in angioplasty balloons , an object is to apply a high pressure to the interior wall of the lumen to compress the plaque and / or to fully expand the stent . this relies on a robust balloon with a sturdy out wall and a high pressure capability . the compliance of the balloon , i . e ., the expansion of the balloon as a function of internal pressure , is preferably low or flat to more accurately control the amount of pressure applied to the arterial wall . however , the deliverability of the balloon is also a factor , especially where tortuous body lumens are involved . stiff balloons ( i . e ., high modulus materials ) tend to have poor flexibility and lack the maneuverability to navigate the various body lumens , and thus make poor choices for catheter balloons . conversely , flexible balloons ( low modulus materials ) that have high compliance are poorly suited to apply a precise known pressure on the arterial wall due to a high expansion rate per applied pressure . the goal is thus to increase the rupture strength by adding the high modulus material such as nylon to the softer polyamide material . soft polyamide materials such as pebax ® are semi - crystalline polymers and usually include an amorphous segment . the amorphous segment has a lower density than the crystalline structure and thus is weaker in general than crystalline segments . if the amorphous segment can be reinforced by adding a small amount of a higher modulus material the response of the amorphous segment can be delayed and the overall strength of the material can be strengthened . the high modulus material preferably has a shore d durometer hardness of 78 d or more . suitable materials include transparent amorphous nylon such as nylon 12 , and more preferably a nylon 12 with a aliphatic segment , an aromatic segment , or a cycloaliphatic segment . these nylons are transparent amorphous because they are essentially amorphous , lacking the crystalline structure of other more conventional nylon 12 . the aliphatic segment , aromatic segment , or cycloaliphatic segment does not crystallize with the main chain , disrupting the formation of longer crystalline chains in the polymer . the amorphous segment of the transparent amorphous nylon 12 combines with the amorphous segment of the pebax to strengthen the pebax by enhancing the weakest link in the chain , thereby increasing the overall strength of the polymer . fig1 illustrates a balloon catheter which embodies features of the invention . the catheter 10 of the invention generally comprises an elongated catheter shaft 11 having a proximal section , 12 a distal section 13 , an inflatable balloon 14 formed of a blend of polymeric materials on the distal section 13 of the catheter shaft 11 , and an adapter 17 mounted on the proximal section 12 of shaft 11 . in fig1 , the catheter 10 is illustrated within a patient &# 39 ; s body lumen 18 , prior to expansion of the balloon 14 . in the embodiment illustrated in fig1 , the catheter shaft 11 has an outer tubular member 19 and an inner tubular member 20 disposed within the outer tubular member and defining , with the outer tubular member , inflation lumen 21 . inflation lumen 21 is in fluid communication with the interior chamber 15 of the inflatable balloon 14 . the inner tubular member 20 has an inner lumen 22 extending therein which is configured to slidably receive a guidewire 23 suitable for advancement through a patient &# 39 ; s coronary arteries . the distal extremity of the inflatable balloon 14 is sealingly secured to the distal extremity of the inner tubular member 20 and the proximal extremity of the balloon is sealingly secured to the distal extremity of the outer tubular member 19 . fig2 and 3 show transverse cross sections of the catheter shaft 11 and balloon 14 , respectively , illustrating the guidewire receiving lumen 22 of the guidewire &# 39 ; s inner tubular member 20 and inflation lumen 21 leading to the balloon interior 15 . the balloon 14 can be inflated by radiopaque fluid introduced at the port in the side arm 24 into inflation lumen 21 contained in the catheter shaft 11 , or by other means , such as from a passageway formed between the outside of the catheter shaft and the member forming the balloon , depending on the particular design of the catheter . the details and mechanics of balloon inflation vary according to the specific design of the catheter , and are well known in the art . non - compliant or low - compliant balloon 14 and / or the shaft 11 is formed of a blend of a first polyamide having a shore d durometer hardness greater than 78 d and a copolyamide of lower durometer hardness , preferably less than 76 d . a preferred polyamide having a shore d durometer hardness greater than 78 d is an amorphous polyamide such as ems tr 55 ( transparent amorphous nylon 12 ), arkema rilsan g110 ( transparent amorphous nylon 12 ), or cristamid ms 110 ( transparent amorphous nylon 12 ). the polyamide is preferably includes a cycloaliphatic segment , an aromatic segment , or an aliphatic segment . such polyamides are also referred to as transparent polyamide . the preferred copolyamide material for forming the polymeric blend for the balloon is pebax , and more preferably pebax 72 d , pebax 70 d , pebax 63 d , or pebax 55 d . alternatively , the copolyamide of lower durometer hardness is preferably a block copolymer of nylon 12 and polytetramethylene oxide . the flexural modulus of the polyamide is preferably greater than 1700 mpa ( 240 , 000 psi ) and the flexural modulus of the copolyamide is less than 850 mpa ( 120 , 000 psi ). the tensile strength at break of both polyamides is at least 50 mpa , and elongation at break of both polyamides is at least 150 %. the catheter shaft will generally have the dimensions of conventional dilatation or stent deploying catheters . the length of the catheter 10 may be about 90 cm to about 150 cm , and is typically about 135 cm . the outer tubular member 19 has a length of about 25 cm to about 40 cm , an outer diameter ( od ) of about 0 . 039 in to about 0 . 042 in , and an inner diameter ( id ) of about 0 . 032 in . the inner tubular member 20 has a length of about 25 cm to about 40 cm , an od of about 0 . 024 in and an id of about 0 . 018 in . the inner and outer tubular members may taper in the distal section to a smaller od or id . the length of the compliant balloon 14 may be about 1 cm to about 4 cm , preferably about 0 . 8 cm to about 4 . 0 cm , and is typically about 2 . 0 cm . in an expanded state , at nominal pressure of about 8 to about 10 atm , the balloon diameter is generally about 0 . 06 in ( 1 . 5 mm ) to about 0 . 20 in ( 5 . 0 mm ). and the wall thickness is about 0 . 0006 in ( 0 . 015 mm ) to about 0 . 001 in ( 0 . 025 mm ), or a dual wall thickness of about 0 . 025 mm to about 0 . 056 mm . the burst pressure is typically about 20 to 26 atm , and the rated burst pressure is typically about 18 atm . in a presently preferred embodiment , the balloon 14 may include wings , which may be folded into a low profile configuration ( not shown ) for introduction into and advancement within the patient &# 39 ; s vasculature . when inflating the balloon to dilate a stenosis , the catheter 10 is inserted into a patient &# 39 ; s vasculature to the desired location , and inflation fluid is delivered through the inflation lumen 21 to the balloon 14 through the inflation port 24 . the semi - compliant or noncompliant balloon 14 expands in a controlled fashion with limited radial expansion , to increase the size of the passageway through the stenosed region . similarly , the balloon has low axial growth during inflation , to a rated burst pressure of about 14 atm , of about 5 to about 10 %. the balloon is then deflated to allow the catheter to be withdrawn . the balloon may be used to deliver a stent ( not shown ), which may be any of a variety of stent materials and forms designed to be implanted by an expanding member , see for example u . s . pat . no . 5 , 514 , 154 ( lau et al .) and u . s . pat . no . 5 , 443 , 500 ( sigwart ), incorporated herein in their entireties by reference . a proximal shaft for the over - the - wire catheter may have a tapered tubing coextruded and tapered with tr55 inner layer and pebax 72 d outer layer . the proximal wall thickness of tr55 may be approximately 0 . 005 ″ and a proximal wall thickness of pebax 72 d may be approximately 0 . 001 ″. a distal wall thickness of tr55 is approximately 0 . 002 ″ and a distal wall thickness of pebax 72 d is approximately 0 . 001 ″. in addition to balloons , the blended composition has usefulness as other parts of the catheter , such as the guidewire enclosure 20 of fig1 - 3 . the inner member of the multi - layered tubing can have a lubricious inner layer ( hdpe . uhmwpe , and the like ) with bonding mid layer and polymer blend outer layer . like the catheter balloon , the blend is comprised of one polymer having a shore d durometer greater than 78 and another polymer having lower durometer , preferably less than 76 d . both polyamides preferably have same amide block or segment , i . e . one type of amide ( nylon ) block , solely comprised of nylon 12 , nylon 11 , nylon 6 , or nylon 6 , 6 but not combination of these . the polyamide having shore d durometer greater than 78 d is preferably amorphous polyamide selected from polyamide such as ems tr 55 ( transparent amorphous nylon 12 ), arkema rilsan g110 ( transparent amorphous nylon 12 ), or cristamid ms 110 ( transparent amorphous nylon 12 ). this polyamide is preferably a copolyamide comprising cycloaliphatic , and / or aromatic , and / or aliphatic segment . the other copolyamide of lower durometer is preferably a block copolymer of nylon 12 and polytetramethylene oxide , such as pebax 72 d , pebax 70 d or pebax 63 d . the high durometer polymer serves to increase resistance to collapse of the tubing and provides enhanced pushability while the lower durometer polymer provides flexibility and kink resistance . although it is preferred to have blends of high miscibility , the blend ratio is such that the lower durometer polymer forms a “ virtual ” continuous phase while the higher durometer polymer forms “ virtual ” reinforcement . as shown in fig5 , an outer layer 60 of the catheter shaft can be comprised of an amorphous polyamide selected from polyamide such as ems tr 55 ( transparent amorphous nylon 12 ), arkema rilsan g110 ( transparent amorphous nylon 12 ), cristamid ms 110 ( transparent amorphous nylon 12 ), polyamide 11 , polyamide 6 , or polyamide 6 , 6 . this polyamide is preferably a copolyamide comprising cycloaliphatic , and / or aromatic , and / or aliphatic segment . in one embodiment , the outer layer 60 is blended with a softer polyamide such as a crystalline or semi - crystalline copolymer of nylon 12 and polytetramethylene oxide or polytetramethylene glycol , e . g . pebax 72 d or pebax 70 d . this blending offers a higher strength outer layer that offers higher pushability and resists collapse , while the copolymer operates to resist kinking and yield greater flexibility . although it is preferable to have blends of high miscibility , blend ratios are such that the lower durometer polymer forms a virtual continuous phase and the high durometer polymer forms a virtual reinforcement . the intermediate layer 70 is a bonding layer , such as primacore , to meld the inner and outer layers together . the inner layer 80 can be a lubricious material that reduces the friction of a guide wire passing through the lumen 90 , such as hdpe or uhmwpe . other materials are also contemplated , as long as the outer layer has a glass transition or melting temperature that is preferably lower than , or at least approximately equal to , the surface temperature of the mold during the blowing or forming process of the balloon . fig6 shows another embodiment of a catheter shaft 120 having a lumen 125 extending therein , the shaft 120 having an inner layer 130 comprising a low friction material such as high density polyethylene and an intermediate layer 140 serving as a bonding layer . an outer layer comprising a first polymer having a first shore d durometer value of no greater than 76 d , such as pebax 72 d or pebax 63 d is impregnated with a second polymer having a shore d durometer value that is greater than the first shore d durometer value , and preferably greater than 78 such as tr55 or the other transparent nylon 12 materials discussed above . the second polymer 160 can be wrapped around the shaft 120 like a helix or coil to reinforce the outer layer 150 . fig7 illustrates another embodiment of a catheter shaft having an inner layer 220 of a high modulus material with a high shore d durometer value such as amorphous nylon 12 . this inner layer material provides a high strength catheter shaft for higher pushability . however , the transparent nylon 12 has a tendency to kink , and it is susceptible to solvents used in cleaning or other manufacturing processes . to resist kinking , and to protect the catheter from solvents , a thin outer layer 240 of pebax or other soft copolyamide is formed over the inner layer 220 . the two layers 220 , 240 can be co - extruded in a single operation to create the shaft 200 of fig7 . the shaft 220 also incorporates a tapered section 250 as the shaft transitions from a main body portion to the portion 260 to the portion 270 where a balloon may be attached . in existing catheter shafts , this section requires a mid shaft section that must be separately attached to the catheter shaft using expensive laser equipment . the tapered transition from the main body portion 260 to the balloon attachment portion 270 eliminates the need for a mid shaft and thus the need for the laser equipment and assembly line personnel required to operate the laser equipment , resulting in a more efficient and cost effective catheter . the shaft of fig7 preferably has both co - extruded layers 220 , 240 with a common amide block or segment for better adhesion or compatibility , i . e ., one type of amide ( nylon ) block , comprising one and only one of nylon 12 , nylon 11 , nylon 6 , or nylon 6 , 6 . the inner polymer is preferably a polyamide having a shore d durometer value of greater than 78 , such as amorphous polyamide selected from ems tr55 , arkema rilsan g110 , or cristamid ms 110 , all commonly referred to as transparent nylon 12 . this polyamide preferably comprises cycloaliphatic , aromatic , and / or aliphatic segments . the outer layer 240 may preferably be a copolyamide block copolymer of nylon 12 and polytetramethylene glycol . various embodiments are described above in effort to illustrate the concepts of the present invention , but these embodiments are not intended to be limiting or exclusive . rather , the scope of the invention is to be determined by the words of the appended claims , interpreted in the context of the above description but not limited to those examples and embodiments described above and shown in the figures .
a balloon catheter having a multilayer catheter shaft is formed to have an inner layer and an outer layer , where the inner layer and outer layer are selected from materials that enhance the pushability of the catheter while preserving the flexibility . using a combination of a high shore d duromater value material and a lower shore d duromater value material , various combinations of multilayer catheter shafts are disclosed utilizing different glass transition temperatures and block copolyamides to obtain the desired characteristics .