laminated to a central layer of fabric.
26. The vascular graft of claim 21 wherein said pore sizes in said inner and outer subsurfaces are each less than about 50 microns.
27. The vascular graft of claim 21 in the form of a branched tube.
28. The vascular graft of claim 21 wherein said elongate tube has at least one integrally-formed branch small bore graft constructed as defined in claim 11.
Priority Applications (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/095,151 US4374669A (en) | 1975-05-09 | 1979-11-19 | Cardiovascular prosthetic devices and implants with porous systems |
| CA360,677A CA1105652A (en) | 1976-05-02 | 1980-09-19 | Heart valve structure |
| US06/351,526 US4459252A (en) | 1975-05-09 | 1982-02-23 | Method of forming a small bore flexible vascular graft involving eluting solvent-elutable particles from a polymeric tubular article |
| US06/486,796 US4627836A (en) | 1975-05-09 | 1983-06-30 | Cardiovascular prosthetic devices and implants with porous systems |
| US06/924,060 US4936317A (en) | 1975-05-09 | 1986-12-08 | Cardiovascular prosthetic devices and implants with porous systems |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US683,382 | 1976-05-02 | ||
| US05/683,382 US4101984A (en) | 1975-05-09 | 1976-05-05 | Cardiovascular prosthetic devices and implants with porous systems |
| US824,296 | 1977-08-15 | ||
| US05/824,296 US4281669A (en) | 1975-05-09 | 1977-08-15 | Pacemaker electrode with porous system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1092303A true CA1092303A (en) | 1980-12-30 |
Family
ID=27103092
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA259,054A Expired CA1092303A (en) | 1975-05-09 | 1976-08-13 | Flexible vascular graft of polymeric material with internal porous surface |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1092303A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4604762A (en) * | 1981-02-13 | 1986-08-12 | Thoratec Laboratories Corporation | Arterial graft prosthesis |
| US4871361A (en) * | 1987-02-26 | 1989-10-03 | Kanegafuchi Kagaku Kogyo Kabushiki Kaisha | Artificial vessel |
| US5081161A (en) * | 1990-06-15 | 1992-01-14 | E. I. Du Pont De Nemours And Company | Process for making shaped articles of a thermoplastic resin having a microcellular structure |
-
1976
- 1976-08-13 CA CA259,054A patent/CA1092303A/en not_active Expired
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4604762A (en) * | 1981-02-13 | 1986-08-12 | Thoratec Laboratories Corporation | Arterial graft prosthesis |
| US4731073A (en) * | 1981-02-13 | 1988-03-15 | Thoratec Laboratories Corporation | Arterial graft prosthesis |
| US4871361A (en) * | 1987-02-26 | 1989-10-03 | Kanegafuchi Kagaku Kogyo Kabushiki Kaisha | Artificial vessel |
| US5081161A (en) * | 1990-06-15 | 1992-01-14 | E. I. Du Pont De Nemours And Company | Process for making shaped articles of a thermoplastic resin having a microcellular structure |
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| MKEX | Expiry |